REPORT TO:

U.S. Department of the Interior

Minerals Management Service

Office of International Activities and Marine Minerals

on

Impacts and Direct Eftects of Sand Dredging

for Beach Renourishment on the

Benthic Organisms and Geology of the West Florida Shelf

Contract Number 14-35-0001-30644

FINAL REPORT

September 1996

Principal Investigators:

Norman J. Blake, University of South Florida

Larry J. Doyle, University of South Florida

James J. Culter, Mote Marine Laboratory

Program Manager:

Sandra L. Vargo, Florida Institute of Oceanography

Submitted by:

Florida Institute of Oceanography

830 First Street South

St. Petersburg, Florida 33701

(813)893-9100

FINAL REPORT

OCS Report MMS 95-0005
FINAL REPORT

OCS Report MMS 95-0005

DISCLAIMER

This report was prepared under contract between the Minerals Management Service

(MMS) and the University of South Florida, Florida Institute of Oceanography (FlO). This

report has been technically reviewed by the MMS and approved for publication.

Approval does not signify that the contents necessarily reflect the views and policies of

the Service, nor does mention of trade names or commercial products constitute

endorsement or recommendation for use. It is, however, exempt from review and

compliance with MMS editorial standards.

REPORT AVAILABILITY

Extra copies of the report may be obtained from the Public Information Unit (Mail Stop

4030) at the following address:

U.S. Department of the Interior

Minerals Management Service

Office of International Activities and Marine Minerals

Public Information Unit (MS4030)

381 Elden Street

Herndon, Virginia 22070

Telephone Number: 1-703-787-1300

CITATION

Suggested citation:

Blake, N.J., L.J. Doyle, and J.J. Culter. 1996. Impacts and direct effects of sand

dredging for beach renourishment on the benthic organisms and geology of the

West Florida Shelf, Final Report. OCS Report MMS 95-0005. U.S. Department of

the Interior, Minerals Management Service, Office of International Activities and

Marine Minerals, Herndon, Va. 109 pp.
TABLE OF CONTENTS

List of Tables iii

List of Figures iii

Chapter 1

1.1 INTRODUCTION 1 1.2 POTENTIAL BIOLOGICAL IMPACTS OF MARINE MINING

ACTIVITIES 2

Immediate Effects 3

Chronic Effects 4

Community Resionses 6

Recolonization of Borrow Sites 9

1.3 OBJECTIVES OF THIS STUDY 12

1.4 SCOPE OF STUDY 12

1.5 PROGRAM MANAGEMENT AND PRINCIPAL INVESTIGATORS 13

1.5.1 Specific Program Responsibilities 13

1.6 METHODS AND APPROACH 15

1.6.1 Geophysical Surveys 15

1.6.2 Benthic Community Survey 28

Chapter 2

2.1 BASELINE INFORMATION 41

2.2 ENVIRONMENTAL CONDITIONS AT THE STUDY SITES 41

2.3 DREDGING TECHNIQUES EMPLOYED AT THE EGMONT KEY

AND LONGBOAT KEY SITES 42

Chapter 3

3.1 SEDIMENT AND GEOPHYSICAL RESULTS 43

Sediment Analyses 43

Geophysical Results 50

3.2 EPIBENTHIC RESULTS 54

Trawls 54

Underwater Video 70

3.3 INFAUNAL COMMUNITY RESULTS 70

Pre-Dredging Faunal Community Conditions 71

Egmont Key 75

Faunal Abundance, Richness, and Diversity 86

Faunal Composition 86

Faunal Similarity 91

FINAL REPORT

OCS Report MMS 95-0005
FINAL REPORT

OCS Report MMS 95-0005

3.3 INFAUNAL COMMUNITY RESULTS (continued)

Sarasota 97

Faunal Abundance, Richness, and Diversity 97

Faunal Composition 97

Faunal Similarity 97

Longboat Key 98

Manasota Key ioi

Chapter 4

4.1 SUMMARY AND CONCLUSIONS 102

Chapter 5

5.1 LITERATURE CITED 104

APPENDICES

Sediment grain size distribution for all sites

and stations A-i to A-i 43

Sediment total organic carbon (TOC) and

calcium carbonate (CaCO3) composition B-i to B-17

Complete phylogenetic list of taxa and composite

species list for each station and date C-i to C-36

11
tracks

1.6-4 Detailed survey track,

1.6-5 Detailed survey track,

1.6-6 Detailed survey track,

1.6-7 Detailed survey track,

1.6-8 Detailed survey track,

1.6-9 Detailed survey track,

FINAL REPORT

OCS Report MMS 95-0005

LIST OF TABLES

3.1-1 Weight percent CaCO3 50

3.2-1 Combined species list, all cruises 56

3.2-2 Species list for trawls, 07/13-16/92 58

3.2-3 Combined species list in order of prevalence 61

3.2-4 Species list for trawls, 01/1 9-21/93 62

3.2-5 Combined species list in order of prevalence 64

3.2-6 Species list for trawls, 09/08-09/93 65

3.2-7 Combined species list in order of prevalence 67

3.2-8 Species list for trawls, 05/24-25/94 68

3.2-9 Combined species list in order of prevalence 69

3.3-1 Total number of taxa and individuals (and percent of total

taxa and individuals) for each major faunal group 73

3.3-2 Benthic fauna parameters: Statistical summary for each station

and date 74

3.3-3 Total number of individuals in each major faunal group for

each station and date 77

3.3-4 Percent of individuals in each major faunal group for each station

and date 79

3.3-5 Total number of taxa in each major faunal group for each station

and date 81

3.3-6 Percent of taxa in each major faunal group for each station

and date 83

3.3-7 Wet weight biomass (g) for each major faunal group for each

station and date 85

3.3-8 Composite species list. Longboat Key borrow site, pre-dredging

sample 99

LIST OF FIGURES

1.5-1 Program management plan 14

1.6-1 General location of the study sites 16

1.6-2 Towing configuration for geophysical and video surveys 17

1.6-3 Relative positions of the four sites in the study and the survey

tip

18

Site I, July 1992 19

Site I, January 1993 20

Site I, September 1993 21

Site I, May 1994 22

Site II, July 1992 23

Site II, January 1993 24
iv

FINAL REPORT

OCS Report MMS 95-0005

LIST OF FIGURES (Continued)

1.6-10 Detailed survey track, Site II, May 1994 25

1.6-11 Detailed survey track, Site III, July 1992 26

1.6-12 Detailed survey track, Site IV, September 1993 27

1.6-13 Final preparation of the box corer prior to deployment 30

1.6-14 Box corer on deck and ready for deployment 31

1.6-15 Deployment of the box corer 32

1.6-16 Box core on deck showing ripple marks on its surface 33

1.6-17 Box core on deck with worm tubes 34

1.6-18 Initial benthic sample processing 35

3.1-1 Sediment grain size distribution, Site I, Station 1 44

3.1-2 Sediment grain size distribution, Site I, Station 2 45

3.1-3 Sediment grain size distribution, Site I, Station 3 46

3.1-4 Sediment grain size distribution for subsamples A-G, Site I

Station 3, September 1993 47

3.1-5 Sediment grain size distribution for subsamples A-G, Site II

Station 2, May 1994 48

3.1-6 Sediment grain size distribution for subsamples A-G, Site II

Station 1, July 1992 49

3.1-7 Seismic profile of Site I, Egmont Key, showing parasequences . . . 51

3.1-8 Bathymetry at Site I, Egmont Key, July 1992 prior to dredging 52

3.1-9 Bathymetry at Site I, Egmont Key, May 1992 almost two years after

dredging activity was completed 53

3.1-10 Bathymetry at Site IV, Longboat Key, September 1993,

post-dredging 55

3.3-1 Species saturation curves for four station-date combinations 72

3.3-2 Linear regression of equitability (Pielou's J) and Shannon

Index for all stations during July, 1992

(p <0.001; r = 0.953) 76

3.3-3 Temporal trends in number of taxa (top) and number of individuals

(bottom) at each site. I = Egmont Key; II = Sarasota;

Ill = Manasota Key; IV = Longboat Key. (C = control;

D = dredged) 87

3.3-4 Temporal trends in species diversity (Shannon's H') and equitability

(Pielou's J') at each site. I = Egmont Key; II = Sarasota;

Ill = Manasota Key; IV = Longboat Key. (C = control;

D = dredged) 88

3.3-5 Temporal trends in number of taxa (top) and individuals per square

meter (bottom) at Egmont Key 89

3.3-6 Trellis diagram of Bray-Curtis faunal similarity for each station and

date based on group-averaged sorting 92
V

FINAL REPORT

OCS Report MMS 95-0005

LIST OF FIGURES (Continued)

3.3-7 TreHis diagram of Bray-Curtis faunal similarity for each

station and date (Presence/absence transform) 93

3.3-8 Dendrogram of Bray-Curtis faunal similarity for each station and

date based on group-averaged sorting 94

3.3-9 Dendrogram of Bray-Curtis fauna! similarity for each station and

date. (Presence/absence transform) 95

3.3-10 Trellis diagram showing number of taxa in common for each

pair of stations and dates 96
1

FINAL REPORT

OCS Report MMS 95-0005

Chapter 1

1.1 INTRODUCTION

The Department of the Interior (DOl) bears the responsibility for managing the

development of the submerged lands of the continental shelf seaward of state territorial

waters. This federal jurisdiction was first mandated under the 1953 Outer Continental

Shelf (OCS) Lands Act (67 Stat. 462). Under this Act the Secretary of the Interior bears

direct responsibility for administration of oil, gas, and mineral exploration; for

development of the OCS; and for formulation of regulations to meet provisions of the Act.

The Bureau of Land Management (BLM) was designated by the Secretary of the Interior

to administer leasing of submerged federal lands, and the Geological Survey to supervise

production. In May 1982, these functions were centralized under the Minerals

Management Service (MMS).

Complementary to the 1953 OCS Lands Act, the Nattonal Environmental Policy Act

of 1969 requires that MMS use a systematic interdisciplinary approach to plan

development which may have an impact on the environment. The Environmental Impact

Statements (ES), Environmental Assessment Teams, data acquisition and analysis,

public hearings, and special studies are mechanisms used by MMS to fulfill this

requirement.

As an expression of continuing concern about the effect on the environment of

man's development of the OCS, the OCS Lands Act Amendments of 1978 were

promulgated. These Amendments authorize the Secretary to conduct studies to obtain

the information required to predict, assess, and manage the coastal environments of the

OCS and those coastal areas that may be affected by mineral mining activities.

To meet its responsibilities the MMS has four priority goals of OCS non-energy

minerals leasing: 1. to safeguard the ocean and coastal environments by assuring that

OCS mineral activities are environmentally sound and acceptable, 2. to assure that OCS

mineral activities are fully coordinated and compatible with other uses of the sea, 3. to

provide an effective consultation process for coastal States and the Federal government

on offshore minerals, and 4. to evaluate and achieve the potential of the U.S. OCS as a

domestic supply source for strategic and other minerals.

To fulfill its environmental protection responsibilities the MMS has used a variety

of approaches, primarily related to the OCS oil and gas leasing program. These

approaches have included ElSs, marine environmental data acquisition and analysis

studies, literature surveys, socioeconomic analysis studies, public conferences, and

special studies (toxicity trials, modeling of spill trajectories, etc.). With the recent location

and evaluation of various OCS hard mineral deposits of potential economic value, there

exists the possibility of offshore hard mineral development for various mineral

commodities. Therefore, environmental studies are being developed in order to evaluate

potential adverse impacts of mineral leasing or development and to identify mitigation

measures to minimize these impacts.
2

FINAL REPORT

OCS Report MMS 95-0005

1.2 POTENTIAL BIOLOGICAL IMPACTS OF MARINE MINING ACTIVITIES

Environmental disturbance is an important fact of life for shallow water organisms.

Storm waves, shifting substrata, longshore currents, temperature variations, and other

physical factors, as well as various biological influences (e.g., competition and

predation), play an important role in determining the structure and composition of benthic

communities (Bowen and Marsh, 1988). Species living in this environment must either

be capable of withstanding these influences or of quickly recolonizing locally perturbed

areas from which they have previously been extirpated. For most benthic invertebrates,

the latter response is more common.

Consequently, most nearshore benthic invertebrates tend to be r-strategists rather

than K-strategists, which are more common in deeper, relatively stable areas of the

seafloor (Sanders, 1960). According to Odum (1969), r-strategists are characteristically

small bodied, short lived, and have high fecundity, efficient dispersal mechanisms, and

rapid growth rates. Species possessing these r-selected characteristics are relatively

poor biotic competitors and, in the course of succession, are eventually replaced by

more competitive K-selected species. The K-strategists are generally larger in size than

r-strategists, long lived, and have low fecundity, poor dispersal mechanisms, and slow

growth rates. Recolonization of a disturbed area is thus generally initiated by rstrategists. Theoretically, r-selected species change the physical environment so that it

can later be occupied by the more K-selected species (Conneu and Slatyer, 1977;

Rhoads et al., 1977). In unstable or frequently perturbed habitats, however, r-selected

species may continue to predominate.

Benthic organisms are commonly monitored because of their intimate contact with

the dredged sediments. Organisms living in the immediate vicinity of the dredging and

disposal areas either are transported from one site to the other or are buried by the

spoils. Also, organisms that feed on suspended and deposited materials in these areas

ingest dredged sediments resuspended and redeposited during dredging and spoil

disposal.

A second reason for studying benthic organisms stems from their utility as

indicator organism. Being less mobile than fish, they are not likely to escape or

selectively avoid the affected areas. Their relatively long life-spans make them useful as

indicators of past perturbations. Mollusk shell fragments provide a long-term record of

changes in birth and death rates (Gordon etal., 1972). Benthic macrofauna are relatively

easy to collect and identify in the field. The benthic community makes up a spectrum

of species that vary greatly in habitat, modes of feeding, and tolerance of environmental

stress (Gordon et al., 1972; Taylor et al., 1970).

A third reason for monitoring benthos is that they provide a crucial link in the

detritus-based food chain. They eat organic matter and thus recycle nutrients that

otherwise would collect and remain trapped in the sediments. Benthic organisms are

food for demersal fish and other predatory aquatic organisms.

Finally, clams, mussels, oysters, scallops and lobsters are important as

commercial fishery resources.
HNAL REPORT

OCS Report MMS 95-0005

Immediate Effects:

Both Jones (1950) and Scanland (1966) consider "bottom type" as the single-fnost

influential factor for all benthic communities regardless of the physical and chemical

characteristics or geographic locations. Both turbidity and sediment deposition rates

could affect the substrates, and both could exert their independent influences on filterfeeders and other bottom-dwelling organisms (Collard and D'Asaro, 1973).

Direct burial by spoils discharged in large quantities within the short time interval

of spoiling is the most obvious effect on benthic organisms. Sessile or attached animals

such as oysters, mussels, and barnacles are killed outright by direct burial (Lunz, 1938,

1942; Wilson, 1950; Brehmer, 1965; Carriker, 1967; Saila et al., 1972; Rose, 1973). In

general, when sediments are anoxic, smaller animals are even more vulnerable to burial

because they are unable to reach the surface before they suffocate. Small crustaceans

respond to oxygen deficiency by increased ventilation and rapidly use up the available

dissolved oxygen (DO)(Saila et al., 1972). Some bivalve mollusks, however, can incur

an oxygen debt and certain polychaetes can reduce their activity and metabolism when

DO levels are low, thus providing a longer time for escape (Nicol, 1967).

Saila et al. (1972) showed that Nephtys incisa, a large polychaete, and Mulinia

Iateralis, a small fflter-feeding bivalve, reached the surface through 21 cm of sediments

in the laboratory. Streblospio benedicti, a small tube-dwelling polychaete, surfaced

through 6 cm of sediments. Bivalves of the genera Macoma, Yoldia, and Nucula, which

can move horizontally, would also be expected to escape from spoils deposited upon

them (Saila et aL, 1972).

Another critical effect of dredging and disposal is habitat destruction resulting from

change in the physical and chemical characteristics of the sediments, loss of vegetative

cover, filling in of spawning grounds, or change in circulation patterns at the dredge or

disposal site (Brehmer, 1965; Chapman, 1968; Cottam, 1968; Marshall, 1968; Taylor et

al., 1970; Kaplan et al., 1974). Barnard and Reish (1959) cautioned that dredging in

Newport Bay would eliminate the shell fragments from the bottom, leaving behind muddy

sand and possibly rendering the habitat no longer suitable for the amphipod

Metaceradocus occidentalis and the polychaete Scyphoproctus oculatus. Saloman et

al. (1982) described alterations in the physical structure of borrow site substratum in

relatively shallow water (18 meters) high energy area. Evidence of post mining sediment

alterations included lower sand content, poorer sorting, and a higher organic content.

These differences became obscured with time and borrow site sediments were very

similar to undisturbed areas after a period of one year. Saloman showed that the fauna

of the borrow pits of Panama City, Florida, showed a complete recovery within 9 months

to one year. However, samples obtained beyond one year for this same study indicated

a lack of complete recovery, which was attributed to inherent spatial variations. Buelow

(1968) suggested that sewage sludge dumped at the head of Hudson Canyon might

endanger the breeding grounds of lobsters and reduce crab populations. Bruer (1962)

reported that oyster populations were destroyed in the northern end of South Bay, Texas,

during a shell dredging project. Spoil deposition decreased depth from 1 .2m to 0.4m,

3
I

Contract.rlq and Subcontracting

Dr. tcflaro Streeter, Oirectcr

DivisiOn of Sponsored ResearCfl

Geophysical. Survey

Dr. L.J. Doyle

MMS

Mr. B. Drucker, Physical Scientist, COTR

Dr. T. Ahifeld, Oceanographer, Tech. Consultant

Program Manager

S. Vargo

Benthic SanrnUng

Dr. N.J. Blaxe

Technical Support Technical Support

14

FINAL REPORT

OCS Report MMS 95-0005

Figure 1.5-1. Program Management Plan

Business Manacesent & ACCOUntiflQ

s. Adele Bernett

Associate Controller

Division of FinanCe & ACcounting

Benthic Sanole

Analysi.S

Mr. J. Culter

I

Technical Super
15

FINAL REPORT

OCS Report MMS 95-0005

cruise plan. He supervised the technical staff collecting and conducting the initial

processing of the benthic macroinfaunal samples. In particular, he supervised the

collection and analysis of the video tapes of the macro-epibenthic assemblages and the

collection and species verification of the epibenthic trawis. He prepared the reports

pertinent to this data and in cooperation with Dr. Doyle interpreted the sediment and

faunal data.

Benthic Infauna Sample Analysis:

Mr. James K. Culter was responsible for the sorting, biomass determinations, and

faunal identification of the benthic samples. He was assisted by four Senior Biologists

and one Staff Biologist at Mote Marine Laboratory (MML). He prepared the data in the

appropriate data base for submission to MMS and prepared the sections of the report

dealing with sample processing and analysis. He coordinated his interpretations with

those of Drs. Doyle and Blake. He was the project manager for MML and was the

principal liaison with USF/FlO.

1.6 METHODS AND APPROACH

1.6.1 Geophysical Surveys

Survey Outline

The sampling program was conducted at each of four sites (Figure 1.6-1)

selected after consultation with MMS, the Army Corps of Engineers, principal

investigators, and the program manager. The general station locations in latitude and

Prior to each benthic sampling event a geophysical survey was conducted at each site.

A maximum of 12 nautical miles of high resolution seismic reflection profiling, side scan

sonar data, and continuous video tape of the bottom was collected simultaneously.

Figure 1.6-2 shows the gear array used. Line spacing was as close as possible and

depended on the site sizes. Lines were adjusted in surveys following the pre-dredging

survey in order to pass over actual dredged areas. Navigation was by LORAN C with

fixes marked at 5 minute intervals on the high resolution seismic reflection profiling and

side scan sonar surveys and every 10 minutes on the video system. Surveys were

conducted at two knots or less (the ROV towing speed was the limiting factor).

Figure 1.6-3 shows the relative position of the four sites and the survey tracks.

Figures 1.6-4 to 1.6-12 show the details of all four sampling sites. The positions of each

of the benthic box core stations (BC) [each of which had 10 replicate samples taken (AJ)], the geophysical track lines, including TV (solid lines), and finally the locations of the

otter trawls (OT) are shown.

longitude, site designations, and number of samplings are as follows:

Egmont Key Site I 27°37' N, 82°49'W 1-pre, 3-post

Sarasota Site II 27°15' N, 82°35'W 3-pre, never dredged

Manasota Site III 26°29' N, 82°27'W 1-pre, never dredged

Longboat Site IV 27°14' N, 82°36'W 1-post
87° 86°

ocs

GULF OF MEXICO REGION

850

EASTERN

16

84°

FINAL REPORT

OCS Report MMS 95-0005

83° 82°

.. DRY TORTUGAS

Figure 1.6-1. General location of the study sites (A on inset map and

hatched area on large map).

300

29°

280

27°

26°

25

24°
B.

DECK LAYOUT

voLovri

Modified underway

sediment samoer

Figure 1.6-2. Towing configuration for geophysical and video surveys

A. Geophysical towing system. B. ROV towing system.

17

FINAL REPORT

OCS Report MMS 95-0005

SIDE.SCAN

NAR
a,

50

48

46

44

42

40

38

36

34

32

30

28

26

24

-4 -2 02

0

z

4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

LATITUDE File MMSALL4A.STG

Figure 1.6-3. Relative positions of the four sites in the study and the survey tracks. Site I - Egmont Key, Site II - Sarasota,

Site III - Manasota, and Site IV - Longboat.
!LOn1cr0 C') 0, 000n) ec a.ec 911R 0T2.3VJAF2MM ac a.ac 8C a.8C GUTITAJ vv-ii, ,A3Bht3jjj '1UIQQ1 bnE yjtiunsl. QQ1 V051 .AztntiIT Is3tdqo9 bilfi VO5Ibint 9Th b: ii biloaniI 13110 IwiiiI (TO) ii b3tItib3nuI bilE xod nho3 noiIia8) sd bito2Job
0 475

35 35.5 36 36.5 37 37.5 38 38.5

LATITUDE

39 39.5 40

File MMS1AL1D.STG

Figure 1.6-5. Detailed survey track, Site 1, January 1993. The geophysical and ROV tracks are shown as a solid line, otter trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

O2

C)

(1)

rn O-U

(1)

010

00

Ui
!EO c) <C) 1't ac a.ac 'cc 8C .8C oi aauiii 9IuR OT28JA2MMC') 13dmtq3 3dT IB3iarLqo bilE V051 Aziiits nwoita s bito2niI b viiia btntti j anoiitita(8)d a biloa Job 0 aJwlcl (TO) au ii b3ttnb3nhI bilE xod niio
Figure I.6..7. Detailed survey track, Site 1, May 1994. The geophysical and ROV tracks are shown as a solid line, otter Irawis (UT) as a dashed line, and box coring stations (BC) by a solid dot.

37 37.5

LATITUDE

38 38.5 39 39.5 40

File MMS1AL5B.STG
TO a.r 8r .8r @t a.@r Os a.Err a.tr ar ear ar .8t r 3UTITAJ sIR TBVJA2MM b31 wiija brciiti2 JI tnt. .QQ1t1T tfi3iadqo bnfi VO5I Aznntm nwoik vi s biIonit l3flo (TO) au t brIiibnI brui xod flflO3 anoi1BI(DII) d ii biloaJob
I

Contract.rlq and Subcontracting

Dr. tcflaro Streeter, Oirectcr

DivisiOn of Sponsored ResearCfl

Geophysical. Survey

Dr. L.J. Doyle

MMS

Mr. B. Drucker, Physical Scientist, COTR

Dr. T. Ahifeld, Oceanographer, Tech. Consultant

Program Manager

S. Vargo

Benthic SanrnUng

Dr. N.J. Blaxe

Technical Support Technical Support

14

FINAL REPORT

OCS Report MMS 95-0005

Figure 1.5-1. Program Management Plan

Business Manacesent & ACCOUntiflQ

s. Adele Bernett

Associate Controller

Division of FinanCe & ACcounting

Benthic Sanole

Analysi.S

Mr. J. Culter

I

Technical Super
15

FINAL REPORT

OCS Report MMS 95-0005

cruise plan. He supervised the technical staff collecting and conducting the initial

processing of the benthic macroinfaunal samples. In particular, he supervised the

collection and analysis of the video tapes of the macro-epibenthic assemblages and the

collection and species verification of the epibenthic trawis. He prepared the reports

pertinent to this data and in cooperation with Dr. Doyle interpreted the sediment and

faunal data.

Benthic Infauna Sample Analysis:

Mr. James K. Culter was responsible for the sorting, biomass determinations, and

faunal identification of the benthic samples. He was assisted by four Senior Biologists

and one Staff Biologist at Mote Marine Laboratory (MML). He prepared the data in the

appropriate data base for submission to MMS and prepared the sections of the report

dealing with sample processing and analysis. He coordinated his interpretations with

those of Drs. Doyle and Blake. He was the project manager for MML and was the

principal liaison with USF/FlO.

1.6 METHODS AND APPROACH

1.6.1 Geophysical Surveys

Survey Outline

The sampling program was conducted at each of four sites (Figure 1.6-1)

selected after consultation with MMS, the Army Corps of Engineers, principal

investigators, and the program manager. The general station locations in latitude and

Prior to each benthic sampling event a geophysical survey was conducted at each site.

A maximum of 12 nautical miles of high resolution seismic reflection profiling, side scan

sonar data, and continuous video tape of the bottom was collected simultaneously.

Figure 1.6-2 shows the gear array used. Line spacing was as close as possible and

depended on the site sizes. Lines were adjusted in surveys following the pre-dredging

survey in order to pass over actual dredged areas. Navigation was by LORAN C with

fixes marked at 5 minute intervals on the high resolution seismic reflection profiling and

side scan sonar surveys and every 10 minutes on the video system. Surveys were

conducted at two knots or less (the ROV towing speed was the limiting factor).

Figure 1.6-3 shows the relative position of the four sites and the survey tracks.

Figures 1.6-4 to 1.6-12 show the details of all four sampling sites. The positions of each

of the benthic box core stations (BC) [each of which had 10 replicate samples taken (AJ)], the geophysical track lines, including TV (solid lines), and finally the locations of the

otter trawls (OT) are shown.

longitude, site designations, and number of samplings are as follows:

Egmont Key Site I 27°37' N, 82°49'W 1-pre, 3-post

Sarasota Site II 27°15' N, 82°35'W 3-pre, never dredged

Manasota Site III 26°29' N, 82°27'W 1-pre, never dredged

Longboat Site IV 27°14' N, 82°36'W 1-post
87° 86°

ocs

GULF OF MEXICO REGION

850

EASTERN

16

84°

FINAL REPORT

OCS Report MMS 95-0005

83° 82°

.. DRY TORTUGAS

Figure 1.6-1. General location of the study sites (A on inset map and

hatched area on large map).

300

29°

280

27°

26°

25

24°
B.

DECK LAYOUT

voLovri

Modified underway

sediment samoer

Figure 1.6-2. Towing configuration for geophysical and video surveys

A. Geophysical towing system. B. ROV towing system.

17

FINAL REPORT

OCS Report MMS 95-0005

SIDE.SCAN

NAR
c c oc 8 a o 8r ar r r or 8 

D&IR 3OUTITAJ 

,A tnom3 

- 

I 33i .abst 'viva d) bus buta tli iii aii iuoI grIt 10 noitiaoq 3viiBb5I I iui1 

.1sodnoJ 

- 

VI 1i bus stontiM 

- 

Ill ti 

oa 

8 

8 

ac 

0 

8 

co 

a C,10 

- - 

V 

0 
36 36.5 37 37.5 38 38.5 39 39.5 40

LATITUDE File MMS1AL7C.STG

:d survey track, Site 1, July 1992 and January 1993 ROV track. The geophysical and ROV tracks are

as a solid line, otter trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

(D3

0-U

U)

to

U'

0

0

U'
0 475

35 35.5 36 36.5 37 37.5 38 38.5

LATITUDE

39 39.5 40

File MMS1AL1D.STG

Figure 1.6-5. Detailed survey track, Site 1, January 1993. The geophysical and ROV tracks are shown as a solid line, otter trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

O2

C)

(1)

rn O-U

(1)

010

00

Ui
!EO c) <C) 1't ac a.ac 'cc 8C .8C oi aauiii 9IuR OT28JA2MMC') 13dmtq3 3dT IB3iarLqo bilE V051 Aziiits nwoita s bito2niI b viiia btntti j anoiitita(8)d a biloa Job 0 aJwlcl (TO) au ii b3ttnb3nhI bilE xod niio
Figure I.6..7. Detailed survey track, Site 1, May 1994. The geophysical and ROV tracks are shown as a solid line, otter Irawis (UT) as a dashed line, and box coring stations (BC) by a solid dot.

37 37.5

LATITUDE

38 38.5 39 39.5 40

File MMS1AL5B.STG
0T3' /

13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20

LATITUDE File MMS2AL7B.STG

led survey track, Site II, July 1992. The geophysical and ROV tracks are shown as a solid line, otter

(OT) as a dashed line, and box coring stations (BC) by a solid dot.
37 36.536 35.5 w0 35 I- 34.5 r') C,) 34 33.5 r)33 rn0-u (1) (001 Figure 1.6-8. Detailed survey track, Site II, July 1992. The geophysical and ROV tracks are shown as a solid line, otter 8 32.512.5 13 -.40 z 13.5 14 14.5 15 15.5 16 LATITUDE16.5 17 17.5 trawls (OT) as a dashed line, and box coring stations (BC) by a solid dot. 18 18.5 19 19.5 20 File MMS2AL7B.STG
37

36.5

36

35.5

w

o 35

34.5

0

-J

34

33.5

32.5

12.5 13

-4

0 z

Figure 1.6-9. Detailed survey track, Site II, January 1993. The geophysical and ROV tracks are shown as a solid line, otter

trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

0-n

C) (0

(D

0-U

(0

U'

0

Cii

13.5 14 14.5 15 15.5 16 16.5 17 17.5 19

LATITUDE

18 18.5

File MMS2AL1C.STG

19.5 20
37

36.5

36

35.5

w0 35

I34.5

r') 0

01 i

34

33.5

33

32.5

12.5 13

0

z

Figure 1.6-10. Detailed survey track, Site II, May 1994. The geophysical and ROV tracks are shown as a solid line, otter trawls (OT) as a dashed line, and box coring stations (BC) by a solid dot.

0-n

C)

C,)

:1,,-

(D0-U

(I) co

(n0

0

Ui

13.5 14 14.5 15 15.5 16

LATITUDE

16.5 17 17.5 18 18.5 19

File MMS2AL5B.STG

19.5 20
28

27.5

27

26.5

26

25.5

25

Figure 1.6-11. Detailed survey track, Site III, July 1992. The geophysical and ROV tracks are shown as a solid line,

otter trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

-4 -3.5 -3 -2.5 -2 -1.5

LATITUDE

-1 -0.5 0 0.5 1 1.5

File MMS3AL7B.STG
03

r

25.5 I'.)

-.1z

26 26.5 27 27.5 28

Figure 1.5-12. Detailed survey track, Site IV, September 1993. The geophysical and ROV tracks are shown as a solid

line, otter trawis (OT) as a dashed line, and box coring stations (BC) by a solid dot.

LATITUDE Fi'e MMS4AL9B.STG
FINAL REPORT

OCS Report MMS 95-0005

High Resolution Seismic Reflection Profiling

Seismic reflection data was collected using an ORE Geopulse profiling system

consisting of an ORE power supply, acoustic source, 20 element hydrophone array,

receiver/filter/amplifier, and an EPC 1650 graphic recorder. The seismic profiles were

recorded using a 62 ms sweep with band pass filters typically set for 700-3000 Hz. Prior

experience has shown that these settings are optimal for the west Florida shelf, but of

course, were adjusted during the survey in order to optimize the records. The raw

unfiltered analog signal was recorded on magnetic tape.

Side Scan Sonar Survey

Side scan sonar records were obtained using an EG&G model 260 Sea Floor

Mapping System with automatic slant range correction. Sonographs were typically

recorded with a horizontal range of 75 m on a side (150 m total swath). Processed

digital data was recorded on magnetic tape as well as on paper record.

1.6.2 Benthic Community Survey

Video Camera System

A video camera mounted on a PHANTOM 500 ROV was towed a few feet above

the bottom behind a torpedo-like weight (Figure 1.6-2) that helps maintain depth control.

The system was remotely flown from the vessel laboratory. Video camera output was

recorded on VCR tape. Observations of bottom type and biology were logged in real

time aboard ship every 10 minutes or as specific features or changes in bottom type or

epibenthos were encountered. A LORAN fix was taken at the time of each log entry. Dr.

Norman Blake, who served as Chief Scientist on all cruises, was responsible for on-board

video observations. On-board video observations of epibenthos included the presence

of dominant epifaunal species such as bottom fish, crabs, sponges, corals, and shellfish

as well as major attached and rolling algae.

After each video camera/side scan/seismic site survey, three trawis were taken for

epibenthic species verification using a 30 foot otter trawl. The location of each 20 minute

trawl was determined by the chief-scientist and depended upon the on-board

observations with the video camera. The individuals collected in each trawl sample were

counted and representative individuals were preserved and returned to the laboratory for

analysis to the lowest practical taxon.

Precision Depth Recorder

PDR records were obtained using a Furuno Model FE881 depth recorder with a

hull mounted transducer.

Box Coring Program

The benthic infaunal and sediment sampling programs were conducted at each

of four sites. All four sites were off the West coast of Florida between Egmont Key and

Venice. A total of three stations at each site (two in the dredge area and one outside)

were sampled by box corer. The control station was outside the dredge area and one

28
FINAL REPORT

OCS Report MMS 95-0005

mile removed from the limits of the disposal area, but in a sediment environment similar

to the dredge area. Although an attempt was made for the first sampling period to be

prior to any dredging operation and the remaining three periods after dredging, this did

not prove practical for all four locations.

1. On-Board Processing

Quantitative benthic samples were collected using a box corer. Figure 1.6-13

shows the box corer on deck prior to deployment. Completely rigged it weighs about

2,000 pounds and obviously can only be used in small seas. Figures 1.6-14 to 1.6-15

show how the box corer is deployed, while Figures 1.6-16 and 1.6-17 show two box

cores on deck prior to subsampling for sediment and infauna analyses. Each box core

removed a sediment plug measuring 21.3 cm x 30.5 cm in surface dimensions with a

maximum depth of penetration of 32 cm. The box corer gives a relatively undisturbed

sample, both surficially and stratigraphically. Note the ripple marks on the surface of the

sample in Figure 1.6-16 and the worms in place on the surface of the sample shown in

Figure 1.6-17. Nine replicate cores were collected at each station (A-I). (An additional

replicate (J) was collected, archived and maintained as a backup). Previous sampling

in the area has shown that nine cores are required to obtain a statistically valid

description of the benthic macroinfauna (Culter, personal comm.)

After each box core was brought on board, it was catalogued and labelled with

the appropriate sample number. Salient visual characteristics, including color, texture,

stratigraphy, and conspicuous epibiota, were recorded. Figure 1.6-18 shows the initial

biological screening of a sample.

Sediment Samples

Each box core was sub-sampled with a 5 cm diameter coring device to the depth

of core penetration. The resultant samples were placed in clearly labelled containers for

later sediment analyses.

Infauna Samples

After a 5 cm subsample was extracted for sediment analysis, the top 15 cm of

sediment remaining in each box core was removed for faunal processing. The sample

was placed in a 50 gallon drum mounted on a swivel and frame and subjected to a

gentle stream of running seawater. As the can filled with water, the sample was gently

stirred to bring the soft-bodied organisms out of the sediment. The water was then

poured through a spout in the can chute onto a 500p mesh screen.

The material from the sieve was rinsed into a pre-labelled plastic quart jar with

filtered seawater. (A matching internal label was placed in the jar). A buffered formalin

and rose bengal solution was then added to the jar to bring the final formalin

concentration to ten percent. The sediment left in the can (along with the remaining

fauna) was transferred to prelabelled cotton bags and placed in a drum of 15%

magnesium chloride for fifteen minutes to relax the organisms. Finally, the bags were

transferred to a drum of 10% formalin. After each cruise, all infaunal samples were

29
r

-J

Figure 1.6-13. Final preparation of the box corer prior to deployment.

30

FINAL REPORT

OCS Report MMS 95-0005
Figure 1.6-14. Box corer on deck and ready for deployment.

31

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32

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Figure 1.6-15. Deployment of the box corer.
33

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OCS Report MMS 95-0005

Figure 1.6-16. Box core on deck showing ripple marks on its surface.
Figure 1.6-17. Box core on deck with worm tubes.

34

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OCS Report MMS 95-0005
Figure 1.6-18. Initial benthic sample processing.

35

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FINAL REPORT

OCS Report MMS 95-0005

inventoried (each sample recorded on custody sheets) and transported to Mote Marine

Laboratory.

2. Laboratory Analyses

Sediment Analyses

As part of the framework portion of the study to determine recolonization after

dredging, the standard sedimentary parameters of grain size, carbonate content, and

organic content were determined for each of the ten samples at each station for each

sampling period. Samples were taken from the box cores with a stainless steel scoop.

Figures 1.6-16 and 1.6-17 show one of the box core samples on deck. Notice that worm

tubes protrude from the sediment. Box coring is the best method to obtain undisturbed

samples. Figure 1.6-16 shows that even surface ripple marks are preserved. Only the

top 15 cm was collected for sediment analyses, since that is the depth to which

organism samples were taken. Sediment samples were analyzed for texture, carbonate

content, and total organic carbon.

Grain size (texture) was measured by the standard technique of sieving an aliquot

through sieves nested at 1 intervals ; that is -1 (2mm), 0 (1mm), 1 (500

microns), 2 (250 microns), 3 (125 microns), 4 (62 microns), and pan (< 62

microns) in the method of Folk, 1980. This whole range is considered to be the sand

sized fraction. For Site I, the only one in which we have sampling before, during and

after dredging, measurements of all ten replicate samples were combined at each of the

three stations and histograms were constructed for comparison of sampling periods.

Carbonate content was determined by acidifying a weighed aliquot with 10% HCI,

dissolving the carbonate minerals, drying the sample and re-weighing. Organic content

was determined by combustion of a carbonate free subsample.

Infauna Analyses

After 48 hours, samples were transferred to 70% isopropyl alcohol and stored until

processing. Samples were first rough sorted to major categories (annelids, crustaceans,

molluscs, echinoderms, hemichordates and miscellaneous) and then identified to the

lowest practical taxonomic level, which for most fauna was either the species or genus

level.

Wet weight biomass (g) was measured for each major taxonomic group. Wet

weights were obtained by pouring the sample into a small sieve (250 micron mesh)

which separated the specimens from the preservative. The samples were rinsed with tap

water to remove excess isopropyl alcohol. Specimens were blotted dry, placed in a

small aluminum pan and weighed to the nearest mg.

Epibenthic Samplinq

Upon return to the laboratory, the video tapes were reduced to a slower speed

and the species verified (Dr. N. Blake) with the samples collected with the otter trawl.

The results of this analysis were used in conjunction with the video tape to describe the

epibenthic assemblages that were observed during each survey of each site.

36
FINAL REPORT

OCS Report MMS 95-0005

Geophysical Data Reduction and Products

Sequence boundaries at each site were mapped from the high resolution seismic

reflection data. Isopach maps of the sequences present, including the sand bodylo be

mined, were constructed for each sampling period. Side scan sonographs were

analyzed for topographic changes, bedform character, and sediment textural variation.

Seismic and side scan records were correlated with bathymetry as determined by PDR

records and with the observations taken from the video data.

General Macroinfaunal and Epibenthic Data Analysis

Species were coded for computer entry utilizing National Oceanographic Data

Center (NODC) numeric coding system. All computer entries were 100% verified for

accuracy and completeness prior to analysis. Mote Marine Laboratory analyzed the

collected macroinfaunal data utilizing accepted statistical procedures. Emphasis was on

statistical parameters that numerically defined species composition and relative

abundance and that showed whether or not correlations existed between combinations

of substratum characteristics (such as grain size) and faunal characteristics. Analysis of

the data included the foflowing when appropriate:

Species diversity

Species evenness

Species richness

Definition of community assemblages based on classification and ordination

analysis procedures, such as cluster analysis.

Association of assemblages with substratum variables by

discriminate multivariate analysis.

Analysis of distribution of fauna by species and numbers among major

faunal groups. The loss of a particular type of organism (example

amphipods) representing a particular functional morphology, is often

indicative of an alteration of the habitat structure.

Data analysis was conducted with Mote Marine Laboratory developed SuperCalc

5.0 spreadsheet software and BioStat II, community analysis software (Pimentel and

Smith, 1993)

Representative epibenthic samples from the trawl were identified to the lowest

practical taxon. Combined with the counts from the traw' this provided data on

numerical abundance of epibenthic species in the sampling area.

Infaunal Data Analyses

Each sample collected within each area was treated as a replicate. These data

were tested for homogeneity of variance and normality. Data sets used for comparisons

consisted of species richness (total taxa) and total individuals for each taxa. These data

sets were tested for normality (Kolmogorov-Smirnov test) and homogeneity of variance

(Levene Median test) using SigmaStat software (Jandel Scientific, 1992). Data sets that

37
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passed the tests for normality and homogeneity of variance were tested for spatial and

temporal differences utilizing a one-way ANOVA and the Student-Newman-Kuels method

of pairwise comparisons to identify significantly different groups. Data sets that did not

pass the tests for normality and homogeneity of variance were analyzed utilizing the nonparametric statistic, Kruskal-WaIIis one-way ANOVA by ranks (Siegel, 1956).

Stewart-Oaten et al. (1986) described a rationale for the evaluation of

environmental impact assessment based upon the magnitude of variation between

control and affected areas before and after impact. Description of the environment to be

affected must include estimates of the variances of the sample means of the relevant

variables, for it is only against this variation that impacts can be detected (Underwood,

1992).

One objective of the pre-dredging sampling was to define natural pre-impact or

baseline levels of variation throughout all areas. The baseline variations were then

utilized as a comparative measure for post-dredging impact variations of community

parameters, with the control stations continuing to serve as a guide for °natural0

variations.

The level of natural variation in species composition and faunal abundance can

serve as a measure of stress in marine communities. Warwick and Clarke (1993)

examined variability in species diversity (H) and species abundances for meiobenthos,

macrobenthos, coral reefs and reef fish. A clear log-log relationship was found between

the variance and the mean abundance for all species. The slope of the log-log

regression increased significantly between control and impacted sites. Additionally, the

variability in macrobenthic species diversity (H') tended to increase with increasing levels

of perturbation.

Standard descriptive community parameters were calculated for each sample.

These parameters are:

Faunal density was calculated as the number of organisms per square meter of

substratum by the formula: FD = i/a where 1" is the total number of individuals collected

at a station, and "a° is the total area sampled, in square meters.

Wet weight biomass was obtained for each abundant species or taxonomic group.

Species richness was calculated as the number of identifiable taxa present for

each sample and each area (total species for 10 samples).

Srecies diversity was calculated as the Shannon Index (Shannon and Weaver,

1972) using the formula:

S

H' = -(p)(log p1)

where s = total number of species for the sample and p = the proportion of total

38
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OCS Report MMS 95-0005

individuals for the ith species. The index was calculated using various log bases (log10,

log2, In) to enable comparisons to other data sets.

The Shannon Index has been strongly criticized by several authors (Hurlbert, 1971;

Goodman, 1975; Patten, 1968; Washington, 1984) as to the biological meaning of the

index. An increase or decrease in H' does not necessarily indicate an improvement or

decline in the quality of a benthic community. Environmental impact assessments must

take into consideration the natural state of the community under consideration. Caution

should be used when interpreting values of H'as related to impact assessments.

Equitability is considered a component of diversity in that it provides an idea about

the evenness of species distribution at a site. Usually, a positive correlation exists

between diversity and equitability i.e., a high equitability would indicate a high diversity

and probably a "healthy condition" of the fauna. Reduction of equitability almost always

occurs with an increase in oligomixity. Pielou's (1966) method of measuring equitability

is most widely used. The computational formula is:

LI' J,- logS

where e = 2.30, H' = value for Shannon Index, and S = total number of species for a

sample.

Margalef's index assumes a theoretical relationship between the number of

individuals (N) and the number of species (S) in a sample and is expressed as:

M

S - 1 (Margalef, 1958)

IogN

Faunal similarity analysis: A number of coefficients for measuring faunal

similarities are available (Whittaker, 1967; Lie and Kelly, 1970; Sanders, 1960; Bray and

Curtis, 1957; Field and MacFarlane, 1968; Morisita, 1959). However, most of the

available coefficients consider only the number and rank of common species and not the

distribution of individuals. The Bray-Curtis Index (Bray and Curtis, 1957), which takes

into consideration both the number of species in common and the number of individuals

shared, was used in the current study. The index has a range from 0 to 1, with 0

representing identical faunal composition. The computational formula for the index is:

S

- X,J

i=1

B=

S

+ Xk)

39
40

FINAL REPORT

OCS Report MMS 95-0005

where B = Bray-Curtis measure of dissimilarity; X1 = individuals for the ith species in the

jth sample; XIk = individuals for the /th species in the kth sample and s = the number of

species over all samples. The index is relatively free from sample size effects: The

results of the faunal similarity analyses are presented as a trellis diagram and as a

dendrogram cluster graph. The use of this analysis in environmental studies is

invaluable, since differences in community structure between stations can be inferred.

From the clusters (or groupings) of similar stations, statements on the extent of

environmental impact can be made.

The Bray-Curtis Index was calculated for all pair-wise combinations of stations and

dates. The pair-wise combinations of the index were then used as input for the cluster

analysis.

Faunal distribution among taxonomic groups was ca'culated as the relative

percentage of species and individuals comprising major faunal groups, such as;

polychaetes, oligochaetes, bivalves, gastropods, decapods, amphipods, cumaceans, etc.

The change in proportion of a particular type of organism (for example, amphipods)

representing a particular functional morphology, may be indicative of an alteration of the

habitat structure. This study was compared to historical surveys and to post-dredging

data to determine differences in taxonomic distributions.

Alomerative Hierarchical Cluster Analysis was conducted utilizing the

Czekanowski's Index as the matrix of association coefficients. The agglomerative

technique starts by linking the highest similarity pairs and then proceed to the next

highest in order. Hierarchical refers to the tree-like branching form of the output. The

group average sorting technique was utilized as the clustering method (Sneath and

Sokal, 1973), where the similarity between a sample and an existing cluster equals the

arithmetic mean of similarities between the sample and all the members of the cluster

(Krebs, 1989).

Similarity and cluster analyses were conducted using BioStat Il® Software

(Pimentel and Smith, 1993).

Reference Collections

Mote Marine Laboratory and the University of South Florida maintain an

invertebrate museum collection. Any species collected by this study, not currently

contained in the collection, were verified and added to the archive.
41

FINAL REPORT

OCS Report MMS 95.0005

Chapter 2

2.1 BASELINE INFORMATION

The bottom topography at all the sampling sites is essentially a flat, sand sheet

with no consolidated substrate or hard-bottom communities observed. Turbidity made

observations difficult during dredging at Site I but dredged holes could be observed from

the clamshell dredge used at this location. Small sand waves reflect the current activity

in the area and this current activity also occasionally caused an increase in turbidity.

2.2 ENVIRONMENTAL CONDITIONS AT THE STUDY SITES

The sites studied in this survey all lie in the innermost portion of the west Florida

Continental Shelf. Water depths ranged from 5-6 m at all sites with the exception of the

ship channel off Egmont Key (Site I) where depths were 10-15 m. Doyle and Sparks

(1980) have described the geology and sediments of this continental margin. The west

Florida margin, like the peninsula itself is made up of about 5 kilometers of carbonate

rocks intercalated with evaporites which have been deposited more or less continuously

since Jurassic Time. Most of the west Florida continental shelf is veneered with a

surficial sand sheet of relatively coarse carbonate sands composed predominantly of

mollusk fragments. However, the Florida Peninsula is covered with a number of Tertiary

quartz sand terrace deposits brought south by long shore currents from the Appalachian

Province during higher stands of sea level. The inner 10 miles or so of the west Florida

continental shelf is also veneered with this quartz sand mixed with varying amounts of

carbonates. Quartz sand also composes the majority of the west Florida beaches.

Rivers that drain into the west Florida margin are small and slow flowing with little

capacity to carry suspended sand sized material. In fact, they carry a very small

suspended load of any size. What the rivers do bring down is trapped in estuaries or

lagoons behind barrier islands. The beaches are therefore sediment poor and somewhat

ephemeral. It is therefore probable that the only new material being added to the inner

west Florida system is carbonate.

The quartz sand band is thin and sand sources for beach renourishment, the

dredging of the west Florida Margin that led to the inception of this project, are rare.

Most sources are found in the ebb tidal deltas that lie offshore associated with either

active or closed inlets in the barrier island system. The largest of these is the giant

feature at the mouth of Tampa Bay where the Egmont Key site (Site I) is located. The

only new sand coming into the system is from the erosion of headlands or from retreat

of the dunes along the barrier islands. Many of the narrow barrier islands along the

study area coast have been undergoing erosion and exhibit the bluff formation

characteristic of a retreating coast.
FINAL REPORT

OCS Report MMS 95-0005

23 DREDGING TECHNIQUES EMPLOYED AT THE EGMONT KEY AND

LONGBOAT KEY SITES

It should be noted that the dredging techniques and equipment employed at the

two study sites that were dredged were quite different. These differences may be

responsible for some of the observed differences in seafloor impacts

At the Egmont Key site (Site I), a clamshell dredge was used to excavate the sand

deposits which were then placed in a hopper barge for transport into shallower waters.

Clamshell dredges use buckets (sizes 1-8 cubic meters) which are mechanically

activated to "bite into" the seabed to remove material (typically for low-cost/low-volume

mining close to shore). Material may then be loaded into its own hopper or onto a

separate barge. Resulting small pits usually leave an irregular seafloor topography and

turbidity plumes throughout the water column are common (Groat et al., 1993).

At the Longboat Key site (Site IV), Bean Dredging Corporation's Beachbuilder was

employed. The Beachbuilder is a dustpan dredge. It has a wide, flat head designed to

skim thin layers of sand from the bottom and uses high-pressure jets of seawater to

loosen sand in a wide, shallow path. Because the dustpan dredge removes a much

thinner layer of sand than a conventional dredge, it tends to leave some of the substrate

intact (Taylor, 1993).

42
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Chapter 3

3.1 SEDIMENT AND GEOPHYSICAL RESULTS

Sediment Analyses

Grain size (texture) was measured by the standard technique of sieving an aliquot

through sieves nested at 1 4) intervals; that is-i 4) (2mm), 0 4) (1mm), 1 4) (500p), 2

4) (250 p), 3 4) (125 /.1), 4 4) (62 p), and pan (<62p) in the method of Folk, 1980. This

whole range is considered to be the sand sized fraction. For Site I, the only one in which

we have before, during and after dredging sampling, measurements of all ten replicate

samples were combined at each of the three stations and histograms were constructed

for comparison of sampling periods. These are shown as Figures 3.1-1 to 3.1-5.

Appendix A is the source data for these histograms.

Figures 3.1-ito 3.1-3 show that there is no significant difference in texture through

time. At Stations I-i and 1-3 the majority of the particles are concentrated in the 2-3 4)

(25O-125p) size class with a strong secondary concentration in the 3-44) (i25-62p) size

range. These sizes are commonly described as fine sand and very fine sand,

respectively. Station 1-2 shows an anomalous concentration in the coarse sand range

0-1 4) (1 mm-500 p) in the 01/93 sampling as well as more sediment in the coarser

fractions as well. Station 1-2 generally shows more variation between sampling periods

as well.

Normally it would be expected that a newly created depression in relatively

shallow water such as at the Egmont Key site (Site I), where waves and current affect the

bottom, would begin to be filled Immediately with sediment moved by these forces

around the inner portion of the shelf. Normally depressions are thought to be sinks for

fine grained sediments (finer than sand sized) first. Apparently that is not the case here.

A plausible explanation may be found by examining Figures 3.1-1 to 3.1-6. There is only

a tiny finer than sand sized fraction present in the inner west Florida shelf surficial sand

sheet. There is simply virtually no fine fraction with which to fill the depression.

The sediment on the inner few miles of the west Florida shelf is dominantly fine

to very fine quartz sand, thus the heavy concentration in the 2-4 4) size fractions.

However, there is a second important component, calcium carbonate, composed mostly

of molluscan shell fragments. These make up the coarser size fractions. In some places

they can be quite concentrated and their distribution is patchy and can vary even within

a station wide area. Station 1-2 has a higher carbonate content that accounts for its

variability.

Figures 3.1-4 to 3.1-6 show the within station variability for stations 1-3-09-3, 11-2-54,

and 11-1-072. Examination of the within station variability for Station 3-1-09-3 (Figure

3.1-4) shows the expected concentrations in the 2-3 4) and 3-4 4) size fractions. It also

shows that when the coarser carbonate fractions increase there is a concomitant

decrease in the finer quartz sand fractions. Figure 3.1-5 and 3.1-6 show the between

station variability of two stations at Site II. Table 3.1-1 shows the carbonate content for

these two stations for the same sampling periods. Station 11-2-054, composed

predominantly of quartz sand shows heavy concentrations in the 2 to 4 4) size ranges

43
>-1 p -1-0 p 0-1 p Grain Size I-i 1-2 p 2-3 p 3-4 p <4p I $ -1.072 1-1-013 0 -1 -093 0 i -1-054 Figure 3.1-1. Sediment grain size distribution, Site I, Station 1.
c%J c' c' c'J0CC 0 N-.-J c"J cJ 45 OCS Report MMS 95-0005 FINAL REPORT
Grain Size 1-3 I 1-3-072 1-3-013 1-3-093 0 1-3-054 >-1 plu -1-0 p 0_i p 1-2 p 2-3 p 3-4 p <4p Figure 3.1-3. Sediment grain size distribution, Site I, Station 3.
80-

70

60

w

c 30

en 20

10

g

>-1 p -1 0 p 0-1 p 1 2 p 2.3 p 3-4 p <4p

Figure 3.1-4. Sediment grain size distribution for subsamples A-G, Site I, Station 3, September 1993.

3.A

3B

3.D

3.E

3-F
U<Owu C, CC2I. 0c N p I I C C C C C C,, CJ ._C.=_48 C C,) C,) 0C' C' I-'I, N00I-. - C) 0EC) - =I-C.) C
() L; w u (! --- 49 OCS Report MMS 95-0005 FINAL REPORT
FINAL REPORT

OCS Report MMS 95-0005

while Station 11-1-072 has a coarser distribution, reflecting high carbonate content.

TABLE 3.1-1

Weight Percent CaCO3

Carbonate content was determined by acidifying a weighed aliquot with 10% HCI,

dissolving the carbonate minerals, drying the sample and re-weighing. Organic content

was determined by combustion of a carbonate free subsample. Data for all stations is

in Appendix B.

Geophysical Results

The geophysical surveys provided a framework for the benthic sampling. Several

techniques were used - side scan sonar, high resolution seismic profiling, and precision

depth recording. Precision depth recording (PDR) of bathymetry provided the most

useful data. Should such a study be undertaken again, it would be wise to dispense with

the high resolution seismic profiling and side scan sonar work and concentrate on

repeating with precise navigation a complete bathymetric survey of the excavation. The

pre-dredge survey of the Egmont Key site (Site I) was used as data by Mr. David Duncan

in his Master's thesis. Figure 3.1-7 (after Duncan 1993) shows the seismic stratigraphy

and structure North to South across the main ship channel and the Egmont study area.

The Tampa Bay ebb tidal delta is the largest on the peninsular west coast of Florida. It

was formed by sand transported by the long shore currents being swept seaward by the

ebb tidal currents flowing out of Tampa Bay around Egmont Key.

Bathymetry turned out to be by far and away the most sensitive geophysical tool.

A pre-dredging example of Site I, the only one that was dredged, is shown in Figure

3.1-8. Note the vertical exaggeration. Figure 3.1-9 (post-dredging) shows the primary

lasting effect of the dredging; that is the excavation itself. Even as late as 1994, after

several storm and frontal system seasons, the excavation is clearly visible. It is clear that

50

Subsample Site/Location/Date

11-2-054

Site/Location/Date

11-1-072

A 12.0 82.5

B 12.8 87.6

C 15.6 77.3

D 13.9 84.6

E 17.3 86.3

F 10.4 82.5

G 11.4 80.8

H 11.2 87.3

I 14.7 89.9

J 16.6 78.2
-t CD 

CD 

-t 

CD 

CD 

O(D 

CD1 

C 

0 

CD 

CD 

CD 

= 

CD 

CD 

-1 CD 

C, 

CD 

1 

C/) 

CD 

CD 

- 

-I 0 

cJQ 

r (I) 

soo iode svwg S000-S6 

1VNId .LOdJ 

(msec) travel-time Two-way 

I 

2 

w 

= 

C 2. 

I I I 

m.tsr. In dspth Approx. 

5. 

3 

3 

C, 

r 

0 

(msec) travel-time Two-way 

g 0 

I I I I 

(iD 

M 0 . 

d.pth Approx. mst.rs In 
FINAL REPORT

OCS Report MMS 95-0005

the excavation was below local wave base and that even in this shallow system sediment

supply is insufficient to quickly hide the dredge scar.

Figure 3.1-10 shows the post-dredging bathymetry at the Longboat Key site. No

pre-dredge data is available for this site. However perusal of adjacent areas at this site

suggests that a smooth sea floor is the norm along this portion of the coast. Clearly

dredging activity has caused an irregular topography but the pronounced dredge scar

visible at Egmont Key (Site I) is not present.

Longboat Key was dredged with a dustpan dredge which is different from the

clam-shell bucket dredge used off Egmont Key. As discussed in Section 2.3, a dustpan

dredge skims thin layers of sand from the bottom using high-pressure jets of seawater.

Comparison of the post-dredging profiles from both locations does not reveal major

differences in bathymetric profile. While at first glance at Figure 3.1-10, the Longboat

Key site may appear to be more irregular, much of that appearance is due to the very

greater vertical exaggeration (see Figure 3.1-10 vertical scale 6 feet; horizontal scale 1

mile). A diver on the bottom site would not be impressed by the bottom undulations at

either site although the actual dredged excavation would be more visible at Egmont Key

(Site I).

3.2 EPIBENTHIC RESULTS

Although epibenthic surveys were done extensively on the outer continental shelf

of the eastern gulf of Mexico in the early 1970's as part of baseline surveys conducted

by the Bureau of Land Management, little to no information exists for the epibenthos of

the nearshore, subtidal, sand environment. The epibenthos of this area are highly

patchy and mobile. In addition they are often nocturnal and may dig into the sediment

during the daylight hours. Because of these factors, the epibenthic surveys of this study

were qualitative and relied upon the use of otter trawls and a towed, underwater video.

Trawls

Table 3.2-1 shows a list by abundance of all the invertebrate and vertebrate taxa

collected at each sampling site and at each station for the four sampling periods. A total

of 41 different taxa were observed during the study, a low species richness reflecting the

constancy of the habitat in this area. The crab, Portunus gibbesii, and the sand dollar,

Mellita tenuis were by far the most dominant species present during the study. Although

both species were absent from Site II during the May, 1994 sampflng, this site had not

been dredged as planned by the Army Corps of Engineers. The shrimp, Penaeus

duorarum a predominantly nocturnal species, was a distant third and showed great

variability between samples.

Tables 3.2-2 through 3.2-9 list the species collected by number of individuals for

each trawl and the location of each trawl. Although an attempt was made to make each

trawl location constant, current and wind conditions would not make this possible.

However, Portunus gibbesii and Me/I/ta tenuis remained the dominant epibenthic species

throughout the course of the study at both dredged and undredged locations.

54
Dredged Area II I I I 9 I nautical mile 4 r. Figure 3.1-10. Bathmetry at Site IV, Longboat Key, September 1993, post-dredging.
>-1 p -1-0 p 0-1 p Grain Size I-i 1-2 p 2-3 p 3-4 p <4p I $ -1.072 1-1-013 0 -1 -093 0 i -1-054 Figure 3.1-1. Sediment grain size distribution, Site I, Station 1.
c%J c' c' c'J0CC 0 N-.-J c"J cJ 45 OCS Report MMS 95-0005 FINAL REPORT
Grain Size 1-3 I 1-3-072 1-3-013 1-3-093 0 1-3-054 >-1 plu -1-0 p 0_i p 1-2 p 2-3 p 3-4 p <4p Figure 3.1-3. Sediment grain size distribution, Site I, Station 3.
80-

70

60

w

c 30

en 20

10

g

>-1 p -1 0 p 0-1 p 1 2 p 2.3 p 3-4 p <4p

Figure 3.1-4. Sediment grain size distribution for subsamples A-G, Site I, Station 3, September 1993.

3.A

3B

3.D

3.E

3-F
U<Owu C, CC2I. 0c N p I I C C C C C C,, CJ ._C.=_48 C C,) C,) 0C' C' I-'I, N00I-. - C) 0EC) - =I-C.) C
() L; w u (! --- 49 OCS Report MMS 95-0005 FINAL REPORT
FINAL REPORT

OCS Report MMS 95-0005

while Station 11-1-072 has a coarser distribution, reflecting high carbonate content.

TABLE 3.1-1

Weight Percent CaCO3

Carbonate content was determined by acidifying a weighed aliquot with 10% HCI,

dissolving the carbonate minerals, drying the sample and re-weighing. Organic content

was determined by combustion of a carbonate free subsample. Data for all stations is

in Appendix B.

Geophysical Results

The geophysical surveys provided a framework for the benthic sampling. Several

techniques were used - side scan sonar, high resolution seismic profiling, and precision

depth recording. Precision depth recording (PDR) of bathymetry provided the most

useful data. Should such a study be undertaken again, it would be wise to dispense with

the high resolution seismic profiling and side scan sonar work and concentrate on

repeating with precise navigation a complete bathymetric survey of the excavation. The

pre-dredge survey of the Egmont Key site (Site I) was used as data by Mr. David Duncan

in his Master's thesis. Figure 3.1-7 (after Duncan 1993) shows the seismic stratigraphy

and structure North to South across the main ship channel and the Egmont study area.

The Tampa Bay ebb tidal delta is the largest on the peninsular west coast of Florida. It

was formed by sand transported by the long shore currents being swept seaward by the

ebb tidal currents flowing out of Tampa Bay around Egmont Key.

Bathymetry turned out to be by far and away the most sensitive geophysical tool.

A pre-dredging example of Site I, the only one that was dredged, is shown in Figure

3.1-8. Note the vertical exaggeration. Figure 3.1-9 (post-dredging) shows the primary

lasting effect of the dredging; that is the excavation itself. Even as late as 1994, after

several storm and frontal system seasons, the excavation is clearly visible. It is clear that

50

Subsample Site/Location/Date

11-2-054

Site/Location/Date

11-1-072

A 12.0 82.5

B 12.8 87.6

C 15.6 77.3

D 13.9 84.6

E 17.3 86.3

F 10.4 82.5

G 11.4 80.8

H 11.2 87.3

I 14.7 89.9

J 16.6 78.2
-t CD 

CD 

-t 

CD 

CD 

O(D 

CD1 

C 

0 

CD 

CD 

CD 

= 

CD 

CD 

-1 CD 

C, 

CD 

1 

C/) 

CD 

CD 

- 

-I 0 

cJQ 

r (I) 

soo iode svwg S000-S6 

1VNId .LOdJ 

(msec) travel-time Two-way 

I 

2 

w 

= 

C 2. 

I I I 

m.tsr. In dspth Approx. 

5. 

3 

3 

C, 

r 

0 

(msec) travel-time Two-way 

g 0 

I I I I 

(iD 

M 0 . 

d.pth Approx. mst.rs In 
FINAL REPORT

OCS Report MMS 95-0005

the excavation was below local wave base and that even in this shallow system sediment

supply is insufficient to quickly hide the dredge scar.

Figure 3.1-10 shows the post-dredging bathymetry at the Longboat Key site. No

pre-dredge data is available for this site. However perusal of adjacent areas at this site

suggests that a smooth sea floor is the norm along this portion of the coast. Clearly

dredging activity has caused an irregular topography but the pronounced dredge scar

visible at Egmont Key (Site I) is not present.

Longboat Key was dredged with a dustpan dredge which is different from the

clam-shell bucket dredge used off Egmont Key. As discussed in Section 2.3, a dustpan

dredge skims thin layers of sand from the bottom using high-pressure jets of seawater.

Comparison of the post-dredging profiles from both locations does not reveal major

differences in bathymetric profile. While at first glance at Figure 3.1-10, the Longboat

Key site may appear to be more irregular, much of that appearance is due to the very

greater vertical exaggeration (see Figure 3.1-10 vertical scale 6 feet; horizontal scale 1

mile). A diver on the bottom site would not be impressed by the bottom undulations at

either site although the actual dredged excavation would be more visible at Egmont Key

(Site I).

3.2 EPIBENTHIC RESULTS

Although epibenthic surveys were done extensively on the outer continental shelf

of the eastern gulf of Mexico in the early 1970's as part of baseline surveys conducted

by the Bureau of Land Management, little to no information exists for the epibenthos of

the nearshore, subtidal, sand environment. The epibenthos of this area are highly

patchy and mobile. In addition they are often nocturnal and may dig into the sediment

during the daylight hours. Because of these factors, the epibenthic surveys of this study

were qualitative and relied upon the use of otter trawls and a towed, underwater video.

Trawls

Table 3.2-1 shows a list by abundance of all the invertebrate and vertebrate taxa

collected at each sampling site and at each station for the four sampling periods. A total

of 41 different taxa were observed during the study, a low species richness reflecting the

constancy of the habitat in this area. The crab, Portunus gibbesii, and the sand dollar,

Mellita tenuis were by far the most dominant species present during the study. Although

both species were absent from Site II during the May, 1994 sampflng, this site had not

been dredged as planned by the Army Corps of Engineers. The shrimp, Penaeus

duorarum a predominantly nocturnal species, was a distant third and showed great

variability between samples.

Tables 3.2-2 through 3.2-9 list the species collected by number of individuals for

each trawl and the location of each trawl. Although an attempt was made to make each

trawl location constant, current and wind conditions would not make this possible.

However, Portunus gibbesii and Me/I/ta tenuis remained the dominant epibenthic species

throughout the course of the study at both dredged and undredged locations.

54
Dredged Area II I I I 9 I nautical mile 4 r. Figure 3.1-10. Bathmetry at Site IV, Longboat Key, September 1993, post-dredging.
Species

Portunus gibbesii

Mellita tenuis

Pci iaeus duorarum

Penaeus sp.

Anadarn transversa

Port unus spuunzanus

Arenaeus cr1 brarius

Peuaeus aztecus

Pagurus inipressus

Squilla enipusa

Luidia clathrata

Lytechinus variegatus

Argopecten gibbus

Callinectes sapidus

Diadeina sp.

Men ippe niercenaria

Menippe ,uercenaria juvenile

Ophiodernia cinereum

OpJ:ioderma sp.

Astropccten coin plus

Callincctes siinilis

Lchinaster niodestus

Pk'ria colyinbus

Stroinhus alatus

Astropecten duplicatus

Cithippa fiwninea

Hepa Ins epheliticus

Libinia dubia

TABLE 3.2-1

Combined species list in order of prevalence and which trawls the species was found in for all four MMS cruises

X= present 0= absent

D7tJ3-1SI)2 I 01/19-21193 I 09/08-09/93 I 05/24-25/94

Site I I Site II I Site III I Site I I Site II I Site I I Site IV I Site I I Site II

Number 123 123 1123 1123 1123 1123 1123 123 1123

>1424 XXX IXXX IXXX lxxx IXXO IXXX lxxx IXXO 1000

>1157 OXX IOXO 1000 IOXX 1000 1OXX I OXX 1 OXX I 000

129 000 1000 1000 IXOX ixxo ixxx 100010001000

2 000 I000IXOOI000I000I000I000I000I000

90 000 IXOO IXXX 1000 IXOX 1000 100010001000

75 XXO I OXX 1000 IXXX I OXO lxxx I X00 10001 000

55 OXX 1000 1000 IXXX I000IXXX I X00I000I X00

52 000 1000 I000IXXX IXXO 1000 100010001000

42 000 IOOX IOOX 1000 IXOO (000 1000(0001000

36 000 I000I000IXXX I000IXXX 100010001000

'32 XXX IOXO I000IXOX IOOX IXOX I XOXIOXO 1000

30 XXO IOXO IXOO IOXO IXOX 1000 100010001 X00

25 000 I000IXOX 1000 10001000 100010001 X00

15 OXX OXO IXOO 1000 l000lXxx I OXOI000I OXO

7 000 I000IXOX 1000 10001000 100010001000

6 000 IOXX 10001000 1000 IOOX 100010001000

1 000 100010001000 10001000 I 00010001 X00

4 000 100010001000 ixxx 1000100010001000

2 000 IOOX IOOX 1000 10001000 100010001000

3 XOX I000I000I000I000I000I000I000I000

3 000 1000 IOOX 1000 100010001 XXOI000I 000

3 000 I000IXOX 1000 10001000 100010001000

3 000 I000l00Xl000I000I000l000I000l000

3 X00 10001 X00 1000 10001000 I 00010001 000

2 000 100010001000 l000l00X I OXOI000I 000

2 000 bOX 1000 IOXO 10001000 100010001000

2 000 1000 000 IOOX 10001000 100010001 X00

2 000 IOXO I000l0X0 10001000 100010001000

Persephona punctata aquilonaris 2 000 I000I000IOXO 0001000 00010001 000

Podochela riisei 2 000 I000IOOXI000 0001000 00010001000

Synaptuta hydriforruis 2 000 l000l000(000 0001000 OXOI000I 000

Botrylloides sp. 1 000 100010001000 0001000 OXOI000I 000
(Ti

t7I13-152

Site I I Site II

I 01119-21/93 I 09/08-09/93 I 05/24-25/94

Site III I Site I I Site H I Site I Site IV I Site I I Site II

Species Number 1 2 3 I 1 2 3 123 1123 1123 1123 1231123 I 123

Hepatus pudibundus juvenile 1 0 0 0 I 0 0 0 0001000 I X00 1000 00010001000

1-lippocanipus sp. 1 0 0 0 I 0 0 0 X0O 1000 10001000 00010001000

Holothuria princeps 1 0 0 0 I 0 0 0 000 IOXO 10001000 00010001 000

Holothuria sp. 1 0 0 0 I 0 0 0 X00 1000 10001000 00010001000

Luidia alternata 1 0 0 0 I X 0 0 0001000 10001000 00010001000

Panopeus herbstii juvenile 1 0 0 0 I 0 0 0 0001000 10001000 OOXI000I 000

Pleziroploca giganlea juvenile 1 0 0 0 I 0 0 0 OOX 1000 10001000 00010001000

Podochela sidneyi 1 0 0 0 I X 0 0 0001000 10001000 00010001000

Polynices duplicatus 1 0 0 0 I 0 0 0 000 IOXO 10001000 00010001 000

Port linus ordwayi juvenile 1 0 0 0 0 0 0 OOX 1000 I 0001000 00010001000
58

FINAL REPORT

OCS Report MMS 95-0005

TABLE 3.2-2

Species List for Trawis Made on MMS Cruise 07/13-16/92 RJV Suncoaster

Site I Trawl 1 07/16/92 0654 27°37.92'N 82°49.40'W

0711 27°38.00'N 82°48.65'W

Species Number

Portunus gibbesii >100

LUidia clathrata 2

Lyrechinus variegatus 2

Astropecten comptus 1 Portunus spinimaneus 1 Strombus alatus 1 Site I Trawl 2 07/16/92 0729 27°37.43'N 82°48.23'W

0750 27°37.24'N 82°49.35'W

Species Number

Portunus gibbesii >100

Mellita quinquesperforata >50

Laidia clathrata 5

Callinectes sapidus 4

Lytechinus variegatus 2

Arenaeus cribrarius 1 Portunus spinimaneus 1 Site I Trawl 3 07/16/92 0818 27°37.85'N 82°48.76'W

0840 27°37.04'N 82°48.69'W

Species Number

Portunus gibbesii >200

Mellita quinquespeiforata 20

Astropecten comptus 2

Luidia clathrata 2

Arenaeus cribrarius 1 Callinectes sapidus 1 Site ilTrawl 1 07/15/92 1931 27°15.74'N 82°35.21'W

1950 27°16.52'N 82°35.67'W

Species Number

Anadara transversa 20

Portunus gibbesii 6

Laidiaaltemata 1 Podochela sidneyi 1
59

FINAL REPORT

OCS Report MMS 95-0005

SitellTrawj2 07/15/92 1850 27°17.03'N 82°35.11'W

1911 27°16.05'N 82°34.94'W

Species Number

Portunus gibbesii 35

Mellita quinquespe,forata 27

Lytechinus variegatus 6

Menippe mercenaria 4

Callinectes sapidus 2

Luidia clathrata 2

Portunus spinimaneus 2

Libinia dubia 1 Site II Trawl 3 07/15/92 2000 27°17.08'N 82°36.06'W

2020 27°18.04'N 82°36.79'W

Species Number

Portunus gibbesii 18

Portunus spinimaneus 8

Calappaflamea 1 Menippe mercenaria 1 Ophioderma sp. 1 Pa gurus impressus 1 Site ifi Trawl 1 07/14/92 2245 26°57.68'N 82°26.34'W

2310 26°58.24'N 82°25.47'W

Species Number

Argopecten gibbus 23

Anadara transversa 17

Diadema sp. 5

Portunus gibbesii 4

Callinectes sapidus 3

Lytechinus variegatus 3

Penaeus sp. 2

Strombus alatus 2

Echinaster modesrus 1

Hippocampus sp. 1

Holothuria sp. 1 Site ifi Trawl 2 07/15/92 0044 26°59.4FN 82°27.04W

0106 26°58.72'N 82°27.04'W

Species Number

Anadara transversa 30

Portunus gibbesii 1
60

FINAL REPORT

OCS Report MMS 95-0005

Site ifi Trawl 3 07/14/92 2335 26°58.22'N 82°25.52'W

2350 26°57.69'N 82°26.13'W

Species Number

Pa gurus impressus 40

Anaáara transversa 14

Pteria colymbus 3

Diadema sp. 2

Echinaster modestus 2

Podochela riisei 2

Argopecten gibbu 1 Callinectes similis 1

Ophiodenna sp. 1 Pleuroploca gigantea juvenile 1 Portunus gibbesii 1 Portunus ordwayi juvenile 1
FINAL REPORT

OCS Report MMS 95-0005

TABLE 3.2-3

Combined species list in order of prevalence and which trawls the species was found in

61

MMS Cruise

Species

07/13 - 16/92 R/V Suncoaster

Site 1 Site II

Number 1 2 3 1 2 3 Site III

1 2 3 Portunus gibbesii >465 X X X X X X X X X Mellita quinquespeiforata >97 X X X Anadara transversa 81 X X X X Pagurus impressus 41 X X Argopecten gibbus 24 X X

Lyrechinus variegarus 13 X X X X

Portunus spinimaneus 12 X X X X Luidia clarhrata 11 X X X X

Callinecres sapidus 10 X X X X Diadema sp. 7 X X Menippe mercenaria 5 X X

Astropecten comptus 3 X X

Echinaster modestus 3 X X

Pteria co1ymbu. 3 X

Strombus alatus 3 X X

Arenaeu.s cribra rius 2 X X

Ophiodermasp. 2 X X

Penaeussp. 2 X

Podochela riisei 2 X

Calappaflamea 1 X

Callinectes similis 1 X

Portunus ordwayi juvenile 1 X Hippocampussp. 1 X

Holothuria sp. 1 X

Libinia dubia 1 X

Luidia alz'ernata 1 X

Pleuroploca gigantea juvenile 1 X

Podochela sidneyi 1 X
62

TABLE 3.2-4

Species List for Trawis Made on MMS Cruise

01/19-21/93 R/V Suncoaster

Site I Trawl 1 01/19/93 2140 27°37.98'N 82°49.40'W

0711 27°38.OffN 82°48.40'W

Species Number

Portunus gibbesii 150

Penaeus duo rarwn 12

Squilla empusa 12

Penaeus aztecus 5

Luidia clathrata 2

Arenaeus cribrarius 1 Portunus spinimanus 1 Site I Trawl 2 01/19/93 2237 27°37.43'N 82°48.45'W

2257 27°37.20'N 82°49.64'W

Species Number

Mellita tenuis 372

Portunus gibbesii 24

Penaeus aztecus 18

Squilla empusa 7

Portunus pinimanus 4

Arenaeus cribrarius 2

Persephona punctata aquilonaris 2

Calappaflwmnea 1 Holothuria princeps 1 Libinia dubia 1 Lytechinus variegatus 1 Polynices duplicatus 1 Site I Trawl 3 01/19/93 2335 27°37.82'N 82°48.78'W

2355 27°36.93'N 82°48.72'W

Species Number

Mellita tenuis 226

Portunus gibbesii 88

Penaeu. aztecus 23

Squilla empusa 6

Penaeus duora ruin 3

Portunus spinimanus 3

Arenaeus cribrarius 1

Heparus epheliticus 1

Lthdia clathrata 1

FINAL REPORT

OCS Report MMS 95-0005
63

FINAL REPORT

OCS Report MMS 95-0005

Site II Trawl 1 01/20/93 0705 27°15.80'N 82°35.26'W

0720 27°16.55'N 82°35.72'W

Species Number

Lytechinus variegatus 14

Anadara transversa 6

Portunus gibbesii 6

Penaeus aztecus 2

Penaeus duorarwn 2

Hepatus pudibundus juvenile 1 Ophiodenna cinereum 1 Pagarus impressus 1 Site llTrawl2 01/20/93 0735 27°16.90'N 82°35.16'W

1950 27°16.00'N 82°34.90'W

Species Number

Penaeus aZtecus 4

Penaeus duorarum 4

Ophioderma cinereum 1

Portunus gibbesii 1 Portunus spinimanus 1 Site llTrawI3 01/20/93 0845 27°17.00'N 82°36.00'W

0905 27°17.80'N 82°36.70'W

Species Number

Anadara transversa 3

Ophioderma cinereum 2

Luidia clathrata 1 Lytechinus variegatus 1
TABLE 3.2-5

Combined species list in order which trawis the species

64

x

x

x

FINAL REPORT

OCS Report MMS 95-0005

of prevalence and was found in

Species Number

Mellita tenuis 598

Portunus gibbesii 269

Penaeus aZtecus 52

Squilla empusa 25

Penaeus duora rum 21

Lytechinus variegatus 16

Anadara transversa 9

Portunus spinimanus 9

Arenaeus cribrarius 4

Luidia clathrata 4

Ophioderma cinereum 4

Persephona puncrara aquilonans 2

Calappaflam,nea 1 Hepatus epheliticus 1 Heparus pudibundus juvemle 1 Holothuria princeps 1 Libinia dubia 1 Pagarus impressus 1

Polynices duplicarus 1

MMS Cruise 01/19 2 1/93 RJV Suncoaster
TABLE 3.2-6

Species List for Trawis Made on MMS Cruise

09/08-09/93 R/V Suncoaster

Site I Trawl 1 09/08/93 2239 27°37.53'N 82°49.5 1W

2259 27°38.20'N 82°48.48'W

Species Number

Portunus gibbesii 339

Penaeus duora rum 57

Portunus spinimanus 25

Arenaeuscrjbrarjus 12

Squilla empusa 3

Luidia clathrata 2

Callinectes sapidus 1 Site I Trawl 2 09/08/93 2321 27°38.02'N 82°48.O0'W

2343 27°37.14'N 82°46.68W

Species Number

Portunus gibbesii 207

Penaeus duora rum 30

Arenaeus cribrarius 23

Mellita tenuis 21

Portunus spinimanus 15

Squilla empusa 5

Callinectes sapidus 1 Site I Trawl 3 09/09/93 0038 27°38.09'N 82°47.87'W

0058 27°37.24'N 82°48.43'W

Species Number

Portunus gibbesii 122

Penaeusduorarwn 21

Luidia clathrata 12

Mellita renuis 10

Portunus spinimanus 9

Arenaeus cribrarius 8

Squilla empusa 3

Astropecten duplicatus

Callinectes sapidus 1 Menippe mercenaria

65

FINAL REPORT

OCS Report MMS 95-0005
66

FINAL REPORT

OCS Report MMS 95-0005

Site IV Trawl 1 09/09/93 0812 27°26.18'N 82°41.87'W

0821 27°26.07'N 82°42.07'W

Species Number

Portunus spinimanus 5

Arenaeus crLbrarius 4

Portunus gibbesii 3

Callinecres similis 1 LUidia clathrata 1 Site IV Trawl 2 09/09/93 0834 27°26.06'N 82°41.95'W

0839 27°26.11'N 82°41.86'W

Species Number

Portunus gibbesii 2

Synaptula hydrformis 2

Astropecten duplicatus 1

Botrylloides sp. 1 Callinectes sapidus 1 Callinectes similis 1 Mellita tenuis

Site IV Trawl 3 09/09/93 0922 27°25.80'N 82°41.54'W

0933 27°25.70'N 82°41.96'W

Species Number

Mellita tenuis 359

Luidia clathrata 1

Panopeus herbstii juvenile 1 Portunus gibbesii 1
TABLE 3.2-7

Combined species list in order of prevalence and which trawis the species was found in

67

FINAL REPORT

OCS Report MMS 95-0005

MMS Cruise 09/08 - 09/93 R/V Suncoaster

Site I Site IV

Species Number 1 2 3 1 2 3

Portunus gibbesii 674 X X X X X X

Mellira tenuis 391 X X X X

Penaeus duora rum 108 X X X

Portunus spinimanus 54 X X X X

Arenaeus cribrarius 47 X X X X

Luidia clathrata 16 X X X X

Squilla empusa 11 X X X

Callinecres sapidus 4 X X X X

Asrropecten duplicatus 2 X X

Callinectes similis 2 X X

Synaprula hydrformis 2 X

Borrylloides sp. 1 X

Menippe mercenaria 1 X

Panopeus herbsrii juvenile 1 X
TABLE 3.2-8

Species List for Trawis Made on MMS Cruise

05/24-25/94 RJV Suncoaster

Site I Trawl 1 05/25/94 0702 27°38.00'N 82°47.00'W

0735 27°38.98'N 82°47.35'W

Species Number

Portunus gibbesii 10

Site I Trawl 2 05/25/94 0807 27°37.59'N 82°47.40'W

0829 27°37.41'N 82°48.23'W

Species Number

Mellita tenuis 21

Portunus gibbesii 6

Luidia clathrara 1

Site I Trawl 3 05/25/94 0846 27°37.8TN 82°47.68'W

0903 27°37.19'N 82°47.58'W

Species Number

Mellita tenuis 50

Site II Trawl 1 05/24/94 2243 27°16.15'N 82°34.25'W

2301 27°16.58'N 82°34.45'W

Species Number

Arenaeus cribrarius 2

Argopecten gibbus 1 Hepatus epheliticus 1 Lytechinus variegatus 1 Menippe mercenaria juvenile 1 Site II Trawl 2 05/24/94 2330 27°17.00'N 82°34.20'W

2350 27°16.32'N 82°33.87'W

Species Number

Callinectes sapidus 1 Site II Trawl 3 05/25/94 0035 27°17.135'N 82°36.085'W

0055 27°16.15'N 82°34.92'W

Species Number

NOTHING

68

FINAL REPORT

OCS Report MMS 95-0005
TABLE 3.2-9

Combined species list in order of prevalence and which trawls the species was found in

69

FINAL REPORT

OCS Report MMS 95-0005

MMS Cruise 05/24 - 25/94 WV Suncoaster

Site I Site II

Species Number 1 2 3 1 2 3

Mellita tenuis 71 X X

Portunus gibbesli 16 X X

Arenaeus cribrarius 2 X

Argopecten gibbus 1 X

Callinectes sapidus 1 X

Hepatus epheliticus 1 X

Luidia clathrara 1 X

Lytechinus variegatus 1 X

Menippe mercenaria juvenile 1 X
70

FINAL REPORT

OCS Report MMS 95-0005

The smallest number of epibenthic species and the smallest number of individuals

were collected on the last cruise in May, 1994 (Table 3.2-8 and 9). This probably reflects

seasonal changes and not a result of dredging since on this date only Sites I and II were

sampled and only Site I had been dredged.

Underwater Video

Underwater video was recorded over each transect at each location for each

sampling cruise. This represents a total of approximately 120 hours of video recorded

during the course of the study. There was little variability observed between locations

or between sampling dates.

Observations of flora and fauna were rare. The flora observed was unattached,

drifting macroalgae and not seagrass. Occasional worm tubes belonging to the infaunal

species, Diopatra cuprea, were observed protruding above the sediment and an

occasional portunid crab was observed swimming away from the light. These

observations reflect the constancy of this very dynamic sand habitat and the low

epibenthic diversity of the area.

3.3 INFAUNAL COMMUNITY RESULTS

Stewart-Oaten et al. (1986) described a rationale for the evaluation of

environmental impact assessment based upon the magnitude of variation between

control and affected areas before and after impact. Description of the environment to be

affected must include estimates of the variances of the sample means of the relevant

variables, for it is only against this variation that impacts can be detected (Underwood,

1992).

One objective of the pre-dredging analysis was to define natural pre-impact or

baseline levels of variation throughout all areas. The baseline variations were then

utilized as a comparative measure for post-impact variations of community parameters,

with the control stations continuing to serve as guide for "natural" variations.

The level of natural variation in species composition and faunal abundance can

serve as a measure of stress in marine communities. Warwick and Clarke (1993)

examined variability in species diversity (H') and species abundances for meiobenthos,

macrobenthos, coral reefs and reef fish. A clear log-log relationship was found between

the variance and the mean abundance for all species. The slope of the log-log

regression increased significantly between control and impacted sites. Additionally, the

variability in macrobenthic species diversity (H') tended to increase with increasing levels

of perturbation.

Overall results are presented and discussed first on an areawide basis prior to

dredging and second, on a site by site basis according to site specific dredging

schedules. Each site had its own dredging design and schedule. As it turned out,

Egmont Key was dredged in the Fall of 1992 and Longboat Key was dredged in the

Summer of 1993. Both the Sarasota and Manasota Key sites were not dredged during
FINAL REPORT

OCS Report MMS 95-0005

the time frame of this study. A comparison of community parameters among sites prior

to dredging will also be presented.

Species saturation curves are generally constructed to determine the appropriate

number of replicate samples for any given benthic study. This analysis considers the

number of new species added to the total number of species with each additional

replicate sample collected. After a certain number of samples, the contribution of new

taxa to total taxa drops off. When the percent of new taxa falls below some

predetermined number (generally 5%) then a sufficient number of replicates have been

collected to describe faunal composition. A species saturation curve for the present

study is shown in Figure 3.3-1.

Total number of taxa and individuals (and percent of total taxa and individuals) for

each major faunal group are presented in Table 3.3-1. A total of 620 taxa and 52,295

individuals were identified during the study. Annelids (segmented worms) contributed

44 and 49 percent of the taxa and individuals, respectively. Molluscan fauna represented

22% of the taxa and 29% of the total fauna, while arthropods comprised 27% of the taxa

and 11% of the individuals. These three taxonomic groups represented 93% of the taxa

and 89% of all fauna.

Pre-Dredging Faunal Community Conditions

Three of the four study sites were sampled in July, 1992, prior to the

commencement of any dredging activity. These three sites were: Egmont Key,

Sarasota, and Manasota Key. This section summarizes spatial patterns in community

parameters among all sites in order to describe the general conditions of the benthic

faunal communities prior to dredging.

A statistical summary of faunal parameters for all stations sampled in July, 1992

is presented as part of Table 3.3-2. Manasota Key had the highest mean number of taxa

per station (142 ± 29 taxa), followed by Sarasota (101 ± 9) and Egmont Key (77 ± 26).

The difference in number of taxa between Manasota Key and Egmont Key was

statistically significant (p < 0.05). Manasota Key also had the highest mean number of

individuals per square meter (3635 ± 1175). Sarasota and Egmont Key had similar

faunal abundance, with mean numbers of individuals per square meter of 1832 ± 812

and 2296 ± 1030, respectively. None of the differences in mean number of individuals

per square meter were statistically different (p = 0.05).

Manasota Key had the highest species diversity (Shannon Index) among the three

stations (3.67), followed by Sarasota (3.19) and Egmont Key (2.47). There was a

statistically significant difference (p < 0.05) in Shannon Index between Manasota Key

and Egmont Key. Equitability (a measure of the evenness of species distribution) was

highest at Manasota Key (0.743 ± 0.12), followed by Sarasota (0.697 ± 0.09) and

Egmont Key (0.573 ± 0.12). There were no statistical differences in equitability among

stations. Usually, a positive relationship exists between diversity and equitability i.e., a

high equitability would indicate a high diversity and probably a "healthy condition" of the

fauna. This was evident among all stations during July 1992, where there was a

71
200

1 75

150

125

100

50

25

0

o 12 Jul-92

13 Jan-93

o 12 May-94

IV1 May 94

Number of Replicates

Figure 3.3-1. Species saturation curves for four station-data combinations.

72

FINAL REPORT

OCS Report MMS 95-0005

2 3 4 5 6 7 8 9
ANAL REPORT

OCS Report MMS 95-0005

Table 3.3-1. Total number of taxa and individuals (and percent of total

taxa and individuals) for each major faunal group.

Station: All Total Taxa 620

Date: All Total Indivduals 52295

Fauna 1 Orou

Number

of Taxa

Percent

of Taxa

Number of

Individuals

Percent of

Individuals

NEMERTEA 7 1.13 1911 3.65

ANNELIDA-Total. 271 43.71 25379 48.53

Polychaeta 267 43.06 21727 41.55

Oligochaeta 2 .32 3630 6.94

Misc. Annelids 2 .32 22 .04

MOLLUSCA-Total 135 21.77 15078 28.83

Gastropoda 66 10.65 3679 7.04

Bivalvia 65 10.48 11394 21.79

Misc. Molluscs 4 .65 5 .01

ARTEROPODA-Total 169 27.26 5992 11.46

Nysidacea 5 .81 27 .05

Cumacea 9 1.45 620 1.19

Tanaidacea 6 .97 52 .10

Isopoda 13 2.10 175 .33

Amp)iipoda 78 12.58 3441 6.58

Decapoda 52 8.39 1667 3.19

Insecta 2 .32 5 .01

Misc Arthropods 4 .65 5 .01

ECHINODERMATA 21 3.39 939 1.80

HEMICHORDATA 2 .32 87 .17

VERTEBR.ATA 1 .16 5 .01

MISCElLANEOUS 14 2.26 2904 5.55

TOTAL 620 100.00 52295 100.00
Table 3.3-2. Benthic fauna parameters: Statistical summary for each station and date.

Date Station

No. of Number of Individuals Shannon Shannon Shannon

Taxa Individuals per m2 loqE loqlO loq2 Pielou Marqalef Simpson 0ii

Jul-92 Ic 99 1830 3129 3.14 1.36 4.53 .68 13.05 .082 .91

Jul-92 ID 49 670 1145 2.33 1.01 3.36 .60 7.38 .184 .81

Jul-92 ID 84 1529 2614 1.94 .84 2.80 .44 11.32 .415 .5E

Jul-92 lID 92 588 1005 3.56 1.55 5.14 .79 14.27 .053 .91

Jul-92 lID 101 1537 2628 2.84 1.23 4.10 .62 13.63 .186 .81

Jul-92 IIC 110 1090 1863 3.18 1.38 4.58 .68 15.58 .147 .85

Jul-92 hID 121 1336 2284 3.65 1.59 5.27 .76 16.67 .056 .91

Jul-92 IIIC 176 2458 4202 4.02 1.75 5.80 .78 22.42 .031 .9

Jul-92 hID 131 2585 4419 3.34 1.45 4.82 .69 16.54 .068 .9

Jan-93 Ic 94 1553 2655 3.07 1.33 4.42 .67 12.66 .094 .9C

Jan-93 ID 109 1170 2000 3.12 1.36 4.51 .67 15.29 .132 .8

Jan-93 ID 35 558 954 1.98 .86 2.86 .56 5.38 .294 .7C

Jan-93 hID 166 1233 2108 4.45 1.93 6.42 .87 23.18 .017 .96

Jan-93 lID 114 1516 2592 3.56 1.55 5.14 .75 15.43 .055 .94

Jan-93 hIC 131 1433 2450 3.98 1.73 5.74 .82 17.89 .030 97

Sep-93 IC 120 3249 5555 3.13 1.36 4.52 .65 14.72 .084 .91

Sep-93 ID 142 1547 2645 3.59 1.56 5.18 .72 19.20 .067 .9

Sep-93 ID 62 453 774 3.02 1.31 4.35 .73 9.97 .090 .91

Sep-93 IVD 100 726 1241 3.78 1.64 5.46 .82 15.03 .038 .96

Oct-93 IVD 91 3730 6377 2.43 1.06 3.50 .54 10.94 .191 .80

Oct-93 IVC 98 1200 2052 3.43 1.49 4.94 .75 13.68 .059 .94

May-94 IC 124 3600 6155 3.19 1.39 4.61 .66 15.02 .082 .91

May-94 ID 184 4347 7432 3.72 1.62 5.37 .71 21.84 .052 .94

May-94 ID 81 2359 4033 1.69 .73 2.44 .38 10.30 .485 .51

May-94 lID 193 3517 6013 3.60 1.56 5.20 .68 23.51 .081 .91

May-94 lID 159 3582 6124 3.66 1.59 5.28 .72 19.31 .053 .94

May-94 IIC 133 2899 4956 3.51 1.53 5.07 .72 16.56 .059 .94
FINAL REPORT

OCS Report MMS 95-0005

significant positive relationship (p < 0.001; r = 0.953) between species diversity and

equitability (Figure 3.3-2).

A breakdown of individuals into major faunal groups (phyla) is presented in Table

3.3-3. The major groups are further subdivided phylogenetically into classes and orders.

The percent of individuals in each major faunal group is presented in Table 3.3-4.

Annelids comprised approximately 50% of the total fauna at all sites. At two stations

(one Sarasota and one Manasota Key), oligochaetes contributed over 10% of the total

fauna. The contribution by molluscs varied greatly within and between sites. Molluscs

varied from 14 individuals (2.1 %) at one Egmont Key station to 1125 individuals (73.6%)

at another Egmont Key station. This fluctuation in molluscan fauna was due to

differences in the distribution of the bivalve, Parvilucina multilineata. Gastropods were

slightly more abundant at Manasota Key with respect to the other two sites. Arthropods

were consistent in abundance at all sites, contributing between five and ten percent of

the total fauna. Amphipods and decapods were the most abundant arthropods.

Echinoderms were rare at Egmont Key, while they represented one to three percent of

the fauna at Sarasota and Manasota Key. Finally, miscellaneous taxa, dominated by the

lancelet Branchiostomma, showed high variability within each site, ranging from 0.2 to

17.8% of the fauna at any given station.

The composition of fauna during pre-dredging sampling shows slight differences

among stations in dominant taxa (Table 3.3-5). A composite species list for all stations

can be found in Appendix C. Tubificid oligochaetes were the dominant taxon at

Manasota Key, followed by the lancelet Branchiostomma sp. and the polychaete

Prionospio cristata. The bivalve, Pa,vilucina multilineata, was dominant at Egmont Key

and Sarasota during this period. Other differences in species composition among the

three stations include: higher relative abundance of the polychaeteAglaophamus verrilli

at Sarasota and Manasota Key; higher relative abundance of Mooreonuphis nebulosa,

Isolda pulchella, Goniadides carolinae, and Aricidea cf. suecica (polychaetes), Anadara

trans versa (bivalve), at Manasota Key; and a high percentage of the gastropod Ceacum

bipartitum at Egmont Key (Table 3.3-6). Biomass for the major faunal groups is shown

in Table 3.3-7.

Overall, faunal richness and abundance at each of the three borrow sites indicate

healthy, diverse infaunal communities along the west Florida coastal zone.

Egmont Key

Egmont Key was sampled four times during this study. This included a predredging sampling (July, 1992), one sampling during dredging activities (January, 1993)

and two post-dredging sampling events (September, 1993 and May, 1994, respectively).

This section discusses the temporal trends in faunal community response to dredging

at Egmont Key. It will also look at differences over time among the two dredged and one

control stations as determined by two-way analysis of variance.

75
66

FINAL REPORT

OCS Report MMS 95-0005

Site IV Trawl 1 09/09/93 0812 27°26.18'N 82°41.87'W

0821 27°26.07'N 82°42.07'W

Species Number

Portunus spinimanus 5

Arenaeus crLbrarius 4

Portunus gibbesii 3

Callinecres similis 1 LUidia clathrata 1 Site IV Trawl 2 09/09/93 0834 27°26.06'N 82°41.95'W

0839 27°26.11'N 82°41.86'W

Species Number

Portunus gibbesii 2

Synaptula hydrformis 2

Astropecten duplicatus 1

Botrylloides sp. 1 Callinectes sapidus 1 Callinectes similis 1 Mellita tenuis

Site IV Trawl 3 09/09/93 0922 27°25.80'N 82°41.54'W

0933 27°25.70'N 82°41.96'W

Species Number

Mellita tenuis 359

Luidia clathrata 1

Panopeus herbstii juvenile 1 Portunus gibbesii 1
TABLE 3.2-7

Combined species list in order of prevalence and which trawis the species was found in

67

FINAL REPORT

OCS Report MMS 95-0005

MMS Cruise 09/08 - 09/93 R/V Suncoaster

Site I Site IV

Species Number 1 2 3 1 2 3

Portunus gibbesii 674 X X X X X X

Mellira tenuis 391 X X X X

Penaeus duora rum 108 X X X

Portunus spinimanus 54 X X X X

Arenaeus cribrarius 47 X X X X

Luidia clathrata 16 X X X X

Squilla empusa 11 X X X

Callinecres sapidus 4 X X X X

Asrropecten duplicatus 2 X X

Callinectes similis 2 X X

Synaprula hydrformis 2 X

Borrylloides sp. 1 X

Menippe mercenaria 1 X

Panopeus herbsrii juvenile 1 X
TABLE 3.2-8

Species List for Trawis Made on MMS Cruise

05/24-25/94 RJV Suncoaster

Site I Trawl 1 05/25/94 0702 27°38.00'N 82°47.00'W

0735 27°38.98'N 82°47.35'W

Species Number

Portunus gibbesii 10

Site I Trawl 2 05/25/94 0807 27°37.59'N 82°47.40'W

0829 27°37.41'N 82°48.23'W

Species Number

Mellita tenuis 21

Portunus gibbesii 6

Luidia clathrara 1

Site I Trawl 3 05/25/94 0846 27°37.8TN 82°47.68'W

0903 27°37.19'N 82°47.58'W

Species Number

Mellita tenuis 50

Site II Trawl 1 05/24/94 2243 27°16.15'N 82°34.25'W

2301 27°16.58'N 82°34.45'W

Species Number

Arenaeus cribrarius 2

Argopecten gibbus 1 Hepatus epheliticus 1 Lytechinus variegatus 1 Menippe mercenaria juvenile 1 Site II Trawl 2 05/24/94 2330 27°17.00'N 82°34.20'W

2350 27°16.32'N 82°33.87'W

Species Number

Callinectes sapidus 1 Site II Trawl 3 05/25/94 0035 27°17.135'N 82°36.085'W

0055 27°16.15'N 82°34.92'W

Species Number

NOTHING

68

FINAL REPORT

OCS Report MMS 95-0005
TABLE 3.2-9

Combined species list in order of prevalence and which trawls the species was found in

69

FINAL REPORT

OCS Report MMS 95-0005

MMS Cruise 05/24 - 25/94 WV Suncoaster

Site I Site II

Species Number 1 2 3 1 2 3

Mellita tenuis 71 X X

Portunus gibbesli 16 X X

Arenaeus cribrarius 2 X

Argopecten gibbus 1 X

Callinectes sapidus 1 X

Hepatus epheliticus 1 X

Luidia clathrara 1 X

Lytechinus variegatus 1 X

Menippe mercenaria juvenile 1 X
70

FINAL REPORT

OCS Report MMS 95-0005

The smallest number of epibenthic species and the smallest number of individuals

were collected on the last cruise in May, 1994 (Table 3.2-8 and 9). This probably reflects

seasonal changes and not a result of dredging since on this date only Sites I and II were

sampled and only Site I had been dredged.

Underwater Video

Underwater video was recorded over each transect at each location for each

sampling cruise. This represents a total of approximately 120 hours of video recorded

during the course of the study. There was little variability observed between locations

or between sampling dates.

Observations of flora and fauna were rare. The flora observed was unattached,

drifting macroalgae and not seagrass. Occasional worm tubes belonging to the infaunal

species, Diopatra cuprea, were observed protruding above the sediment and an

occasional portunid crab was observed swimming away from the light. These

observations reflect the constancy of this very dynamic sand habitat and the low

epibenthic diversity of the area.

3.3 INFAUNAL COMMUNITY RESULTS

Stewart-Oaten et al. (1986) described a rationale for the evaluation of

environmental impact assessment based upon the magnitude of variation between

control and affected areas before and after impact. Description of the environment to be

affected must include estimates of the variances of the sample means of the relevant

variables, for it is only against this variation that impacts can be detected (Underwood,

1992).

One objective of the pre-dredging analysis was to define natural pre-impact or

baseline levels of variation throughout all areas. The baseline variations were then

utilized as a comparative measure for post-impact variations of community parameters,

with the control stations continuing to serve as guide for "natural" variations.

The level of natural variation in species composition and faunal abundance can

serve as a measure of stress in marine communities. Warwick and Clarke (1993)

examined variability in species diversity (H') and species abundances for meiobenthos,

macrobenthos, coral reefs and reef fish. A clear log-log relationship was found between

the variance and the mean abundance for all species. The slope of the log-log

regression increased significantly between control and impacted sites. Additionally, the

variability in macrobenthic species diversity (H') tended to increase with increasing levels

of perturbation.

Overall results are presented and discussed first on an areawide basis prior to

dredging and second, on a site by site basis according to site specific dredging

schedules. Each site had its own dredging design and schedule. As it turned out,

Egmont Key was dredged in the Fall of 1992 and Longboat Key was dredged in the

Summer of 1993. Both the Sarasota and Manasota Key sites were not dredged during
FINAL REPORT

OCS Report MMS 95-0005

the time frame of this study. A comparison of community parameters among sites prior

to dredging will also be presented.

Species saturation curves are generally constructed to determine the appropriate

number of replicate samples for any given benthic study. This analysis considers the

number of new species added to the total number of species with each additional

replicate sample collected. After a certain number of samples, the contribution of new

taxa to total taxa drops off. When the percent of new taxa falls below some

predetermined number (generally 5%) then a sufficient number of replicates have been

collected to describe faunal composition. A species saturation curve for the present

study is shown in Figure 3.3-1.

Total number of taxa and individuals (and percent of total taxa and individuals) for

each major faunal group are presented in Table 3.3-1. A total of 620 taxa and 52,295

individuals were identified during the study. Annelids (segmented worms) contributed

44 and 49 percent of the taxa and individuals, respectively. Molluscan fauna represented

22% of the taxa and 29% of the total fauna, while arthropods comprised 27% of the taxa

and 11% of the individuals. These three taxonomic groups represented 93% of the taxa

and 89% of all fauna.

Pre-Dredging Faunal Community Conditions

Three of the four study sites were sampled in July, 1992, prior to the

commencement of any dredging activity. These three sites were: Egmont Key,

Sarasota, and Manasota Key. This section summarizes spatial patterns in community

parameters among all sites in order to describe the general conditions of the benthic

faunal communities prior to dredging.

A statistical summary of faunal parameters for all stations sampled in July, 1992

is presented as part of Table 3.3-2. Manasota Key had the highest mean number of taxa

per station (142 ± 29 taxa), followed by Sarasota (101 ± 9) and Egmont Key (77 ± 26).

The difference in number of taxa between Manasota Key and Egmont Key was

statistically significant (p < 0.05). Manasota Key also had the highest mean number of

individuals per square meter (3635 ± 1175). Sarasota and Egmont Key had similar

faunal abundance, with mean numbers of individuals per square meter of 1832 ± 812

and 2296 ± 1030, respectively. None of the differences in mean number of individuals

per square meter were statistically different (p = 0.05).

Manasota Key had the highest species diversity (Shannon Index) among the three

stations (3.67), followed by Sarasota (3.19) and Egmont Key (2.47). There was a

statistically significant difference (p < 0.05) in Shannon Index between Manasota Key

and Egmont Key. Equitability (a measure of the evenness of species distribution) was

highest at Manasota Key (0.743 ± 0.12), followed by Sarasota (0.697 ± 0.09) and

Egmont Key (0.573 ± 0.12). There were no statistical differences in equitability among

stations. Usually, a positive relationship exists between diversity and equitability i.e., a

high equitability would indicate a high diversity and probably a "healthy condition" of the

fauna. This was evident among all stations during July 1992, where there was a

71
200

1 75

150

125

100

50

25

0

o 12 Jul-92

13 Jan-93

o 12 May-94

IV1 May 94

Number of Replicates

Figure 3.3-1. Species saturation curves for four station-data combinations.

72

FINAL REPORT

OCS Report MMS 95-0005

2 3 4 5 6 7 8 9
ANAL REPORT

OCS Report MMS 95-0005

Table 3.3-1. Total number of taxa and individuals (and percent of total

taxa and individuals) for each major faunal group.

Station: All Total Taxa 620

Date: All Total Indivduals 52295

Fauna 1 Orou

Number

of Taxa

Percent

of Taxa

Number of

Individuals

Percent of

Individuals

NEMERTEA 7 1.13 1911 3.65

ANNELIDA-Total. 271 43.71 25379 48.53

Polychaeta 267 43.06 21727 41.55

Oligochaeta 2 .32 3630 6.94

Misc. Annelids 2 .32 22 .04

MOLLUSCA-Total 135 21.77 15078 28.83

Gastropoda 66 10.65 3679 7.04

Bivalvia 65 10.48 11394 21.79

Misc. Molluscs 4 .65 5 .01

ARTEROPODA-Total 169 27.26 5992 11.46

Nysidacea 5 .81 27 .05

Cumacea 9 1.45 620 1.19

Tanaidacea 6 .97 52 .10

Isopoda 13 2.10 175 .33

Amp)iipoda 78 12.58 3441 6.58

Decapoda 52 8.39 1667 3.19

Insecta 2 .32 5 .01

Misc Arthropods 4 .65 5 .01

ECHINODERMATA 21 3.39 939 1.80

HEMICHORDATA 2 .32 87 .17

VERTEBR.ATA 1 .16 5 .01

MISCElLANEOUS 14 2.26 2904 5.55

TOTAL 620 100.00 52295 100.00
Table 3.3-2. Benthic fauna parameters: Statistical summary for each station and date.

Date Station

No. of Number of Individuals Shannon Shannon Shannon

Taxa Individuals per m2 loqE loqlO loq2 Pielou Marqalef Simpson 0ii

Jul-92 Ic 99 1830 3129 3.14 1.36 4.53 .68 13.05 .082 .91

Jul-92 ID 49 670 1145 2.33 1.01 3.36 .60 7.38 .184 .81

Jul-92 ID 84 1529 2614 1.94 .84 2.80 .44 11.32 .415 .5E

Jul-92 lID 92 588 1005 3.56 1.55 5.14 .79 14.27 .053 .91

Jul-92 lID 101 1537 2628 2.84 1.23 4.10 .62 13.63 .186 .81

Jul-92 IIC 110 1090 1863 3.18 1.38 4.58 .68 15.58 .147 .85

Jul-92 hID 121 1336 2284 3.65 1.59 5.27 .76 16.67 .056 .91

Jul-92 IIIC 176 2458 4202 4.02 1.75 5.80 .78 22.42 .031 .9

Jul-92 hID 131 2585 4419 3.34 1.45 4.82 .69 16.54 .068 .9

Jan-93 Ic 94 1553 2655 3.07 1.33 4.42 .67 12.66 .094 .9C

Jan-93 ID 109 1170 2000 3.12 1.36 4.51 .67 15.29 .132 .8

Jan-93 ID 35 558 954 1.98 .86 2.86 .56 5.38 .294 .7C

Jan-93 hID 166 1233 2108 4.45 1.93 6.42 .87 23.18 .017 .96

Jan-93 lID 114 1516 2592 3.56 1.55 5.14 .75 15.43 .055 .94

Jan-93 hIC 131 1433 2450 3.98 1.73 5.74 .82 17.89 .030 97

Sep-93 IC 120 3249 5555 3.13 1.36 4.52 .65 14.72 .084 .91

Sep-93 ID 142 1547 2645 3.59 1.56 5.18 .72 19.20 .067 .9

Sep-93 ID 62 453 774 3.02 1.31 4.35 .73 9.97 .090 .91

Sep-93 IVD 100 726 1241 3.78 1.64 5.46 .82 15.03 .038 .96

Oct-93 IVD 91 3730 6377 2.43 1.06 3.50 .54 10.94 .191 .80

Oct-93 IVC 98 1200 2052 3.43 1.49 4.94 .75 13.68 .059 .94

May-94 IC 124 3600 6155 3.19 1.39 4.61 .66 15.02 .082 .91

May-94 ID 184 4347 7432 3.72 1.62 5.37 .71 21.84 .052 .94

May-94 ID 81 2359 4033 1.69 .73 2.44 .38 10.30 .485 .51

May-94 lID 193 3517 6013 3.60 1.56 5.20 .68 23.51 .081 .91

May-94 lID 159 3582 6124 3.66 1.59 5.28 .72 19.31 .053 .94

May-94 IIC 133 2899 4956 3.51 1.53 5.07 .72 16.56 .059 .94
FINAL REPORT

OCS Report MMS 95-0005

significant positive relationship (p < 0.001; r = 0.953) between species diversity and

equitability (Figure 3.3-2).

A breakdown of individuals into major faunal groups (phyla) is presented in Table

3.3-3. The major groups are further subdivided phylogenetically into classes and orders.

The percent of individuals in each major faunal group is presented in Table 3.3-4.

Annelids comprised approximately 50% of the total fauna at all sites. At two stations

(one Sarasota and one Manasota Key), oligochaetes contributed over 10% of the total

fauna. The contribution by molluscs varied greatly within and between sites. Molluscs

varied from 14 individuals (2.1 %) at one Egmont Key station to 1125 individuals (73.6%)

at another Egmont Key station. This fluctuation in molluscan fauna was due to

differences in the distribution of the bivalve, Parvilucina multilineata. Gastropods were

slightly more abundant at Manasota Key with respect to the other two sites. Arthropods

were consistent in abundance at all sites, contributing between five and ten percent of

the total fauna. Amphipods and decapods were the most abundant arthropods.

Echinoderms were rare at Egmont Key, while they represented one to three percent of

the fauna at Sarasota and Manasota Key. Finally, miscellaneous taxa, dominated by the

lancelet Branchiostomma, showed high variability within each site, ranging from 0.2 to

17.8% of the fauna at any given station.

The composition of fauna during pre-dredging sampling shows slight differences

among stations in dominant taxa (Table 3.3-5). A composite species list for all stations

can be found in Appendix C. Tubificid oligochaetes were the dominant taxon at

Manasota Key, followed by the lancelet Branchiostomma sp. and the polychaete

Prionospio cristata. The bivalve, Pa,vilucina multilineata, was dominant at Egmont Key

and Sarasota during this period. Other differences in species composition among the

three stations include: higher relative abundance of the polychaeteAglaophamus verrilli

at Sarasota and Manasota Key; higher relative abundance of Mooreonuphis nebulosa,

Isolda pulchella, Goniadides carolinae, and Aricidea cf. suecica (polychaetes), Anadara

trans versa (bivalve), at Manasota Key; and a high percentage of the gastropod Ceacum

bipartitum at Egmont Key (Table 3.3-6). Biomass for the major faunal groups is shown

in Table 3.3-7.

Overall, faunal richness and abundance at each of the three borrow sites indicate

healthy, diverse infaunal communities along the west Florida coastal zone.

Egmont Key

Egmont Key was sampled four times during this study. This included a predredging sampling (July, 1992), one sampling during dredging activities (January, 1993)

and two post-dredging sampling events (September, 1993 and May, 1994, respectively).

This section discusses the temporal trends in faunal community response to dredging

at Egmont Key. It will also look at differences over time among the two dredged and one

control stations as determined by two-way analysis of variance.

75
0.9

0.8

40.7

0 06

0.5

0.4

FINAL REPORT

OCS Report MMS 95-0005

76

1.5 2.0 2.5 -zr 4.0 4.5

Shannon Index (logE)

Figure 3.3-2 Linear regression of equitability (Pielou's J) and Shannon Index for all

stations during July, 1992 (p<O.001, r=O.953).
Table 3.3-3.

Fat.nal Gro,

Total number of individuals in each major faunal group for each station and date.

III III III

IC ID ID 110 lID IIC D C 0 IC ID ID lID lID IIC IC ID ID I r IVC IC ED ID lID 110 EEC

Jut Jut Jut Jut Jut Jut Jut Jut Jut Jan Jan Jan Jan Jan Jan Sep Sep Sep Sep Oct Oct Nay May May Nay Nay Nay

-92 -92 -92 -92 -92 -92 -92 -92 -92 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93 -94 -94 -94 -94 -94 -94

NEMERTEA 89 1 23 1 47 31 11 33 4 166 fl 20 21 62 47 201 92 66 42 17 54 114 133 98 76 254 137

ANNELIDA-Totat 1080 470 316 366 539 427 899 1407 1056 787 483 55 710 668 727 2083 948 104 323 446 320 2131 2446 226 2594 1805 1963

Potychaeta 886 468 314 282 514 420 647 1285 962 456 354 55 710 668 727 1841 634 96 320 446 320 1878 1769 216 1745 1796 1918

Otiqochaeta 194 0 2 83 25 7 252 122 91 331 127 0 0 0 0 242 305 8 3 0 0 253 677 10 845 9

U

MiscAriietids 0 2 0 1 0 0 0 0 3 0 2 0 0 0 0 0 9 0 0 0 0 0 0 0 4 0

1NOLLUSCA-Totat 599 141125 51837488241 880 661 551465 360 195 472 373 513 280 176 148775234117910771779341 895 369

Gastropoda 308 7 46. 8 79 13 100 100 483 107 1 4 16 3 15 20 39 15 97 512 67 418 113 122 36 702 248

Bivalvia 290 7 1079 42 758 475 141 779 177 444 '.64 356 178 469 358 493 241 161 51 263 167 761 964 1657 305 193 121

Nisc.Nottuscs 1 0 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0

0

ARTHR(WODA-Totat 52 74 61 52 89 127 70 108 317 43 121 76 257 278 245 426 137 83 172 950 351 161 589 142 381 347 283

Nysidacea 1 0 0 0 1 0 2 1 1 0 1 0 1 0 0 11 1 1 0 0 0 0 1 1 2 1

1 C. Cunacea 2 18 20 0 24 15 4 19 30 28 39 3 17 43 10 173 11 3 3 12 9 17 87 2 7 6

18

Tanaidacea 0 0 0 0 0 0 0 1 0 0 3 0 15 0 1 0 3 0 1 0 0 5 4 0 11 3

5

Isopoda 1 26 0 1 11 8 2 3 15 1 1 1 1 10 2 5 10 1 5 34 16 9 1 1 10 0

0

Cl Ançthipoda 16 17 16 15 45 54 32 32 166 13 77 72 190 217 193 213 82 69 25 822 263 90 363 45 161 96

57

Decapoda 32 13 25 35 8 50 30 51 103 1 0 0 33 8 39 22 29 9 138 82 63 40 133 93 187 241 202

Insecta 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0
0

HiscArthropods 0

0

ECHINODERMATA 2

HENICIIORDATA 0

2

NISCELLANE(IJS 8

13

TOTAL 1830

C

C

Ci I

C

C

Ci C' C

C

C

C

0 0 1 0 0 0 0 1 0 0 0 0 0 0 2 1 0 0 0 0 0 0 0 0 0

0 1 22 11 10 20 20 88 2 8 8 16 3 3 2 41 1 21 44 118 6 22 88 50 202 130

0 0 0 0 0 0 0 0 0 0 0 0 2 1 1 0 0 5 3 1 0 0 6 0 66

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3

111 3 96 14 7 95 10 459 4 22 39 34 31 37 23 49 23 15 1495 122 9 80 20 75 10

670 1529 588 1537 1090 1336 2458 2585 1553 1170 558 1233 1516 1433 3249 1547 453 726 3730 1200 3600 4347 2359 3517 3582 2899

VERTEBRATA 0

2
Table 3.3-4. Percent of individual, in each major faunal group for each station and date.

-.1

Fatnal Grot

IC ID

Jul Jul -92 -92

ID Jut -92

III III III lID lID IIC 0 C 0 IC ID ID 110 lID IIC IC ID ID I' IVD

Jut Jul Jul Jut Jut Jut Jan Jan Jan Jan Jan Jan Sep Sep Sep Sep Oct

-92 -92 -92 -92 -92 -92 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93

IVC IC 10 10 lID lID IIC Oct Nay May May Nay Nay May

-93 -94 -94 -94 -94 -94 .94 NEPRTEA 4.9 .1 1.5 .2 3.1 2.8 .8 1.3 .2 10.7 6.1 3.6 1.1 4.1 3.3 6.2 5.9 14.6 5.8 .5 4.5 3.2 3.1 4.2 2.2 1.1 4.7

ANNELIDA-Totat 59.0 70.1 20.7 62.2 35.1 39.2 67.3 57.2 40.9 50.7 41.3 9.9 57.6 44.1 50.7 64.1 61.3 23.0 44.5 12.0 26.7 59.2 56.3 9.6 73.8 50.4 67.7

PoLychaeta 48.4 69.9 20.5 48.0 33.4 3&5 48.4 52.3 37.2 29.4 30.3 9.9 57.6 44.1 50.7 56.7 41.0 21.2 44.1 12.0 26.7 52.2 40.7 9.2 49.650.1 66.2

Otigochaeta 10.6 .0 .114.1 1.6 .6 18.9 5.0 3.5 21.3 10.9 .0 .0 .0 .0 7.4 19.7 1.8 .4 .0 .0 7.0 15.6 .4 24.0 .3 1.5 M3sc.Arwetids .0 .3 .0 .2 .0 .0 .0 .0 .1 .0 .2 .0 .0 .0 .0 .0 .6 .0 .0 .0 .0 .0 .0 .0 .1 .0 .0 NOLLUSCA-Total 32.7 2.1 73.6 8.7 54.5 44.8 18.0 35.8 25.6 35.5 39.7 64.5 15.8 31.1 26.0 15.8 18.1 389 20.4 20.8 19.5 32.8 24.8 15.4 9.7 25.0 12.7 Gastropoda 16.8 1.0 3.0 1.4 5.1 1.2 7.5 4.1 18.7 6.9 .1 .7 1.3 .2 1.0 .6 2.5 3.3 13.4 13.7 5.6 11.6 2.6 5.2 1.0 19.6 8.6

Bivalvia 15.8 1.0 70.6 7.1 49.3 43.6 10.6 31.7 6.8 28.6 39.7 63.8 14.4 30.9 25.0 15.2 15.6 35.5 7.0 7.1 13.9 21.1 22.2 70.2 8.7 5.4 4.2

Misc.Moltuscs .1 .0 .0 .2 .0 .0 .0 .0 .0 .0 .0 .0 .1 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0

.0 ARTHROPODA-Totat 2.8 11.0 4.0 8.8 5.8 11.7 5.2 4.4 12.3 2.8 10.3 13.6 20.8 18.3 17.1 13.1 8.9 18.3 23.7 25.5 29.3 4.5 13.5 6.0 10.8 9.7 9.8

Nysidacea .1 .0 .0 .0 .1 .0 .1 .0 .0 .0 .1 .0 .1 .0 .0 .3 .1 .2 .0 .0 .0 .0 .0 .0 .1 .0

.0 Cuimcea .1 2.7 1.3 .0 1.6 1.4 .3 .8 1.2 1.8 33 .5 1.4 2.8 .7 5.3 .7 .7 .4 .3 .8 .5 2.0 .1 .2 .2

.6 Tanaidacea .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .3 .0 1.2 .0 .1 .0 .2 .0 .1 .0 .0 .1 .1 .0 .3 .1 .2 C Isopoda .1 3.9 .0 .2 .7 .7 .1 .1 .6 .1 .1 .2 .1 .7 .1 .2 .6 .2 .7 .9 1.3 .3 .0 .0 .3 .0 .0 Aahipoda .9 2.5 1.0 2.6 2.9 5.0 2.4 1.3 6.4 .8 6.6 12.9 15.4 14.3 13.5 6.6 5.3 15.2 3.4 22.0 21.9 2.5 8.4 1.9 4.6 2.7 2.0

Decapoda 1.7 1.9 1.6 6.0 .5 4.6 2.2 2.1 4.0 .1 .0 .0 2.7 .5 2.7 .7 1.9 2.0 19.0 2.2 5.3 1.1 3.1 3.9 5.3 6.7 7.0

Insecta .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .1 .0

.0 NiscArthropods .0 .0 .0 .2 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .1 .1 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0

C

C ECHINODERMATA .1 .0 .1 3.7 .7 .9 1.5 .8 3.4 .1 .7 1.4 1.3 .2 .2 .1 2.7 .2 2.9 1.2 9.8 .2 .5 3.7 1.4 5.6 4.5
HEMI CHORDATA .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .1 .1 .0 .0 .0 .7 .1 .1 .0 .0 .3 .0 1.8

VERTEBRATA .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .0 .1

MISCELLANEOUS .4 16.6 .2 16.3 .9 .6 7.1 .4 17.8 .3 1.9 7.0 2.8 2.0 2.6 .7 3.2 5.1 2.1 40.1 10.2 .3 1.8 .8 2.1 .3

.4

TOTAL 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
Table 3.3-5. Total number of taxa in each major faunal group for each station and date.

Fainat Gro

IC

JuL

-92

ID

Jut

-92

ID

JuL

-92

lID

Jut

-92

lID

Jut

-92

III

IIC 0

Jut Jut

-92 -92

III CJut

-92 -92

Ill

0

Jut

IC

Jan

-93

ID

Jan

-93

ID

Jan

-93

110

Jan

-93

lID IIC IC ID ID I IVD

Jan Jan Sep Sep Sep Sep Oct

-93 -93 -93 -93 -93 -93 -93

IVC IC ID ID 110 lID IIC

Oct Nay Nay Nay Nay Nay Nay

-93 -94 -94 -94 -94 -94 -94

NENERTEA 4 1 4 1 4 4 4 4 3 4 4 3 5 3 3 4 4 3 2 2 4 4 4 3 4 4

5

ANNELIDA-Totat 54 23 44 49 50 55 62 77 51 45 67 15 81 59 64 61 78 28 48 38 38 60 88 34 107 89

72

Potychaeta 53 22 43 46 48 54 61 75 48 44 65 15 81 59 64 59 75 27 47 38 38 59 87 33 104 87

70

Otigochaeta 1 0 1 2 2 1 1 2 2 1 1 0 0 0 0 2 2 1 1 0 0 1 1 1 2 2

Misc.Ametids 0 1 0 1 0 0 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0

1NOLLUSCA-Totat 22 8 20 17 24 20 27 54 34 23 15 7 26 18 26 20 22 12 16 16 13 28 40 20 32 30

19

Gastropoda 13 4 12 5 13 7 15 24 15 10 1 3 10 2 9 7 9 8 9 11 8 15 19 13 13 16

8

Bivalvia 8 4 8 11 11 13 12 29 18 13 14 4 15 16 17 13 13 4 7 5 5 13 21 7 19 14

11

Nisc.Nottuscs 1 0 0 1 0 0 0 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0

0 U

Ct -cC ARTHRCPIJ)A-Totat 16 15 13 19 14 23 19 35 34 16 16 6 43 26 29 28 27 15 25 26 29 25 40 16 41 24

24

Nysidacea 1 0 0 0 1 0 1 1 1 0 1 0 1 0 0 1 1 1 0 0 0 0 1 i 1 i

1 U

ci Ciaacea 1 2 2 0 2 1 2 3 3 4 4 2 3 4 2 5 3 1 2 5 6 2 3 2 2 2

2 C

C

Tanaidacea 0 0 0 0 0 0 0 1 0 0 2 0 2 0 1 0 1 0 1 0 0 1 2 0 3 1
Isopoda 0 Mphipoda 12 Decapoda 8 Insecta 0 NiscArthropods 0ECRINODERKATA 7HENICHORDATA VERTEBRATA HISCELLANEOUS 4 TOTAL 1670020o1 2830000o2 05611 001002 16011005 173003006 2137003005 210416 004005 211101005 3187113006 1101002004 180002005 13013 002002 123003008 2146001106 2195001107 4143011105 2118016005 17511 001003 29004104 2109003105 2138006107 312716 004003 117006006 17004105146 3 217204005 014 0064 Oz U)>j 99 49 84 92 101 110 121 176 131 94 109 35 166 114 131 120 142 62 100 91 98 124 184 81 193 159 133
Table 3.3-6.

Fatnal Groii

Percent of taxa in each major faunal group for each itation and date.

111 III 111

IC ID ID lID lID IIC D C D IC ID ID 110 lID LIC IC ID ID IVD 1W

Jul JuL Jul JuL Jul Jut Jut Jul Jul Jan Jan Jan Jan Jan Jan Sep Sep Sep Sep Oct

-92 -92 -92 -92 -92 -92 -92 -92 -92 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93 -93

IVC IC ID ID lID LID ZIC

Oct May Play May May May May

-93 -94 -94 -94 -94 -94 -94 NENERTEA 4.0 2.0 4.8 1.1 4.0 3.6 3.3 2.3 2.3 4.3 3.7 8.6 3.0 2.6 2.3 3.3 2.8 4.8 2.0 2.2 4.1 3.2 2.2 3.7 2.1 2.5 3.8

ANNELIDA-TotaL 54.5 46.9 52.4 53.3 49.5 50.0 51.2 43.8 38.9 47.9 61.5 42.9 48.8 51.8 48.9 50.8 54.9 45.2 48.0 41.8 38.8 48.4 47.8 42.0 55.4 56.0 54.1 PoLychaeta 53.5 44.9 51.2 50.0 47.5 49.1 50.4 42.6 36.6 46.8 59.6 42.9 48.8 51.8 48.9 49.2 52.8 43.5 47.0 41.8 38.8 47.6 47.3 40.7 53.9 54.7 52.6

Oligochaeta 1.0 0.0 1.2 2.2 2.0 0.9 0.8 1.1 1.5 1.1 0.9 0.0 0.0 0.0 0.0 1.7 1.4 1.6 1.0 0.0 0.0 0.8 0.5 1.2 1.0 1.3 0.8

Misc. Amelids 0.0 2.0 0.0 1.1 0.0 0.0 0.0 0.0 0.8 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.8

MOLLUSCA-Total 22.2 16.3 23.8 18.5 23.8 18.2 22.3 30.7 26.0 24.5 13_a 20.0 15.7 15.8 19.8 16.7 15.5 19.4 16.0 17.6 13.3 22.6 21.7 24.7 16.6 18.9 14.3 Gastropoda 13.1 8.2 14.3 5.4 12.9 6.4 12.4 13.6 11.5 10.6 0.9 8.6 6.0 1.8 6.9 5.8 6.3 12.9 9.0 12.1 8.2 12.1 10.3 16.0 6.7 10.1 6.0

Biva(via 8.1 8.2 9.5 12.0 10.9 11.8 9.9 16.5 13.7 13.8 12.8 11.4 9.0 14.0 13.0 10.8 9.2 6.5 7.0 5.5 5.1 10.5 11.4 8.6 9.8 8.8 8.3

Misc. Molluscs 1.0 0.0 0.0 1.1 0.0 0.0 0.0 0.6 0.8 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

ARTHROPODA-Total 16.2 30.6 15.5 20.7 13.9 20.9 15.7 19.9 26.0 17.0 14.7 17.1 25.9 22.8 22.1 23.3 19.0 24.2 25.0 28.6 29.6 20.2 21.7 19.8 21.215.1 18.0 Mysidacea 1.0 0.0 0.0 0.0 1.0 0.0 0.8 0.6 0.8 0.0 0.9 0.0 0.6 0.0 0.0 0.8 0.7 1.6 0.0 0.0 0.0 0.0 0.5 1.2 0.5 0.6 0.8

Cusacea 1.0 4.1 2.4 0.0 2.0 0.9 1.7 1.7 2.3 4.3 3.7 5.7 1.8 3.5 1.5 4.2 2.1 1.6 2.0 5.5 6.1 1.6 1.6 2.5 1.0 1.3 1.5 Tanaidacea 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 1.8 0.0 1.2 0.0 0.8 0.0 0.7 0.0 1.0 0.0 0.0 0.8 1.1 0.0 1.6 0.6 0.8

Isopoda 1.0 4.1 0.0 1.1 1.0 1.8 1.7 1.1 2.3 1.1 0.9 2.9 0.6 1.8 1.5 3.3 1.4 1.6 2.0 2.2 2.0 2.4 0.5 1.2 1.0 0.0 0.0 AiInpoda 6.1 16.3 6.0 6.5 6.9 11.8 8.3 6.3 13.7 10.6 7.3 8.6 13.9 12.3 14.5 11.7 7.7 11.3 9.0 11.0 13.3 9.7 9.2 8.6 8.8 8.8 9.0

Decapoda 7.1 6.1 7.1 12.0 3.0 6.4 3.3 9.1 5.3 1.1 0.0 0.0 7.8 5.3 3.8 2.5 5.6 8.1 11.0 9.9 8.2 5.6 8.7 6.2 7.3 3.8 6.0

Insecta 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0

Misc Arthropods 0.0 0.0 0.0 1.1 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 'C ECHINODERNATA 2.0 0.0 1.2 1.1 3.0 2.7 33 0.6 2.3 2.1 1.8 5.1 1.8 0.9 0.8 0.8 4.2 1.6 4.0 3.3 6.1 3.2 3.3 4.9 2.1 3.8 5.3

ci HEMICHORDATA 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.9 0.8 0.8 0.0 0.0 1.0 1.1 1.0 0.0 0.0 1.2 0.0 0.6 0.8

CCC VERTEBRATA 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.8
MISCELLANEOUS 1.0 4.1 2.4 5.4 5.9 4.5 4.1 2.3 4.6 4.3 4.6 5.7 4.8 5.3 5.3 4.2 3.5 4.8 4.0 5.5 7.1 2.4 3.3 3.7 2.6 2.5 3.0

TOTAL 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

CC

C

-c

C

CaC

C

C

C
FINAL REPORT

OCS Report MMS 95-0005

Table 3.3-7. wet weight biomass (g) for each major faunal group for each station

85

and date..

Annelida Mollusca Arthropoda Echinoderinata Miscellaneous Total

Jul-92 Ic 5.029 4.587 0.061 0.047 0.578 10.300

Jul-92 ID 1.430 4.621 0.029 0.000 2.473 8.554

Jul-92 ID 2.952 11.610 0.036 0.919 0.351 15.867

Jul-92 lID 5.410 11.144 2.546 0.043 4.849 23.992

Jul-92 lID 8.869 15.579 0.933 0.163 0.812 26.356

Jul-92 lIC 21.316 30.854 5.849 2.324 1.176 61.519

Jul-92 hID 5.171 1.341 0.124 0.488 0.826 7.950

Jul-92 IIIC 9.893 357.138 0.788 0.639 0.423 368.882

Jul-92 hID 3.549 4.943 0.338 1.344 10.898 21.072

Jan-93 IC 7.019 0.639 0.010 0.683 0.635 8.985

Jan-93 ID 13.406 1.542 0.050 31.633 0.588 47.219

Jan-93 ID 0.642 0.549 0.057 0.134 1.573 2.955

Jan-93 lID 21.633 122.747 3.926 2.188 4.385 154.880

Jan-93 lID 11.624 69.387 0.973 0.150 3.252 85.386

Jan-93 IIC 45.110 10.310 9.267 3.249 4.347 72.283

Sep-93 IC 4.935 0.166 0.142 0.000 0.441 5.684

Sep-93 ID 18.830 0.880 0.088 2.828 6.091 28.718

Sep-93 ID 0.550 1.456 0.050 0.000 0.591 2.647

Sep-93 IVD 7.119 0.359 0.209 1.905 3.846 13.438

Sep-93 IVD 2.554 0.606 0.881 1.398 29.572 35.010

Sep-93 IVC 3.005 2.154 0.277 117.852 7.135 130.422

May-94 IC 4.223 3.805 0.073 24.292 0.608 33.000

May-94 ID 51.631 15.813 1.288 38.133 1.646 108.511

May-94 ID 1.208 1.540 0.032 15.992 1.287 20.060

May-94 lID 8.318 34.806 1.137 1.808 22.934 69.003

May-94 lID 4.445 1.609 0.157 11.307 1.343 18.859

May-94 IIC 3.516 0.738 0.244 59.149 4.681 68.328
86

FINAL REPORT

OCS Report MMS 95-0005

Faunal Abundance, Richness and Diversity. Figure 3.3-3 shows temporal trends

in number of taxa and number of individuals at each site. The first three panels

summarize trends at Egmont Key (Site I). Temporal trends in species diversity

(Shannon's H') and equitability (Pielou's J') are found in Figure 3.3-4. These data are

also presented in Table 3.3-2. Temporal responses in number of taxa and faunal

abundance (individuals/square meter) were distinct for each station at this site. The

control station (I-C) experienced a slight decrease in both parameters shortly after

dredging operations were completed (between July, 1993 and January, 1994). One of

the two dredged stations (l-D2) showed a much more drastic decline in number of taxa

and individuals during this same period. From January to September, 1993, station I-C

experienced a substantial increase in both parameters, while the aforementioned

dredged station (l-D2) underwent an increase in number of taxa, but a decrease in faunal

density. By the end of the study, station l-D2 had not recovered to faunal levels

experienced by the control station. The other dredged station (l-D1), however, showed

no apparent declines in faunal parameters associated with dredging activities. This

station showed a continual increase in both faunal diversity and abundance. At the end

of the study, station 1-Di had far more taxa present and more individuals than either of

the other stations at the Egmont Key site.

Species diversity and equitability at Egmont Key were fairly constant at the control

station (Figure 3.3-4). These parameters showed wide fluctuations at station l-D2,

especially during postdredging sampling events. The other dredged station (1-Di), which

had lower diversity and equitability values prior to dredging, showed a continual increase

in these parameters until the end of the study.

A two-way analysis of variance (ANOVA) was performed on all station and date

combinations to look at the interaction between these two variables. The test was

designed to detect differences in mean number of taxa and faunal density. Although

there are inherent inaccuracies associated with applying analysis of variance to replicate

benthic samples through space and time, the test will allow us to determine if there is

an appreciable interaction between stations and sampling dates, If there is, then it

makes it inappropriate to discuss differences between control and dredged stations at

any one time as statistically significant. In any case, there was a significant (p < 0.001)

interaction effect between sampling time and station at the Egmont Key site. This effect

can be seen in Figure 3.3-5, where temporal trends in number of taxa and faunal density

behaved differently at each of the three stations over time. This makes it impossible to

attribute any of the observed changes to the effects of dredging alone. This finding,

along with the observed differences in response of the two dredged stations, does not

allow for an accurate analysis of dredging effects at Egmont Key. However, a look at

changes in faunal composition at these stations should help pinpoint which species were

mainly responsible for the observed community oscillations.

Faunal Composition. Total number and percent of individuals in each major faunal

group for Egmont Key stations are found in Tables 3.3-3 and 3.3-4, respectively.

Annelids contributed the lowest percent of total fauna throughout the study at the second

dredge station (l-D2). Typically, annelids constituted 20% or less of the total fauna
200

1 75

1 50

125

1 00

75

50

25

0

E

L

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c'4Ytr)* c'rq- c')ri* C4r)P)+ c.Irtr)l- a) a) 0) a) 0)0) a) 0) 0) a) 0)0) 010) a) 0) 0)0)0)0) liii CQ' liii liii ca tilt C0 5O.> lilt liii till till liii lit! liii liii aqO rjI0 ouo ow0 _)o)o _)O)0 CO>. OtD ca ca ,0I)O D0Q)o -o0 .0Uo c>.- >oQ0 '-&n ))(fl )(fl )(f) )fl )(/) 3(fl )(fl )(fl )O

Figure 3.3-3 Temporal trends in number of taxa (top) and number of individuals (bottom) at each site. I =

Egmont Key; II = Sarasota; Ill = Manasota Key; IV = Longboat Key. (C = control; D = dredged).

0

II III I I III III I I III 200

. 175

150

125

. 100

75

50

25 III It II I I I I It II 1111 0

1112C IIID3 IV1D 1V2D 1V3C II I I I I I II II tIlt I I I I - 7500

5000'

2500

IlC

7500 - I I I I

5000

2500

13D IllD I2D 113C IllllD III I 11/ - I I I I I II I I I I 1112C lllD3 IV1D 1V2D 1V3C

1111 lIlt

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0.8

0.7

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Figure 3.3-4.

liC I2D 13-0 II1D 12D 113C lIlI1D 1112C 111-03 IV1D lV2D 1V3

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010)0)0) 0)0)0)0)

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0.9

0.8

0.7

0.6

0,5

CoUI Temporal trends in species diversity (Shannon's H) and equitability (Pielous J) at each site. i Egmont Key; II = § = Sarasota; III = Manasota Key; IV = Longboat Key. (C = control; D = dredged).

liii

iii

till

/

ili

Ill

.-A

lilt

lilt

A

liii

(ill

II I

1111

liii

Ill I

till

liii

.

III I_

till

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tilt

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ill i

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liii

. . .CIII

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lilt

V lIlt

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lii

I V 1⁄4) - liii

Ill
200

150

100

50

8000

7000

6000

5000

4000

3000

2000

1000

0

Egmont Key

Dredge 1

Jul-92 Jan-93 Sep-93 May-94

liME

Figure 3.3-5. Temporal trends in number of taxa (top) and individuals per

square meter (bottom) at Egmont Key.

Egm

7

89

FINAL REPORT

OCS Report MMS 95-0005

Control I

dge 2

Drecce 1

Dredae 2

Jul-92 Jan-93 Sep-93 May-94

TIME
FINAL REPORT

OCS Report MMS 95-0005

(compared to roughly 60% at the other two stations) at station l-D2 throughout the study.

This was countered by a substantially higher percent of molluscs at station l-D2

compared to the other two stations (70% to 25%, respectively). This difference in the

composition of the fauna at station l-D2 compared to the other two stations at Egmont

Key could play an important role in the ability of fauna to recolonize the second dredge

site. This is due to differences in the reproductive and dispersal potential between

polychaetes and molluscs.

Differences in total and percent of taxa in major taxonomic groups among the

three Egmont Key stations were less evident (Tables 3.3-5 and 3.3-6). While the total

number of annelid and molluscan taxa at the second dredge station were lowest, the

percent of total taxa for annelids and molluscs among all stations were similar. This

indicates that, although overall faunal conditions were poorest at the second dredge

station, the number of taxa were in proportion to the number of individuals present. In

other words, the fauna were not limited to a few taxa, but rather were spread among a

number of taxa comparable to the other two stations.

Several species contributed to the high faunal density at the control station during

July, 1992. Tubificid oligochaetes, Prionospio cristata (polychaete) and Caecum

bipartitum (gastropod) were found almost exclusively at the control station, while the

bivalve, Parvilucina multilineata was much more plentiful at the second dredge station.

During January, 1993, faunal abundance dropped off noticeably at the second dredge

station because of the absence of this bivalve. The higher total abundance at the control

site was partly due to tubificid oligochaetes and nemerteans. Other significant species

at the control station include Cylichnella bidentata, Caecum bipartitum, Mediomastus

spp., Prionospio pygmaea, and Aricidea cf. suecica. Caecum johnsoni and Acteocina

sp. were found exclusively at the first dredge station, while Myriowenia sp. was present

only at the second dredge station. A number of species contributed to the large

increase in faunal abundance at the control station during September, 1993. These

species were: Parvilucina multilineata, Prionospio cristata, Prionospio pygmaea,

Nemertean sp. B, Cyclaspis cf. varians, and Paraprionospio pinnata. These species are

all surface-deposit feeding organisms (three are polychaetes in the family Spionidae).

This suggests a stable surface with a sufficient organic component to support such a

diverse and abundant fauna. The dredged stations may have had a disturbed surface

which prevented the early colonization of these stations. By May, 1994, the distribution

of species between the control and the dredge stations revealed some interesting

distinctions. The second dredge station, which had depressed faunal abundance

throughout the study, had a large abundance of the bivalve Tel/ma sp. This species

represented 70% of the fauna at this station (no other species contributed more than 4%

to the total fauna). This disparity in species distribution led to the low species diversity

and equitability at this station during May, 1994. The other two stations (control and first

dredge station) had several dominant species, although this dominance was distinct for

each station. Parvilucina multilineata, Prionospio cristata, Cylichnella bidentata

(gastropod), and Spiophanes bombyx (polychaete) were abundant at the control station.

Branchiostomma sp., Prionospio perkinsi, Mooreonuphis nebulosa, Cara.zziella hobsonae,

and Erichthonius brasiliensis were specifically dominant at the first dredge station.

90
91

FINAL REPORT

OCS Report MMS 95-0005

Overall diversity and equitability at these two stations was high, reflecting the abundant

and diverse species composition.

An interesting shift in faunal composition was observed at the second dredge

station (l-D2). Bivalves contributed a much greater percent of the fauna at this station

than the other two (Table 3.3-4). Before dredging, the bivalve Parvilucina multilineata

represented 64% of the total fauna. The next two sampling periods (immediately post

dredging) revealed very low faunal abundance with no clear dominance by any

organism. By May 1994, the bivalve Tell/na sp. comprised 69% of the fauna. This clear

shift in species composition was not observed at the other two stations.

This slow recolonization by bivalves has been demonstrated in other studies.

Bowen and Marsh (1988) found that periodic molluscan settlement in a Delray Beach,

Florida borrow site was in most cases followed by nearly complete mortality. The

authors did not speculate on the cause of this mortality but only noted that no adults

were found. Oliver et al. (1977) reported similar molluscan mortality in a study of

dredged material disposed at various depths in Monterey Bay, California. Simon and

Dauer (1977) also noted the slow appearance of molluscs in a disturbed area in Tampa

Bay. The authors surmised that the phenomenon may be related to their more limited

dispersal abilities and reproductive seasonality. The cause of the sharp decline in

Parvllucina multilineata at the second dredge station combined with the slow, but steady

increase in Tellina sp. may reflect these inherent patterns of recolonization exhibited by

molluscs.

Faunal Similarity. Distinctions in faunal composition among Egmont Key stations

are also reflected in faunal similarity values (Figure 3.3-6). Not surprisingly, only two

combinations showed moderate similarity, and they were temporal similarities at the

same station. The first dredge station (1-Di) showed moderate similarity between

January, 1993 and September, 1993, while the control station showed moderate similarity

between September, 1993 and May, 1994. When a presence/absence data transform

was performed, several more Egmont Key station combinations showed moderate

similarity through space and time (Figure 3.3-7). Moderate similarity occurred between:

dredge station two and control station, July, 1992; control station, July, 1992 and

January, 1993; and control station, January, 1993 and dredge station two, July, 1992.

All other station-date combinations showed low to very low faunal similarity. These

faunal relationships among stations are also displayed as dendrograms in Figures 3.3-8

and 3.3-9 and a trellis diagram in Figure 3.3-10.

In summary, each station at the Egmont Key site underwent different temporal

patterns in benthic community composition. The two dredged stations responded quite

differently from each other, making data interpretation difficult. Most of the difficulty

involves the distinct contrast in faunal community response between the two dredged

stations. In general, the control station exhibited less variable temporal trends, while the

two dredged stations showed widely fluctuating and contrary taunal responses.
- - . Very Low Similarity --- Low Similarity +4-4- Moderate Similarity

Figure 3.3-6. Trellis diagram of Bray-Curtis faunal similarity values for each station and date based on groupaveraged sorting.

IC ID ID lID lID IIC hID IIIC hID

Jul Jul Jul Jul Jul Jul Jul Jul Jul -92 -92 -92 -92 -92 -92 -92 -92 92

IC Jan

-93

ID

Jan

-93

ID

Jan

-93 hID

Jan

-93 hID

Jan

-93 IIC Jan-93

IC ID ID IVD IVD IVC IC ID ID lID lID IIC

Sep Sep Sep Sep Oct Oct Hay Hay Hay May May May

-93 -93 -93 -93 -93 .93 -94 -94 -94 -94 -94 -94

IC Jul-92

ID Jul-92 .942 . .

ID Jul-92 .720 .924

lID Jul-92 .853 .724 .943 - lID Jul-92 .665 .909 .395 .883 -s-s-i- IIC Jul-92 .664 .925 .547 .864 .385 . - 1110 Jul-92 .606 .887 .825 .731 .718 .749

IIIC Jul-92 .705 .950 .773 .816 .680 .685 .627

1110 Jul-92 .821 .884 .950 .828 .902 .909 .817 .869

IC Jan-93 .628 .939 .817 .882 .717 .803 .599 .777 .898

ID Jan-93 .822 .899 .865 .802 .784 .844 .683 .772 .839 .565 - -I-H- - - - - ID Jan-93 .961 .868 .906 .918 .854 .951 .861 947 .927 .712 .512 . . - - - -. - - - . -. 110 Jan-93 .806 .932 .863 .800 .778 .728 .736 .677 .888 .822 .772 .938

110 Jan-93 .763 .931 .697 .899 .637 .663 .777 .709 .926 .663 .648 .741 .653 - ... - IIC Jan-93 .749 .939 .776 .859 .677 .595 .692 .577 .921 .767 .785 .902 .497 .514

IC Sep-93 .605 .960 .785 .907 .751 794 .748 733 .827 .645 .754 .864 .852 .624 .749 . - -s--s-i- ID Sep-93 .728 .919 .859 .774 .813 .854 .567 347 .813 .599 .488 .705 .800 .725 .194 .670 ---

ID Sep-93 .918 .926 .886 .885 .849 .886 .844 .895 .916 .811 .641 .630 .893 .831 .848 .861 .656 . - - IVD Sep-93 .829 .927 .817 .872 .769 .805 .788 .861 .927 .833 .808 .873 .767 745 .794 .848 .720 .735 . - - IVD Oct-93 934 .912 .941 .930 .923 959 .907 .936 .711 .875 .825 .819 937 .868 931 .881 .807 .874 .883

IVC Oct-93 .879 .828 .857 .841 .806 .886 .787 .896 .817 .806 .731 .732 .883 .792 .855 .846 .696 .685 .681 .712

IC May-94 .604 .983 .799 .922 .757 .803 .724 374 .854 .609 .717 .840 .884 .692 .820 .395 .715 .883 .834 .868 .853

ID May-94 .805 .967 .857 .906 .816 .830 .726 .674 .870 .697 .674 .859 .805 .706 .724 .687 .625 .888 .858 .870 .856 .642

ID May-94 .918 .976 .929 .969 .908 947 .911 .939 959 .808 .708 .761 .941 .837 .930 .868 .788 .836 .876 .869 .821 .799 .806

lID May-94 .872 .930 .951 .834 .938 .925 .794 .819 .825 .814 .821 .950 .837 .887 .868 .826 .715 .905 .898 .943 .903 .838 .661 .916 - - lID May-94 .854 .976 .862 .953 .833 .869 .812 .792 .951 .851 .883 .962 .817 .754 .758 .813 .819 .899 .763 .927 .820 .703 .769 .872 .752 -i--s-+ LIC May-94 .823 .972 .870 .921 .805 .850 .806 .806 .937 .811 .842 .951 .792 .709 .709 .795 .799 .892 .766 .927 .830 .713 .729 .889 .753 .352
CA)

-. Very Low Similarity - -. Low Similarity 4-4-f Moderate Similarity

Figure 3.3-7. Trellis diagram of Bray-Curtis faunal similarity values for each station and date. (Presence/absence

transform).

IC 10 130 110 110 IIC 1110 IIIC 1110

Jul Jul Jul Jul Jul Jul Jul Jul Jul

-92 -92 -92 -92 -92 -92 -92 -92 92

IC Jan

-92

ID Jan

-93

ID Jan

-93 lID

Jan

-93 lID Jan-93 IIC Jan-93

IC Sep

-93

ID Sep

-93

ID Sep

-93 IVD Sep-93 IVD Oct-93 IVC Oct

-93

IC Hay

-94 ID Hay-94

ID May

-94 lID Hay.94 lID Hay-94 IIC May.94

IC Jul-92 --- -i-s-i ------------------ -i-s--i- ID Jul-92 .667 . --: . - ID Jul-92 .376 .618 -f-HlID Jul-92 .617 .608 642 --------------- ---------

lID Jul-92 .520 .610 .421 .574 i-i-' -'-s-i ------------ ------------

tIC Jul-92 .600 .637 .531 .606 .393 4--f 4-f-I --------- +++ -I-f+ -I-f-f

1110 Jul-92 .500 .690 .533 .594 .474 .444 4-H- +++

IIIC Jul-92 .558 352 .588 .591 .521 .462 .460 ......... -f++ 4-H- -f-i-i

hID Jul-92 .615 .663 .609 .559 .538 .508 .488 .548 -- - IC Jan-93 .467 .697 .481 .755 .538 .571 .589 .594 .651 - - . . ID Jan-93 .629 .663 .633 .675 .589 .536 .564 .566 .582 .502

ID Jan-93 .778 .694 .736 .859 .727 .766 .723 .858 .763 .708 .655 . lID Jan-93 .515 343 .630 .594 .596 .496 .541 .448 .550 .627 .525 .823 i-H- +++

lID Jan-93 .579 .732 .590 .643 .514 .438 .513 .483 .556 .560 .500 .812 .418

tIC Jan-93 .554 .727 543 .628 .536 .449 .533 .443 .596 .561 .523 .798 .375 .344 --- - - . - IC Sep-93 .563 .793 .581 .714 .570 .590 .613 .580 .628 .534 .607 .811 .610 .529 .603 -. - ID Sep-93 .584 .720 .602 .588 .606 .600 .562 .546 .570 .624 .492 .751 .566 .583 .583 .482

ID Sep-93 .675 .690 .737 .761 .706 .693 .695 .769 .750 .727 .693 .703 .795 .778 .749 .716 .630 --- IVD Sep-93 .561 .742 .560 .677 .550 .572 .607 .609 .649 .600 .647 .757 .612 .589 .538 .555 .506 .602 --- i-s-+

IVO Oct-93 .685 .728 .683 .737 .692 .710 .701 .758 .662 .719 .710 .727 .751 .697 .713 .656 .555 .644 545 i-s-iIVC Oct-93 .710 .707 .648 .730 .611 .631 .645 .731 .643 .653 .622 .718 .731 .665 .683 .619 .564 .607 .491 .402 -- ......

IC May-94 545 .839 .571 .687 .596 .641 .597 .613 .651 .560 .675 .836 .658 .622 .650 .492 .584 .737 .581 .647 .645 -------- -i-*-+ -s-i-i- ID May-94 .649 .796 .653 .691 .654 .620 .618 .546 .624 .686 .614 .827 .598 .619 .610 .618 .516 .769 .593 .688 .699 .521 ...... -i--s-i- .--

ID May-94 335 .771 .713 793 .730 .728 .688 .767 .712 .739 .717 .724 .775 .733 .757 .746 .697 .701 .688 .618 .638 .678 .684 ------ C

lID May-94 .707 .779 .736 .638 .738 .704 .679 .546 .591 .792 .684 .878 .580 .662 .621 .679 .605 .800 .666 .725 .754 .648 .509 .731

lID May-94 .562 .790 .610 .676 .614 .622 .577 .548 .646 .663 .622 .867 .549 .541 .522 .563 .548 .717 .525 .650 .640 .486 .490 .585 537 +-i-+ - IIC May-94 .545 .792 .598 .664 .603 .597 .626 .586 .670 .614 .597 833 .568 .587 .511 .564 .569 .688 .529 .635 .633 .486 .541 .598 .517 .311
IC Jul-92 I I IC Sep-93 I I I I IC May-94 I I I hID Jul-92 I I I IC Jan-93 I-- I I ID Jan-93 I I I- -I ID Sep-93 I I I ID Jul-92 I I I I lID Jul-92 I I I I I IIC Jul-92 I I I I IIIC Jul-92 I I I ---I lID Jan-93 I I I I I I IIC Jan-93 I I I I I hID Jan-93 I I I ID May-94 I I I I lID May-94 I I I II hID May-94 I I I I IIC May-94 I I I ID Jan-93 I I I I ID Sep-93 I I I I II IVD Sep-93 I I II II IVC Oct-93 I I II ID May-94 I II orn hID Jul-92 I II IVD Oct-93 I I r- Im ID Jul-92 I -, lID Jul-92 I C,) High Similarity < > Low Similarity UI 08 Figure 33-8. Dendrogram of Bray-Curtis similarity for each station and date based on group-averaged sorting. °'
IC Jul-92 I I ID Jul-92 I I I IC Jan-93 I I lID Jul-92 I I I lID Jul-92 I I I I hID Jul-92 I I----I I--.I IIIC Jul-92 I I I I I IIC Jan-93 I I II I I lID Jan-93 I I II I I IIC Jan-93 I IT--I I I hID Jul-92 II I I ID Jan-93 I I I IC Sep-93 I I I I ID Sep-93 I I---I I IC May-94 I I I I hID May-94 I I I---! I-I °IIC May-94 I I II ID May-94 I---I I I lID May-94 I I I ID Sep-93 I III I IVD Sep-93 I I I I I I IVD Oct-93 I I I-I I I IVC Oct-93 I I I o-n ID May-94 I I I ID Jul-92 I I I lID Jul-92 j rn Tfl T 1IJ JUII ./.) U) High Similarity < > Low Similarity Figure 3.3-9. Dendrogram of Bray-Curtis similarity for each station and date. (Presence/absence transform).
13 Ill 112 113 111 112 113 Ii 12 13 Ill 112 113 Ii 12 13 Jut Jut Jul Jut Jul Jut Jul Jan Jan Jan Jan Jan p

+++ --- +++ +++ +++ +++ ... ............. -- ...........................

+++ +4+ +++ +++ - -- +++ - - - ... +++ -- - +++ - - - +++ ... 32 ---------+++ +++ --- .., +++ ---------+++ ... 55 42 ++ +++ --- ... +++ 4+4 +4+ 4+4 +++

46 40 65 --- +++ ... 4+4 +++ ... 49 44 60 65 -- +++ ... +++ ... 54 55 67 77 81 +++ ... 43 50 55 60 66 70 --- +++ +++ +++

47 23 46 44 45 55 40 +++ ... +++ --- +++ +++ -- 36 33 44 51 51 62 51 51 +++ - 16 9 19 iT 22 15 20 19 25 47 53 55 70 67 95 65 48 65 18 a ..

41 37 53 63 58 75 55 45 55 14 81 +++ +++

50 42 55 67 60 86 54 49 57 17 93 80 +++

44 31 49 48 48 63 48 50 45 15 56 55 47 50 50 52 60 76 61 45 65 23 68 54 20 19 25 27 29 28 25 22 27 15 24 20

42 32 47 46 45 55 42 39 37 17 52 44 29 25 .31 30 33 33 39 27 30 18 33 32

34 27 41 40 41 38 43 34 40 20 36 36

45 34 46 42 50 58 45 46 38 13 50 45 47 43 50 56 59 82 60 43 56 19 70 56

24 18 25 26 32 30 31 23 27 16 28 26 37 52 39 45 51 84 67 30 48 14 76 52 5722484151516076524351

44 38 47 49 48 64 44 44 49 14 65 51

30 23

51 14 50 24

24 15 43 27

53 19 1374627062703263454873885082

0-30 Taxa (1st QuartiLe 30 Texa)

31-45 Taxa (Median 45 laxa)

+++ 46-55 Taxa (3rd Quartile 55 Taxa)

>55

(0

- - -

Figure 3.3-10. Trellis diagram showing number of taxa in common for each pair of stations and dates.

46

53 61 ---------------

48 39 41 58 44 43 74 - - - 29 34 34 33 42 --- 50 40 37 56 93 37

56 42 44 66 73 43 79 101

Ii Jut

Ii Jut12 Jul

12 Jut 25

13 Jut 58 26

Ill Jut 37 28

112 Jut 49 30

113 Jul 42 29

1111 Jul 56 27

1112 Jut 61 28

1113 JuL 45 31

11 Jan 52 22

12 Jan 39 27

13 Jan 15 13

Iii Jan 57 28

112 Jan 45 22

113 Jan 52 25

11 Sep 49 18

12 Sep 52 28

13 Sep 27 18

lvi Sep 45 20

1V2 Oct 31 20

1V3 Oct

11 May

12 May

13 May

lvi May

lV2May

1V3 May

lvi lV2 p Oct1V3 Oct

Ii 12 May13 IV1 M

lV2 1v3 +++ +++ +4+ .. _.. +++ ... - - - +++ - - - +4+ +++ .-- ++ ... +4+ +++

.-. +++ +4+

--. +++ +++ +4+

+++ .-. - . +++

+++ +++ +++ +++ +4+ +++

--- +++

+++ +++ +++ ++ - - - --- . . - - - - ............

+++ +++ +++

50 ..

58 70 - - - 25 27 40

54 50 62 34

33 38 55 29 37 43 55 34 45 63 57 25

61 58 80 29 26 26 35 22 62 51 68 26

65 56 61 31
FINAL REPORT

OCS Report MMS 95-0005

Sarasota

The Sarasota site was sampled on three occasions: July, 1992, January,- 1993

and May, 1994. This site was not dredged during the course of the project, so this site

can serve as an illustration of natural temporal trends in community parameters. These

trends can then be compared to trends from Egmont Key to delineate impacts

associated with dredging at Egmont Key.

Faunal Abundance. Richness and Diversity. Temporal trends in number of taxa

and number of individuals per square meter at Sarasota (Area II) are found in Figure 3.3-

3. Temporal trends in species diversity (Shannon's H') and equitability (Pielou's J') are

found in Figure 3.3-4. These data are also presented in Table 3.3-1.

Both number of taxa and number of individuals per square meter increased

through time at the Sarasota site. This trend was evident at all three stations. Species

richness was similar at all three stations in July, 1992, ranging from 92 to 110 taxa (mean

= 101). By January, 1993, mean species richness increased to 137 taxa. The station

with the least number of taxa in July (ll-D1) had the most taxa in January, an increase

from 92 to 166 taxa. This station showed a less dramatic increase in the number of

individuals. Species diversity at Sarasota was highest in January, 1993. This is due to

a substantial increase in species richness coupled with only a slight increase in faunal

density from July, 1992 to January, 1993. By May, 1994, there was a further increase in

species richness and a large increase in faunal density. This resulted in a decrease in

species diversity from January, 1993 to May, 1994.

Faunal Composition. The relatively low faunal abundance at station lI-Di

compared to the other two stations during July, 1992 was due to the absence of several

dominant species at this station, most notably the bivalve Parvilucina multilineata and the

polychaete Aglaophamus verrilli, which were numerous at the other two stations. By

January, 1993, these two species were no longer dominant. They were replaced by

tubificid oligochaetes and a suite of lesser dominant taxa, all of which were equally

abundant at all three stations. Consequently, faunal density was similar among all sites

by January, 1993. Between January, 1993 and May, 1994, there was more than a

twofold increase in faunal density, from a mean of 2,383 individuals per square meter in

January, 1993 to 5,698 individuals per square meter by May, 1994. An increase in the

abundance of a variety of organisms contributed to this overall rise in faunal density.

Faunal Similarity. Faunal similarity values for Sarasota stations can be found in

Figure 3.3-6 (trellis diagram) and Figure 3.3-8 (dendrogram). Figures 3.3-7 and 3.3-9

display faunal similarity values as trellis and dendrogram diagrams, respectively, for

presence/absence data transformations. Stations Il-C and ll-D showed moderate

similarity during July, 1992 and May, 1994 for both normal and transformed data. These

stations were the most similar in faunal composition of any station-date combinations for

the entire study. All other Sarasota station comparisons showed bw similarity.

97
98

FINAL REPORT

OCS Report MMS 95-0005

This pattern of change in faunal communities at Sarasota is consistent with models

of temporal variability in natural systems (Maurer et al., 1993; Rakocinski et al., 1991;

Boesch etal., 1976). Faunal density and diversity from estuarine systems showed peaks

during spring and early summer (Leverone et al., 1991; Mahoney and Livingston, 1982;

Boesch et al., 1976). Differences in population-based parameters (e.g., density and

diversity) through space and time are often quite variable (Osenberg et al., 1994). This

variable pattern in faunal density and species diversity was also observed at the Sarasota

site during the present study.

Longboat Key

The Longboat Key site was sampled once (a six month post-dredging event in

September, 1993) during the present study. However, an independent Mote Marine

Laboratory study was conducted within the proposed borrow site during June, 1991.

Despite differences in sample size and sampling frequency between the two studies,

results from the MML study can be used to make qualitative observations and

comparisons of faunal composition at this site. Also keep in mind that there was over

a two year difference between the two sampling events, rendering any temporal

relationships between the two studies inappropriate.

A composite species list of fauna from the MML Longboat Key study is presented

as Table 3.3-8. No analysis on faunal abundance, species richness, diversity and

equitability are available for this study. A total of fifty species were found in this limited

study. The dominant species during the 1991 MML study were the lancelet,

Branchiostomma sp. (comprising 65% of the total fauna), followed by, in decreasing

abundance: Tel/ma sp. (bivalve), Spio pettiboneae (polychaete), Rhepoxynius epistomus

(amphipod), Olive/la flora/ia (gastropod), and Myodocopa sp. E (ostracod). The top ten

species constituted 90% of the total fauna, which indicates a relatively high level of

oligomixity. This may, however, be a reflection of the limited sampling effort during this

study. A more comprehensive study might have revealed a higher degree of diversity

and equitability.

Branch iostomma sp. was also the dominant species at Longboat Key during the

present study. This species was followed by Actiocina caniliculata (gastropod), Tel/ma

sp. (bivalve) and Rhepoxynius epistomus (amphipod). Several other species were

relatively abundant during the present study. These species include: Eudevenopus

honduranus, Acanthohaustorius uncinus, and Paraonis fulgens (po lychaete).

These cursory comparisons between the two studies suggest a consistency in

faunal composition over time at this site. The dominant fauna present are characteristic

of well sorted sandy environments typical of the nearshore coastal environment.

Because of the relative similarity in fauna between the two studies, it appears that any

effects of dredging at the Longboat Key borrow site were minimal.
Table 3.3-8. Composite species list. Number of individuals for each taxa from Mote Marine Laboratory beach

renourishment study, 1991. Longboat Key borrow site, pre-dredging sampling.

BS1-1 BS1-1 BS1-1 BS12 BS1-2 BS1-2 BS1-2 Overall

3 Total 1 2 3 Total Total

29 15 143 195 133 170 498 641

9 4 23 14 12 17 43 66

0 1 3 16 13 11 40 43

14 2 21 7 4 2 13 34

3 7 11 7 7 5 19 30

0 0 10 5 5 4 14 24

2 1 9 1 3 4 8 17

0 0 0 3 3 10 16 16

0 3 5 1 2 2 5 10

5 1 9 0 0 1 1 10

1 2 3 3 1 2 6 9

1 0 1 0 2 5 7 8

2 1 6 0 2 0 2 8

2 0 2 3 2 1 6 8

1 0 2 0 3 2 5 7

0 0 0 1 2 1 4 4

0 0 0 2 1 1 4 4

i 2 3 0 0 0 0 3

1 0 1 1 0 1 2 3

2 0 2 0 0 0 0 2

1 0 1 0 0 1 1 2

0 0 2 0 0 0 0 202!

1 1 2 0 0 0 0

C-) 2

0 0 0 0 0 2 2

0 0 0 0 0 2 2 9.. m

0 0 0 0 1 1 2 2°

0 0 2 0 0 0 0

i 1 2 0 0 0 0 2

0 0 0 0 0 2 2

(0

0 1 1 0 0 1 1

0 0 0 0 1 0 1

0 0 1 0 0 0 0

0 0 0 1 0 0 1

Taxa NODC

Branch iostcn,a floridae 8500010102

Tél lina 55153102

Spio pettiboneae 5001430706

Rhepoxynius epistanus 6169421501

Olivella floralia 5105100108

Plyodocopa sp. E 6111000095

Eudevenopus honduranus 6169422101

Prionosplo cristata 5001430510

Nemertea 43

Acanthohaustor ius pansus 6169220608

Mellita tenuis 8155040101

Paraonis fulgens 5001410302

Dispio uncinata 5001431901

Spisula solidissima 5515250102

Cyclaspis sp. G 6154090293

Armandia iriaculata 5001580204

Podocopa sp. H 6113000092

Goniada littorea 5001280205

Nat i ca 51037602

Sigambra tentaculata 5001220201

Nephtys picta 5001250117

Prionospio pygnaea 5001430507

Magelona riojal 5001440107

Parvi lucina multi lineata 5515010102

Asteropterygion sp. A 6111031499

Apanthura magn I fica 6160012001

Batea catharinensis 6169100101

Monocu 1 odes edwards i 6169370820

I tic i fer faxon I 6177020201

I'rocessa hctipl:i lii 6179170101

Athenari a 3759

Cerabratu lus lacteus 4303020209

Ilypereteone lactea 5001130208

BS1-1

1

99

10

2

5

1

10

6

0

2

3

0

0

3

0

1

0

0

o

0

0

0

2

0

0

0

0

2

o

0

0

o

1

0
BS11 BS1-1 BS1-1 BS1-1 BS1-2 BS1-2 BS1-2 BS1-2 Overall

Taxa NODC 1 2 Total 1 3 Total Total

Onuphis ereinita oculata 500129010701 0 0 0 0 0 1 0 1 1 Spionidae 500143 0 0 0 0 1 0 0 1 1 Arinandia agilis 5001580203 1 0 0 1 0 0 0 0 1 Capi tell idae 500160 0 0 0 0 1 0 0 1 1 Loimia inedusa 5001682001 0 0 0 0 0 1 0 1 1 Chone cf. americana 5001700107CF 0 0 0 0 1 0 0 1 1 Gastropoda 51 0 0 0 0 1 0 0 1 1 Bival via 55 0 0 0 0 0 0 1 1 1 Eusarsiella spinosa 6111040414 1 0 0 1 0 0 0 0 1 Poclocopa sp. A 6113000099 0 0 1 1 0 0 0 0 1 Cyclaspis sp. E 6154090295 0 0 0 0 0 1 0 1 1

Edotea triloba 6162020703 0 0 1 1 0 0 0 0 1

Glottidia pyramidata 8002010101 0 0 0 0 1 0 0 1 1

Oph 1 ophraç,vius wurdeinan,

Micropholis atra

8129030603

8129031201 01 00 10 11 00 00 00 00 11

-& Enteropneusta 8201 0 0 0 0 0 0 1 1 1 8 Ascidiacea 8401 0 0 1 1 0 0 0 0 1
101

FINAL REPORT

OCS Report MMS 95-0005

Manasota Key

Manasota Key was sampled during July, 1992. Faunal conditions at this site have

been previously discussed in the section "Pre-Dredging Faunal Community Conditions".

These results are briefly reiterated here. Manasota Key had the highest mean number

of taxa per station (142 ± 29 taxa). The difference in number of taxa between Manasota

Key and Egmont Key was statistically significant (p <0.05). Manasota Key also had the

highest mean number of individuals per square meter (3635 ± 1175). Manasota Key

also had the highest species diversity (Shannon Index) during July (3.67). There was a

statistically significant difference (p < 0.05) in Shannon Index between Manasota Key

and Egmont Key. Equitability (a measure of the evenness of species distribution) was

highest at Manasota Key (0.743 ± 0.12). There were no statistical differences in

equitability among stations. These findings indicate that Manasota Key sustained a rich

and diverse fauna during the present study.

The results support the contention of Osenb erg et al. (1994) in that relatively few

of the population parameters provide adequate power given the time constraints of the

study. This indicates that greater emphasis should be placed on individual-based

parameters in field assessments of environmental impacts. It will be critical to develop

and test predictive models that link these impacts with effects on populations. In order

to provide accurate descriptions of temporal variability in the soft-bottom communities

of estuaries and coastal embayments, low bias and highly precise estimates from each

sampling occasion are required.
102

FINAL REPORT

OCS Report MMS 95-0005

Chapter 4

4.1 SUMMARY AND CONCLUSIONS

The objectives of this study were to assess the possible impacts of sand dredging

on the benthic communities, both epifaunal and infaunal, and the possible changes to

the geology and topography as a result of the dredging operations. To achieve these

objectives geophysical and benthic surveys were conducted.

The geophysical surveys included precision depth recording, high resolution

seismic reflection profiling, side scan sonar, and box coring for sediment samples. The

precision depth recording was the most useful geophysical data collected due to the

persistent nature of the excavation left by the dredging operation. On the last cruise in

1994, almost 2 years after dredging and after several storm and frontal system periods

the excavation at the Egmont Key Site (Site I) was still clearly visible. It is clear that the

excavation was below the local wave base and that even in this shallow system sediment

supply is insufficient to quickly hide the dredge scar. There was no significant difference

in sediment grain size at Site I comparing pre- and post dredging samples. However,

grain size determinations did offer an explanation why wave and current action did not

fill the depressions created by the dredging operation with finer grain sediments. The

reason for this is that the finer than sand fraction of the sediments is very small for the

inner west Florida shelf surficial sand sheet. Therefore, there is no fine fraction to fill the

depressions. The variation in the coarser grain sizes is explained by increased amounts

of calcium carbonate composed primarily of shell fragments.

The epifaunal community was surveyed by otter trawl and video camera. The

epibenthos sampled by otter trawl displayed some seasonal variability. Portunus gibbesii

and Mellita tenuis were the dominant species at both the dredged and undredged sites.

There was no detectable difference between pre- and post-dredging at Site I. The

underwater video also showed little variability between sites or sampling dates and

observations of flora and fauna were rare except for an occasional portunid crab or

surface tubes of infaunal species. This reflects the constancy of this very dynamic sand

habitat and the low epibenthic diversity.

The infauna was sampled by box corer. The infauna at all sites was much more

abundant than the epibenthic fauna. A between site comparison of species richness and

diversity pre-dredging indicated healthy, diverse infaunal communities typical of the west

Florida coastal zone. There was some variation in the dominant taxa between sites.

As Egmont Key (Site I) was the only site with pre- and post-dredging sampling

occurring during the period of study, the infauna analysis focused on this location. Each

station at this site underwent different temporal patterns in benthic community

composition. Compounding the difficulty of interpreting the data is the observation that

the two stations in the dredged area responded quite differently from each other. In

general, the control station exhibited much less temporal variability. Therefore, it was not

possible to attribute differences between stations solely to dredging.
103

FtNAL REPORT

OCS Report MMS 95-0005

Temporal natural trends in infauna community parameters were determined from

the three sampling dates at the Sarasota site (Site II), which was not dredged. Faunal

density and diversity showed peaks in spring and early summer, although there was

considerable variability in the pattern.

The Longboat Key site (Site IV) was only sampled post-dredging during this study.

Comparison with data from other areas indicates a consistency in faunal composition

over time at this site, with infauna exhibiting characteristics common to a well sorted

sandy environment typical of the nearshore coastal zone. Because of this consistency,

it appears that any effects of dredging at the Longboat Key site were minimal. No

dredge hole or pits were observed in the geophysical records. Overall the analysis of

the infauna samples indicated that relatively few of the population parameters provided

adequate power to detect dredging impacts given the time and spatial constraints of the

study. Greater emphasis should be placed on individual-based parameters in field

assessments of environmental impacts.

In conclusion, the only demonstrable impact of the dredging from this study was

the physical alteration of the bottom topography which persisted almost two years after

dredging activities using a clamshell dredge ceased at the Egmont Key site (Site I).

There were no observable physical alterations at the Longboat Key site (Site IV) where

a dustpan dredge was used.
FINAL REPORT

OCS Report MMS 95-0005

Chapter 5

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