Diatom Paleoecology Pass Key Core 37,

Everglades National Park, Florida Bay

by

Laura Pyle1,2, Sherri R. Cooper2, and Jacqueline K. Huvane2

1 U.S. Geological Survey, Reston, VA

2

Duke University Wetland Center

Nicholas School of the Environment

Durham, NC

Open-File Report 98-522

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey

editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or

firm names is for descriptive purposes only and does not imply endorsement by the U.S.

Government

1998
3

TABLE OF CONTENTS

Abstract ...................................................................................................................................... 1

Introduction ................................................................................................................................ 2

Diatoms As Paleoecological Indicators..................................................................................2

Acknowledgements..................................................................................................................... 4

Methods...................................................................................................................................... 4

Collection and Dating of Core ............................................................................................... 4

Diatom methods.................................................................................................................... 4

Data Analysis ........................................................................................................................ 4

Results........................................................................................................................................ 8

Diatom Flora and Species Abundances .................................................................................. 8

Species Richness and Diversity .............................................................................................. 13

Centric to Pennate Ratio........................................................................................................ 13

Diatom Habitat Preferences................................................................................................... 16

Marine Taxa.......................................................................................................................... 16

Brackish Taxa ....................................................................................................................... 18

Freshwater Taxa.................................................................................................................... 18

Epiphytic and Epipelic Taxa .................................................................................................. 18

Discussion................................................................................................................................... 23

Summary..................................................................................................................................... 26

References cited.......................................................................................................................... 27

Appendix .................................................................................................................................... 30

FIGURES

1. Map of the core location ....................................................................................................... 3

2. Concentration of diatom valves ............................................................................................. 9

3. Select digitized images of diatom valves from the Pass Key core 37....................................... 10

4. Select digitized images of diatom valves from the Pass Key core 37....................................... 11

5. Select digitized images of diatom valves from the Pass Key core 37....................................... 12

6. Diatom species richness......................................................................................................... 14

7. Diatom species diversity ........................................................................................................ 14

8. Centric to pennate diatom ratios............................................................................................ 15

9. Percent abundance of marine diatoms.................................................................................... 17

10. Percent abundance of brackish species................................................................................... 19

11. Percent abundance of freshwater species................................................................................ 20

12. Percent abundance of epiphytic species.................................................................................. 21

13. Percent abundance of epipelic species.................................................................................... 22

14. Percent abundance of planktonic taxa .................................................................................... 25

TABLES

1. Percent abundances of diatom species in the Pass Key core 37................................................. 5-7
1

Diatom Paleoecology Pass Key Core 37,

Everglades National Park, Florida Bay

by

Laura Pyle, Sherri R. Cooper, and Jacqueline K. Huvane

ABSTRACT

During the 20th century, there have been large-scale anthropogenic modifications to the

South Florida ecosystem. The effects of these changes on Florida Bay and its biological

communities are currently of political and scientific interest. This study is part of a larger effort to

reconstruct the history of environmental changes in the bay, using paleoecological techniques. We

are using diatom indicators preserved in Florida Bay sediments to infer long-term water quality,

productivity, nutrient, and salinity changes. We are also obtaining information concerning the

natural variability of the ecosystem.

Diatoms are microscopic algae, the remains of which are generally well preserved in

sediments, and their distributions are closely linked to water quality. Diatoms were extracted

from a 70cm sediment core collected from the Pass Key mudbank of Florida Bay by the U.S.

Geological Survey. Between 300-500 diatom valves from each of 15 core samples were identified

and counted. Estimates of absolute abundance, species richness, Shannon-Wiener diversity, and

centric:pennate ratios were calculated for each sample that was counted. Information on the

ecology of the diatom species is presented, and changes in diatom community composition are

evaluated. 

Samples contained an average of four million diatom valves per gram of sediment. Major

changes in the diatom community are evident down core. These include increases in the percent

abundance of marine diatoms in the time period represented by the core, probably the result of

increasing salinity at Pass Key. Benthic diatoms become less abundant in the top half of the core.

This may be related to a number of factors including the die-off of sea grass beds or increased

turbidity of the water column.

Once the chronology of the Pass Key core 37 is established, these down-core changes can

be related to historical events and compared with other indicators in the sedimentary record that

are currently being investigated by U.S Geological Survey researchers.
2

INTRODUCTION

Florida Bay is a large, shallow lagoonal estuary at the southernmost tip of Florida. The

majority of freshwater flows into the bay are derived from the Everglades watershed, a region that

has been greatly impacted by human activities during the last century (Davis and Ogden 1994). In

1994, the Everglades Forever Act was passed that mandates that the ecosystem should be

returned to its “natural state”. However, without historical data on baseline conditions, restoration

management decisions are difficult. Paleoecological techniques provide a powerful tool for

obtaining such baseline data that is otherwise unavailable.

The goal of the “Ecosystem History of Florida Bay” project is to examine paleoecological

indicators found within sediment cores taken from the bay that can be used to quantify the amount

of natural variability in the estuary and to separate this from anthropogenic changes. Analyses of

diatom communities will allow interpretations regarding both salinity and nutrient changes that

may have occurred during the last few centuries in Florida Bay.

This report focuses on a short core (70 cm in length) taken from the mudbank south of

Pass Key in eastern Florida Bay (Fig. 1). Sampling of modern diatom assemblages is currently

underway in order to provide ecological information that can be used to refine paleoecological

interpretations.

Diatoms As Paleoecological Indicators

Diatoms are microscopic algae that occur in both freshwater and marine environments.

They have a siliceous shell, or frustule, consisting of two valves, that are generally preserved in

sediments. They occur in a variety of habitats; for instance, there are planktonic diatoms that grow

in open water, epiphytic diatoms that grow on plants and macroalgae, and epipelic diatoms that

grow on sediments. 

Diatoms are particularly useful as environmental indicators because many species have a

narrow range of environmental conditions that are optimal for growth and survival, and diatom

populations respond rapidly to environmental change (e.g. Dixit et al. 1992). Diatoms have been

used increasingly in studies concerning anthropogenic impacts on the environment (e.g. Cooper,

1995a and 1995b; Sweets et al. 1990), and in recent years, advances in statistical methods have

allowed some researchers to develop “transfer functions” that allow quantitative reconstruction of

past environmental characteristics. For example, Fritz et al. (1993) derived a diatom-based

transfer function that allowed them to calculate total phosphorus levels in several Michigan lakes

over the last 200 years. Similar functions have been developed for salinity in Great Plains lakes

(Fritz et al. 1991), chlorophyll in Antarctic lakes (Jones and Juggins 1995), and salinity in the

Thames estuary, England (Juggins 1992).
20

JOHN PENNEKAMP

CORAL REEF

STATE PARK

ONAL

1
4

ACKNOWLEDGMENTS

This project was funded by the U.S. Geological Survey and the Duke Wetland Center,

Nicholas School of the Environment, Duke University. We would like to thank G. Lynn

Brewster-Wingard and Gary Dwyer for their support, assistance, and comments on an earlier

draft. We thank Gene Shinn and Marci Marot of the U.S. Geological Survey, St. Petersburg,

Florida for collecting the core and making it available for analysis. Thanks also are due to the

following people at U.S. Geological Survey headquarters in Reston, Virginia: Bruce Wardlaw,

Tom Cronin, Deb Willard, Lisa Weimer, Steve Wandrei, Jill D’Ambrosio, and Nancy Carlin.

Jennifer Purvis, an undergraduate at Duke University, provided assistance in the lab. Eugene

Stoermer of the University of Michigan and Michael Sullivan of Mississippi State University

provided help with diatom taxonomic identifications and ecological information.

METHODS

Collection and Dating Of Cores

The Pass Key core 37 was collected by Gene Shinn and Marci Marot of the U.S.

Geological Survey, St. Petersburg, Florida. Age models are being developed.

Diatoms Methods

The core was subsampled at 2 cm intervals. Diatoms were extracted from sediment using

a modification of the method by Funkhauser and Evitt (1959), and permanently mounted on slides

with Naphrax for viewing with a light microscope. In each of 15 samples spaced throughout the

core, 300-500 diatom valves were identified and counted. Counts were recorded as percent

abundance within a sample (Table 1). An estimate of the total number of valves per gram of dry

sediment also was made by relating the number of valves counted on a slide to the proportion of

the area on the slide that was counted, taking into account dilution factors and the weight of

sediment processed. No such estimate could be made for the sample at 30 cm, which boiled over

during processing, resulting in the loss of part of the sample. The 10 cm, 34 cm, and 54 cm

samples were processed as wet sediment, and these samples were not dried and reweighed. 

Therefore, only the number of valves per gram of wet sediment could be calculated, which would

underestimate the number of valves per gram dry sediment. Light microscopic digital images

were captured via CCD video camera and frame grabber of many of the species identified in the

Pass Key core 37.

Data Analysis

Down-core changes in diatom assemblages can be analyzed by various methods, including

the examination of changes seen in the relative abundance of dominant species. Species richness

(total number of species seen in a sample) and Shannon-Wiener diversity (calculated as -Σpi(ln

pi), where pi represents the proportion of the total number of individuals of a particular species

(Begon et al. 1996)) also were calculated for each depth interval. Long-term
Table 1: Percent abundance of diatom species in Pass Key core 37, and summary statistics for each depth interval. [0 cm refers to the 0-2 cm sample, etc.]

0cm 4cm 10cm 14cm 20cm 24cm 30cm 34cm 40cm 44cm 50cm 54cm 60cm 64cm 70cm Mean

Statistics:

Number of valves counted 344 352 361 370 400 313 368 316 374 377 338 418 352 484 417 347

Species richness 48 54 48 62 47 49 54 47 50 52 37 53 40 50 52 49

Shannon-Wiener diversity 2.97 3.39 3.18 3.26 3.28 2.87 3.09 2.90 3.06 3.17 2.52 3.18 2.53 2.40 3.10 2.99

Centricpennate ratio 0.29 0.23 0.22 0.25 0.18 0.36 0.30 0.33 0.24 0.24 0.22 0.15 0.22 0.17 0.18 0.24

Valves per gram sediment 

 (in millions of valves)

Species:

Achnanthesdelicatula ssp. hauckiana

 (Grunow) Lange-Bertalot & Ruppel

Amphora coffeaeformis (Agardh) Kützing 3.78 3.69 7.20 5.14 9.00 1.92 3.80 1.27 2.14 1.86 0.59 2.15 0.28 1.65 2.64 3.14

Amphora cf. Costata Wm. Smith 0.58 1.14 1.11 0.54 2.00 1.28 3.53 6.33 1.60 1.86 1.48 1.67 0.00 0.62 0.72 1.63

Amphora dubia Gregory 0.00 0.00 0.28 0.54 0.00 0.32 0.27 0.00 0.00 0.27 0.00 0.24 0.00 0.00 0.24 0.14

Amphora aff. Proboscidea (Gregory) Cleve 0.58 1.42 0.83 1.08 4.50 0.00 0.82 0.00 0.53 0.53 0.00 1.20 0.28 0.21 2.16 0.94

Amphora cf. Proteus (Gregory) 1.16 0.85 1.94 0.54 1.00 1.92 2.99 2.53 1.07 1.06 1.48 1.91 2.56 0.62 0.72 1.49

Amphora rhombica Kitton 0.00 1.14 0.00 0.27 0.50 0.00 0.00 0.00 0.00 0.00 0.00 0.96 0.00 0.41 0.00 0.22

Amphora ventricosa Gregory 3.20 3.41 2.77 1.62 0.75 0.96 2.45 0.32 0.53 0.53 0.30 0.72 0.28 0.41 2.40 1.38

Amphora sp. 4 0.00 0.00 0.00 0.81 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.05

Caloneis cf. Liber (Wm. Smith) Cleve 0.29 0.00 0.00 0.00 0.25 0.64 0.27 0.95 0.27 0.53 1.18 0.48 0.28 2.27 0.24 0.51

Campylodiscuss ubangularis Grunow 0.00 0.57 0.28 0.54 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.72 0.16

Climaconeis scopulorioides Hustedt 0.58 1.99 6.09 2.70 2.25 0.32 2.17 0.00 1.87 0.53 0.00 1.20 0.85 0.62 3.60 1.65

Cocconeis placentula cf. var. euglypta

 (Ehrenberg) Cleve

Cocconeis scutellum Ehrenberg 0.00 0.00 0.83 0.54 0.00 0.32 0.27 0.00 1.07 1.33 1.18 1.44 1.42 1.03 0.24 0.64

Coscinodiscus sp. 1 0.29 0.85 0.28 0.00 0.25 0.00 0.27 0.32 0.00 0.27 0.30 0.00 0.00 0.21 0.24 0.22

Cyclotella cf. litoralis Lange & Syvertsen 28.20 20.17 20.50 22.43 16.75 32.91 29.62 29.75 24.06 21.22 16.57 12.92 17.61 14.67 17.03 21.63

Cyclotella cf. meneghiniana Kützing 0.00 0.00 0.00 0.81 0.00 0.00 0.00 0.00 0.00 0.53 0.00 0.00 0.00 0.00 0.00 0.09

Cyclotellastriata? (Kützing) Grunow 0.29 0.29 0.00 0.27 0.25 0.65 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.12

Cyclotella cf. stylorum Brightwell 0.29 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.00 0.41 0.00 0.06

Cyclotella sp. 0.29 0.00 0.83 0.54 0.50 2.56 0.00 2.22 0.00 1.33 5.03 1.20 4.83 1.24 0.48 1.40

Cyclotella sp. 1 0.00 0.00 0.55 0.54 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.00 0.21 0.48 0.13

Cymatosira lorenziana Grunow 0.00 0.00 0.28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Diploneis didyma Ehrenberg 0.00 0.28 0.28 0.00 0.75 0.32 0.82 1.58 0.00 0.53 0.30 0.00 0.00 0.21 0.48 0.37

Diploneis ovalis (Hilse) Cleve 0.58 0.85 0.28 0.27 0.00 0.96 0.54 0.00 0.27 0.27 0.00 0.00 0.00 0.00 0.72 0.32

Diploneis suborbicularis var. constricta

 Hustedt

2.52 7.15 10.69 3.10 6.94 3.11 N/A 2.46 3.52 6.07 1.67 2.61 3.72 3.38 4.26 4.37

1.74 0.28 1.94 0.00 2.00 0.00 0.00 0.00 0.00 0.53 0.00 0.24 0.00 0.00 0.24 0.47

2.91 3.98 6.93 7.03 4.00 3.19 4.35 0.32 4.81 8.22 0.59 7.66 9.38 3.31 6.71 4.89

0.87 0.28 0.00 0.54 0.00 1.60 0.27 3.80 0.53 0.00 1.18 0.00 0.85 0.83 0.24 0.73
Entomoneis alata (Ehrenberg) Ehrenberg 0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.03

Epithemia cf. turgida Kützing 0.00 0.57 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.53 0.00 0.48 0.00 0.21 1.92 0.26

Fragilaria tabulata var. tabulata (Agardh)

 Lange-Bertalot

Frustulia interposita (Lewis) de Toni 0.29 0.85 0.28 1.35 0.75 0.96 0.82 0.95 0.00 0.27 1.18 0.96 0.00 0.00 0.72 0.62

Frustulia sp. 2 1.16 1.14 0.28 0.27 1.50 0.32 0.54 0.63 0.27 0.00 0.00 0.48 0.28 0.21 0.00 0.47

Grammatophora oceanica var. macilenta

 (Wm. Smith) Grunow

Gyrosigma balticum (Ehrenberg) Cleve 1.74 1.14 1.94 1.35 0.50 0.32 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.48

Mastogloia angulata Lewis 0.29 0.00 0.00 0.00 1.00 0.00 0.00 1.58 0.27 0.53 0.30 0.00 0.00 0.00 0.00 0.26

Mastogloia cf. angusta Hustedt 0.29 0.28 0.00 0.00 0.75 0.00 0.00 0.00 0.00 0.27 0.00 0.72 0.28 0.21 0.00 0.19

Mastogloia cf. apiculata Wm. Smith 1.16 0.57 0.00 0.54 0.25 0.64 0.00 0.32 0.53 0.00 0.00 0.24 0.00 0.41 0.48 0.34

Mastogloia barbadensis (Grev.) Cleve 0.00 0.00 0.28 0.27 0.00 0.32 0.00 0.00 0.27 0.00 0.00 0.72 0.00 0.62 0.48 0.20

Mastogloia binotata (Grunow) Cleve 0.87 0.57 0.55 0.27 0.00 0.32 0.27 0.63 1.87 0.00 0.00 0.48 0.00 0.41 0.48 0.45

Mastogloia biocellata (Grunow) Novarino 

 & Muftah

Mastogloia braunii Grunow 0.29 0.00 0.00 0.81 3.25 0.32 0.27 0.95 0.27 0.53 1.78 0.48 0.28 0.41 0.48 0.67

Mastogloia corsicana Grunow 0.29 0.57 1.66 0.27 4.00 2.56 2.17 0.95 4.81 2.92 1.18 1.67 1.70 1.03 1.20 1.80

Mastogloia cribrosa Grunow 0.29 0.57 0.55 0.54 0.25 0.64 0.27 0.63 0.80 0.27 1.78 0.24 0.28 0.62 0.48 0.55

Mastogloia crucicula Grunow 5.52 4.55 3.05 5.95 5.25 7.67 4.35 5.70 13.10 11.67 5.33 4.55 14.20 4.34 6.71 6.80

Mastogloia cyclops Voight 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.02

Mastogloia cf. decipiens Hustedt 0.00 0.00 0.00 0.54 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.48 0.00 0.00 0.00 0.09

Mastogloia discontinua Paddock & Kemp 0.00 0.00 0.28 0.54 3.75 0.64 0.27 0.32 0.80 2.12 1.18 2.63 1.14 0.62 0.48 0.98

Mastogloia elegans Lewis 4.94 4.55 0.55 1.62 1.50 0.00 1.36 0.32 0.27 1.06 1.48 0.72 0.28 0.21 0.24 1.27

Mastogloia erythrea Grunow 4.94 4.55 1.66 1.35 4.00 0.96 3.26 1.58 3.74 3.18 0.30 5.98 0.57 1.24 3.84 2.74

Mastogloia fimbriata (Brightwell) Cleve 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.28 0.21 0.00 0.03

Mastogloia cf. labuensis Cleve 0.00 0.57 0.00 0.54 0.25 0.00 0.00 0.00 0.53 0.00 0.00 0.00 0.00 0.00 0.00 0.13

Mastogloia cf. lanceolata Thw. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04

Mastogloia ovalis A. Schmidt 3.20 3.69 2.77 2.70 2.75 1.60 3.53 0.32 4.01 2.65 0.89 2.87 1.42 1.65 1.68 2.38

Mastogloia ovulum Hustedt 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.02

Mastogloia cf. pseudolatecostata Yohn 

 & Gibson

Mastogloia punctifera Brun. 0.29 0.28 1.11 1.35 0.75 0.64 1.90 0.95 0.80 1.06 1.18 0.96 0.28 0.62 0.24 0.83

Mastogloia pusilla Grunow 4.94 1.14 0.55 0.00 0.00 0.96 0.82 0.63 1.60 1.06 0.00 0.00 0.00 0.21 0.00 0.79

Mastogloia rhombica Cleve 0.00 0.28 0.00 0.27 0.00 0.96 1.36 2.53 0.27 1.33 2.66 0.24 0.28 0.00 0.24 0.69

Mastogloia rimrosa Cleve 0.00 0.00 0.00 0.00 0.00 0.00 0.27 0.32 0.00 0.00 0.30 0.48 0.28 0.00 0.00 0.11

Mastogloia rostellata Grunow 0.58 0.57 0.28 0.81 1.00 0.32 0.27 0.00 0.27 0.53 0.89 0.00 0.00 0.41 0.00 0.40

Mastogloia cf. sturdyi Paddock & Kemp 0.00 0.00 0.00 0.00 0.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.21 0.00 0.05

Mastogloia subaffirmata Hustedt 0.00 0.57 0.00 0.00 0.25 0.32 0.82 0.63 1.07 1.33 0.59 0.24 0.00 0.00 0.48 0.42

1.16 1.42 1.94 2.97 6.00 5.75 4.35 6.96 6.42 4.24 3.25 3.59 1.70 3.10 2.88 3.72

0.87 0.85 0.00 0.54 0.50 1.28 0.27 2.22 0.53 0.00 1.78 0.72 1.14 1.65 0.96 0.89

0.00 1.14 0.00 0.27 0.50 0.00 0.82 0.00 0.27 0.00 0.00 0.72 0.00 0.21 0.00 0.26

0.00 0.00 0.28 0.27 1.00 0.32 0.54 0.00 1.60 0.80 0.30 1.20 0.85 0.21 0.24 0.51
Mastogloia subaffirmata cf. var. angusta

 Hustedt

Mastogloia tenera? Hustedt 0.00 0.00 0.28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Mastogloia varians Hustedt 0.87 0.85 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.44 0.00 0.00 0.00 0.21

Mastogloia sp.1 0.00 1.70 1.94 0.54 0.50 0.00 0.00 0.00 1.07 0.53 0.00 0.00 0.00 0.00 0.00 0.42

Mastogloia sp.2 0.00 0.00 0.00 0.27 0.00 0.00 0.27 0.00 0.80 0.80 0.00 0.72 0.00 0.00 0.72 0.24

Mastogloia sp.3 1.16 0.85 0.00 1.08 2.25 1.92 0.00 0.63 0.00 0.80 0.00 0.00 0.00 0.21 0.48 0.63

Navicula cf. barbara Heiden & Kolbe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Navicula cf. cancellata Donkin 0.00 0.57 0.00 1.35 0.00 0.64 0.54 1.58 1.07 0.80 0.30 0.00 0.28 0.41 0.24 0.52

Navicula cf. congerana Hagelstein 0.87 0.57 0.55 1.35 1.00 0.32 1.90 0.63 0.53 1.33 0.59 1.91 0.57 0.00 0.24 0.83

Navicula cf. elegans Wm. Smith 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.02

Navicula kuwaitiana Hendey 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.53 0.00 0.00 0.00 0.00 0.00 0.04

Navicula cf. zostereti Grunow 2.62 5.11 7.76 6.22 5.25 1.28 3.26 0.00 0.80 2.12 0.00 3.83 0.85 1.24 5.52 3.06

Navicula sp. 1 0.00 0.00 0.28 0.00 0.00 0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.04

Navicula sp. 3 0.00 5.40 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.38

Nitzschia aequorea Hustedt 0.29 0.00 0.28 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.07

Nitzschia cf. frustulum (Kützing) Grunow 1.45 2.27 4.99 2.70 0.50 0.00 1.36 0.32 1.07 2.39 0.00 0.72 2.56 0.62 12.23 2.21

Nitzschia granulata Grunow 7.56 1.70 1.11 1.89 1.00 5.11 3.53 10.13 3.74 7.69 36.39 20.57 26.42 45.25 9.11 12.08

Nitzschia aff. Maxima Grunow 0.58 1.42 1.94 4.05 2.50 6.07 2.45 2.22 1.60 1.06 1.78 0.72 0.85 1.86 4.32 2.23

Nitzschia panduriformis Gregory 0.00 0.28 1.39 1.62 0.00 0.00 0.27 0.00 0.80 0.00 0.00 0.00 0.28 0.00 0.00 0.31

Nitzschia punctata (Wm.Smith) Grunow 0.00 0.00 0.00 0.00 0.75 0.00 0.27 0.00 0.00 0.53 0.00 0.00 0.00 0.00 0.00 0.10

Oestrupia powelli (Lewis) Heid. ex Hustedt 0.00 0.00 0.00 0.81 0.00 0.32 0.27 0.32 0.00 0.80 0.00 0.96 0.28 0.00 0.00 0.25

Opephora sp. 0.29 0.28 0.55 0.27 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.57 0.00 0.00 0.15

Paralia sulcata (Ehrenberg) Cleve 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Pleurosigma cf. strigosum Wm. Smith 0.29 0.57 0.83 0.27 0.25 0.64 0.27 0.32 0.27 0.27 0.30 0.96 0.28 1.03 0.24 0.45

Rhopalodia musculus (Kützing) O. Möll. 2.62 3.13 3.32 1.08 0.75 2.56 2.17 1.90 2.67 1.59 3.25 0.96 1.42 0.41 1.20 1.94

Surirella fatuosa (Ehrenberg) Kützing 1.16 0.85 2.77 2.43 0.00 1.28 0.82 1.27 1.34 0.00 0.00 0.00 1.42 0.62 0.00 0.93

Synedra bacillaris (Grunow) Hustedt 0.29 0.85 0.83 0.27 0.25 0.96 0.54 0.32 0.27 0.00 0.59 0.24 0.28 0.21 0.24 0.41

Synedra undulata Bail. 0.00 0.00 0.00 0.27 0.00 0.64 0.27 0.32 0.27 0.27 0.30 0.24 0.00 0.21 0.00 0.18

Tropidoneis lepidoptera (Gregory) Cleve 0.00 0.00 0.00 0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

Tryblionella litoralis (Grunowin Cleve

 & Grunow) D.G. Mann

Unknown # 1 0.00 1.99 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.17

Unknown # 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.24 0.00 0.00 0.00 0.02

0.00 0.00 0.00 0.27 0.00 0.00 0.00 0.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04
8

trends in several parameters, including species richness and diversity, were examined by fitting

first order regressions to the data points using Sigma Plot software.

RESULTS

Diatom Flora and Species Abundances

Diatom valves were generally well preserved and abundant in the Pass Key core 37, with

estimates of the number of valves per gram of sediment ranging from just under 2 million to over

10 million (Fig. 2). Diatom concentration estimates are not constant with depth in the core; rather,

these estimates fluctuate. The largest fluctuation is near the surface of the core, where estimates

of around 3 million valves per gram in the 24-26 cm sample rise to over 10 million valves per

gram in the 10-12 cm sample. Estimates return to just over 2 million valves per gram in the 0-2

cm sample. It appears that the diatom concentration has increased over time; a simple linear

regression on these data results in a line with a slope that decreases toward the bottom of the core

(r2

=0.15). This trend may reflect an increase in the productivity of the diatom community in the

Pass Key area over the time period represented by the core. However, some or all of the changes

could be due to other factors, such as a variable sedimentation rate or preservation of the valves.

For example, a lower sedimentation rate may result in more diatom valves per unit of sediment

given the same rate of diatom productivity, as there is less sediment to “dilute” the valves. A

more precise estimate of sedimentation rate is necessary to assess diatom productivity. In

addition, the diatom taxa in the Pass Key core 37 are of varying size and shape. Biovolumes

would have to be determined in order to get a more accurate estimate of diatom productivity.

In general, the diatom flora represented in the Pass Key core 37 are similar to that of

localities in the Caribbean and other tropical and subtropical areas for which taxonomic works

have been completed, including Puerto Rico (Hagelstein 1938, Navarro et al. 1989), Cuba (Foged

1984), Greece (Foged 1986b), and Africa (Foged 1975, Foged 1986a). A complete list of all

species counted in the core, along with the percent abundance per sample and mean percent

abundance over all samples, can be found in Table 1. Ninety-five species and varieties were

identified; genera with the most species were Mastogloia (34 species and varieties), Amphora (8

species), and Navicula (8 species). The ten species with the highest mean percent abundance

were Cyclotella cf. litoralis (mean percent abundance=21.6), Nitzschia granulata (12.1%),

Mastogloia crucicula (6.8%), Cocconeis placentula cf. var. euglypta (4.9%), Fragilaria tabulata

var. tabulata (3.7%), Amphora coffeaeformis (3.1%), Navicula cf. zostereti (3.1%), Mastogloia

erythrea (2.7%), Mastogloia ovalis (2.4%), and Nitzschia maxima (2.2%). Some of these species

are shown in Figures 3-5.

The percent abundances of many of the more common species show changes throughout

the time period represented by the Pass Key core 37 (Table 1). Nitzschia granulata, which is an

epipelic species, shows some of the largest changes in abundance. This species is much more

common deeper in the core, with percent abundances as high as 45.3% and 36.4% in the 64-66

cm and 50-52 cm samples, respectively. Above the 44-46 cm sample, N. granulata is much less

common, with percent abundances of 10% or less.
9

Figure 2. Concentration of diatom valves in the Pass Key core 37 (r 2 = 0.15).

Concentration of diatom valves

Concentration X 106

0 2 4 6 8 10 12

Sample Depth

0

10

20

30

40

50

60

70

80

Wet sediment

Dry sediment

Regression line
10

Figure 3. a. Caloneis cf. liber (Wm. Smith) Cleve. b. Diploneis didyma Ehrenberg.

c. Mastogloia elegans Lewis d. & e. Mastogloia corsicana Grunow. f. Diploneis suborbicularis

var. constricta Hustedt. g. Cocconeis placentula cf. var. euglypta Cleve.
11

Figure 4. h. & i. Mastogloia cribrosa Grunow j. Grammatophora oceanica var. macilenta (Wm.

Smith) Grunow. k. Mastogloia discontinua Paddock & Kemp. l. Mastogloia binotata (Grun.)

Cleve. m. Mastogloia crucicula Grunow. n. & o. Mastogloia biocellata (Grun.) Novarino &

Muftah.
12

Figure 5. p. Navicula cf. congenera Hagelstein. q. Nitzschia cf. frustulum (Kutzing) Grunow

r. Navicula zostereti Grunow. s. Frustulia interposita (Lewis) de Toni. t. Navicula sp. 2.

u. & v. Mastogloia sp. 3. w. Nitzschia panduriformis Gregory. x. Amphora coffeaeformis

(Agardh) Kutzing.
13

Cyclotella cf. litoralis, a planktonic marine species, also shows changes in abundance,

ranging from 12-18% in the deeper samples, and increasing to over 20% above the 44-46 cm

sample. The percent abundance of C. litoralis reaches a high of 32.9% in the 24-26 cm sample,

decreases to 16.8% in the 20-22 cm sample, and resumes an increasing trend towards the surface

of the core. Mastogloia elegans, a marine species common on the coast of North America, shows

an increasing trend in abundance, with percent abundances <1% below the 50-52 cm sample,

increasing to almost 5% at the top of the core. In contrast, Nitzschia cf. frustulum, a brackishwater benthic species, appears to have become less common through time. The percent abundance

of N. cf. frustulum decreases from a high of 12.2% in the 70-72 cm sample to <1% in the 64-66

cm sample; its percent abundance remains <3% until the 10-12 cm sample, where it increases to

5%, decreasing again in the top sample of the core.

Many Florida Bay diatom species can be categorized by habitat and salinity preference.

There is information in the literature describing species as planktonic, epiphytic, or epipelic in

growth form, and whether they are generally found in fresh water, estuaries, or the ocean. Some

of the species identified from the Pass Key core 37 have only been recently described; for

example, Mastogloia discontinua, which made up over 2% of the valves counted in some

samples, was first described in 1990 (Kemp and Paddock 1990). It is not known whether the

ecological information from the literature that is available from other geographical regions applies

to the same species living in Florida Bay. Several species described by Hagelstein (1938) and

Foged (1984) as marine in Puerto Rico and Cuba, respectively, are listed by DeFelice (1975) as

occurring in upper Florida Bay (where salinities are normally <30 ppt) or in salinities ranging from

16-42 ppt by Stephens and Gibson (1979, 1980a, 1980b) in the Indian River Lagoon, Florida. 

The Appendix of this report contains ecological information for the species in the Pass Key core

37 that made up at least 1% of the valves in any sample; images of several of these species are

shown in Figures 3-5.

Species Richness and Diversity

Species richness and Shannon-Wiener diversity of diatom communities in the core

fluctuate together (Figs. 6 and 7), with deeper samples generally having lower species richness

and diversity (especially the 50-52 cm, 60-62 cm, and 64-66 cm samples). Diversity is highest in

the 4-6 cm, 14-16, and 20-22 cm samples, and species richness reaches its peak in the 14-16 cm

sample. There appears to have been a gradual increasing trend in diatom community diversity

with time; a regression on the diversity data results in a line with a slope that decreases toward the

bottom of the core (r2=0.30).

Centric to Pennate Ratio

Centric:pennate ratios (c:p ratios), which are ratios of the number of individuals of centric

(in this case, planktonic) species to the number of individuals of pennate (usually benthic) species,

can be useful as an indicator of the relative availability of planktonic and benthic habitats (Cooper

1995a & 1995b). An environmental change that causes a decrease in the availability of benthic

habitat may be reflected in an increased c:p ratio as centric species gain a competitive advantage. 

C:p ratios increase in the Pass Key core 37 from between 0.12 and 0.22 in the deepest samples

(Fig. 8) to over 0.35 in the 24-26 cm sample, decreasing to 0.18 in the 20-22 cm sample then

resuming a gradually increasing trend toward the top of the core. 
14

Figure 6. Diatom species richness (number of species per sample) with the fitted regression line

(r2= 0.08).

Figure 7. Shannon-Weiner diversity of diatom species with the fitted regression line (r2

=0.30)

Diatom Diversity

Shannon-Wiener Diversity Index

2 3 4

Sample Depth

0

10

20

30

40

50

60

70

Species Richness

Number of Species

35 40 45 50 55 60 65

Sample Depth

0

10

20

30

40

50

60

70
15

Figure 8. Centric:pennate diatom ratios with regression line (r2=0.21).

Centric:Pennate

 

0.10 0.15 0.20 0.25 0.30 0.35 0.40

Sample Depth

0

10

20

30

40

50

60

70

80
16

A regression on these data results in a line with negative slope toward the bottom of the

core (r2=0.21), indicating a trend toward increased c:p ratios in the diatom communities near Pass

Key over the time period represented by the core. Environmental changes that could act to

increase c:p ratios include blooms of centric diatoms, larger populations or blooms of other

planktonic algae (both possibly related to higher nutrient concentrations in the water column), or

increased levels of suspended sediment, all of which would increase turbidity and reduce light

availability to the benthic species. A reduction in the area covered by seagrass plants would also

reduce habitat for benthic species, many of which are epiphytic. Increased water depth would

also decrease the amount of light reaching the benthic diatom community and may result in a shift

towards dominance of planktonic species.

Diatom Habitat Preferences

In order to examine potential changes in salinity, substrate availability, and the relative

availability of benthic and planktonic habitats, species for which information on habitat preference

was available were separated into several groups, and down-core changes in the abundance of

these groups were evaluated. The “marine” group included 17 species for which all available

ecological data clearly pointed to a preference for water of salinity >30 ppt (this group therefore

excluded euryhaline species that have been reported growing in salinities as low as 16 ppt). 

However, since many of these marine species had very low percent abundances in the core and

may have been allochthonous, a second group (referred to as “marine dominants”) was

constructed that contained two species, Mastogloia corsicana and Mastogloia elegans. These

two species are benthic and present in at least one sample at a percent abundance of >4% (and

thus are less likely to be allochthonous), and exhibit a marine distribution. The “brackish” group

included those species (Achnanthes delicatula ssp. hauckiana, Amphora coffeaeformis, and

Nitzschia cf. frustulum) with a reported preference for brackish water, and the “freshwater” group

included just two species (Cocconeis placentula and Epithemia turgida) that are distributed

mainly in freshwater and brackish water of low salinity. Similarly, “epiphytes” included those

(Cocconeis spp., Grammatophora oceanica var. macilenta, and several Mastogloia species) that

occur predominantly on seagrasses and algae, “epipelics” included 7 species normally found

growing on sediment, and the “planktonic” group included the centric species. Due to a lack of 

ecological information, some species were not included in any group; as a result, the patterns of

changing abundance demonstrated by these ecological groupings do not reflect the responses of

every member of the diatom assemblage.

Marine Taxa

 Between 25-50% of the valves in the Pass Key core 37 (Fig. 9), are classified as

“marine,” and it appears that these species generally have been increasing in abundance

throughout the history of the core. A regression line fitted to these data has a slope that increases

toward the top of the core (r2=0.48). Similarly, the two species that comprise the “marine

dominant” group increase from about 1% in the 70-72 cm sample to over 5% of the 0-2 cm

sample (Fig. 9; r2=0.32). The percent abundances of both the “marine” and “marine dominant”

groups begin to increase at about the 44-46 cm sample, and reach near their highest levels

between 24 and 40 cm. The percent of marine taxa decreases between 10 and 20 cm, and

gradually resumes an increasing trend above 10 cm to the top of the core.
17

Figure 9. Percent abundance of marine and marine dominant groups, and their fitted regression

lines (marine r2

 = 0.48 and marine dominant r2= 0.32)

Marine Taxa

Percent

0 10 20 30 40 50

Sample Depth

0

10

20

30

40

50

60

70

80

Marine

Marine Dominant

Regression Lines
18

Brackish Taxa

The “brackish” group has its highest percent abundance in the 70-72 cm sample (Fig. 10),

mainly due to the large number of valves belonging to Nitzschia cf. frustulum, a brackish-water

benthic species. The percent abundance of this group drops to below 4% between 50 and 64 cm,

begins increasing at the 44-46 cm sample to almost 12% by the 20-22 cm sample. Abundance of

brackish-water species remains high until the 4-6 cm sample, dropping below 7% at the top of the

core. A regression line fitted to these data results in an increasing slope toward the top of the

core, reflecting an increase in the percent abundance of brackish-water species over time, but the

r

2

-value is low at 0.06.

Freshwater Taxa

The percent abundance of the species in the freshwater group shows a pattern that is an

inverse of that shown by the marine and marine-dominant groups (Fig. 11). Freshwater species

are more abundant in the deeper samples (although they make up <1% of the valves in the 50-52

cm sample), and show a decrease in abundance above the 44-46 cm sample. Percent abundance

of freshwater species remains relatively low from 40 cm until 20 cm, increases in the 14-16 cm

and 10-12 cm samples, and decreases again near the top of the core. The regression line fitted to

these data has a negative slope toward the top of the core, reflecting a decrease in abundance of

freshwater species over time (r2=0.08).

Epiphytic and Epipelic Taxa

Like the freshwater group, the species in the “epiphyte” group appear to have decreased in

abundance through time (Fig. 12, r

2

=0.04). Below 40 cm, the percent abundance of epiphytic

species such as Cocconeis placentula and Mastogloia crucicula fluctuates, reaching as high as

30% of valves counted. These fluctuations are consistent with DeFelice’s (1975) observation that

these species, especially C. placentula, are “opportunistic,” forming “blooms” when conditions

are favorable. Above 40 cm, the abundance of epiphytic species is much more constant, and

remains below 20%. Epipelic diatoms also show a decreasing trend in abundance toward the top

of the core (Fig. 13, r

2

=0.32).
19

Figure 10. Percent abundance of brackish species with the fitted regression line (r2=0.06).

Brackish Taxa

Percent

0 2 4 6 8 10 12 14 16

Sample Depth

0

10

20

30

40

50

60

70

80
20

Figure 11. Percent abundance of freshwater species and the fitted regression line (r2=0.08)

Freshwater Taxa

Percent

0 2 4 6 8 10

Sample Depth

0

10

20

30

40

50

60

70

80
21

Figure 12. Percent abundance of epiphytic species (r2= 0.04).

Epiphytic Taxa

Percent

5 10 15 20 25 30 35

Sample Depth

0

10

20

30

40

50

60

70

80
22

Figure 13. Percent abundance of epipelic species and the fitted regression line (r2= 0.32).

Epipelic Taxa

Percent

0 10 20 30 40 50 60

Sample Depth

0

10

20

30

40

50

60

70

80
23

DISCUSSION

The patterns of changing abundance shown by the groups of marine and freshwater

species suggest that there has been an increase in salinity in the Pass Key area over the time period

represented by the core. This effect becomes evident at about the 44-46 cm sample, above which

marine species increase in abundance and freshwater species decrease in abundance. There

appears to have been a time period represented by the portion of the core from 20 cm until 10 cm

during which this pattern reversed itself. The trend toward increasing abundance of marine species

is resumed above 10 cm towards the top of the core.

The benthic fauna record from the Pass Key core 37 shows similar fluctuations in both

salinity and epiphytic species (Wingard et. al. 1995). Studies of other Florida Bay cores have also

indicated increasing salinity up-core. These include cores taken from the Little Madeira Bay

(Ishman et al. 1996) and Russell Bank (Brewster-Wingard et al. 1997). A core taken from Bob

Allen Key indicates fluctuations in salinity between 1930 and the present (Wingard et al., 1995).

These findings suggest that the diatom-inferred increase in salinity in the Pass Key core 37 is a

widespread occurrence in Florida Bay.

Changing patterns of diatom assemblage diversity also support the hypothesis that salinity

in the Pass Key area has increased to salinities nearer to that of seawater in more recent

sediments. As salinity increases, more marine species may move into the Pass Key area, increasing

the diversity of species found there. DeFelice (1975) found that diatom communities in Florida

Bay showed increasing diversity along transects that ran from land toward open water; near-shore

epipelic and epiphytic samples tended to have lower diversity and equitability, and were more

likely to be dominated by one or a few species. Similarly, there was also an increase in benthic

faunal diversity in the upper 70 cm (since ca. 1931) of sediments from the Bob Allen core

(Wingard et al. 1995).

The meaning of the patterns exhibited by the species classified as “brackish” is not clear at

this time. The changes in abundance of this group appear to most closely track that of the

freshwater group; this suggests that, at a time represented by the portion of the core between 24

and 40 cm, salinities near Pass Key increased to reach some level above the preference of most

estuarine species. However, with the exception of the 70-72 cm sample, the brackish-water

species are not particularly abundant in the deepest part of the core, and the regression line

indicates an increasing abundance with time. It may be that one or more of these species is

responding to an environmental factor other than salinity.

Several factors could cause the decreasing trend displayed in epiphytic species abundance.

 First, decreasing populations of seagrasses would reduce the habitat area for epiphytic species. 

Second, some other change (such as blooms of planktonic algae, increased levels of suspended

sediment, or increased water depth) could have acted to reduce light availability. Third, the

reported low salinity-tolerance of Cocconeis placentula (a dominant epiphyte in Florida Bay)

suggests that the apparent increase in salinity, inferred from the increase in abundance of marine

species, may underlie the decrease in abundance of epiphytic species. However, the other

dominant epiphyte in Florida Bay, Mastogloia crucicula (DeFelice 1975), can live in salinities up
24

to 42 ppt (Stephens and Gibson 1979). Therefore, an increase in salinity is probably not the sole

factor behind the decline in epiphytic diatoms. 

The marked decline in abundance of epipelic species that occurs above the 50 cm sample

reinforces the pattern seen in the epiphytic species and in the planktonic species, which show an

increasing trend in abundance towards the top of the core (Fig. 14; r2=0.21). These changes

appear to be relatively abrupt. Epipelic species decreased from about 40% abundance in the 50-52

cm sample to about 10% in the 44-46 cm sample. Epiphytes declined from ~30% abundance in

the 40-42 cm sample to ~10% by the 34-36 cm sample; planktonic species increased from <25%

to ~33% during the same time period. The Pass Key core 37 has not yet been dated, but

preliminary results suggest that this core is relatively young (Brewster-Wingard et. al. 1998).

These trends suggest that some factor may have acted to decrease the abundance of both

epiphytic and epipelic species, possibly by reducing the amount of light that penetrated the water

column. Environmental changes that may reduce water clarity include increased nutrient

concentrations (which could stimulate populations of planktonic algae) and increased levels of

suspended sediments (either from terrestrial sources or re-suspension from the sediment surface).

Increased water depth also may have acted to decrease the amount of light reaching the benthic

species; however, this hypothesis is probably less likely than the others just discussed because of

the relative rapidity of these changes. Perhaps these abrupt changes could be due to increased

water depth if the cause was catastrophic (such as storms); the effects of rising sea-level would

probably be more gradual, unless some threshold of water depth was reached, which the epiphytic

and epipelic species could not tolerate.

Inferred changes in substrate availability are more variable between cores taken from

different sites in Florida Bay. The Pass Key core 37 provides some evidence that there were

declines in sea grass communities (Brewster-Wingard et al. 1998). In contrast, the T-24 from

Little Madeira Bay core shows increases in seagrass indicators in the upper 20 cm of the core

(Ishman et al. 1996).

Many of the changes in species abundance and other indicators in the Pass Key core 37

occur between 40 and 50 cm. C:p ratios show an increasing trend starting at about 40 cm. As

mentioned previously, the “marine” and “marine dominant” groups increase in abundance

beginning with the 44-46 cm sample, and the percent abundance of the freshwater group

decreases at about the same point. Epipelic species and epiphytes decrease abruptly above 50 cm

and 40 cm, respectively. Several of these trends are temporarily reversed from around 20 cm to

about 10 cm depth in the core.

It appears that some event or combination of factors has greatly affected the diatom

communities in the Pass Key region of Florida. The time period of greatest change is represented

by the 50-52 cm sample, which also has the lowest estimate of absolute abundance of diatom

valves of any sample in the core. This event probably had an effect on salinity, increasing the

abundance of marine species and decreasing the abundance of freshwater species, and on the

amount of light reaching the benthic species. The factors responsible for these changes appear to

have reversed temporarily during the time period represented by the 10-20 cm portion of the core.

 A decrease in freshwater input from terrestrial sources and reduced flushing would have effects

consistent with those seen in the core; however, without more information on the ecology of the
25

diatom species in Florida Bay and on the chronology of the core, it is premature to accept this

hypothesis.

Figure 14. Percent abundance of planktonic taxa and the fitted regression line (r2=0.21).

Planktonic Taxa

Percent

10 15 20 25 30 35 40

Sample Depth

0

10

20

30

40

50

60

70

80
26

SUMMARY

• Diatom valves in the Pass Key core 37 were generally well-preserved and abundant, with

estimates of the number of valves per gram of sediment ranging from just under 2 million

to over 10 million, with the highest estimates and largest fluctuations in abundance near

the surface of the core.

• 95 species and varieties of diatoms were identified in counts of 15 samples. Many of the

dominant species show large changes in percent abundance down-core.

• Species richness and Shannon-Weiner diversity of diatom assemblages show relatively

large fluctuations throughout the core, with highest values in the 4-6 cm, 14-16 cm, and

20-22 cm samples. Diversity appears to have increased during the time period represented

by the core; this fact is consistent with a hypothesis of increased salinity in the Pass Key

area.

• Centric:pennate diatom ratios range from just under 0.15 in the 54-56 cm sample to over

0.35 in the 24-26 cm sample, with a large drop in the c:p ratio occurring between the 24-

26 cm and 20-22 cm samples. These ratios appear to have increased over time; factors

that could cause an increase in the c:p ratio include increased nutrient concentrations

(resulting in blooms of planktonic algae), increased levels of suspended sediment, or

increased water depth.

• The percent abundance of the marine and “marine dominant” ecological diatom groups

begins to increase at the 44-46 cm sample, reaches highest levels between 24 and 40 cm,

decreases between 10 and 20 cm, and increases again toward the top of the core.

• The pattern of changing abundance for the freshwater ecological diatom group is almost

the exact inverse of the marine and “marine dominant” groups, suggesting that there has

been an increase in salinity over time, with highest salinities reached during the time period

represented by the portion of the core between 24 and 40 cm.

• Epiphytic diatom species have become less abundant with time. Below 40 cm, the percent

abundance of these species shows large fluctuations; above this point, the fluctuations

dampen, and the percent abundance of these epiphytic species does not reach as high as it

does in the deeper samples. Possible causes include reduced populations of seagrasses,

increased levels of nutrients or suspended sediment in the water column, and increased

water depth.

• Similarly, epipelic diatom species have become less common near the surface of the core,

which suggests that the decline in benthic diatoms may be related to some factor that acted

to decrease the amount of light reaching the benthic species.
27

• Many of the changes in diatom species abundance and other indicators occur between 40

and 50 cm; several of these trends are temporarily reversed between 10 and 20 cm. 

Information on the dating of the core will help to link these changes in diatom assemblages

to known historical events that have affected Florida Bay.

• Studies on other Florida Bay cores indicate that a trend towards increasing salinity has

occurred in other areas of the Bay. These studies, along with the Pass Key study, suggest

that changes in macrophyte communities are variable from site to site.

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Begon, M., J. L. Harper, and C. R. Townsend. 1996. Ecology. Oxford: Blackwell Science Ltd.,

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sedimentary diatom assemblages: a cautionary tale. Freshwater Biology 30:1-23.
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changes in salinity and climate using a diatom-based transfer function. Nature 352:706-

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Funkhauser, J. W., and W. R. Evitt. 1959. Preparation techniques for acid insoluble microfossils.

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Palaeoclimatology, Palaeoecology 117:31-54.

Goldman, N., T. B. B. Paddock, and K. M. Shaw. 1990. Quantitative analysis of shape variation

in populations of Surirella fatuosa. Diatom Research 5 (1):25-42.

Hagelstein, R. 1938. The Diatomaceae of Porto Rico and the Virgin Islands. Scientific Surveys of

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Hendey, N.I. 1964. An introductory account of the smaller algae of British coastal waters. Part V:

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Duke University Press, 67 p.

Ishman, S.E., G.L. Brewster-Wingard, D.A. Willard, T.M. Cronin, L.E. Edwards, and C.W.

Holmes. 1996. Preliminary paleontologic report on core T-24, Little Madeira Bay,

Florida. U.S. Geological Survey Open-File Report 96-543.

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Phycologica, 64:1-359.

Jones, V. J., and Stephen Juggins. 1995. The construction of a diatom-based chlorophyll a

transfer function and its application at three lakes in Signy Island (maritime Antarctic)

subject to differing degrees of nutrient enrichment. Freshwater Biology 34:433-445.

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salinity transfer function. Edited by H. Lange-Bertalot. Berlin: Gerbruder Borntraeger.

Bibliotheca Diatomologica. 25: 1-215. 

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Mastogloia with further observations on M. amoyensis and M. gieskesii. Diatom Research

5 (2):311-323.

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Epithemiaceae, Surirellaceae. In Süßwasserflora von Mitteleuropa, edited by J. Ettl, et al.

Stuttgart: Fischer, 596 p.

Lange, C. B., and E. E. Syvertsen. 1989. Cyclotella litoralis sp. nov. (Bacillariophyceae) and its

relationship to C. striata and C. stylorum. Nova Hedwigia 48:341-356.

Miller, W. I., R. T. Montgomery, and A. W. Collier. 1977. A taxonomic survey of the diatoms

associated with Florida Keys coral reefs. In Proceedings of the Third International Coral

Reef Symposium. Miami: Rosentiel School of Marine and Atmospheric Science.
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Navarro, J.N. 1982. Marine diatoms associated with mangrove prop roots in the Indian River,

Florida, U.S.A. Bibliotheca Phycologica. Hirschberg: 61: 1-151.

Navarro, J. Nelson, Carmen Perez, Niurka Arce, and Bryan Arroyo. 1989. Benthic marine

diatoms of Caja de Muertos Island, Puerto Rico. Nova Hedwigia 49 (3-4):333-367.

Novarino, Gianfranco, and A.R. Muftah. 1991. A description of Mastogloia biocellata stat. nov.

from Qatari coastal waters. Diatom Research 6 (2):337-344.

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Hawaii. Vol. 1. Philadelphia: The Academy of the Natural Sciences of Philadelphia, 688 p.

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maritimes voisins. Edited by M. J. Tempère. 491 p., 137 pl.

Stephens, F.C., and R.A. Gibson. 1979. Ultrastructural studies on some Mastogloia

(Bacillariophyceae) species belonging to the group Ellipticae. Botanica Marina 22:499-

509.

Stephens, F. C., and R.A. Gibson. 1980a. Ultrastructural studies of some Mastogloia

(Bacillariophyceae) species belonging to the groups Undulatae, Apiculatae, Lanceolatae,

and Paradoxae. Phycologia 19 (2):143-152.

Stephens, F.C., and R.A. Gibson. 1980b. Ultrastructural studies on some Mastogloia species of

the group Inaequales (Bacillariphyceae). Journal of Phycology 16:354-363.

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investigations of recent lake acidification in northern Florida. Journal of Paleolimnology

4:103-137.

Yohn, T.A., and R. A. Gibson. 1982a. Marine diatoms of the Bahamas: II. Mastogloia Thw. ex

Wm. Sm. Species of the groups Decussatae and Ellipticae. Botanica Marina 25:41-53.

Yohn, T.A., and R. A. Gibson. 1982b. Marine diatoms of the Bahamas III: Mastogloia Thw. ex

Wm. Sm. species of the groups Inaequales, Lanceolatae, Sulcatae, and Undulatae.

Botanica Marina 25:277-288.

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Preliminary analysis of down-core biotic assemblages: Bob Allen Keys, Everglades

National Park, Florida Bay. U.S. Geological Survey Open-File Report 95-628.
30

APPENDIX

Ecological information for diatoms with percent abundances greater than 1% in any sample.

The following summaries of ecological information were compiled from several publications

dealing with diatom taxonomy and ecology. 

Achnanthes delicatula ssp. hauckiana (Grunow) Lange-Bertalot and Ruppel

Hendey (Hendey 1964) lists this as a common species found in brackish waters along the

coasts of Britain. This species and other references for it are discussed in more detail in

Cooper (1995b).

Amphora coffeaeformis (Agardh) Kützing

According to Archibald and Schoeman (1984), this is a brackish-water species. Hustedt

(1955) found it to be "frequent on mud from the beach as well as on piles from the harbor"

near Beaufort, North Carolina. In a study of the Swan River estuary in Australia, John

(1983) found it to be periphytic, and more common at upstream (lower salinity) stations

than downstream. In the upper sounds of Florida Bay, DeFelice (1975) reported that it is

a common epipelic form, as did Hagelstein (1938) for Puerto Rico. Navarro (1982) listed

it as a very rare, sub- and supra-littoral species on the mangroves of the Indian River

Lagoon in Florida. 

Amphora cf. costata Wm. Smith

This species has been described as rare and sub-littoral on mangroves in Florida (Navarro

1982) and common on British coasts (Hendey 1964).

Amphora aff. proboscidea (Gregory) Cleve

This species has two prominent convex “humps” on the dorsal side of the valve and 16

striae in 10 μm; the identification was made with reference to drawings in Peragallo and

Peragallo (1897-1908). According to Hendey (1964), it is occasional on British coasts.

Amphora cf. proteus (Gregory)

Found on grass and sediment by DeFelice (1975) in upper Florida Bay, this species is a

mesohalobe to polyhalobe in Cuba (Foged 1984). It also was reported from the Swan

River estuary (John 1983) and Britain and the English Channel (Hendey 1964). It was

found by Navarro (1982) to be common on the mangroves in Florida in all positions

relative to the tides (sub-, supra-, and littoral). Miller et al. (1977) described it as a

common species on the sand around Florida Keys coral reefs, and Hagelstein (1938) listed

it as a common marine and brackish-water species in Puerto Rico.

Amphora rhombica Kitton

A polyhalobe (Foged 1984).
31

Amphora ventricosa (Gregory)

A polyhalobe in Cuba (Foged 1984), Hustedt (1955) found A. ventricosa "only on mud

from the beach,” and called it uncommon near Beaufort, N.C. It is common in all tidal

positions on Florida mangroves (Navarro 1982), in the Swan River estuary (John 1983),

and along British coasts (Hendey 1964).

Caloneis cf. liber (Wm. Smith) Cleve

This is a marine species (Patrick and Reimer 1966, Foged 1984), common on sandy shores

(Hendey 1964) and in San Juan Bay, Puerto Rico (Hagelstein 1938).

Climaconeis scopulorioides Hustedt

This littoral species was originally described by Hustedt (1927-1964) from the Gulf of

Mexico.

Cocconeis placentula cf. var. euglypta (Ehrenberg) Cleve

Cocconeis placentula has been described variously as a brackish and freshwater species

(Hagelstein 1938) and as an oligohalobe and salinity-indifferent (Foged 1984). DeFelice

(1975) found it in “extremely large numbers” on Thalassia grass in upper Florida Bay, and

Navarro (1982) stated that it was rare, and only found at the lower salinity station sampled

in his study of diatoms on Florida mangroves. Patrick and Reimer (1966) called this

species salt-indifferent, but said that it is “not observed in great numbers in slightly

brackish waters." This species and other references for it are discussed in more detail in

Cooper (1995b).

Cocconeis scutellum Ehrenberg

This marine species has been reported as common in Cuba (Foged 1984), San Juan Bay

(Hagelstein 1938), along British coasts (Hendey 1964), and on Thalassia and sediment in

Florida Bay (DeFelice 1975). Navarro (1982) found it only at the higher salinity station in

the Florida mangroves. This species and other references for it are discussed in more detail

in Cooper (1995b).

Cyclotella cf. litoralis Lange & Syvertsen

A planktonic species, it is probably "truly marine", according to Lange and Syvertsen

(1989), but might be euryhaline. The original description of this morphologically variable

species was published in 1990; under the light microscope C. litoralis is very similar to C.

stylorum, somewhat similar to C. striata, and is often confused with the two (Lange and

Syvertsen 1989). It is possible that a few of the valves identified as C. litoralis are

actually C. stylorum, although such valves probably make up a small percentage of the

total. Further SEM studies will help clarify the range of morphological variation in C.

litoralis and help distinguish it from similar species.
32

Diploneis didyma Ehrenberg

Patrick and Reimer (1966) described this species as euryhaline. According to DeFelice

(1975), it is primarily epipelic, but also epiphytic, in Florida Bay. It was rare at the lower

stations in the Swan River estuary (John 1983) and is common on British coasts (Hendey

1964) and in San Juan Bay (Hagelstein 1938).

Diploneis suborbicularis var. constricta Hustedt

A cosmopolitan species, more frequent on warmer coasts (Hustedt 1955). It is marine

(Hagelstein 1938) and a polyhalobe (Foged 1984), and was collected from sub-littoral and

littoral positions only at the higher salinity station in Navarro’s (1982) study of diatom

communities on mangrove prop roots in Florida. John (1983) collected this species at

both upper and lower stations in the Swan River.

Epithemia cf. turgida Kützing

Hagelstein (1938) reported this species as widely distributed in fresh and brackish waters

in Puerto Rico. He also found it at a marine sampling station but attributed this to

transport by tributary.

Fragilaria tabulata var. tabulata (Agardh) Lange-Bertalot

A euryhaline species found in Cuba (Foged 1984), it is common in all positions on the

Florida mangroves (Navarro 1982).

Frustulia interposita (Lewis) de Toni

DeFelice (1975) found this species to be epipelic and uncommon in upper Florida Bay. 

Patrick and Reimer (1966) reported that it prefers water of low mineral content. 

Hagelstein (1938) listed it as occurring in San Juan Bay and on the coast of North

America.

Frustulia sp. 2

This species has not yet been matched with a published description. Valves are usually

between 40 and 70 μm long, and around 10 μm wide. There are 20-22 curved, radial

striae in 10 μm.

Grammatophora oceanica var. macilenta (Wm. Smith) Grunow

A marine (Foged 1984) epiphyte (John 1983), common on British coasts (Hendey 1964)

and on Florida mangroves (Navarro 1982).

Gyrosigma balticum (Ehrenberg) Cleve

This is a brackish-water and marine species (Hagelstein 1938, Patrick and Reimer 1966,

Foged 1984). Hendey (1964) describes it as a littoral species that forms colonies on mud

and sand. Navarro (1982) found it to be frequent in the sub-littoral and littoral positions

on Florida mangroves, but Hustedt (1955) described it as scarce in Beaufort, North

Carolina.
33

Mastogloia angulata Lewis

According to Foged (1984) and Hagelstein (1938), this is a marine species; however,

Stephens and Gibson (1980b) reported M. angulata as an epiphyte found in salinities

ranging from 16-42 ppt. Navarro (1982) found it to be frequent on Florida mangroves, but

it was rare in Beaufort, North Carolina (Hustedt 1955), the Swan River (John 1983), and

in upper Florida Bay (DeFelice 1975).

Mastogloia cf. apiculata Wm. Smith

This species is also listed as a polyhalobe (Foged 1984) and marine (Hagelstein 1938), yet

was found in salinities from 16-42 ppt by Stephens and Gibson (1980a). It was found as

an epiphyte on Thalassia and on sediment in Florida Bay (DeFelice 1975).

Mastogloia binotata (Grunow) Cleve

Mastogloia binotata is a common epiphytic and epipelic species on Florida mangroves

(Navarro 1982) and in Florida Bay (DeFelice 1975). Hustedt (1955) found it to be scarce

near Beaufort, North Carolina, but Hendey (1964) described it as frequent in the English

Channel. It is a mesohalobe to polyhalobe (Hagelstein 1938, Foged 1984), found in

salinities ranging from 16-42 ppt by Stephens and Gibson (1979).

Mastogloia biocellata (Grunow) Novarino & Muftah

This species was originally regarded as a variety of M. erythrea, but was raised to species

status by Novarino and Muftah (1991), who collected it in the Atlantic Ocean off the coast

of Qatar.

Mastogloia braunii Grunow

A mesohalobe to polyhalobe (Foged 1984), M. braunii is epiphytic and epipelic in Florida

Bay (DeFelice 1975). It is a common brackish water form on North Sea coasts (Hendey

1964), and is found in brackish water throughout North America (Patrick and Reimer

1966). Hagelstein (1938) found it at marine sampling stations in Puerto Rico and in the

San Juan marshes.

Mastogloia corsicana Grunow

Mastogloia corsicana is a polyhalobe collected in Cuba (Foged 1984), and by Yohn and

Gibson (1982b) from the west end of Grand Bahama Island at 0-25 and 219 m depth.

Mastogloia cribrosa Grunow

This species is described as marine (Hagelstein 1938) and a polyhalobe (Foged 1984), but

has also been found throughout a range of salinities from 16-42 ppt (Stephens and Gibson

1979). Navarro (1982) reported it as frequent but only from the higher salinity station in

his study of Florida mangroves. DeFelice also lists it as an epiphytic and epipelic species

in Florida Bay, and Hustedt (1955) reports it as scarce near Beaufort.
34

Mastogloia crucicula Grunow

DeFelice (1975) described M. crucicula as a dominant epiphyte on Thalassia in upper

Florida Bay. It was also a common epiphyte in the mangroves of Florida (Navarro 1982),

but scarce off Beaufort, North Carolina (Hustedt 1955). According to Foged (1984) and

Hagelstein (1938), this species is marine, but was collected in a range of salinities from 16-

42 ppt by Stephens and Gibson (1979).

Mastogloia discontinua Kemp & Paddock

This species, first described in 1990 (Kemp and Paddock 1990), was collected from St.

James Reef off Bermuda.

Mastogloia elegans Lewis

Mastogloia elegans may be a truly marine species. It was described by Foged (1984) as a

polyhalobe, and Hagelstein (1938) found it at marine sampling stations (but also reported

it from a freshwater spring). Yohn and Gibson (1982b) collected it off the west end of

Grand Bahama Island, at depths of 25-50 m, and report that it is common on most of the

Atlantic coast of North America.

Mastogloia erythrea Grunow

Stephens and Gibson (1980b) found this species as an epiphyte on the seagrass Halodule

wrightii in the Indian River Lagoon in Florida in salinities ranging from 16-42 ppt. 

DeFelice (1975) reported it as an epipelic form in upper Florida Bay, and Navarro (1982)

stateed that it was rare, and only found at the higher salinity station, on coastal mangroves

in Florida. Hustedt (1955) and John (1983) found it to be rare near Beaufort, North

Carolina, and in the Swan River, Australia, respectively. It has also been described as

marine (Hagelstein 1938) and a polyhalobe (Foged 1984).

Mastogloia fimbriata (Brightwell) Cleve

Mastogloia fimbriata may be useful as an indicator of higher salinity; however, it was very

rare in the Pass Key core 37. Hagelstein (1938) and Foged (1984) described it as marine,

and Navarro (1982) found it only at the higher salinity sampling station in the Florida

mangroves, where it was very rare. It was also a rare benthic and epiphytic form in the

Swan River estuary (John 1983). Stephens and Gibson (1979) found this species only in

salinities ranging from 28-35.5 ppt; it was absent in salinities <28 ppt.

Mastogloia ovalis A. Schmidt

Stephens and Gibson (1979) found this species at salinities ranging from 16-42 ppt;

however, Navarro (1982) and Foged (1984) reported it as a marine form.

Mastogloia punctifera Brun.

Hustedt (1955) described M. punctifera as “not scarce” near Beaufort, and states that it is

also known from the Mediterranean. Foged (1984) also reported it as a marine form from

Cuba.
35

Mastogloia pusilla Grunow

A meso- to polyhalobe (Foged 1984) collected by Stephens and Gibson (1980b) in water

of 16-42 ppt, M. pusilla is common in all tidal positions in the mangroves of Florida

(Navarro 1982).

Mastogloia cf. pseudolatecostata Yohn & Gibson

This species, first described by Yohn and Gibson (1982a), was collected off the west end

of Grand Bahama Island at depths of 61-300 m.

Mastogloia rhombica Cleve

Probably a polyhalobe, M. rhombica was collected by Yohn and Gibson (1982b) off the

west end of Grand Bahama Island at 50 m depth.

Mastogloia rostellata Grunow

DeFelice (1975) listed this as an epipelic form in Florida Bay. Described by Foged (1984)

as a polyhalobe, it was also collected by Yohn and Gibson (1982a) from the west end of

Grand Bahama Island at depths of 25-300 m.

Mastogloia subaffirmata Hustedt

Found on Thalassia and sediment in Florida Bay (DeFelice 1975), this species is a

polyhalobe also known from the East Indies and the Mediterranean (Foged 1984).

Mastogloia varians Hustedt

A polyhalobe found in Cuba by Foged (1984), M. varians was reported as scarce off the

coast of Beaufort, North Carolina by Hustedt (1955), who said it was known previously

from Indomalaysian and Asian coasts. It was rare, and only at the higher salinity station,

in Navarro’s (1982) study of Florida mangroves.

Mastogloia #3

This species or form has not yet been matched with a published description. Valves

ranging in size from 20x8 μm to 60x12 μm have been counted, with 14-16 radial striae

and 3 elongate, rounded locules in 10 μm. Valves are lanceolate, with rounded cuneate

apices. Some valves appear to have a slightly constricted center; others do not.

Navicula cf. congerana Hagelstein

This species appeared to be a good match to Plate 6, Figure 9 in Hagelstein (1938),

described as a new species from a mangrove marsh in Miramar, Puerto Rico.
36

Navicula cf. cancellata Donkin

According to Hendey (1964), N. cancellata is a highly variable species that is adapted to

large changes in salinity and environment; different morphologies may correspond to

lower or higher salinities although not much more is known about polymorphism in this

species. It is strongly euryhaline, common on sandy beaches in Britain, but less frequent

on muddy shores (Hendey 1964). John (1983) listed it as an epiphyte at the lower stations

(higher salinity) in the Swan River. Hagelstein (1938) reported it from San Juan Bay, and

Foged (1984) described it as a polyhalobe.

Navicula cf. zostereti Grunow

A polyhalobe (Foged 1984), this species is common on sediment and grass in Florida Bay

(DeFelice 1975).

Navicula sp. 3

Valves are about 12 μm long and 3 μm wide, with 12 coarse, parallel striae in 10 μm; the

striae are shorter near the central area. Although quite different in size, this form

resembles Plate 39, Figure 3 in Krammer and Lange-Bertalot (1986).

Nitzschia cf. frustulum (Kützing) Grunow

Hendey (1964) describes N. frustulum as a brackish-water species common in European

estuaries, frequent on muddy shores. Navarro (1982) found it to be abundant in all

positions (sub-, supra-, and littoral) on Florida mangroves. Foged (1984) and Hagelstein

(1938) reported it as a common brackish-water species in the Caribbean.

Nitzschia granulata Grunow

According to Krammer and Lange-Bertalot (1988), this is a cosmopolitan, littoral marine

species, common on the "sandwatt" (which translates as a shallow place in sea covered

only at high tide, or sandflat). Navarro (1982) described it as rare in his study of Florida

mangroves. DeFelice (1975) described N. granulata as a sediment dweller in upper

Florida Bay, and Hendey (1964) said it is frequent on sandy shores. It is a common

benthic form in the lower Swan River estuary and occasionally is found in the upper

estuary (John 1983). Hagelstein (1938) reported it from marine, brackish, and fresh

waters in Puerto Rico, although Foged (1984) described it as a polyhalobe.

Nitzschia af. maxima Grunow

Valve lengths range from under 100 μm to several hundred μm; the ends of the valves are

slightly sigmoid. Striae are very fine, and there are 5 large, rectangular keel punctae in 10

μm. This species is common in the Pass Key core 37, and was identified by comparison to

Plate 24, Figure 2 in Krammer and Lange-Bertalot (1988); no ecological information

could be obtained.
37

Nitzschia panduriformis Gregory

DeFelice (1975) found this species in the sediment of Florida Bay; it is common on

European coasts (Hendey 1964). Foged (1984) listed it as a polyhalobe, and Navarro

(1982) reported it only at the higher salinity station in the Florida mangroves, where it was

very rare. It was a benthic form in the lower Swan River estuary (John 1983), and was

also collected by Hagelstein (1938) in San Juan Bay, Puerto Rico.

Pleurosigma cf. strigosum Wm. Smith

Found in marine and brackish water (Hagelstein 1938, Patrick and Reimer 1966), P.

strigosum is common on muddy shores (Hendey 1964).

Rhopalodia musculus (Kützing) O. Möll.

Hagelstein (1938) reported this species from both marine and freshwater, and Foged

(1984) also described it as euryhaline. DeFelice (1975) found R. musculus on sediment

and grass in upper Florida Bay. It is possible that some of these valves are really R.

operculata or R. gibberula.

Surirella fatuosa (Ehrenberg) Kützing

A polymorphic marine species (Foged 1984, Goldman et al. 1990), S. fatuosa is common

in Puerto Rico (Hagelstein 1938), the Swan River (John 1983), European coastal waters

(Hendey 1964), and Florida Bay (DeFelice 1975). Navarro (1982) reported it only from

the higher salinity station in the Florida mangroves.

Unknown #1

This species is centric, and may be a member of the genus Melosira, although it was not

matched to a species of this genus. To this point it has been seen only in valve view;

valves are about 15 μm in diameter, and are composed of an outer, narrow ring and a

larger, interior circular area. The valve surface has little ornamentation except for a

granular-looking texture that covers the interior area.
38