OCS Study 

•

MMS 99-0069 

Utilization of Sandy Beaches by 

Shorebirds: Relationships to 

Population Characteristics of 

Macrofauna Prey Species and Beach 

Morphodynamics 

Final Technical Summary 

Final Study Report 

 

U.S. Department of the Interior 

Minerals Management Service

Pacific OCS Region 

OCS Study 

MMS 99-0069 

Utilization of Sandy Beaches by 

Shorebirds: Relationships to 

Population Characteristics of 

Macrofauna Prey Species and Beach 

Morphodynamics 

Final Technical Summary 

Final Technical Report 

Author 

Jenifer Dugan 

Principal Investigor 

Prepared under MMS Cooperative 

Agreement No. 14-35-0001-30758 

by 

Coastal Marine Institute 

Marine Science Institute 

University of California 

Santa Barbara, CA 93106 

U.S. Department of the Interior 

Minerals Management Service Camarillo

Pacific OCS Region July 2006
Disclaimer 

This report has been reviewed by the Pacific Outer Continental Shelf Region, Minerals Management 

Service, U.S. Department of the Interior and approved for publication. The opinions, findings, 

conclusions, or recommendations in this report are those of the author, and do not necessarily reflect 

the views and policies of the Minerals Management Service. Mention of trade names or commercial 

products does not constitute an endorsement or recommendation for use. This report has not been 

edited for conformity with Minerals Management Service editorial standards. 

Availability of Report

Extra copies of the report may be obtained from: 

U.S. Dept. of the Interior 

Minerals Management Service 

Pacific OCS Region 

770 Paseo Camarillo 

Camarillo, CA 93010 

phone: 805-389-7621 

A PDF file of this report is available at: 

http://coastalresearchcenter.ucsb.edu/CMI/ 

Suggested Citation 

The suggested citation for this report is: 

Dugan, J. Utilization of Sandy Beaches by Shorebirds: Relationships to Population Characteristics 

of Macrofauna Prey Species and Beach Morphodynamics. MMS OCS Study 99-0069. Coastal 

Research Center, Marine Science Institute, University of California, Santa Barbara, California. MMS 

Cooperative Agreement Number 14-35-0001-30758. 41 pages. 
Table of Contents 

FINAL TECHNICAL SUMMARY........................................................................ 1 

FINAL STUDY REPORT....................................................................................... 7 

 Introduction.......................................................................................................... 7 

 Materials and Methods......................................................................................... 10 

 Results .................................................................................................................. 14 

 Discussion............................................................................................................ 27 

 Acknowledgments................................................................................................ 31 

 References............................................................................................................ 32 

Tables and Figures 

Table 1. Survey data and locations of study beaches............................................... 11 

Figure 1. Relationships between shorebirds, macrofauna, and macrophytes .......... 9 

Figure 2. Locations of the study beaches................................................................. 12 

Figure 3. Morphodynamic state of the study beaches.............................................. 15 

Figure 4. Mean intertidal widths of the study beaches ............................................ 16 

Figure 5. Mean grain sizes of sediments.................................................................. 17 

Figure 6. Mean macrophyte wrack cover ................................................................ 18 

Figure 7. Estimated species richness ...................................................................... 20 

Figure 8. Estimated abundances of Emerita analoga .............................................. 21 

Figure 9. Mean values for wet biomass of Emerita analoga................................... 22 

Figure 10. Mean individual sizes of invertebrates ................................................... 23 

Figure 11. Average number of shorebirds ................................................................ 24 

Figure 12. Relationship between species and sediment sorting................................ 25 

Figure 13. Relationship between macrofaunal biomass and shorebird abundance .. 27 

 

Utilization of Sandy Beaches by Shorebirds

1 

FINAL TECHNICAL SUMMARY 

STUDY TITLE: Utilization of sandy beaches by shorebirds: relationships to population 

characteristics of macrofauna prey species and beach morphodynamics 

REPORT TITLE: Utilization of sandy beaches by shorebirds: relationships to population 

characteristics of macrofauna prey species and beach morphodynamics 

CONTRACT NUMBER: 14-35-0001-30758

SPONSORING OCS REGION: Pacific

APPLICABLE PLANNING AREA: Southern California 

FISCAL YEAR(S) OF PROJECT FUNDING: FY96

COMPLETION DATE OF REPORT: June 2006

COST(S): $6000 

PROJECT MANAGERS: Jenifer E. Dugan, David M. Hubbard

AFFILIATION: Marine Science Institute, University of California Santa Barbara, CA

ADDRESS: Marine Science Institute, University of California, Santa Barbara, CA 93106

PRINCIPAL INVESTIGATOR: Jenifer E. Dugan 

KEY WORDS: Southern California, Ventura County, Santa Barbara County, Santa Barbara 

Channel, intertidal ecology, exposed sandy beaches, shorebirds, invertebrate macrofauna, beach 

morphodynamics, macrophyte wrack 

BACKGROUND: Little information exists on the potential risk from oil related impacts to 

shorebirds and to resources which they depend upon on exposed sandy beaches of Southern 

California. To address this gap in information needed for oil spill contingency planning and 

damage assessment, the distribution and abundance of shorebirds on Ventura County beaches 

was studied by Minerals Management Service personnel. The present study was undertaken to 

complement that project by examining factors which could affect the distribution and abundance 

of shorebirds on beaches, including prey availability and beach morphodynamics. The combined 

results of the Minerals Management Service study and the present study address a major gap in 

our understanding of the vulnerability of sandy beach resources to oil related impacts. 

OBJECTIVES: The present study was designed to provide new information on beach 

morphodynamics and other factors affecting shorebirds and macrofauna community structure on 

exposed sandy beaches on the Southern California coast. We examined relationships between 

shorebirds and their invertebrate macrofauna prey, macrophyte wrack, and physical attributes of 
Final Technical Summary -Dugan 

2 

sandy beaches using the results of field surveys of sandy beaches in Ventura and Santa Barbara 

counties in combination with the results of a study of shorebird distribution. Specifically we 

investigated relationships between: 1) the abundance and species richness of shorebirds on sandy 

beaches and the abundance, biomass and mean individual size of macrofauna prey species, 2) the 

abundance, biomass and mean individual size of macrofauna prey species on sandy beaches and 

physical factors, such as beach morphodynamics and 3) the distribution and abundance of 

shorebirds on a beach and physical factors, such as beach morphodynamics, beach size, 

landward boundary and other factors such as macrophyte wrack. 

DESCRIPTION: To determine the species richness, abundance, biomass and population 

size structure of the macrofauna community and selected species we conducted quantitative 

sampling at each of the Ventura County sandy beach sites (12) in the MMS shorebird study 

(McCrary and Pierson 1997) and at 3 additional Santa Barbara County beaches chosen to expand 

the range of morphodynamic beach types represented in the study. The physical characteristics 

and macrofauna communities of 15 beaches were sampled in September and October of 1996. 

Macrofauna community samples were collected in daylight on spring low tides on fifteen days 

between September 12 and October 13, 1996. On each beach, three transects were established 

extending from the landward boundary of the beach to below the lowest swash level. Each 

transect was sampled with 150 uniformly spaced cores of 10 cm diameter and 20 cm depth. At 

each of 15 tidal levels, 10 consecutive cores were grouped and rinsed through a 1 mm sieve, 

retaining the macrofauna. Macrofauna were preserved for analysis. This sampling design 

yielded a total sampling area of 3.5 m2 and a total of 45 biological samples at each beach. 

The cover and composition of macrophyte wrack was measured on the three transects at the 15 

sites. Amounts of accumulated macrophyte wrack were estimated (as % cover and total cover) 

using point-contact transects across the intertidal zone from the lowest edge of the terrestrial 

vegetation or base of the sea bluff to the high swash zone. 

To estimate beach morphodynamic state, physical parameters including wave height and period, 

sediment grain size and beach slope at three beach levels, swash width and period and beach 

width were measured on the three transects at all sites. 

From November of 1996 through November 1997, surveys of shorebirds, macrophyte wrack and 

physical characteristics were conducted monthly during spring low tides on the three Santa 

Barbara County study beaches using the MMS techniques for shorebirds and the protocols above 

for beaches. Dates of those surveys were selected to coincide with the monthly surveys of 

shorebirds on the Ventura County study beaches by MMS biologists. Monthly shorebird surveys 

of the 14 Ventura County study beaches by MMS biologists were completed in May 1997 

yielding 3 years of data on shorebirds and 20 months of data on sediments and wave climate. 

For comparisons, data from months in which both the Ventura and Santa Barbara County study 

sites were surveyed were used in analyses. 

In March 1997, the 15 study beaches were resurveyed using the protocols above to determine 

physical characteristics and macrophyte cover. In addition, a census of shorebirds and detailed 

observations of shorebird zonation were made at each beach. 
Utilization of Sandy Beaches by Shorebirds

3 

 

All sediment samples from the macrofaunal, winter, and monthly surveys were rinsed, dried and 

analyzed with standard testing sieves by a MMS/CMI student intern. Mean grain size, sorting, 

skewness and kurtosis were calculated for each sample. 

 

Wave height and wave period data were compiled from data collected by MMS biologists from 

that period by the student intern. Dean's parameter for each month and site were calculated from 

the wave and sediment data and used to estimate the modal morphodynamic state of the study 

beaches. 

 

To examine hypotheses concerning shorebirds, their macrofauna prey, and the physical 

characteristics of sandy beaches, data from the macrofauna community and beach surveys and 

from the shorebird surveys were analyzed using univariate and multivariate statistics. 

SIGNIFICANT CONCLUSIONS: Species richness, abundance, and biomass of macrofauna 

inhabiting exposed sandy beaches in Southern California were high compared to values reported 

for similar beaches of other regions. Species richness and abundances of selected taxa were 

positively correlated with macrophyte wrack cover. Beach grooming practices that remove 

wrack may have significant impacts on macrofauna communities. The results of our study in 

conjunction with those of the MMS shorebird study in Ventura county indicate that large 

numbers and high densities of shorebirds utilize exposed sandy beaches on the southern 

California coast. Our results suggest the standing crop and production of macrofauna prey may 

be important to understanding spatial variation in the abundance of shorebirds on exposed sandy 

beaches. 

STUDY RESULTS: The majority of the beaches we surveyed were modally intermediate 

morphodynamic types with values of Dean's parameter between 0.6 (reflective) and 5.5 (high 

intermediate to dissipative). The values for most of the study beaches in that period were 

between 1.5 and 4.4 (intermediate). Average values of Dean's parameter for the study beaches 

obtained from monthly surveys during the study ranged from 0.7 to 3.6 and were similar to 

those obtained in the September/October 1996 surveys, indicating primarily intermediate beach 

types. Although values of Dean's parameter >6 were obtained during some of the monthly 

surveys, no modally dissipative beaches were studied and none occur in the study region. Only 

one modally reflective beach was studied. 

Mean overall beach widths varied from 52 m to over 200m, while intertidal widths varied from 

29 m to 77 m. Mean swash zone widths varied from 5.8 m to 36.3 m and were negatively 

correlated with beach slope at the water table outcrop and the low swash level, and with Dean's 

parameter (p<0.05). Intertidal slopes at the water table outcrop ranged from 1.1 to 7.1 degrees in 

the 1996 surveys. The slopes at the low swash level ranged from 0.8 to 7.0 degrees and were 

positively correlated with the slope at the water table outcrop. The slope of the beach at the high 

tide strand line was quite variable both within and between study sites and mean values ranged 

from -3.0 to 20.7 degrees. Mean sediment diameters varied among sites and intertidal levels, 

mean values ranged from 0.24 to 0.50 mm for the high tide strand, 0.20 to 0.71 mm for the water 

table outcrop and 0.26 to 0.87 for the low swash zone. Sediment sorting varied more than 

sediment diameter among sites and intertidal levels. At the water table outcrop, sediment sorting 
Final Technical Summary -Dugan 

4 

ranged from well sorted, 0.40, to poorly sorted, 0.74. At the high tide strand, sorting varied over 

a similar range, between 0.38 and 0.79. Sorting was poorest at the low swash level, ranging 

from 0.49 to 1.31. 

The majority of the macrophyte wrack cover on the study beaches consisted of giant kelp, 

Macrocystis pyrifera. and surfgrass, Phyllospadix. The mean intertidal cover of marine wrack 

on ungroomed beaches varied over 2 orders of magnitude among beaches ranging from 0.03 m2

to 5.03 m2 per running meter of beach. On groomed beaches, the total cover of marine wrack 

was generally lower and varied from 0.08 m2 to 0.39 m2 per running meter of beach. 

More than 60 species of free-living macrofauna occurred in our surveys. Species richness of 

macrofauna ranged from 12-37 species among sites. More than 24 species of macrofauna 

occurred in samples at 7 of the 15 sites. 

Mean abundance of macrofauna varied more than 25-fold among the study beaches, ranging 

from 3,360 to 88,500 individuals m-1. The most abundant and widespread species was the 

common sand crab, Emerita analoga, which varied over two orders of magnitude, ranging from 

1,278 to 79,000 individuals m-1 among beaches. Sand crabs, E. analoga composed the majority 

of animals on many of the beaches sampled, ranging from 7 to 94% of the total macrofaunal 

abundance. 

Mean biomass (wet) of the macrofauna was more variable than abundance and varied over more 

than an order of magnitude, ranging from 660 to 22,000 gm-1 among the study beaches. Sand 

crabs, Emerita analoga were the dominant component of the biomass at all but two beaches and 

accounted for 31 to 99% (580 to 19,200 gm-1) of the biomass. The mean individual sizes of 

macrofauna varied over an order of magnitude among beaches, ranging from 0.10 to 1.11g. 

The most commonly observed species of shorebirds were sanderlings (Calidris alba), willets 

(Catoptrophorus semipalmatus), marbled godwits (Limosa fedoa), black-bellied plovers 

(Pluvialis squatarola) and whimbrels (Numenius phaeopus). Western snowy plovers 

(Charadrius alexandrinus nivosus) were abundant at selected beaches and occurred at 7 of the 15 

beaches during the study period. The average number of shorebirds per km of shoreline varied 

over an order of magnitude among beaches, ranging from 9 to 177 individuals km-1. In the 

March 1997 surveys, the majority of shorebirds (average = 87%) occurred on saturated sand 

(below the water table outcrop) and in the swash zone. 

Beach morphodynamics as estimated by Dean's parameter did not provide good predictions of 

macrofauna community attributes or shorebird abundance. Macrofauna species richness was 

negatively correlated with mean sediment sorting at the water table outcrop (p < 0.005). The 

abundance and biomass of macrofauna other than Emerita analoga were negatively correlated 

with sediment sorting at the water table outcrop (p < 0.001). 

Species richness of the macrofauna was positively correlated with the amount of marine 

macrophyte wrack (p < 0.05). The abundance of beachhoppers, Megalorchestia spp., varied 

over four orders of magnitude, from 85 to 10,200 individuals m-1 and was positively correlated 

with the cover of marine wrack (p < 0.001). 
Utilization of Sandy Beaches by Shorebirds

5 

The abundance of wintering shorebirds was significantly correlated with some beach and prey 

characteristics measured at the study beaches, including wrack cover and prey biomass. The 

average abundance of wintering shorebirds was positively correlated with mean macrofaunal 

biomass (p < 0.001) in this study. The average abundance of a widely distributed shorebird, 

black-bellied plover, was positively correlated with the cover of macrophyte wrack (p< 0.001). 

The abundance of the western snowy plover, a threatened shorebird species, was also positively 

correlated (p < 0.05) with wrack cover . 

STUDY PRODUCTS: 

Presentations: 

Dugan, J.E. 1997. Community and population responses of macrofauna to sandy beach 

morphodynamics and other environmental parameters. Invited seminar, California State 

University Cal Poly. 

Dugan, J.E., D.M. Hubbard, J.M. Engle, D.L. Martin, K.D. Lafferty, R.F. Ambrose, D.M. 

Richards, and G.E. Davis. 1999. Macrofauna communities of exposed sandy beaches on 

the Southern California mainland and the Channel Islands. Fifth California Islands 

Symposium, Santa Barbara Museum of Natural History. Santa Barbara, CA 

Dugan, J.E. 1999. Studies of sandy beach macrofauna in southern California. Invited seminar, 

 Universidad Austral de Chile, Valdivia, Chile 

Dugan, J.E. 2000. Effects of grooming on the ecology of exposed sandy beaches. Presented at 

the California Shore and Beach Preservation Society/ CalCoast conference, Monterey, 

CA. 

Dugan, J.E. 2000. Macro-scale patterns in sandy beach communities in California and Chile. 

Presented at Marine Macroecology and Conservation Workshop, Vina del Mar, Chile 

Dugan, J.E. 2001. Ecological impacts of grooming on exposed sandy beaches in southern 

California. Invited symposium presentation, Western Society of Naturalists, Ventura, 

CA 

Dugan, J.E. 2002. Riddles in the sand: Ecological patterns and processes on exposed sandy 

beaches. Invited Seminar, Sonoma State University. 

Dugan, J.E. 2002. Ecological impacts of grooming on exposed sandy beaches in southern 

California. Paper presentation, California and the World Ocean ’02, Santa Barbara, CA 

Dugan, J.E. 2002. Ecological effects of grooming on exposed sandy beaches in southern 

California. Invited Seminar, California State University Northridge.

Dugan, J.E. 2002. Effects of beach grooming on sandy beaches in California. Presented to San 

Diego City Council, Natural Resources and Culture Committee, San Diego, CA
Final Technical Summary -Dugan 

6 

Dugan, J.E. 2003. Ecology of sandy beaches. Invited presentation and field trip for the NOAA 

Damage Assessment Center Rapid Assessment Program meetings, September 2003, 

Monterey, CA. 

Dugan, J.E., D.M. Hubbard, and H.M. Page. 2003. Response of sandy beach ecosystems to 

macrophyte wrack subsidies from coastal reefs. Poster for 2003 LTER All Scientists 

Meeting, Seattle WA.

Publications:

Dugan, J.E., D.M. Hubbard, J.M. Engle, D.L. Martin, K.D. Lafferty, R.F. Ambrose, D.M. 

Richards, and G.E. Davis. 2000. Macrofauna communities of exposed sandy beaches on 

the Channel Islands and southern California mainland. Proceedings of the 5th California 

Islands Symposium. OCS Study, MMS 99-0038: 339-346. 

Dugan, J.E., D.M. Hubbard, and M. Lastra. 2000. Burrowing abilities and swash behavior of 

three crabs, Emerita analoga Stimpson, Blepharipoda occidentalis Randall and 

Lepidopa californica Efford (Anomura, Hippoidea), of exposed sandy beaches. J. Exp. 

Mar. Biol. Ecol. 255(2): 229-245. 

Dugan, J.E., D.M. Hubbard, M. McCrary, and M. Pierson. 2003. The response of macrofauna 

communities and shorebirds to macrophyte wrack subsidies on exposed sandy beaches of 

southern California. Estuar. Coastl. Shelf Sci. 58S: 133-148. 

Dugan, J.E., D.M. Hubbard, and H.M. Page. 2005. Ecological effects of grooming on exposed 

sandy beaches in southern California. Pp. 824-826 In: California and The World Ocean 

’02: Revisiting and Revising California’s Ocean Agenda: proceedings of the 

conference. O. T. Magoon, H. Converse, B. Baird, B. Jines and M. Miller-Henson (eds.). 

American Society of Civil Engineers. 1431 pp. 
Utilization of Sandy Beaches by Shorebirds

7 

FINAL STUDY REPORT 

INTRODUCTION

Sandy beaches comprise approximately three-quarters of the world's shorelines (Bascom 1980). 

In southern California, 74, 93, and 66% of the coasts of Santa Barbara, Ventura and Los Angeles 

Counties, respectively, are sandy beaches (Smith et al. 1976; Dugan et al. 1998a). 

This high prevalence means that sandy beaches are likely to receive the majority of 

contamination from a spill or other impact associated with coastal and offshore oil and gas 

activities 

 

Exposed sandy beaches in California are inhabited by an abundant invertebrate macrofauna 

community (Straughan 1982, 1983; Dugan et al. 1995, 1999), which is an important food 

resource for vertebrate predators such as shorebirds, seabirds, marine mammals and fishes. 

Sandy beaches of the region are also nesting sites for two federally listed birds: the threatened 

western snowy plover (Charadrius alexandrinus nivosus) and the endangered least tern (Sterna 

antillarum brownii). A unique fish, the California grunion (Leuresthes tenuis), deposits eggs for 

incubation in the high intertidal zone of sandy beaches. 

 

Sandy beaches are also considered extremely valuable as recreational and scenic resources for 

humans, both residents and tourists (Leatherman 1997). Although human use varies 

considerably among beaches, the majority of the shores of the Southern California Bight are 

heavily used, disturbed, developed and managed. Many beaches in the region are also subject to 

regular grooming, where trash, debris and drift macrophytes are removed with heavy equipment. 

 

Exposed sandy beaches are dynamic habitats and have been difficult to classify using single 

physical parameters such as slope and sediment size. The use of Dean's parameter, a 

dimensionless index of sediment fall velocity and wave height and period that expresses the 

dynamic interaction between the wave regime and available sediments (Short and Wright 1983; 

Short 1996), has provided a more functional classification of beaches. Using this 

morphodynamic classification, three major categories of exposed sandy beaches can be 

identified: reflective, intermediate and dissipative. Reflective beaches (Dean's parameter < 1) 

are characterized by small waves (<0.5 m), narrow surf zones, coarse sediments and steep slopes 

and are a harsh environment for intertidal fauna. Dissipative beaches (Dean's parameter >6) are 

characterized by large waves (>2 m), wide surf zones, fine sand and flat slopes, and are the most 

physically benign sandy beach habitat for fauna. Intermediate beaches (Dean's parameter 1 - 6) 

exhibit characteristics that fall between those extremes (Short and Wright 1983) and are the most 

variable type. Information on the morphodynamics of sandy beaches on the California coast is 

limited compared to other parts of the worl, such as. Australia (Short 1996, Dugan et al. 1998b). 

 

The use of Dean's parameter and other morphodynamic indices to ordinate exposed sandy 

beaches for comparisons of macrofauna community structure has allowed predictions of 

community attributes to be made with respect to beach characteristics (e.g., McLachlan 1990, 

McLachlan et al. 1993). Several general trends have been identified for macrofauna 

communities of exposed sandy beaches: 1) species richness increases, 2) total abundance 

increases, 3) total biomass increases and mean individual body size decreases across the 
Final Study Report - Dugan 

8 

spectrum from reflective to dissipative beach types and with increasing values of Dean's 

parameter (McLachlan 1990, McLachlan et al. 1993). Macrofauna community abundance and 

biomass could also be affected by surf zone productivity and wrack input. Dean's parameter may 

be also useful in predicting population characteristics of macrofauna species (Jaramillo and 

McLachlan 1993, Dugan and Hubbard 1996, Dugan and Hubbard in prep.). 

 

Many shorebirds utilize sandy beaches for feeding, roosting and breeding in Ventura and Santa 

Barbara counties. Shorebirds occurring on sandy beaches consist of migrant, wintering, and 

breeding or resident species. The distribution, abundance and utilization patterns of shorebird 

species on a beach may be related to a variety of factors, including prey availability, beach 

morphodynamic type, width and condition, macrophyte wrack cover, time of year, and human 

activity. 

 

Shorebirds have high metabolic rates and relatively high daily energy expenditures (Kersten and 

Piersma 1987), hence rich and productive food resources are critical to the survival of breeding 

and nonbreeding shorebirds. The abundant macrofaunal invertebrate community (Straughan 

1982, 1983, Dugan et al. 2000) inhabiting exposed sandy beaches of Southern California may 

represent an important prey resource for shorebirds, including federally listed species such as the 

western snowy plover. Shorebirds feed on a variety of sandy beach invertebrate species, 

including polychaete worms, insects, amphipods, isopods, hippid crabs, and bivalve mollusks. 

Some shorebird species forage opportunistically on exposed sandy beaches, but several species 

of shorebirds, including sanderlings, feed primarily on sandy beaches during the nonbreeding 

season. 

 

The abundance, biomass and mean individual size of macrofauna prey species (Dugan and 

Hubbard 1996, Dugan et al. 1995, 2000) and the distribution and abundance of their shorebird 

predators (Shuford et al. 1989, Webster et al. 1980) can vary on a variety of spatial and temporal 

scales in California (McCrary and Pierson 2002). The distribution and abundance of shorebird 

species on sandy beaches may be related to the distribution and abundance of their macrofauna 

prey as well as other factors. 

 

Macrophyte wrack is an important source of carbon for the semi-terrestrial upper intertidal 

macrofauna, including several species of talitrid amphipods, two species of isopods, two species 

of kelp flies and numerous beetle species, all of which are preyed upon by shorebirds. The 

distribution and abundance of shorebirds that feed on the upper beach could thus be related to the 

abundance of wrack. 

 

Relationships between sandy beach macrofauna and beach morphodynamics similar to those 

reported elsewhere in the world may well occur on California beaches. However, relationships 

between species occupying higher trophic levels that prey upon the macrofauna, such as 

shorebirds, and the physical characteristics of beaches, such as beach morphodynamics, but have 

not been studied. If such relationships exist, they could provide a valuable tool for 

understanding and predicting shorebird use patterns on sandy coasts. 

 

Despite the high prevalence of exposed sandy beaches along the coast of southern California, 

macrofauna communities and shorebirds of this important coastal habitat have received 
Utilization of Sandy Beaches by Shorebirds

9 

relatively little attention from marine ecologists. As such, little information exists on the 

potential risk from oil related impacts to shorebirds and to resources which they depend upon on 

exposed sandy beaches of southern California. To address this gap in information needed for oil 

spill contingency planning and damage assessment, the distribution and abundance of shorebirds 

on Ventura County beaches was studied by Minerals Management Service personnel (McCrary 

and Pierson 2002). The present study was undertaken to complement that project by examining 

factors which could affect the distribution and abundance of shorebirds on beaches, including 

prey availability and beach morphodynamics. The combined goal of the Minerals Management 

Service study and the present study was to address a major gap in our understanding of the 

vulnerability of sandy beach resources to oil-related impacts. 

In this study, we examined relationships between shorebirds and their invertebrate macrofauna 

prey, macrophyte wrack, and physical attributes of sandy beaches, as outlined in Figure 1, using 

the results of field surveys of sandy beaches in Ventura and Santa Barbara counties in 

combination with the results of the concurrent MMS study of shorebird distribution (McCrary 

and Pierson 2002). Specifically we investigated relationships between: 1) the abundance and 

species richness of shorebirds on sandy beaches and the abundance, biomass and mean 

individual size of macrofauna prey species; 2) the abundance, biomass and mean individual size 

of macrofauna prey species on sandy beaches and physical factors, such as beach 

morphodynamics; and 3) the distribution and abundance of shorebirds and physical factors, such 

as beach morphodynamics, beach size, landward boundary and other factors, including the cover 

of macrophyte wrack.. 

Shorebirds

Beach Morphodynamics 

and associated factors

Invertebrate 

Macrofauna

Macrophyte 

Wrack

Figure 1. Possible relationships between shorebirds, macrofauna prey, macrophyte wrack, and beach 

morphodynamics. Solid arrows indicate relatipnships we are currently investigating, dashed arrows indicate other 

potential relationships. 

MATERIALS AND METHODS
Final Study Report - Dugan 

10 

To determine the species richness, abundance, biomass and population size structure of the 

macrofauna community and selected species, we conducted quantitative sampling at 12 of the 

Ventura County study beaches surveyed in the MMS shorebird study (McCrary and Pierson 

2002) and at 3 additional Santa Barbara County beaches chosen to expand the range of 

morphodynamic beach types represented in the study. Table 1 contains a list of the study 

beaches and sampling/survey dates. Two of the MMS shorebird study beaches (Hobson Park 

and Mugu Rock) which either are washed completely at high tide or contain significant amounts 

of rocky habitat, were not sampled in the present study and are not included in this report. The 

physical characteristics and macrofauna communities of 15 beaches were sampled in September 

and October of 1996 (Table 1, Figure 2). 
Utilization of Sandy Beaches by Shorebirds

11 

Table 1. Survey dates and locations of study beaches from north to south. 

 * MMS study sites not sampled, ** additional sites surveyed in this study 

Beach Location Macrofauna Sampling Date Winter Survey Date Shorebird surveys

SANTA BARBARA COUNTY 

Sands Beach** 10/13/96 3/16/97 monthly 

East Campus** 9/27/96 3/16/97 monthly 

Santa Claus Lane** 9/15/96 3/17/97 monthly 

VENTURA COUNTY 

La Conchita 9/16/96 3/17/97 monthly 

Rincon 9/13/96 3/6/97 monthly 

Hobson Park* not sampled not sampled monthly 

Solimar 9/12/96 3/6/97 monthly 

Marina Park 9/26/96 3/11/97 monthly 

Surfer's Knoll 10/12/96 3/7/97 monthly 

5th Street 10/10/96 3/7/97 monthly 

Silver Strand 10/11/96 3/11/97 monthly 

Ormond Beach 3 9/28/96 3/19/97 monthly 

Ormond Beach 2 9/25/96 3/19/97 monthly 

Ormond Beach 1 9/25/96 3/19/97 monthly 

Point Mugu* not sampled not sampled monthly 

Deer Creek 9/29/96 3/10/97 monthly 

Leo Carrillo 9/24/96 3/10/97 monthly 
Final Study Report - Dugan 

12 

San 

Miguel

Santa Rosa

Santa 

Cruz

San 

Nicolas

Santa 

Barbara

Santa 

Catalina

San 

Clemente

Santa Barbara

Pt. Hueneme

Long 

Beach

50 km

Sands 

East Campus Santa Claus Ln.

La Conchita

Rincon

Solimar

Marina Pk.

Surfer's Knoll

5th St.

Silverstd.

Ormond 

 3, 2,1 Leo Carrillo N.

Deer Creek

N

34

120 119

33

Figure 2. Locations of the study beaches.

Macrofaunal community samples were collected in daylight on spring low tides on fifteen days 

between September 12 and October 13, 1996. On each beach, three transects were established 

extending from the landward boundary of the beach to below the lowest swash level. When 

possible, we sampled an area of the beach with a natural landward boundary and a measurable 

supralittoral zone. The distances between transects were randomly selected, but a minimum 

distance of at least 10 m between transects was used to avoid disturbance of mobile macrofauna , 

such as Emerita analoga, in adjacent transects.Each transect was sampled with 150 uniformly 

spaced cores of 10-cm diameter and 20-cm depth. At each of 15 tidal levels, 10 consecutive 

cores were grouped and rinsed through a 1-mm sieve, retaining the macrofauna. All macrofauna 

were preserved for later analysis in buffered formalin in seawater. This sampling design yielded 

a total sampling area of 3.5 m2 and a total of 45 biological samples at each beach. 

 

To estimate the standing crop of macrophyte wrack, the cover and composition of wrack were 

measured using a line intercept method along each of the three transects sampled for macrofauna 

(see above). All wrack, debris, driftwood, carrion, or tar of 0.01 m or more in width that 

intersected the transect line was measured, categorized, recorded. The total width of wrack 

encountered was then totaled for each transect. Means of wrack cover were calculated for the 

three transects at each site and expressed as square meters of wrack m-1 of beach. The percent 

cover of wrack was calculated by dividing the total wrack intersected (m) by the intertidal width 

(m) of each transect. Means of percent cover were also calculated for the three transects at each 

beach. 
Utilization of Sandy Beaches by Shorebirds

13 

 

To estimate beach morphodynamic state, physical parameters, including wave height and period, 

sediment grain size and beach slope at three beach levels (driftline or high tide strand, water 

table outcrop, and low swash limit), swash width and period, and beach width, were measured on 

the three transects at all study beaches. 

 

From November 1996 through November 1997, surveys of shorebirds, macrophyte wrack and 

physical characteristics were conducted monthly during spring low tides on the three Santa 

Barbara County study beaches using the MMS techniques for shorebirds (see McCrary and 

Pierson 2002) and the protocols above for beaches. In both studies, shorebirds were counted 

monthly along standard one kilometer transects on each of the 15 beaches from November 1996 

to May 1997. The 15 one kilometer transects were surveyed for shorebirds on low tides (0 to 

0.75 m MLLW) during a three to four day period in the same tide sequence each month. All 

birds were counted and identified to species using binoculars by a single observer on each 

transect. Mean shorebird abundance was calculated for each beach. The dates of the Santa 

Barbara County surveys were selected to coincide with the monthly surveys of shorebirds on the 

Ventura County study beaches by MMS biologists. Monthly shorebird surveys of the 14 

Ventura County study beaches by MMS biologists were completed in May 1997, yielding three 

years of data on shorebirds and 20 months of data on sediments and wave climate. For 

comparisons, data from months in which both the Ventura and Santa Barbara County study 

beaches were surveyed for shorebirds were used in the analyses. 

 

In March 1997, the 15 study beaches were resurveyed using the protocols above to measure 

physical characteristics and macrophyte cover (Table 1). In addition, a census of shorebirds and 

detailed observations of shorebird zonation were made at each study beach. 

 

All sediment samples from the macrofaunal, winter, and monthly surveys were rinsed in distilled 

water, dried and shaken through standard sieves by an MMS/CMI student intern. The fraction in 

each sieve was weighed to determine grain size distribution. Mean particle size and the 

inclusive graphic standard deviation (IGSD), an estimate of sediment sorting was calculated for 

each sample (Folk 1968). Sediment diversity was calculated using the Shannon Weiner diversity 

index (Zar 1984) as in Etter and Grassle (1992). Sand fall velocity was calculated using the 

conversion for mean particle size given by Gibbs et al. (1971) for each sample. Dean's 

parameter was calculated from the breaker height divided by the wave period and sand fall 

velocity (Short and Wright 1983) for each site. 

 

Wave height and wave period data were compiled by student interns from data collected by 

MMS biologists from that period. Dean's parameter values for each month and study site were 

calculated from the wave and sediment data then used to estimate the modal morphodynamic 

state of the study beaches. 

 

To examine hypotheses concerning shorebirds, their macrofauna prey, and the physical 

characteristics of sandy beaches, data from the macrofauna community and beach surveys and 

from the shorebird surveys were analyzed using linear regression analyses.. 

RESULTS 
Final Study Report - Dugan 

14 

General Characteristics 

We observed considerable spatial and temporal variation in physical characteristics of the study 

beaches. Most of the beaches sampled are subject to prevailing west winds and large winter 

swells from the west or northwest. Beaches in the central and southern portion of Ventura 

County are regularly exposed to southern swells in the summer months. 

 

The degree of human alteration and disturbance differed among the 15 study beaches. Several of 

the beaches (Santa Claus, Solimar, La Conchita, Marina Park, and Deer Creek) had artificially 

narrow upper beach zones due to the presence of riprap or seawalls in front of former foredunes 

or bluffs, while several other beaches (Surfer's Knoll, 5th Street and Silverstrand) had 

abnormally wide, flat upper beach zones that were groomed regularly and may have been 

enhanced with imported sand. In addition, piers and groins altered the wave regime at several of 

the study beaches (Rincon, Marina Park, Surfer's Knoll and Silverstrand). Large scale sandbypassing activities has influenced beach conditions at Ormond 1, 2, and 3 for decades. The 

most physically unaltered and natural beach types were Sands, East Campus, and Leo Carrillo. 

Human use of the study beaches, including numbers of dogs, varied spatially and temporally. 

Morphodynamics and other physical factors

 

The majority of the beaches we surveyed were modally intermediate morphodynamic types with 

values of Dean's parameter between 0.6 (reflective) and 5.5 (high intermediate to dissipative) 

measured during the surveys in September/October 1996 (Figure 3) and in other periods. The 

values of Dean’s parameter for the majority of the study beaches during that period were 

between 1.5 and 4.4 (intermediate). Those surveys followed a period of strong southern swells. 

 
Utilization of Sandy Beaches by Shorebirds

15 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0

1

2

3

4

5

6

7

8

9

10

Dean's Parameter

Reflective

Intermediate

Dissipative

Figure 3. Morphodynamic state of the study beaches estimated by Dean's parameter in September/October 1996 

surveys. 

In the winter (March 1997) surveys, values for Dean's parameter were lower for most of the 

study beaches, ranging from 0.1 to 4.7, and four of the beaches had values of <1, indicating 

reflective conditions. These surveys coincided with a period of unseasonably low swell activity, 

which could have resulted in the reflective conditions observed at some beaches. 

 

Average values of Dean's parameter for the study beaches obtained from monthly surveys during 

the study period ranged from 0.7 to 3.6 and were similar to those obtained in the 

September/October 1996 surveys, indicating primarily intermediate beach types. Although 

values of Dean's parameter > 6 were obtained during some of the monthly surveys, no modally 

dissipative beaches were studied and none occur in the study region. Only one modally 

reflective beach was studied (East Campus, Santa Barbara County, values of Dean's parameter 

ranging from 0.2 to 1.2, average = 0.7). 

In the September-October surveys, mean overall beach widths varied from 52 to over 200 m, 

while intertidal widths varied from 29 to 77 m among the 15 study beaches (Figure 4). Mean 

swash zone widths varied from 5.8 to 36.3 m and were negatively correlated with beach slope at 

the water table outcrop and the low swash level, as well as with Dean's parameter (p < 0.05). 
Final Study Report - Dugan 

16 

During the winter (March 1997) surveys, mean intertidal widths (Figure 4), swash widths and 

slopes were comparable to the late summer values for the majority of the beaches. Sands East Campus Santa Claus La Conchita Rincon Solimar Marina Surfer's Knoll 5th Street Silverstrand Ormond3 Ormond2 Ormond1 Deer Creek Leo Carrillo

0

20

40

60

80

September/October 

March 

Meters

Figure 4. Mean intertidal widths of the study beaches in the September/October 1996 and the March 1997 surveys. 

Intertidal slopes at the water table outcrop ranged from 1.1 to 7.1 degrees in the 

September/October 1996 surveys. The slopes at the low swash level ranged from 0.8 to 7.0 

degrees and were positively correlated with the slope at the water table outcrop (p < 0.05). The 

slope of the beach at the high tide strand line was quite variable both within and among study 

beaches, with mean values ranging from -3.0 to 20.7 degrees. Mean intertidal widths were 

significantly negatively correlated with the slope at the water table outcrop (p <0.05). 

 

Sediment diameter varied among beaches and intertidal levels: mean values ranged from 0.24 to 

0.50 mm for the high tide strand, 0.20 to 0.71 mm for the water table outcrop, and 0.26 to 0.87 

mm for the low swash zone (Figure 5). In general, the coarsest sediments occurred at the low 

swash level at most beaches. The mean sediment diameter at the water table outcrop was 

relatively consistent among the study beaches, with mean values between 0.20 and 0.30 mm. 

None of the study beaches had sediments with grain sizes < 0.20 mm, and only two of the 

beaches, Silverstrand and Leo Carrillo, had mean values for sediment size > 0.30 mm at the 

water table outcrop level. 
Utilization of Sandy Beaches by Shorebirds

17 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0.0

0.2

0.4

0.6

0.8

1.0

HTS

WTO 

LSL 

Mean Grain Size (mm)

Figure 5. Mean grain sizes of sediments at three intertidal levels (HTS- high tide strand, WTO- water table outcrop 

and LSL- low swash level) at the study sites during surveys in September/October 1996. 

Sediment sorting varied more than sediment diameter among beaches and intertidal levels. At 

the water table outcrop, sediment sorting ranged from well sorted, 0.40, to poorly sorted, 0.74. 

At the high tide strand, sorting varied over a similar range, between 0.38 and 0.79. Sorting was 

poorest at the low swash level, ranging from 0.49 to 1.31. In the March 1997 survey, sediments 

were distinctly coarser and less well sorted at most of the study beaches. 

Macrophyte Wrack

 

The majority of the macrophyte wrack cover on the study beaches consisted of giant kelp, 

Macrocystis pyrifera. and surfgrass, Phyllospadix spp. Three of the beaches sampled were 

subject to regular grooming to remove accumulated trash and macroalgal wrack (Silverstrand, 

5th Street and Surfer's Knoll). 

 
Final Study Report - Dugan 

18 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0.0

1.0

2.0

3.0

4.0

5.0 September/October 1996

March 1997

Marine Macrophyte Cover (m)

Figure 6. Mean macrophyte wrack cover on the study beaches in September/October 1996 and March 1997 

surveys. 

The mean intertidal cover of marine wrack on ungroomed beaches varied over two orders of 

magnitude among beaches ranging from 0.03 to 5.03 m2 per running meter of beach (Figure 6). 

On groomed beaches, the total cover of marine wrack varied from 0.08 to 0.39 m2 per running 

meter of beach. The lowest cover was found on the three groomed beaches and on the Ormond 

beaches. Estimates of the mean percent cover of marine macrophyte wrack on the study beaches 

varied from 0.0 to 9.7%. On the three beaches subject to regular grooming, the mean percent 

cover of marine wrack was generally <0.2%. Mean cover of macrophyte wrack was lower in 

March 1997 than in September/October 1996 at most of the study beaches, ranging from 0.0 to 

1.81m2 per running meter of beach (Figure 6). 

 

Regional variation in the cover of wrack were also apparent. Cover of wrack was generally low 

(<1%) on the Ventura County study beaches. The only two Ventura County beaches with wrack 

cover greater than 1% were the easternmost beaches, Leo Carrillo and Deer Creek, which are 

located in areas with adjacent subtidal rocky habitat. Two of the Santa Barbara County beaches 

had moderately high cover of wrack, 5-10% (Sands and East Campus), while the third had <1% 

cover (Santa Claus). 

Invertebrate Macrofauna 
Utilization of Sandy Beaches by Shorebirds

19 

Species Richness

 

More than 60 species of free-living macrofauna occurred in our surveys of 15 beaches. Species 

richness of macrofauna ranged from 12 to 37 species among the study beaches, not including 

incidental and commensal species (Figure 7). More than 24 species of macrofauna occurred in 

our samples at 7 of the 15 study beaches. The greatest number of species of macrofauna (37) 

occurred on an intermediate type beach protected by oil piers, Rincon, and the second greatest 

number of species (35) occurred on a modally reflective beach, East Campus. 

 

Species richness was lowest on the three beaches subject to regular grooming and wrack 

removal, with <15 species in those samples (range 11 to 15 species; Surfer's Knoll, 5th Street, 

Silverstrand). That depression in species richness was particularly noticeable in the upper 

intertidal sampling levels. Beaches with naturally low amounts of wrack also had lower species 

richness (17 to 22 species; e.g., Ormond 1, 2, 3, Leo Carrillo) than those with abundant wrack. 

 

Eggs and newly hatched larvae of the California grunion, Leuresthes tenuis, occurred 

abundantly in upper beach samples from Solimar Beach. High numbers of a small staphylinid 

beetle, Bledius fenyesi, were associated with the grunion eggs at that site. 
Final Study Report - Dugan 

20 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0

10

20

30

40

Number of Species

Figure 7. Estimated species richness of the macrofauna on the study beaches from the September/October 1996 

surveys. 

Abundance

 

The mean values of total macrofaunal abundance varied more than 25-fold among study beaches, 

ranging from 3,360 to 88,500 individuals m-1 among the 15 beaches sampled (Figure 8). The 

estimated mean abundance of macrofauna exceeded 12,000 individuals m-1 at all but three of the 

study beaches. Mean abundance of macrofauna was >20,000 individuals m-1 at six of the study 

beaches (Figure 8). Macrofaunal abundance was generally lower on groomed beaches than on 

ungroomed beaches. This was particularly noticeable in the upper beach sampling levels. The 

lowest mean value of macrofaunal abundance occurred on a groomed beach (3,360 individuals 

m-1; 5th Street). 

 

The most abundant and widespread species was the common sand crab, Emerita analoga. This 

species occurred on every beach sampled and was the most abundant species on 11 of the 15 

beaches surveyed (Figure 8). Mean abundance of this species was >10,000 individuals m-1 in 

samples from three of the beaches. Abundance of this decapod species ranged over two orders 

of magnitude, from 1,280 to 79,000 individuals m-1 of shoreline, among the study beaches. The 

presence of high densities of E. analoga in the swash zone accounted for the majority of the 
Utilization of Sandy Beaches by Shorebirds

21 

animals (>50%) on four of the study beaches, with sand crabs making up 7% to 94% of the total 

macrofaunal abundance across all the study beaches. 

Other macrofauna species for which mean values of abundance exceeded 10,000 individuals m-1

at one or more beaches included, talitrid amphipods, Megalorchestia spp. (up to 10,200 

individuals m-1), and the deposit-feeding polychaete, Euzonus mucronata (up to 23,000

individuals m-1). Talitrid amphipods, Megalorchestia spp., were widespread and occurred at 

every study beach. These amphipods were the most abundant wrack-associated species present 

in samples from all but three of the study beaches, with mean values for abundance ranging from 

85 to 10,200 individuals m-1. The high beach isopod, Tylos punctatus, was found in samples 

from five of the study beaches and was the most abundant wrack-associated species at two of 

those beaches with mean abundance values of 890 and 8970 individuals m-1. 

 

Two free-living bivalve species, the Pismo clam, Tivela stultorum, and the bean clam, Donax 

gouldii, occurred at 10 and 8 of the study beaches, respectively. These two clam species cooccurred at 9 of the study beaches. When present, values for mean abundance of these clams 

ranged from 89 to 800 individuals m-1 for T. stultorum and 83 to 1,940 individuals m-1 for D. 

gouldii. 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0

20000

40000

60000

80000

100000

Other macrofauna

Emerita analoga

Number/m

Figure 8. Estimated abundances of Emerita analoga and other macrofauna on the study beaches from the 

September/October 1996 surveys. 
Final Study Report - Dugan 

22 

Biomass

 

Mean biomass (wet) of the macrofauna was more variable than abundance and ranged over more 

than an order of magnitude, from 660 to 22,000 gm-1 (Figure 9). All but four of the study 

beaches had biomass values of >4,000 gm-1 and total biomass exceeded 10,000 gm-1 at four of 

the study beaches. The lowest biomass values (<1,000g m-1) occurred in our surveys of two 

groomed beaches. The sand crab, E. analoga, was the dominant component of the biomass at all 

but two beaches (Figure 9). This species alone accounted for 31 to 99% (580 to 19,200 gm-1) of 

the biomass at the study beaches. The biomass at one beach (Ormond 2) was dominated by the 

Pismo clam, T. stultorum (6,590 gm-1), and that of second beach (East Campus) by the spiny 

sand crab, Blepharipoda occidentalis (1,821 gm-1). Sands East Campus Santa Claus La Conchita Rincon Solimar Marina Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0

5000

10000

15000

20000

25000

Other macrofauna

Emerita analoga

Biomass g/m

Figure 9. Mean values for wet biomass of Emerita analoga and for other macrofauna at the study beaches from the 

September/October 1996 surveys.

Mean Individual Size

 

The mean individual sizes of macrofaunal invertebrates varied over an order of magnitude 

among the study beaches and ranged from 0.10 to 1.11g (Figure 10). The largest animals in our 

samples were several Pismo clams, T. stultorum, weighing over 700 g (live wt.) each, which 

occurred at a single site (Rincon). However, because the size of those animals exceeded the 
Utilization of Sandy Beaches by Shorebirds

23 

0.1m core diameter, their masses were reduced accordingly. The smallest individual species 

weighed <0.001 g wet weight. The largest crustacean in the samples was the spiny sand crab, 

Blepharipoda occidentalis, which weighed more than 47 g wet weight. Mean individual weights 

of Emerita analoga ranged from 0.25 to 1.99 g among the study beaches. Sands East Campus Santa Claus La Conchita Rincon Solimar Marina Surfer's Knoll 5th Street Silverstrand Ormond3 Ormond2 Ormond1 Deer Creek

Leo Carrillo

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Figure 10. Mean individual size of macrofaunal invertebrates on the study beaches from the September/October 

1996 surveys. 

Shorebirds 

 

Shorebirds were present on the study beaches during all of our surveys. The most commonly 

observed species of shorebirds were: sanderlings (Calidris alba), willets (Catoptrophorus 

semipalmatus), marbled godwits (Limosa fedoa), black-bellied plovers (Pluvialis squatarola) 

and whimbrels (Numenius phaeopus). Western snowy plovers (Charadrius alexandrinus 

nivosus)were abundant at selected beaches (e.g. Sands, Ormond 1, 2, 3) but did not occur at 8 of 

the 15 study beaches during the study period. The average number of shorebirds km -1 (per 

kilometer of shoreline) varied over an order of magnitude among beaches, ranging from 9 to 177 

individuals km-1 (Figure 11). The highest average numbers of shorebirds occurred on Ormond 1 

and the lowest at Solimar. In the winter (March 1997) surveys, the majority of shorebirds 

(average = 87%) occurred on saturated sand (below the water table outcrop) and in the swash 

zones of the study beaches. 
Final Study Report - Dugan 

24 

Sands

East Campus

Santa Claus

La Conchita

Rincon

Solimar

Marina

Surfer's Knoll

5th Street

Silverstrand

Ormond3Ormond2Ormond1

Deer CreekLeo Carrillo

0

50

100

150

200

Figure 11. Average number of shorebirds km -1 on the study beaches from monthly surveys conducted between 

November 1996 and May 1997. 

Relationships between Shorebirds, Macrofauna, Morphodynamics and Macrophyte Wrack 

Associations with Beach Morphodynamics and Physical Factors

 

Beach morphodynamics as estimated by Dean's parameter did not provide useful predictions of 

macrofaunal community attributes or shorebird abundance. Sediment sorting was the only 

physical parameter that was correlated with macrofaunal community attributes. Macrofauna 

species richness was negatively correlated with sediment sorting at the water table outcrop (p < 

0.005, Figure 12). The abundance and biomass of the macrofauna other than E. analoga were 

also negatively correlated with sediment sorting at the water table outcrop (abundance- r = 

0.800, p < 0.001; biomass- r = 0.790, p < 0.001, n = 15). 
Utilization of Sandy Beaches by Shorebirds

25 

0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

10

20

30

40

Sediment Sorting

Number of Species

y = 49.9 - 52.4x r = 0.744, n = 15, p < 0.005

Figure 12. Relationship between macrofauna species richness and mean sediment sorting at the water table outcrop 

for the 15 study beaches sampled in September/October 1996.

Associations with Macrophyte Wrack 

 

Species richness of the macrofauna was positively correlated with the amount of marine 

macrophyte wrack as estimated by cover (r = 0.533, p < 0.05, n = 15). This is due primarily to 

the presence of a number of species of insects and crustaceans associated with stranded drift 

algae and macrophytes. Beetle species included a carabid, Dyschirius marinus, a tenebrionid, 

Phalaria rotundata, a hydrophilid, Cercyon luniger, several histeriids, Neopachylophus 

sulcifrons and others, a curculionid, Emphyastes fucicola, and several species of staphylinids, 

including Thinopinus pictus. Larvae and pupae of two species of kelp fly, Coelopa vanduezei

and Fucellia costalis, occurred in association with macrophyte wrack. Two species of isopods, 

Alloniscus perconvexus and Tylos punctata, and four species of talitrid amphipods, 

Megalorchestia spp. were often abundant on ungroomed beaches with accumulated macrophyte 

wrack. 

 

Upper beach macrofaunal invertebrates, including talitrid amphipods (Megalorchestia spp.), kelp 

flies, and a variety of beetles, were widespread. Talitrid amphipods or beachhoppers, 

Megalorchestia spp. occurred at all beaches and were generally the most abundant upper beach 

species. The abundance of beachhoppers ranged over four orders of magnitude, from 85 m-1 to 

10,200 individuals m-1 and was positively correlated with the cover of marine wrack (p < 

0.001). The mean abundance of beachhoppers was generally higher on ungroomed beaches (594 
Final Study Report - Dugan 

26 

to 10,200 individuals m-1) than on groomed beaches (85 to 654 m-1). The mean abundance of 

intertidal beetles was also generally higher (50 m-1 to 5,160 m-1) on ungroomed beaches than on 

groomed beaches (0 to 60 individuals m-1). 

 

The average total abundance of shorebirds was not correlated with the cover of macrophyte 

wrack. However, the average abundance of one common species of shorebird, black-bellied 

plover, was positively correlated with the cover of macrophyte wrack ( r = 0.865, p < 0.001, n = 

15). The abundance of the western snowy plover, Charadrius alexandrinus nivosus, was also 

positively correlated with wrack cover (r = 0.564, p < 0.05, n = 15). 

Shorebirds and Macrofauna Prey

 

The average abundance of shorebirds (all species combined) was not significantly correlated 

with species richness or mean macrofaunal abundance in this study. Average abundance of 

shorebirds was positively correlated with mean macrofaunal biomass (g wet weight) (r = 0.822, p 

< 0.001, n =15) (Figure 13). A positive but non-significant relationship was found between the 

average abundance of shorebirds and the mean individual size (g wet weight of the macrofauna) 

on the study beaches. 
Utilization of Sandy Beaches by Shorebirds

27 

0 5000 10000 15000 20000 25000 30000

0

50

100

150

200

Macrofauna Biomass g/m

Shorebird Abundance  number/km

y = 18.3 +.006x r = 0.822

n = 15, p < 0.001 

Figure 13. Relationship between mean macrofaunal biomass and average shorebird abundance at study beaches in 

Ventura and Santa Barbara Counties. Shorebird abundance is the average number of birds per km in surveys from 

November 1996 through May 1997. Macrofaunal biomass is from the macrofauna surveys of September/October 

1996. 

DISCUSSION

 

Exposed sandy beaches of the coast of southern California harbor a surprisingly high diversity, 

abundance and biomass of macroinvertebrate species for modally reflective and intermediate 

beaches. Modally dissipative beaches were not present in the study region (see Dugan et al. 

1998b). The lack of macrofaunal data from dissipative beaches in our dataset precludes a 

definitive evaluation of possible relationships between community structure and 

morphodynamics in the Southern California Bight. However, our results suggest that other 

factors, including sediment sorting; recruitment dynamics for species such as Emerita analoga 

(e.g. Dugan and Hubbard 1996), Donax gouldii and Tivela stultorum (Coe 1955); disturbance; 

human activities; and the input of macrophyte wrack may strongly influence the structure of 

macrofaunal communities inhabiting exposed sandy beaches in southern California. 

 

The results of our surveys and of earlier studies (Straughan 1982, 1983) indicate that the 

macrofaunal invertebrate communities of exposed sandy beaches of southern California are 
Final Study Report - Dugan 

28 

generally much richer in species than reported for beaches of similar morphodynamic type 

elsewhere in the world. For example, in a synthesis of studies of macrofaunal community 

structure of beaches in Australia, South Africa, Chile and Oregon using survey techniques 

similar to those used in our study, the greatest number of macrofaunal species reported from a 

single beach was 30 on a macrotidal ultradissipative beach in Australia (McLachlan et al. 1996). 

Species richness ranged from 5 to 19 macrofauna species per beach for ten intermediate beaches 

in New South Wales, Australia (Hacking 1998). In Chile, where a number of congeners of the 

species found here occur, species richness for ten beaches ranged from 1 to 14 species, with the 

greatest number of species occurring on a dissipative beach and the lowest numbers (1 to 4) on 

reflective beaches (McLachlan et al. 1993; Jaramillo and McLachlan 1993). In addition, on 

three fully dissipative beaches in Oregon, macrofaunal species richness ranged from 17 to 21 

species (McLachlan 1990), a value lower than we found on many of the intermediate and even 

the reflective beach surveyed in our study. 

 

Our surveys of exposed sandy beaches in Ventura and Santa Barbara Counties also found the 

abundance of macrofauna to be high relative to that reported for reflective and intermediate type 

beaches in other parts of the world. For macrofauna of exposed sandy beaches, abundance 

values of greater than 10,000 individuals m-1 are considered high and have been reported 

primarily on dissipative beaches (McLachlan et al. 1996). Values of macrofaunal abundance 

greater than 10,000 individuals m-1 were reported for only 13 of 75 beaches from around the 

world, those 13 were high energy intermediate to dissipative types (McLachlan et al. 1996). 

Mean values of total abundance less than 10,000 individuals m-1 occurred on only three of the 

15 beaches surveyed in the present study, two of those beaches were subject to regular grooming 

and macrophyte wrack removal. Macrofaunal abundance values of an order of magnitude 

greater (100,000 individuals m-1) have been reported only for dissipative beaches in Oregon 

(McLachlan 1990). 

 

On many of the beaches we surveyed, the majority of individuals were sand crabs, Emerita 

analoga. High values for macrofaunal abundance (>10,000 m-1) were also reported for 

intermediate to dissipative state beaches in Chile where E. analoga occurs (Jaramillo and 

McLachlan 1993, McLachlan et al. 1993). 

 

The biomass of macrofauna on the sandy beaches we sampled was variable, but generally high 

relative to that reported for intermediate type beaches in other parts of the world. McLachlan et 

al. (1996, 1993) considered dry biomass values greater than 1,000 gm-1 to be high and a value of 

5,000 gm-1 a ceiling value for macrofaunal communities of exposed sandy beaches. 

Macrofaunal biomass greater than 1,000 gm-1 was reported for only 13 of 75 beaches from 

around the world; those 13 were high intermediate to dissipative types (McLachlan et al. 1996). 

We estimated (dry biomass = 25% of wet biomass, McLachlan personal communication) mean 

dry biomass values greater than 1000 gm-1 for surveys at ten of our 15 study beaches and a 

maximum value greater than 5,000 gm-1 for modally intermediate beaches in southern 

California. 

 

Again, on many of the beaches we surveyed, the sand crab, Emerita analoga, composed the 

majority of the macrofaunal biomass. Relatively high macrofaunal biomass (>1000 gm-1) was 
Utilization of Sandy Beaches by Shorebirds

29 

also reported for four intermediate to dissipative state beaches in Chile where E. analoga occurs 

(Jaramillo and McLachlan 1993, McLachlan et al. 1993). 

 

Macrofaunal communities inhabiting sandy beaches are supported primarily by allocthonous 

sources of carbon as little or no primary production occurs on the beach itself (Brown and 

McLachlan 1990). In southern California, the main sources of primary production are drift 

macrophytes and phytoplankton. Drift macrophyte input was estimated as 473 kg wet weight m1y-1 for an exposed sandy beach in southern California (Hayes 1974). Macrofaunal 

communities of sandy beaches depend upon the production of nearshore kelp forests, seagrass 

and macroalgal beds and oceanographic processes for food subsidies. Drift macrophyte 

consumers, including talitrid amphipods and insects, inhabit the upper beach and move down to 

the mid and low intertidal to feed. Suspension feeders that utilize phytoplankton and associated 

particulate organic material, including hippid crabs and bivalves, inhabit the lower intertidal 

zone. Scavengers and predators, such as albuneid crabs, isopods, polychaetes and beetles, prey 

upon primary consumers of both types and feed on drift carrion. Vertebrate predators, such as 

shorebirds and fishes, can utilize all of the trophic levels of this intertidal food web as prey. 

Changes in either wrack input or phytoplankton production may shift community structure and 

energy flow in the infaunal community and at higher trophic levels. 

 

Many beaches on the southern California coast are subject to grooming, the regular removal of 

trash, macrophyte wrack and other debris with heavy equipment. The ecological effects of this 

widespread management practice have rarely been examined, and no direct studies exist for 

California beaches. The fact that several of the beaches we surveyed were subject to regular 

grooming allowed an opportunity to make comparisons with less disturbed beaches. In general, 

macrofauna species richness, abundance and biomass were lower in surveys from groomed 

beaches and those with low amounts of wrack, particularly for upper intertidal species, than in 

samples from beaches with abundant wrack. In addition, the significant relationships between 

the abundance of selected upper beach taxa and species richness, and the cover of wrack found 

in our study suggest that some aspects of the community structure of sandy beach macrofauna 

are closely linked with the input and fate of marine macrophyte wrack. The positive correlation 

we found between the average abundance of two visually searching shorebird species, the blackbellied plover and the western snowy plover, and the cover of macrophyte wrack suggests that 

wrack dynamics could also affect the distribution of prey for shorebirds. Human alteration of 

wrack dynamics through beach grooming appears to be associated with substantial alteration in 

macrofauna community structure and potential reduction of prey resources for shorebirds on 

exposed sandy beaches in southern California. 

 

Predictions of shorebird densities using physical factors, such as sediment characteristics, have 

been made in protected soft sediment marine habitats (e.g. Yates et al. 1993). The distribution of 

shorebirds on exposed sandy beaches could be potentially related to physical factors, such as 

beach morphodynamics and sediments, through effects on prey densities, swash climate and 

roosting sites. On South African beaches, the density of white-fronted plovers was inversely 

correlated with median sand grain size (Hockey et al. 1983). The lack of correlations between 

shorebird abundance and physcial factors including beach morphodynamics in the present study 

is not conclusive, but does not support this idea in the study area. However, other factors not 

examined in the present study, such as the presence of alternative foraging habitats, could also be 
Final Study Report - Dugan 

30 

important and potentially confound the above comparisons. For example, on the Pacific coast of 

North America, densities of sanderlings were highest on beaches linked to estuaries; away from 

estuaries, densities were higher on extensive beaches than on shorter beaches, (Myers et al. 1984 

as cited in Shuford et al. 1989). 

 

The correlations we found between the abundance of shorebirds and the total biomass of 

macrofauna suggest that shorebirds may also frequent beaches with more favorable conditions 

for the growth and survival of macroinvertebrae prey. The majority of the macrofaunal biomass 

on many of the study beaches was composed of suspension feeding species, such as clams and 

hippid crabs, a result which suggests that many common shorebird species, particularly tactile 

feeders, may prey upon those species or that the presence of these species might be a proxy for 

favorable conditions for other prey species. Some common suspension feeding species, 

including clams and hippid crabs, also reach the largest individual sizes among the macrofauna, 

and many older individuals can be too large to be ingested by a shorebird. In addition, the 

observation that the majority of shorebirds (average = 87%) occurred on saturated sand and in 

the swash zones of the study beaches supports the idea that lower intertidal macrofauna such as 

sand crabs, the two clam species and other species may be important prey for shorebirds on 

exposed sandy beaches in the Southern California Bight. This is further supported by the 

observation that Donax gouldii and Emerita analoga were major components of shorebird pellets 

collected at the study beaches (Dugan and Walling unpublished). 

 

The lack of correlations between shorebird abundance and the abundance of macrofaunal prey 

raises interesting questions and may be related to the overwintering survival and recruitment 

dynamics of dominant macrofauna species, such as Emerita analoga. Beaches that are favorable 

for the recruitment of the planktonic larvae of E. analoga may not provide good overwintering 

habitats, and intraspecific competition may reduce growth rates and ultimately overwintering 

success (Dugan and Hubbard 1996, Dugan et al. 1991, 1994, Wenner et al. 1993). In addition, 

large numbers of wintering and migratory shorebirds may be capable of reducing the total 

abundance and standing crop of macrofaunal prey on beaches they frequent. Our study 

measured the standing crop of invertebrate macrofauna to estimate prey availability for 

shorebirds. Measuring macrofaunal production would provide a useful approach to refine this 

estimate and to better understand the dynamics of shorebird predators and prey communities. 

For example, a study of South African sandy beaches estimated that migrant and resident 

shorebirds consumed 2 to 65% of the standing crop and 10 to 49% of the annual invertebrate 

production (Hockey et al. 1983). 

 

The results of this study in conjunction with those of the MMS shorebird study in Ventura 

county indicate that large numbers and high densities of shorebirds use exposed sandy beaches 

on the southern California coast. In addition, beaches in the study area support rich macrofaunal 

communities with high abundance and biomass of potential prey species for shorebirds. Our 

results suggest the standing crop and production of macrofaunal prey may be important to 

understanding spatial variation in the distribution and abundance of shorebirds on exposed sandy 

beaches. 

 
Utilization of Sandy Beaches by Shorebirds

31 

ACKNOWLEDGMENTS 

We thank M. McCrary and M. Pierson for their initiative and inspiring intellectual interest and 

support of this study of the intertidal ecology of sandy beaches. We gratefully acknowledge the 

able assistance of R. Castelli, B. Creese, E. Diehl, S. Diehl, S. Jacques, M. Lastra, M. 

McCrary, M. Meeker, M. Pierson, and K. Schmidt in the field. We especially thank M. Meeker, 

S. Jacques, K. Schmidt, and K. Woods for assistance with sample processing and M. Lastra and 

M. Page for assistance with species identifications. This study was made possible by a grant to 

J. Dugan from Minerals Management Service under MMS Agreement # 14-35-001-30758 and 

the Coastal Marine Institute, University of California, Santa Barbara. 
 

32 

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35 

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