Utilization of Sandy Beaches by Shorebirds

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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 
Utilization of Sandy Beaches by Shorebirds

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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 

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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

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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 

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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. 
Final Technical Summary -Dugan 

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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.