COMMUNITY STUDIES IN SEAGRASS MEADOWS: A COMPARISON 

 OF TWO METHODS FOR SAMPLING MACROINVERTEBRATES 



AND FISHES 1 



Kenneth M. Leber 2 and Holly S. Greening 3 

 ABSTRACT 



r 



The effectiveness of using an otter trawl for estimating macrofaunal species ranks and abundances in 

 seagrass meadows is unknown. In this study, we compare the catch effectiveness of the commonly used 

 5 m otter trawl with that of a 0.9 m wide epibenthic crab scrape for fishes, decapod crustaceans, molluscs, 

 and echinoderms, using data from both day and night collections from a northeast Gulf of Mexico sea- 

 grass meadow. The crab scrape collected significantly more individuals and species of all taxa except (water- 

 column) fishes. Clear discrepancies existed between trawl and scrape estimates of species ranks and relative 

 abundances, with trawl collections estimating a higher degree of dominance within groups of shrimps 

 and demersal fishes, and lower dominance among crabs. Whereas the crab scrape was clearly superior 

 to the trawl for sampling macroinvertebrates and demersal fishes, the trawl was the better device for 

 collecting water-column fishes. Explanations for observed differences in the sampling effectiveness of 

 these gears are discussed. Sampling was considerably more productive at night than during the day. The 

 combined approach of day-night sampling with both a crab scrape (for demersal fishes and epibenthic 

 invertebrates) and an otter trawl (for water-column fishes) is recommended for community-wide studies 

 in seagrass meadows. 



Hypotheses concerning ecological community 

 dynamics should be based upon accurate descriptions 

 of the habitats and species involved. It is thus essen- 

 tial that collection methods maximize sampling ef- 

 ficiency in "community" (sensu Pielou 1977) studies. 

 Because estimates of species composition, relative 

 abundances, and biomass in aquatic environments 

 may vary with different sampling devices (eg., Lewis 

 and Stoner 1981; Stoner et al. 1983), knowledge of 

 sample gear effectiveness allows a more rigorous ap- 

 proach to sampling design and interpretation of 

 results from studies of aquatic communities. 



Seagrass community studies often employ a small, 

 semiballoon otter trawl (try net) for sampling fishes 

 and epibenthic invertebrates (Kikuchi 1966; Living- 

 ston 1975, 1976, 1982; Heck 1976, 1977, 1979; Hooks 

 et al. 1976; Heck and Wetstone 1977; Weinstein and 

 Heck 1979; Heck and Orth 1980; Orth and Heck 

 1980; Ryan 1981; Dugan and Livingston 1982; 

 Dugan 1983). Although a small otter trawl may be 

 one of the most effective samplers for estimating 

 relative abundances of juvenile and small pelagic 



Contribution No. 439 of the Harbor Branch Foundation, Ft. 

 Pierce, FL 33450. 



department of Biological Science, Florida State University, 

 Tallahassee, FL 32306; present address: The Oceanic Institute, 

 Makapuu Point, Waimanalo, HI 96795. 



department of Biological Science, Florida State University, 

 Tallahassee, FL 32306; present address: Martin Marietta Environ- 

 mental Systems, 9200 Rumsey Road, Columbia, MD 21045. 



Manuscript accepted January 1985. 

 FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



fishes in shallow nonvegetated waters (Kjelson and 

 Johnson 1978; Orth and Heck 1980), there are few 

 published accounts of its effectiveness in sampling 

 benthic fishes or epibenthic invertebrates in vege- 

 tated habitats. Greening and Livingston (1982) noted 

 that a Chesapeake Bay crab scrape appeared to col- 

 lect more invertebrate species per sample effort in 

 vegetated habitats than did an otter trawl. Miller et 

 al. (1980) found a crab scrape to be more effective 

 than either an otter trawl or a push net for collect- 

 ing juvenile blue crabs, Callinectes sapidus, in the 

 Chesapeake Bay area. Blue crab fishermen routine- 

 ly use crab scrapes, rather than trawls, in grassbeds 

 in Chesapeake Bay (Warner 1976). 



In this study, the catch effectiveness of a 5 m otter 

 trawl is compared with that of a 0.9 m epibenthic 

 scrape in the shallow grassbeds of Apalachee Bay, 

 FL. Species richness and abundance are examined 

 within four taxonomic groups (decapod crustaceans, 

 molluscs, echinoderms, and fishes). Because many 

 grassbed organisms are more susceptible at night 

 to certain sampling methods (Ryan 1981; Greening 

 and Livingston 1982), both day and night samples 

 are considered. 



METHODS 



Day and night samples were taken in about 1.7 m 

 of water from seagrass beds in Apalachee Bay, FL. 



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