FISHERY BULLETIN: VOL. 84, NO. 2 



Table 3.— Species ranks, relative abundances, and dominance for each taxonomic group. Combined night samples, x = mean number 



of individuals per sample (per group), Dl = dominance (McNaughton 1967). 



tor of 4.6) substratum surface area was sampled per 

 tow by the otter trawl, the crab scrape collected more 

 species and individuals per tow, across taxa, with few 

 exceptions. The trawl was the better faunal collect- 

 ing gear in this seagrass habitat only for numbers 

 of individuals of certain water-column fishes and for 

 two species of caridean shrimps. The scrape was 

 notably more effective than the trawl (day and night) 

 for collecting penaeid, alpheid, and processid 

 shrimps, brachyuran and pagurid crabs, molluscs, 

 echinoderms, syngnathid fishes, and demersal fishes 

 (Opsanus, Paraclinus, Gobiosoma, and Centropris- 

 tis). 



The otter trawl appears to collect fewer species 

 and individuals of demersal animals in grassbeds 

 than does the scrape because the weighted (tickler) 

 chain on the trawl is not in contact with the sub- 

 stratum. Under tow, the cylindrical bottom crossbar 

 of a crab scrape bends grassblades flat against the 

 substratum, sweeping demersal and epifaunal 

 organisms over the bar and into the net, whereas 



the otter trawl tickler chain is generally supported 

 8-10 cm above the substratum by the buoyant vege- 

 tation (Leber, pers. obs.). Grassblades do not yield 

 as much to the relatively light weight of a tickler 

 chain (as they do to a scrape crossbar), and any 

 organisms remaining close to the substratum as the 

 chain passes over them evade capture Most epi- 

 benthic inhabitants of grassbeds, including several 

 fishes, are more closely associated with seagrasses 

 and red drift algae than with the water column above 

 the vegetation or bare patches within beds (Hooks 

 et al. 1976; Heck and Wetstone 1977; Stoner 1980; 

 Stoner and Livingston 1980; Gore et al. 1981). The 

 crab scrape is more effective because it samples 

 more grassblade surface area, including an addi- 

 tional microhabitat, the region <10 cm above the 

 substratum (Leber, pers. obs.). 



The greater effectiveness of both devices at night 

 is probably accounted for, in part, by nocturnal in- 

 creases in faunal activity on the substratum, on blade 

 tips, and in the water column above vegetation. 



448 



