Community Composition, Structure, Areal and Trophic Relationships of Decapods Associated with Shallow- and Deep-Water Oculina Varicosa Coral Reefs: Studies on Decapod Crustacea from the Indian River Region of Florida, XXIV

Decapod crustaceans associated with living colonies of the scleractinian coral Oculina varicosa were sampled quantitatively for 1 year at 4 reef stations encompassing depths of 6, 27, 42, and 80 m off the central eastern Florida coast. A total of 42 samples of individual colonies yielded over 2,300 decapods in 15 families, 35 genera and 50 species, and was species-rich in xanthid and majid crabs (10, 6 spp., respectively), and alpheid shrimp (9 spp.). The community was predominantly anomuran with two species of hermit crabs (Pagurus carolinensis, P. piercei), a porcellanid crab (Megalobrachium soriatum) and a galatheid crab (Galathea rostrata) comprising four of the six most abundant species which accounted for 70% of all collected individuals.

Similarity between stations was low (8%) with only four species present at all stations. A gradient of species assemblages from shallow to deep stations corresponded with a similar gradient in environmental factors, with mean temperatures of 24.6, 18.4, and 16.2°C recorded at 6, 42, and 80 m, respectively. These temperatures and periodic cold-water summer upwelling affected species composition, with several species being lost at 6 m and never occurring at deeper stations. Wave surge and sedimentation, greatest at 6 m, affected trophic partitioning, with a filter feeder (M. soriatum) numerically dominant here, whereas a detritivore (P. carolinensis) dominated deeper, less disturbed stations. The biotope also differed topographically among stations. At 6 m Oculina grew as thick-branched, wave-resistant colonies with encrusting bases and were widely scattered among a cover of algae and sponges on limestone ledges. At 80 m massive coral thickets formed banks composed solely of O. varicosa. Greater heterogeneity of the habitat surrounding the 6-m corals may be one reason this station had the highest species numbers (30) and species distribution (32% occurred nowhere but here).

Analyses of the effects of coral age on numbers of decapod species (S) and individuals (N) showed no significant correlation, whereas 48.8% of the variance in Sand 42.9% in N were related to the percentage of dead dry weight of the coral colony (r = .709, P < .001; r = .667, P < .001, respectively). Mean densities of individuals decreased with depth (44.4–7.5 N/100 g dead coral wt) and densities of most dominant species were positively correlated with size of the dead, rather than the live portion of the coral. Densities of the obligate commensals Domecia acanthophora and Troglocarcinus corallicola, however, were independent of coral size.