Benthic microalgae serve as the major food resource for porcelain crabs (Petrolisthes spp.) in oyster reefs: gut content and pigment evidence1

Suspension-feeding porcelain crabs (Petrolisthes spp.) are often the most abundant decapod crustaceans in oyster reef habitat. Analysis of water column and subtidal algal biomass from three Texas estuaries suggests that planktonic food resources are insufficient for porcelain crab growth. Pigment composition of porcelain crab muscle and digestive track contents included the diatom pigment fucoxanthin and cyanobacterial pigment canthaxanthin with digestive track samples containing attached (adnate) benthic diatoms as well as benthic cyanobacteria not found in the water column. Feeding appendages on porcelain crabs include numerous cirri with serrated edges as well as fewer more brush-like longer units. Benthic food resources are in sufficient supply to support porcelain crab biomass.

Size, sex and individual-level behaviour drive intrapopulation variation in cross-ecosystem foraging of a top-predator

Large-bodied, top-predators are often highly mobile, with the potential to provide important linkages between spatially distinct food webs. What biological factors contribute to variation in cross-ecosystem movements, however, have rarely been examined. Here, we investigated how ontogeny (body size), sex and individual-level behaviour impacts intrapopulation variation in cross-ecosystem foraging (i.e. between freshwater and marine systems), by the top-predator Alligator mississippiensis. Field surveys revealed A. mississippiensis uses marine ecosystems regularly and are abundant in estuarine tidal creeks (from 0·3 to 6·3 individuals per km of creek, n = 45 surveys). Alligator mississippiensis captured in marine/estuarine habitats were significantly larger than individuals captured in freshwater and intermediate habitats. Stomach content analysis (SCA) showed that small juveniles consumed marine/estuarine prey less frequently (6·7% of individuals) than did large juveniles (57·8%), subadult (73%), and adult (78%) size classes. Isotopic mixing model analysis (SIAR) also suggests substantial variation in use of marine/estuarine prey resources with differences among and within size classes between sexes and individuals (range of median estimates for marine/estuarine diet contribution = 0·05-0·76). These results demonstrate the importance of intrapopulation characteristics (body size, sex and individual specialization) as key determinants of the strength of predator-driven ecosystem connectivity resulting from cross-ecosystem foraging behaviours. Understanding the factors, which contribute to variation in cross-ecosystem foraging behaviours, will improve our predictive understanding of the effects of top-predators on community structure and ecosystem function.