Community structure in Florida Escarpment seep and Snake Pit (Mid-Atlantic Ridge) vent mussel beds
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Comparisons between invertebrate communities hosted by similar foundation species under different environmental conditions permit identification of patterns of species distributions that might be characteristic of the different ecosystems. Similarities and differences in community structure between two major types of chemosynthetic ecosystems were assessed by analyzing samples of invertebrates associated with Bathymodiolus heckerae Gustafson et al. mussel beds at the Florida Escarpment seep (Gulf of Mexico, 26°01.8′N; 84°54.9′W; October 2000) and B. puteoserpentis von Cosel et al. mussel beds at the Snake Pit vent (Mid-Atlantic Ridge, 23°22.1′N; 44°56.9′W; July 2001). Macrofaunal species richness was nearly twice as high in the seep mussel bed compared to the vent mussel bed, and only a single morphospecies, the ophiuroid Ophioctenella acies Tyler et al., was shared between the sites. Similarities between the two faunas at higher taxonomic levels (genus and family) were evident for only a small percentage of the total number of taxa, suggesting that evolutionary histories of many of these seep and vent macrofaunal taxa are not shared. The taxonomic distinctiveness of the seep and vent mussel-bed macrofaunal communities supports the hypothesis that environmental and oceanographic barriers prevent most taxa from occupying both types of habitats. Macrofaunal community heterogeneity among samples was similar in seep and vent mussel beds, indicating that spatial scales of processes regulating community variability may be similar in the two types of ecosystems. Suspension feeders were not represented in the macrofauna of seep or vent mussel beds. Primary consumers (deposit feeders and grazers) contributed more to the total abundance of macrofauna of seep mussel beds than vent mussel beds; secondary consumers (polychaetes and shrimp) were more abundant in the vent mussel beds.