The influence of pore‐water chemistry and physiology on the distribution of vesicomyid clams at cold seeps in Monterey Bay: Implications for patterns of chemosynthetic community organization

Abstract

Analyses of sulfide, methane, oxygen, and CO2 in pore‐water samples from three cold seep sites in Monterey Bay indicate that fluid chemistry is a strong determinant of the distribution of chemolithoautotrophic vesicomyid clams. The distribution of Calyptogena pacifica and Calyptogena kilmeri were aligned closely with sulfide concentrations at all cold seeps and reflected species‐specific capabilities for sulfide binding. Live clams occurred only in sediment where sulfide was detectable. Sulfide was not detected in the absence of vesicomyid clams. The relative abundances of five vesicomyid species varied greatly among seeps. C. kilmeri accounted for 85–99% of all vesicomyids at seeps with high sulfide content, and C. pacifica dominated (73%) seeps with low sulfide levels. These species were also partially segregated along sulfide gradients from the center to the margin of seeps, analogous to zonation of rocky intertidal communities. We hypothesize that the absence of thiotrophic or methanotrophic mytilid mussels from Monterey Bay cold seeps is related to the lack of physiological specializations for concentrating reduced sulfur compounds or methane and the absence of hypersaline brines that could extend the persistence of methane or sulfide‐rich fluids very near the sea floor.