Macroinfauna of North Pacific methane seeps: highly adapted or typical margin assemblages?
Lisa Levin, David James, Chris Martin, Anthony Rathburn, Bob Michener, Leslie Harris, Guiermo Mendoza
The community structure and nutritional pathways of macrofauna were compared in methane seep sediments and non-seep sediments from 3 locations in the northeastern Pacific Ocean.Taxonomic composition, diversity and density were similar within and outside seeps on the northern California shelf (35-55 m) and upper slope (500 m off the Eel R.).The same was true for benthic foraminifera.However several taxa (e.g., Capitella sp. And ??) were present exclusively at seeps and several others (the amphipods ??? ) avoided seeps.Stable isotopic analyses (d13C, d 15N) suggest that off N. California, few macrofaunal taxa rely on chemosynthetic food sources; rather they have phytoplankton-based nutrition.Among Calyptogena pacifica beds in close proximity, there were detectable differences in average d13C of infauna.
Preliminary results indicate that seeps on the Oregon margin (600 m) and in the Gulf of Alaska (4410-4440 m)exhibit infaunal communities distinct from surrounding, ambient sediments.Diversity is lower and a greater number of taxa may rely on free-living or symbiotic chemosynthetic bacteria.Off Alaska Calyptogena phaseoliformis beds supported macrofaunal densities similar to those in surrounding turbidite sediments, but nearby pogonophoran fields exhibited much higher densities of infauna.Methane seep environments in the pacific often exhibit textural differences(carbonate concretions), unique porewater geochemistry, and distinct surface assemblages (bivalves, pogonophorans, microbial mats) that contribute to macrofaunal heterogeneity.These settings reflect a broad spectrum of taxonomic and nutritional specialization.Where seeps are ephemeral and relatively shallow (e.g., off Northern California) macrofaunal assemblages are those typical of disturbed or organic-rich margins.Where fluid flux is intense and seeps are persistent the faunas are more highly adapted.
Calyptogena phaseoliformis, Gulf of Alaska, 4440 m
Pogonophoran field, Gulf of Alaska, 4440 m
Calyptogena phaseoliformis bed, Gulf of Alaska 4444 m
Calyptogena sp. bed, Oregon margin, 590 m
Bacterial mat, Oregon margin, 590 m
Deep-Sea Biology MeetingJune 2000, Galway Ireland
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