SEDIMENT COMMUNITY STRUCTURE AROUND A WHALE SKELETON IN THE DEEP NORTHEAST PACIFIC - MACROFAUNAL, MICROBIAL AND BIOTURBATION EFFECTS

Chemoautotrophic communities on lipid-rich whale skeletons are known f rom a total of 16 modern and fossil sites in the deep Pacific Ocean. W hile the attached fauna of modern whale bones has been studied, the im pact of whale falls on surrounding sediment assemblages remains largel y unevaluated. Using the research submersible Alvin, we sampled the se diment community at distances of 0, 0.5, 1, 2, 4, and similar to 100 m from the lipid-rich skeleton of a 21 m balaenopterid on the 1240 m se afloor in Santa Catalina Basin. When sampled in 1988 and 1991, the ske leton had been on the seafloor for > 4 yr and supported a large attach ed chemoautotrophic assemblage. Sedimentary organic content, microbial biomass and bacterial abundance were not significantly different near the skeleton than in background sediments, and pore-water sulfide con centrations were only modestly elevated (to less than or equal to 20 m u M) adjacent to the bones. The species composition of infaunal macrob enthos near the skeleton was similar to that in background sediments, providing little evidence of a specialized enrichment and/or sulfophil ic assemblage. Nonetheless, macrofaunal abundance within 0.5 m of the skeleton was reduced by > 40%, due to a decline in the paraonid polych aete Levinsenia oculata. The reduction in L. oculata (the community do minant) caused a sharp increase in rarefaction diversity near the skel eton. Bioturbation intensities, evaluated from Th-234 profiles, were a lso dramatically reduced in sediments near the skeleton, as were rates of extracellular lipase activity. We postulate that reduced infaunal abundance and bioturbation near the skeleton resulted from the interfe rence effects of vesicomyid clam-shell debris, and that the low biotur bation rates in turn limited extracellular lipase activity. We conclud e that whale skeletons, and the remains of their associated chemoautot rophic assemblages, may physically impact nearby sediment communities for pears after the organic and sulfide enrichment effects of whale fa lls have dissipated, yielding changes in infaunal diversity and biotur bation. (C) 1998 Elsevier Science Ltd. All rights reserved.