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Relationship between geochemical environments, nutritional resources and faunal successions in whale-fall ecosystems

Yuji Onishi*, Toshiro Yamanaka, Ken-Ichi Ozaki, Rei Nakayama, Sho Shimamura, Rie Itami, Ami Fukushima, Megumi Miyamoto, Yoshihiro Fujiwara

*Corresponding author:

ABSTRACT: Faunal succession in whale-fall communities is closely associated with the progress of decomposition of the whale carcass. The main nutritional resources supporting the whale-fall community change from whale-matter to chemosynthetic products over time. To study geochemical aspects of this nutritional succession, we sampled animals over time on and in sediments around whale carcasses in Sagami Bay (mobile-scavenger to early sulfophilic stage) and off Cape Nomamisaki (sulfophilic stage), Japan (500 and 200–300 m water depths, respectively). In these two areas, stable carbon, nitrogen, and sulfur isotopes of the animal soft tissues were measured to precisely elucidate the nutritional resources for each animal. In Sagami Bay, mobile scavengers relied only on the whale soft tissue. Infaunal animals at two weeks after the deployment relied only on the whale soft tissue, while infauna at nine months after the deployment relied on chemosynthetic products. Such changes in nutritional resources were consistent with the transition of the geochemical environment in the sediments. Off Cape Nomamisaki, vigorous microbial sulfate reduction and thioautotrophic primary production nourished the fauna around the carcasses. The fauna in this area consisted of chemosymbiotic bivalves and necrophagous animals with sulfide-tolerant metabolism. We conclude that the changes in microbial processes, biomass and compositions in sediments influence faunal succession in the whale-fall ecosystems via change in the available nutrition for the fauna.