Deep-Sea Food Chains and the Global Carbon Cycle

Volume 360 of the series NATO ASI Series pp 93-104

Possible Roles for Xenophyophores in Deep-Sea Carbon Cycling

  • L. A. LevinAffiliated withDept. of Marine, Earth and Atmospheric Sciences, North Carolina State University
  • , A. J. GoodayAffiliated withInstitute of Oceanographic Sciences Deacon Laboratory

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This paper examines the involvement of xenophyophores. a group of large (<1–25 cm). agglutinating protozoans, in cycling of organic matter on the deep-sea floor. It is suggested that test volumes are usually < 1% protoplasm, and that even where xenopbyophores are abundant, the plasm contributes relatively little biomass to benthic communities. Thus, they are thought to be relatively unimportant as respirers of carbon or as prey, except to specialized predators. However, xenophyophores may have the potential to take up DOM, and could thereby playa role in carbon transformation. The possibility also exists that the copious quantities of fecal material sequestered within xenophyophore tests may be sites of enhanced microbial activity (Tendal, 1979), and as such, could provide food for metazoan test inhabitants and other deposit-feeding taxa in the deep sea. Ideas concerning DOM uptake and microbial enhancement require verification before their importance can be considered. Evidence that xenophyophores enhance deposition of fine particles comes from flow visualization, excess 234Th profiles, and photographic observations. Reticulate and folded tests are believed to act like small, passive particle traps. Increased deposition of organic matter associated with xenophyophore tests is one possible explanation for elevated densities of metazoan fauna associated with tests and surrounding sediments. The activities of xenophyophores and associated biota generate local hotspots of carbon deposition, mineralization, and perhaps burial. Xenophyophores are a significant source of heterogeneity on the sea floor, at the scale of individual tests (ems) and of population patches (kms).