ABSTRACT: The mucous feeding structures or 'houses' of the giant larvacean Bathochordaeus spp. provide a useful detrital system to study biological processes that mediate remineralization of particulate organic carbon in the mesopelagic zone: degradation by bacteria and grazing by zooplankton. The role of particle-associated zooplankton in remineralization in the mesopelagic zone has not previously been studied, mostly due to sampling difficulties. We collected houses between 100 and 500 m in Monterey Bay, California, USA, using a submersible ROV (remotely operated vehicle) and measured community metabolism on houses using oxygen electrodes. Houses were sites of elevated metabolic activity compared to surrounding waters. The average daily oxygen utilization indicates that approximately 1% of house C is used daily to sustain community respiration, although the rate is higher (8%) when large numbers of zooplankton are present. Estimated rates of zooplankton remineralization of houses are similar to bacterial remineralization rates reported for other types of detritus. Respiration rates provide minimal estimates of carbon transformations by communities on detritus, especially when metazoans are present. Based on published estimates of the relationship between zooplankton carbon consumption and respiration rates, and our measurement of zooplankton abundance on houses, we calculate that a mean of 6% and up to 43% of house C is ingested by zooplankton each day. Thus, a substantial part of the house could be consumed by detritus-feeding zooplankton before sinking out of the mesopelagic zone. Particle-associated zooplankton are important in recycling carbon on these houses and potentially on other aggregates at depth, not only by consuming and remineralizing detritus, but also by altering detritus through repackaging it in fecal pellets, releasing it as DOC, and fragmenting its fragile structure into smaller particulate matter.

KEY WORDS: Mesopelagic zooplankton · Respiration · Larvacean · Detritus · Monterey Bay

Published in MEPS Vol. 147 (1997) on February 27
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1997