The use of mesopelagic detritus by zooplankton in Monterey Bay, California

The mucus feeding structures or "houses" of the giant larvacean Bathochordaeus provide model systems for the study of deep-sea detrital communities, particularly the poorly known zooplankton associates of detritus. This dissertation examines the role of detritus or "marine snow" as a habitat and food source for mid-water zooplankton communities, as well as the importance of particle-associated zooplankton in remineralization of particulate organic carbon in the mesopelagic zone. Zooplankton communities on detritus have been largely undetected to date, mostly due to sampling difficulties. For this dissertation, houses were sampled between 100 and 500m in Monterey Bay, CA, using a submersible ROV (remotely operated vehicle).; A unique zooplankton community occurs on giant larvacean houses, and houses are enriched in zooplankton compared to surrounding waters. Copepods are the dominant associates (e.g., Oncaea, Scopalatum, and Microsetella) and many of the species possess benthic-like morphology and feeding adaptations. Investigation of the feeding habits of one of the house-associated copepods, Scopalatum vorax, shows that it feeds on both microbial and metazoan associates of larvacean houses, and possibly the house-mucus matrix itself. This consumption of detritus at depth indicates that metazoans contribute to remineralization of particulate organic carbon in the mesopelagic zone.; The biological processes that mediate remineralization of particulate organic carbon in the mesopelagic zone, decomposition by bacteria and grazing by metazoans, were also studied using larvacean houses. Houses are sites of elevated metabolic activity compared to surrounding waters, with rates of remineralization similar to loss rates reported in previous investigations of material decay in sediment traps. In addition, zooplankton are estimated to contribute proportionately more to house remineralization than bacteria, and zooplankton consume and alter a substantial part of the house before it sinks out of the mesopelagic zone.; This dissertation reveals that mesopelagic detritus provides a benthic-like habitat and serves as a feeding center for mid-water zooplankton. Some of these zooplankton may be "swimmers" previously excluded from sediment trap analyses. Most importantly, particle-associated zooplankton can be important in remineralization and transformation of particulate organic carbon in the mesopelagic zone.