CONTRIBUTION OF ZOOPLANKTON ASSOCIATED WITH DETRITUS TO SEDIMENT TRAPSWIMMER CARBON IN MONTEREY BAY, CALIFORNIA, USA

A major food source to the deep sea is thought to be organic detritus derived ultimately from surface production. Much of the detritus is lo st as it settles, presumably both to microbial and to metazoan consume rs. In the last several decades much research has been devoted to quan tifying this vertical particle flux using sediment traps. In processin g samples from sediment traps 'swimmers', i.e. zooplankton that are th ought to actively enter sediment traps and artificially augment the tr ap contents, are traditionally removed. However, some zooplankton caug ht in the traps are likely to be genuine associates and decomposers of detritus and thus similar to microorganisms on detritus which are, mo stly for practical reasons, included in the 'particle flux'. We determ ine what proportion of the swimmer assemblage is detrital associates, and how these detrital associates may affect mesopelagic particle flux measurements, by comparing zooplankton taxa removed from sediment tra p samples obtained at 450 m depth in Monterey Bay, California, with ta xa observed and collected on large detrital particles (giant larvacean houses) in situ with a submersible ROV (remotely operated vehicle). T rap swimmer composition in Monterey Bay was diverse. Calanoid copepods and adult Hyperia mesudarium amphipods contributed the most to total swimmer carbon; and juvenile hyperiid amphipods, calanoid copepods, an d Oncaea sp. copepods were the most: numerous of all groups. Polychaet e larvae were also a conspicuous part of the assemblage. The entire sw immer component averaged 24 % of total trap POC (= detrital + swimmer C) in traps, but only 1.5% of total trap POC was due to those we consi der detrital associates (e.g, copepods: Oncaea spp., Microsetella spp. , and Scopalatum sp.; polychaetes; juvenile hyperiid amphipods). Thus zooplankton on detritus are a relatively small percentage of the POC f lux in these traps, and their removal introduces Little ambiguity to t rap flux measurements in this area. Important impediments to understan ding the contribution of such zooplankton are our limited knowledge of the zooplankton decomposer community at depth, their different contri butions in low versus high flux environments, and the behavior of zoop lankton on encountering a trap.