MIDWATER ZOOPLANKTON COMMUNITIES ON PELAGIC DETRITUS (GIANT LARVACEANHOUSES) IN MONTEREY BAY, CALIFORNIA

The mucus feeding structures or ''houses'' of the giant larvacean Bath ochordaeus provide abundant material for the study of deep-sea detrita l communities, particularly their poorly known zooplankton associates. We sampled houses between 100 and 500 m in Monterey Bay with a submer sible ROV (remotely operated vehicle) and surveyed houses for metazoan s by database search of video footage taken from the ROV. Up to an ord er of magnitude more metazoans were found on houses than in surroundin g waters. On average, copepods constituted as much as 96% of the assem blage on houses, and many of the species possess benthiclike morpholog y and feeding strategies. Poecilostomatoid copepods (genus Oncaea) ave raged as many as 64.6 house(-1), and scarcely known calanoid copepods (genus Scopalatum) occurred in 56% of the samples. Higher numbers of m etazoans occurred on shallower houses (100-300 m), likely due to a dif ference in the species of larvacean present and (or) to reduce oxygen levels at greater depths. At least one copepod species, Scopalatum vor ax, occurred on houses more frequently during the non-upwelling season , possibly due to the lack of other food. Our results suggest that mid water detritus contains a unique invertebrate community that has been largely undetected, mostly due to sampling difficulties. The houses al so provide benthiclike habitats for midwater zooplankton and serve as feeding centers. These particle-associated zooplankton may therefore c ontribute to remineralization of particulate organic carbon at depth.