DIET OF COPEPODS (SCOPALATUM-VORAX) ASSOCIATED WITH MESOPELAGIC DETRITUS (GIANT LARVACEAN HOUSES) IN MONTEREY BAY, CALIFORNIA

The feeding structures or ''houses'' of the giant larvacean Bathochord aeus sp. serve as both habitat and food for the calanoid copepod Scopa latum vorax. Gut contents of S. vorax include both microbial and metaz oan associates of larvacean houses, and possibly the house-mucus matri x itself. Copepods were observed and collected from larvacean houses b etween 100 and 500 m in Monterey Bay, California, using a submersible ROV (remotely operated vehicle) from the Monterey Bay Aquarium Researc h Institute. Gut contents were compared to potential food items on the houses and in the open water (not associated with the house). Copepod s were generalist feeders, with amorphous detritus, diatoms, and copep ods or other crustacean parts dominating gut contents. Protozoans and algae other than diatoms were rarer in guts. Houses contained a divers e assemblage of microplankton and metazoans, both intact specimens and detrital remains of these. Numbers of diatoms and fecal pellets were enriched by 1 to 3 orders of magnitude on houses compared to numbers i n surrounding water. Many of the abundant species of diatoms and copep ods on houses occurred in S. vorax guts. This observation coupled with S. vorax feeding habits observed in situ and in the laboratory provid e evidence for feeding on houses. S. vorax appears to possess special adaptations to living in a resource-limited environment, such as gorgi ng as a feeding adaptation, chemosensory structures to help locate hou ses, and the ability to change feeding modes. Consumption of detritus at depth by S. vorax provides evidence that metazoans contribute to re mineralization of particulate organic carbon in the mesopelagic zone.