Midwater zooplankton communities on pelagic detritus (giant larvacean houses) in Monterey Bay, California

Abstract

The mucus feeding structures or “houses” of the giant larvacean Bathochordaeus provide abundant material for the study of deep sea detrital communities, particularly their poorly known zooplankton associates. We sampled houses between 100 and 500 m in Monterey Bay with a submersible ROV (remotely operated vehicle) and surveyed houses for metazoans by database search of video footage taken from the ROV. Up to an order of magnitude more metazoans were found on houses than in surrounding waters. On average, copepods constituted as much as 96% of the assemblage on houses, and many of the species possess benthiclike morphology and feeding strategies. Poecilostomatoid copepods (genus Oncaea) averaged as many as 64.6 house−1, and scarcely known calanoid copepods (genus Scopalatum) occurred in 56% of the samples. Higher numbers of metazoans occurred on shallower houses (100–300 m), likely due to a difference in the species of larvacean present and (or) to reduce oxygen levels at greater depths. At least one copepod species, Scopalatum vorax, occurred on houses more frequently during the non‐upwelling season, possibly due to the lack of other food. Our results suggest that midwater detritus contains a unique invertebrate community that has been largely undetected, mostly due to sampling difficulties. The houses also provide benthiclike habitats for midwater zooplankton and serve as feeding centers. These particle‐associated zooplankton may therefore contribute to remineralization of particulate organic carbon at depth.