Benthopelagic Biomass Distribution and Oxygen Consumption in a Deep-Sea Benthic Boundary Layer Dominated by Gelatinous Organisms

A quantitative plankton net sampler with a multicompartment cod-end for use with deep submersible vehicles was developed. This cod-end protects samples from surface temperatures so that deep-sea animals can be recovered alive. The DSV Alvin used it to sample the benthopelagic faunas of two southern California basins, East Cortes and San Clemente, in August 1979 and February 1982. Samples filtering and average of $336 m^3$ were taken at altitudes of 1, 5, 10, 20, 50, and 100 m as well as 1,000-m depth over bottom depths of 1,800-1,900 m. These samples were divided into three categories for weighing and compositional analysis. The pelagic holothuroid Scotoanassa sp. dominated the 20 m immediately above the bottom, averaging $533 mg wet wt m^-3 at 1-m$ altitude in 1982. "Other gelatinous" organisms became dominant at 50 and 100m, averaging $267 mg wet wt m^-3 at 50 m$. "Nongelatinous" forms, a group dominated by copepods and larger crustaceans, were more uniformily distributed and ranged from 2.1 to $7.9 mg wet wt m^-3$. Abundances of Scotoanassa sp., but not other categories, varied greatly between years and between basin. Scotoanassa sp. had a low oxygen consumption rate of $0.0009 \mul O_2$ $(mg wet wt)^-1 h^-1$; the near-bottom crustaceans had rates similar to those of bathypelagic crustaceans, Total metabolism of the sampled groups was dominated by Scotoannassa sp. and nongelatinous plankton near the bottom with other gelatinous plankton becoming dominant higher. Scotoanassa sp. may be a rapid growing, opportunistic species that can respond reproductively to short-term environmental changes.