Epi- and mesopelagic zooplankton and micronekton vertical zonation patterns in the Slope Sea

Le résumé fourni par la source

The ocean’s epi- and mesopelagic zones (~upper 1000 m) host vital but understudied ecosystems. Especially for the mesopelagic, the challenges associated with sampling at spatial, temporal, and taxonomic scales sufficient to characterize ecosystem structure has resulted in large knowledge gaps relative to shallow-water environments that are more easily studied by a single sampling approach. In this study, we combined machine learning-based analysis of high-resolution in situ images, shipboard acoustic measurements, and depth-stratified net sampling to quantify epi- and mesopelagic zooplankton and micronekton vertical distributions in the Slope Sea of the northwest Atlantic. Our results show that different animal groups have distinct layered vertical distributions corresponding to the physicochemical and acoustically resolved biological environment, including deep scattering layers (DSLs) detected at frequencies of 18 and 38 kHz, but are less accurately predicted from the environmental or acoustic measurements alone. Vertical zonation patterns for gelatinous zooplankton taxa were broadly similar to observations previously reported in Monterey Bay Canyon, suggesting predictable habitat utilization strategies for these taxa. Diel vertical migration (DVM) patterns varied across animal groups, with salps and krill showing the strongest DVM tendencies. Strong size-fractionated DVM patterns were observed for copepods, with migration amplitude increasing and the proportion of migrators decreasing with body size. From acoustic scattering models combined with net-tow observations, we constrain identities of mesopelagic fishes responsible for the DSLs. Collectively, these combined perspectives provided high-resolution assessment of mesopelagic communities in the Slope Sea, providing new insights into the distinct vertical distributions of zooplankton and micronekton taxa.

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