Near-reef zooplankton differs across depths in a subtropical seascape

Our knowledge of zooplankton in proximity to benthic marine habitats is hampered by challenges sampling near complex substrates. To address this, we deployed light traps near the benthos of four depth-specific coral reef ecosystems to measure nocturnal zooplankton abundance and assemblage composition. Replicate light traps at shallow shelf (SS10, <10 m) and deep shelf (DS30, 20-30 m) habitats in the Florida Keys and at mesophotic depths at the Dry Tortugas (DT60, 40-60 m) and Pulley Ridge (PR70, 60-70 m) on the west Florida shelf revealed zooplankton assemblages that differed in both magnitude and composition. SS10 and DS30 were dominated by meroplankton, in contrast to the deeper sites where holoplankton were most abundant. Meroplankton and demersal plankton were significantly more abundant at SS10 and DS30 than at DT60 or PR70. Zooplankton assemblage composition overlapped between SS10 and DS30 depths, but shifted beyond those depths such that PR70 zooplankton assemblages were entirely distinct. DT60 assemblages were intermediate and included taxa with both shallow and deep affinities. Reflecting proximity to adult spawning populations and potentially different zooplankton prey with depth, such depth-related differences in zooplankton assemblages likely impact food availability for benthic organisms with consequences to community composition, habitat quality and population connectivity.

Automated summary

This study deployed light traps near benthic marine habitats at four depth-specific coral reef ecosystems to measure the abundance and composition of zooplankton. The results showed significant differences in zooplankton assemblages between shallow and deep habitats, with meroplankton dominating in shallow areas and holoplankton in deeper areas. Zooplankton assemblage composition overlapped at shallow depths, but became distinct at deeper depths, indicating depth-related differences impact food availability for benthic organisms.