Temporal changes in benthic megafaunal abundance and composition across the West Antarctic Peninsula shelf: Results from video surveys

Abstract

The West Antarctic Peninsula (WAP) shelf experiences intense seasonal and interannual variability in phytoplankton production and particulate-organic-carbon flux to the seafloor. To explore the response of the megabenthic community to this production variability, we conducted video surveys of epibenthic megafauna at three stations on the WAP shelf in Nov–Dec 1999, Mar 2000, Jun 2000, Oct–Nov 2000, and Feb–Mar 2001. The epibenthic megafauna was dominated (>90%) by elasipod holothurians, irregular urchins and anthozoans, with total abundances ranging from 19 to 152 ind. 100 m−2. The abundance of three of the dominant taxa (Protelpidia murrayi, Peniagone vignoni, and Amphipneustes spp.) varied significantly across seasons (p<0.05), although variations were not tightly correlated with the summer bloom cycle. The irregular urchins in the genus Amphipneustes varied 5-fold in abundance at single stations, with maximum densities (an average of 10.1 ind. 100 m−2) attained in Jun 2000. Abundances of the elasipod holothurians P. murrayi (1–121 ind. 100 m−2) and P. vignoni (0.7–27.5 ind. 100 m−2) fell within the range for elasipod holothurians from other bathyal regions measured using image analysis. The abundance of P. murrayi increased up to 6-fold from a single Jun–Oct recruitment pulse, while changes in the abundance of P. vignoni (over 2-fold higher in Feb–Mar 2001) apparently resulted from immigration during the presence of a 1–2 cm thick carpet of fresh phytodetritus. Based on the ratio of the number of fecal casts per individual, elasipod holothurians increased surface-deposit feeding rates by 2-fold while phytodetritus was present at the seafloor. Nonetheless, these surface-deposit feeders appeared to feed and egest sediments throughout the winter, which is consistent with year-round persistence of a labile food bank in surficial sediments on the deep WAP shelf.