Abyssal epibenthic holothurians respond differently to food quantity and concentration fluctuations over a decade of daily observation (2007–2017)

Abstract

Deep-sea holothurians rely on food settling from overlying waters onto the seafloor. Long-term, high-temporal-resolution sampling is required to understand how changes in different aspects of food supply elicit different responses across species, and how rapidly these changes may take place. This study examined changes in population density of presumptive holothurian species observed at Station M (∼4000 m depth, Northeast Pacific) using daily time-lapse imagery of the seafloor over a ten-year period (2007–2017). Densities were compared to food supply measured from sediment traps moored 50 m and 600 m above the seafloor with a sampling schedule of 10–17 days per collection cup. Mass flux and particulate organic carbon (POC) flux exhibited numerous peaks (the largest occurred in June 2011), while average weekly holothurian density peaked at 3.1 individuals m−2 in May 2013. Peniagone sp. A consistently dominated the holothurian assemblage, exhibiting a multi-year rise and fall in density that incorporated migration, and is described here as the “Peniagone sp. A event”. Lagged correlations were examined between four-week rolling means of food quantity (POC flux) and concentration (POC flux to mass flux ratio), and the densities of five commonly observed, highly mobile holothurian species. Food concentration (POC flux: mass flux) was strongly and positively correlated with Elpidia sp. A and Scotoplanes cf. globosa densities, albeit with different lags (3 and 68 weeks, respectively). By contrast, food quantity alone (POC flux) did not correlate with lagged densities of any holothurian examined. All species exhibited rapid changes in density over short periods; those species exhibiting the most rapid increases also attained the highest densities. This study suggests correlations between food supply and holothurian densities may be muted when the system experiences frequent periods of food surplus, and potential food storage in the sediments.