Response of an abyssal macrofaunal community to a phytodetrital pulse

The majority of deep-sea benthic communities rely on particulate organic matter (POM) sinking from the euphotic zone for energy, much of which is delivered in pulsed events. But we know little about abyssal plain macrofaunal communities, their response to such events or their role in deep-sea carbon-cycling. In this study, we examined the composition of the macrofaunal community at Station M in the deep NE Pacific and assessed its short-term response to a simulated OM pulse in two 36 h in situ enrichment experiments. In each experiment, 1.2 gC m–2 of 13C-labelled Skeletonema costatum was deposited onto the seafloor using a benthic chamber lander. Macrofaunal abundance and biomass were significantly higher at 0 to 5 cm depth compared to 5 to 10 cm, and were dominated by the Nematoda and Crustacea, respectively. Twenty-five percent of the macrofauna specimens showed 13C signatures indicative of label ingestion, but specific uptake (Δδ13C) and C-turnover rates varied strongly between and within taxa. Two organisms, a single cumacean from 1 chamber and a paraonid polychaete from the second chamber, were responsible for the majority of C-uptake and had ingested up to 2.3% of their body weight in C. Macrofaunal C-turnover was much lower than recorded in the abyssal NE Atlantic, which is most likely due to differences in the timing of the experiments relative to the spring/summer bloom, different experimental durations and disparities in macrofaunal community structure. These results emphasize the degree of plasticity inherent in the macrofaunal response to a food pulse and stress the need for comprehensive in situ investigations to further our understanding of deep-sea benthic ecosystem functioning.