Abstract
Benthic macrofauna, as an element of rich and diverse benthic communities of the shelf seas, play a key role in marine biogeochemical cycles and support a wide range of ecosystem services. To better understand how macrofauna affects mass and energy fluxes within the seabed and between the bed and the pelagic, it is fundamental to characterise their structural and dynamic response to the quantity, quality and timing of food supply. To do so, we have combined long-term time-series of pelagic productivity and macrofaunal abundance with a model of benthic food web to: (1) estimate the characteristic response time scales of major groups of benthic macrofauna to food availability, (2) relate these to carbon fluxes within sediments and across the benthic-pelagic boundary, and (3) explore the mechanisms responsible. The model was designed as a canonical representation of the benthic system, retaining the key pathways that connect benthic macrofauna to pelagic environment, but aggregating variables and groups that were not explicitly observed. Both observations and model simulations revealed pronounced differences between deposit and suspension feeders in their rate of response to phytoplankton blooms: deposit feeders showed a dampened response lagging 26-125 days behind the peak in pelagic production, while suspension feeders responded rapidly, within only 5-7 days. The model parametrisation obtained during calibration relates this to differences in feeding modes, in (trophic) proximity to primary production and in rates of ingestion and losses. Specifically, suspension feeders are predicted to act as a gateway to pelagic productivity, controlling the quantity of organic carbon reaching sediment-dwelling fauna.
Highlights
Shelf seas are productive regions due to external and internal nutrient input and adequate light availability (Nixon et al, 1986; Joint and Pomroy, 1993; Jickells, 1998)
Modelled deposit feeders showed a clear response to phytoplankton blooms through a delayed but steady increase in biomass
There is a modest support in the observations for such close tracking: observed biomasses are generally lower in winter than in summer and there are no indications of suspension feeder biomass lagging noticeably behind peaks in phytoplankton productivity
Summary
Shelf seas are productive regions due to external and internal nutrient input and adequate light availability (Nixon et al, 1986; Joint and Pomroy, 1993; Jickells, 1998). The link between organic matter supply and some elements of the benthic community is not always as clear, as illustrated by Navarro-Barranco et al (2017) These authors studied the response of amphipods to phytoplankton biomass over a 7-year period at the same location as the Zhang et al (2015) study, and did not find any significant correlations with food supply, but did find close correlation with bottom water temperatures. This highlights the complexity and variability of response to pelagic production by various functional groups of benthic fauna
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