Quantifying pelagic-benthic coupling in the North Sea: Are we asking the right questions? (original) (raw)

The importance of benthic–pelagic coupling for marine ecosystem functioning in a changing world

Global Change Biology, 2017

Benthic–pelagic coupling is manifested as the exchange of energy, mass, or nutrients between benthic and pelagic habitats. It plays a prominent role in aquatic ecosystems, and it is crucial to functions from nutrient cycling to energy transfer in food webs. Coastal and estuarine ecosystem structure and function are strongly affected by anthropogenic pressures; however, there are large gaps in our understanding of the responses of inorganic nutrient and organic matter fluxes between benthic habitats and the water column. We illustrate the varied nature of physical and biological benthic–pelagic coupling processes and their potential sensitivity to three anthropogenic pressures – climate change, nutrient loading, and fishing – using the Baltic Sea as a case study and summarize current knowledge on the exchange of inorganic nutrients and organic material between habitats. Traditionally measured benthic–pelagic coupling processes (e.g., nutrient exchange and sedimentation of organic material) are to some extent quantifiable, but the magnitude and variability of biological processes are rarely assessed, preventing quantitative comparisons. Changing oxygen conditions will continue to have widespread effects on the processes that govern inorganic and organic matter exchange among habitats while climate change and nutrient load reductions may have large effects on organic matter sedimentation. Many biological processes (predation, bioturbation) are expected to be sensitive to anthropogenic drivers, but the outcomes for ecosystem function are largely unknown. We emphasize how improved empirical and experimental understanding of benthic–pelagic coupling processes and their variability are necessary to inform models that can quantify the feedbacks among processes and ecosystem responses to a changing world.

Sediment properties and benthic–pelagic coupling in the North Water

Deep-sea Research Part Ii-topical Studies in Oceanography, 2002

Measurements of sediment oxygen consumption were made during spring and summer in the North Water, the polynya that forms between Greenland and Ellesmere Island, and used in conjunction with sediment trap data to assess benthic–pelagic coupling in this system. Bottom sediments ranged from cobble in the north to soft muds in the southern part of the sampling grid. Muddy sediments were often pelletized as shown by disaggregation. Sediment photopigments were generally lower in coarse sediment stations to the north than in finer sediments stations to the south. Shipboard incubation of intact cores provided rates of 0.07–0.17 mmol O2 m−2 h−1, with significantly greater oxygen consumption in summer than in spring. Additional incubation of macrofauna-free sediment aliquots in vials demonstrated significantly lower oxygen consumption in summer than in spring. Partitioning of benthic metabolism via these selective exclusion experiments showed a seasonal change in the response of the benthos to pelagic input, with meio-microbenthos dominating oxygen consumption in spring and macrofauna dominating in summer. Increased oxygen demand in the western polynya is suggested to coincide with the highest rates of carbon input measured by sediment traps and highest levels of sediment pigments. This region is an advective sink for particles produced in the east and subsequently transported by net polynya circulation. Although the benthos of the North Water does not display enhanced rates of carbon processing compared to other Arctic sediments, including other polynyas, the protracted production season of North Water provides a longer period over which the benthos can receive and mineralize organic carbon.