Sediment resuspension by Fish
Gitai Yahel Lab
Benthic (ground) fish resuspend large amount of sediments while foraging and seeking for shelter. We discovered that fish activity alone could maintain a layer of turbid water near the bottom (nepheloid benthic layer), enhance the transport of nutrients and benthic oxygen demand, and considerably reduce organic carbon sequestration (MEPS 372, 195). We showed that benthic fish activity controls sediment resuspension and near bottom water quality in coral reefs (L&O 47, 1071).Benthic fish that resuspend sediment as they search for food and shelter are abundant throughout the ocean. Unlike other resuspension processes, fish-induced resuspension events are typically brief (seconds) and localized, and in some habitats occur at a rate of several events per square meter per hour (L&O 47, 1071, MEPS 372, 195). Nevertheless, the contribution of benthic fish activity to sediment resuspension and nutrient recycling has not been fully acknowledged in marine studies. Using the remotely operated vehicle ROPOS, the VENUS underwater observatory, and a suit of geochemical, optical, and acoustic measurements, we have quantified bottom fish abundance and activity in a partly anoxic north-east Pacific fiord (MEPS 372, 195). Our data suggest that in the Saanich Inlet, fish rework >40% of the seafloor daily. Unlike bioturbation by infauna, the brief resuspension events mediated by fish expose large quantities of sediments to the overlying waters, thereby reducing organic carbon sequestration to 50% of its annual vertical flux. Sediment resuspension by fish also accounts for sediment transport and focusing (L&O 57, 945), and enhances near-bottom turbidity, oxygen demand, as well as the mass flux of inorganic nutrients, which are all vital for primary marine production across the water-sediment interface (MEPS 372, 195). To date, these processes are missing from geochemical models. We have argued that the ongoing decimation of ground fish populations by commercial fisheries is likely to affect global geochemical cycles in unforeseen ways. A striking example of such a process is the regime shift of the Baltic Sea ecosystem (Global Biogeochem. Cycles 23, 16). We are currently focusing on developing new tools for in situ recording and quantifying of benthic fish activity though imaging sonars and optical backscatter devices. We also work on real-time quantification of sediment resuspension rate with novel electronic devices.
