Benthic ecosystem functioning beneath fish farms in different hydrodynamic environments

Abstract

To quantify how fish farming modifies short-term benthic carbon cycling in fjord environments and the role of hydrodynamics in modifying effects on the benthos, we assessed benthic ecosystem structure and respiration and used isotope labeled algae as a tracer to quantify C flow over 48 h through macrofauna and bacteria in sediments collected from beneath fish farm sites in (1) high water-flow areas, (2) low water-flow areas, and (3) two appropriate control sites situated downstream from the farms. Bacterial biomass was significantly greater in sediments collected from the fish farm sites relative to the controls. This was also true for sediment oxygen consumption (SOC) rates averaged over each 48 h investigation, which were significantly correlated with total benthic (macrofauna and bacteria) biomass. Short-term C-uptake rates by macrofauna were elevated in both fish farm treatments compared with bacterial C uptake and were significantly higher in sediments from the low flow fish farm site relative to both controls. While SOC rates were significantly higher in experiments using sediments from the low flow fish farm site; faunal abundance, biomass uptake, C uptake, bacterial biomass, and metabolism in sediments from both fish farm treatments were not significantly different from one another. Fish farming can dramatically alter benthic ecosystem functioning, and significant effects can occur around fish farms irrespective of the water-flow regime the farms are moored in.

Impaired Short-Term Functioning of a Benthic Community from a Deep Norwegian Fjord Following Deposition of Mine Tailings and Sediments

“…Values of SCOC in our control incubations were comparable to those reported in other studies with Norwegian fjord fauna (Ishida et al, 2013;Sweetman et al, 2014Sweetman et al, , 2016. The SCOC measurements after 8 and 13 days of incubation (MT and DS, respectively) informed about the effect of substrate addition on the SCOC, while the second measurement informed about the response of the sediment community to input of algal detritus.…”

“…Oxygen is a key element in the aerobic respiration and metabolism of organisms and, thus, tightly linked to the mineralization of organic carbon and the activity of benthic organisms. Therefore, OPD and SCOC can provide a reliable indication of organic matter remineralization rates (Moodley et al, 1998) and, combined with stable isotope carbon uptake data of the biota, has proven to be a good tool to assess ecosystem functioning and responses of the benthos to environmental disturbances (Bratton et al, 2003;Sweetman et al, 2010Sweetman et al, , 2014Sweetman et al, , 2016.…”

Arctic cold seeps in marine methane hydrate environments: impacts on shelf macrobenthic community structure offshore Svalbard

“…All of the top 5 taxa from these 4 strongly affected replicates, Siboglinidae, Capitella capitata (Fabricius, 1780), Cossura longocirrata Webster & Benedict, 1887, Spiochateopterus typicus, and Mendicula cf. pygmea, all of which are Polychaeta except the latter (which belongs to the Mollusca) are known to inhabit reduced environments and organic-enriched sediments (Oliver et al 2002, Włodarska-Kowalczuk et al 2007, Sweetman et al 2014, Smith et al 2015. Similar to other types of disturbance sources (e.g.…”

Major impacts of climate change on deep-sea benthic ecosystems

“…Present-day reductions in sea-ice and ice-shelf cover (Comiso, 2010) are leading to changes in upper-ocean pelagic dynamics (e.g., increasing surface primary production, and generating shifts from krill to salps; Loeb et al, 1997;Arrigo et al, 2008Arrigo et al, , 2013Arrigo and van Dijken, 2011). Under high O 2 conditions at shallow depths, metazoans tend to outcompete bacteria in terms of organic matter processing when carbon input to the seafloor increases (van Nugteren et al, 2009;Sweetman et al, 2014b). If the same holds true for the deep seafloor, then elevated POC fluxes caused by reduced sea-ice cover could trigger a switch from dominance of benthic organic matter processing by bacteria to dominance by metazoans with consequences for energy flow to upper-trophic levels ( Figure 4D).…”