Seafloor ecological functioning over two decades of organic enrichment

Abstract

Climate change and anthropogenic nutrient enrichment are driving rapid increases in ocean deoxygenation, these changes cause biodiversity loss and have severe consequences for marine ecosystem functioning and in turn the delivery of ecosystem services upon which humanity depends (e.g. fisheries). We seek to understand how such changes will impact seafloor functioning using biological traits analysis. Results from a sewage-sludge disposal site in the Firth of Clyde, UK spanning 26 years of monitoring showed that substantial changes in macrobenthic nutrient cycling and the provision of food for predators occurred, with elevated functioning on the margins 1-2 km from the centre of the disposal grounds.Changes in food-web dynamics are expected, that weaken benthic pelagic coupling and lower secondary production (such as fisheries). Generally, functioning was conserved, but declined below a ~6% total organic carbon threshold. Similar to other severely deoxygenated systems, the recovery was slow and hysteresis was apparent.

Mechanisms and drivers of belemnite body-size dynamics across the Pliensbachian–Toarcian crisis

“…It is, however, worth noting that modern systems have shown us that the interaction between climate change, nutrient input and productivity is complex and might vary regionally (e.g. [57]) and according to the scale considered [58]. Additionally, such variations might be difficult to constrain in the geological record without modelling—so far only available for a limited number of time-slices, such as at the Palaeocene–Eocene Thermal Maximum [59,60].…”

Response of a marine benthic invertebrate community and biotic indices to organic enrichment from sewage disposal

“…The carbon content found in 1995 (on average 8% and a range of 3.78–13.52%) is comparable to that found in impacted sewage disposal sites elsewhere (e.g. at the Garroch Head sludge disposal central point values ranged from 6–15% (Caswell et al ., 2018) and at the Nervion estuary the means at the most impacted sites were around 10%, and at intermediate sites 6–7% (Borja et al ., 2006)). Nevertheless, in 1995, most indices did not detect impacts on the community due to the enrichment.…”

“…The levels of species richness supported at this site (on average 61.9 in 1995 and 71.1 in 1998) are much greater than those reporting sewage impacts elsewhere with similar levels of organic enrichment (e.g. 6.6–24.7 species at the most impacted stations at Garroch Head; Caswell et al ., 2018). The species richness here is similar to that found at disposal sites in Liverpool Bay, where the elevated species richness at disposal sites compared with reference sites was attributed to natural site differences (Whomersley et al ., 2007).…”

“…Stull et al ., 1986; Bowen & Valiela, 2001; Diaz & Rosenberg, 2008; Abdelrhman & Cicchetti, 2012; Caswell et al ., 2018). Eutrophication with deoxygenation due to organic enrichment, can lead to lower benthic species richness; degraded ecosystem functioning, such as bioturbation and nutrient cycling; and decreased capacity to provide ecosystem services, including waste treatment, and climate regulation through reduced carbon sequestration (Worm et al ., 2006; Smith & Schindler, 2009; Caswell et al ., 2018). Changes to benthic invertebrate communities, such as loss of larger species, can have impacts on the wider ecosystem, since they are a key part of the food chain, in particular on predators with specialized feeding strategies, such as some wading birds (Bowgen et al ., 2015).…”

“…This stereotyped response to organic enrichment (including from sewage, pulp and paper mill waste and organic dredged sediments, amongst others) allows detection of environmental impacts; this has been exploited in studies of human impacts on marine ecosystems and through the use of indices of benthic ecosystem health (e.g. Muxika et al ., 2005; Elliott & Quintino, 2007; Borja et al ., 2011; Caswell et al ., 2018).…”