Trophic state of benthic deep-sea ecosystems from two different continental margins off Iberia

Abstract

The bioavailability of organic matter in benthic deep-sea ecosystems, commonly used to define their trophic state, can greatly influence key ecological processes such as biomass production and nutrient cycling. Here, we assess the trophic state of deep-sea sediments from open slopes and canyons of the Catalan (NW Mediterranean) and Portuguese (NE Atlantic) continental margins, offshore east and west Iberia, respectively, by using a biomimetic approach based on enzymatic digestion of protein and carbohydrate pools. Patterns of sediment trophic state were analyzed in relation to increasing water depth, including repeated samplings over a 3 yr period in the Catalan margin. Two out of the three sam- pling periods occurred a few months after dense shelf water cascading events. The benthic deep-sea ecosystems investi- gated in this study were characterized by high amounts of bioavailable organic matter when compared to other deep- sea sediments. Bioavailable organic matter and its nutritional value were significantly higher in the Portuguese margin than in the Catalan margin, thus reflecting differences in pri- mary productivity of surface waters reported for the two re- gions. Similarly, sediments of the Catalan margin were char- acterized by significantly higher food quantity and quality in spring, when the phytoplankton bloom occurs in surface wa- ters, than in summer and autumn. Differences in the benthic trophic state of canyons against open slopes were more ev- ident in the Portuguese than in the Catalan margin. In both continental margins, bioavailable organic C concentrations did not vary or increase with increasing water depth. Overall our findings suggest that the intensity of primary production processes along with the lateral transfer of organic particles, even amplified by episodic events, can have a role in controlling the quantity and distribution of bioavailable organic detritus and its nutritional value along these continental margin ecosystems

Benthic deep-sea fungi in submarine canyons of the Mediterranean Sea

“…Fungi are heterotrophic organisms known to utilise carbohydrates (Richards and Talbot, 2013;Richards et al, 2015, Couturier et al, 2016, which in deep-sea sediments represent one of the most refractory compounds of organic matter (Dell'Anno et al, 2000;Dell'Anno et al, 2013). Therefore, our findings suggest that benthic deep-sea fungi, besides prokaryotes, can be actively involved in the decomposition and utilisation of highly refractory compounds, thus contributing to their cycling.…”

Local Environmental Conditions Promote High Turnover Diversity of Benthic Deep-Sea Fungi in the Ross Sea (Antarctica)

“…In deep-sea ecosystems, fungi are not only highly diversified, but they are likely involved in the degradation and cycling of organic matter [13,18,[35][36][37][38]. In benthic deep-sea ecosystems, organic matter mainly consists of refractory organic compounds [39,40], and fungi are known to be efficient degraders of complex organic molecules not suitable for other heterotrophic microbes [41,42]. However, their role in C and nutrient cycling in benthic deep-sea ecosystems remains poorly understood [24].…”

Spatial and temporal environmental heterogeneity induced by internal tides influences faunal patterns on vertical walls within a submarine canyon

“…The M 2 vertical isopycnal elevation amplitudes diagnosed here may also reflect spatial and temporal variation in internal tide kinetic energy and associated turbulent mixing (Van Haren et al, 2022). In Whittard Canyon, peaks in turbulent kinetic energy dissipation have been linked with resuspension of material, nepheloid formation and sediment movement (Van Haren et al, 2022) that indirectly influences fauna by resuspending and concentrating POM (Dell'anno et al, 2013;Demopoulos et al, 2017;Pearman et al, 2020). Additionally, internal tide kinetic energy influences fauna directly by elevating near-bed current speeds and associated physical stress (Weinbauer and Velimirov, 1996;Johnson et al, 2013; and variation in internal tide kinetic energy has been correlated with fish larvae richness, abundance and assemblage composition in the Midrift Archipelago Region of the Tiburon Basin, Gulf of California (Ruvalcaba-Aroche 2019).…”

“…Variability in the quality and amount of food supply is known to influence canyon faunal distributions (De McClain and Barry, 2010;Cunha et al, 2011;Chauvet et al, 2018). Furthermore, hydrodynamic and geomorphological processes have previously been proposed as factors influencing the supply and resuspension of particulate organic carbon to canyon environments and thus driving trophic structure, faunal assemblage composition and diversity (Dell'anno et al, 2013;Demopoulos et al, 2017). However, to confirm the role of the internal tide in generating spatial heterogeneity in food availability to which fauna respond, further trophic analysis of nepheloid layers in proximity to faunal assemblages in relation to internal tide dynamics would be required.…”