Deep-sea diversity patterns are shaped by energy availability

Abstract

The deep ocean is the largest and least-explored ecosystem on Earth, and a uniquely energy-poor environment. The distribution, drivers and origins of deep-sea biodiversity remain unknown at global scales. Here we analyse a database of more than 165,000 distribution records of Ophiuroidea (brittle stars), a dominant component of sea-floor fauna, and find patterns of biodiversity unlike known terrestrial or coastal marine realms. Both patterns and environmental predictors of deep-sea (2,000-6,500 m) species richness fundamentally differ from those found in coastal (0-20 m), continental shelf (20-200 m), and upper-slope (200-2,000 m) waters. Continental shelf to upper-slope richness consistently peaks in tropical Indo-west Pacific and Caribbean (0-30°) latitudes, and is well explained by variations in water temperature. In contrast, deep-sea species show maximum richness at higher latitudes (30-50°), concentrated in areas of high carbon export flux and regions close to continental margins. We reconcile this structuring of oceanic biodiversity using a species-energy framework, with kinetic energy predicting shallow-water richness, while chemical energy (export productivity) and proximity to slope habitats drive deep-sea diversity. Our findings provide a global baseline for conservation efforts across the sea floor, and demonstrate that deep-sea ecosystems show a biodiversity pattern consistent with ecological theory, despite being different from other planetary-scale habitats.

Global biogeochemical provinces of the mesopelagic zone

“…Consequently, the epi‐mesopelagic boundary is established at the depth where light‐driven primary production can no longer be supported by environmental conditions. We chose to account for both biogeochemistry and ecological studies to define the meso‐bathypelagic boundary at the depth where a vertical change in F POC is not significant over five consecutive 5‐m bins. We assumed that this depth corresponds to the horizon where biogeochemical processes significantly reduce the organic carbon flux and where the influence of shallow waters on deep marine ecosystems is negligible (Woolley et al., ).…”

“…As no quantitative definition of the mesopelagic–bathypelagic boundary is available in the literature, we here propose to define the limit based on the vertical gradient of the flux of particulate organic carbon. We chose this criterion because it reflects change in biogeochemical conditions (Black & Shimmield, ) and food availability in the mesopelagic, and shapes the distribution and biodiversity of deep‐dwelling organisms (Robinson et al., ; Woolley et al., ). The flux of POC ( F POC ) and POC vertical profiles were gathered from Henson, Sanders, and Madsen (), on a 1° grid, and have been modelled following the classical Martin's curve (Martin, ).…”

Hydrothermal activity lowers trophic diversity in Antarctic hydrothermal sediments

“…This relationship may also suggest that the influence of disturbance gradients created by hydrothermalism can result in an impoverished community (McClain and Schlacher, 2015;Bell et al, 2016b). Productivity-diversity relationships in which higher productivity sustains higher diversity have also been suggested for deep-sea ecosystems (McClain and Schlacher, 2015;Woolley et al, 2016), but this is not supported by the Bransfield Strait sites (Bell et al, 2017a). We suggest that in the Bransfield Strait the environmental toxicity in hydrothermal sediments (from differences in temperature and porewater chemistry) causes a concomitant decline in both trophic and species diversity (Bell et al, 2016b) in spite of the potential for increased localised production (Bell et al, 2017a).…”

The Structuring Role of Marine Life in Open Ocean Habitat: Importance to International Policy

“…At the sea surface, distinctive habitats based on oceanographic features and areas of high productivity and biodiversity are identifiable using sea surface temperature, temperature at depth, chlorophyll, and nitrates among other variables (e.g., Hobday et al, 2011). Beneath these areas often lie diverse seabed ecosystems (Woolley et al, 2016) with nutrients, dissolved organic matter, and minerals moved through the water column, mediated by marine life as well as topographically induced currents, which influence both seabed and water column habitat characteristics (Turner, 2015;Soetaert et al, 2016).…”