Slope and basin ecosystems

Slopes and deep basin ecosystems are the most extensive on Earth, accounting for more than 90% of the ocean and 65% of the globe. They represent the largest reservoir of biomass and are suspected to host a large proportion of undiscovered biodiversity. Their role in global biogeochemical and ecological processes is essential for the sustainable functioning of our biosphere and human wellbeing. Many of the goods (biomass, bioactive molecules, oil, gas) and services (climate regulation, nutrient regeneration and food) provided by deep-sea ecosystems are produced and stored on continental slopes and in deep basins.

One of the most challenging aspects of deep-sea ecology is to understand the mechanisms that produce spatial patterns in species diversity. A variety of biological and non-biological explanations have been proposed for why species diversity changes with depth, but the mechanisms controlling these trends remain largely unknown. Whilst knowledge of patterns of biodiversity on an open slope and deep basin scale has increased, understanding of biodiversity patterns and distribution of species on smaller spatial scales is limited. As part of the HERMIONE project new sampling strategies were designed to provide essential information to increase our understanding of how biodiversity supports ecosystem function and ecosystem interconnection in the deep sea at a variety of spatial scales, from millimetres to several kilometres. These studies are essential for planning appropriate management of deep-sea biodiversity and resources.

The consequences of ocean warming for seafloor species are unknown. Using data from previous investigations and new data collected during the HERMIONE project, temporal patterns in benthic biodiversity and ecosystem functioning were studied. By relating these to present-day climate change it may be possible to identify the most important drivers of change.

The response of marine systems to climate change may depend on other human-induced changes in the marine environment. Fishing, ocean acidification, pollution, contamination by organic and inorganic contaminants and heavy metals, introduction of invasive species and litter may result in more fragile marine ecosystems and the effectiveness of management strategies designed to reduce the impacts of climate change may be compromised. HERMIONE studied the ecological consequences of pollution and contamination on key deep-sea species.

Landslides and dense shelf water cascading events periodically disturb deep benthic ecosystems. These events change deep-sea biodiversity, abundance and population dynamics by altering the physical and chemical environment. The overall ecological consequences of these events remain almost completely unknown. Research during the HERMES project suggests that landslides play a significant role in determining patterns of biodiversity along slopes by creating a mosaic of environmental conditions. This hypothesis was tested by using data collected during HERMES research together with new research on stable versus unstable slopes.

A recent study linked benthic biodiversity exponentially to deep-sea ecosystem functioning and efficiency. However, data necessary to evaluate the consequences of biodiversity loss on the functioning of slope and basin ecosystems are insufficient to define specific policy actions. The HERMIONE project aimed to identify hotspots of biodiversity, habitats to be protected and drivers of change on slopes and in basin ecosystems. An interdisciplinary team of oceanographers, biologists and socio-economists investigated the interconnection between slopes, deep basins and other hotspot ecosystems and explored possible mitigation and adaptation strategies.