Chapter 7J: Continental slopes and submarine canyons

Keynote points
• Continental slopes represent 5.2 per cent of the ocean, with over one fifth of the slope comprised of submarine canyons; they are critical transition areas between the continental shelf and the deep sea and are important for carbon burial and as habitats for species of ecological and economic importance.
• Strong vertical hydrographic gradients, complex geomorphic features and fluid fluxes from the sea floor make canyon and slope faunal communities highly heterogeneous.
• Hundreds of newly discovered methane seep, coral and sponge habitats enhance biodiversity and host novel interactions with surrounding sediments.
• Canyons can be hotspots of biological
activity but their communities do not always differ from those on adjacent slopes, which are also highly productive; slope and
basin sediments can be an archive of historical information about climate effects on biodiversity.
• Naturally occurring oxygen minimum zones reveal that biodiversity is highly sensitive to oxygenation; expansion of low oxygen zones will reduce biodiversity; projected declines in pH and food supply are likely to affect cold water coral ecosystems.
• Owing to their proximity to shore, slopes and canyons are subject to expansion of deepwater oil and gas activities, offshore energy installations, bottom fisheries and, potentially, mineral mining activities, as well as to increasing contamination, including litter and mine tailings from land.
• Exploration has accelerated the discovery of new ecosystem functions and services, including novel productivity and carbon transfer mechanisms, nursery grounds, and contaminant and waste transfer. However, most canyons and slope areas remain largely unexplored, with major questions
about species ranges, ecological connectivity, benthopelagic linkages,sensitivity to climate and direct disturbance remaining unanswered, in particular in the southern hemisphere and along African and South American margins.
• Better integration of climate science, connectivity research, conservation biology and resource management, combined with increased taxonomic and geographic expertise, will improve the distribution of knowledge, technology, analytical tools and methodologies required to advance global understanding and promote sustainability of slope and canyon ecosystems.