Seamount ecosystems

Useful links

Seamount news: Tuesday 8 November 2011: RRS James Cook heads off to the southwest Indian Ridge to investigate its seamounts

Seamounts are undersea mountains whose summits rise more than 1,000 meters above the surrounding seafloor. They are hotspots of marine life: enhanced water flow through localised tides, eddies and upwelling may enhance primary production over and around seamounts. On the seamount floor there are often rich communities dominated by suspension feeders such as gorgonians and other corals, many of which form colonies or reefs, as in the case of the coral Lophelia pertusa, which provide extra complexity and structure to seamounts. Though the diversity and localised distribution of species living in these communities are recognised, their biology and life history remain poorly studied. Some species may be extremely long-lived, perhaps in excess of 100 years.

Only a few seamounts have been investigated and species richness and diversity are poorly documented. However it has become evident that fish assemblages associated with seamounts show specific adaptations and represent a relatively large and unique of fish biomass.

The high abundance and commercial value of orange roughy (Hoplostethus atlanticus) and alfosinos (Beryx splendens and B. decadactylus), fish which aggregate on seamounts, has resulted in their intensive exploitation since the late 1970s. Seamount species, especially those forming aggregations, are particularly vulnerable to over-exploitation due to their longer lifespan, later sexual maturity, slower growth and lower natural mortality than other species. Stock depletion of shallow water fisheries has increased pressures on alternative fishing grounds with the characteristic ‘boom and bust’ cycle seen in deep-sea fisheries in general and seamount fisheries in particular, with targeted fish stocks quickly showing signs of overexploitation. If fishing on seamounts continues, even at reduced levels, a number of seamount populations will become extinct.

Side effects of fishing on seamounts include damage to benthic communities dominated by corals and other fragile suspension feeders. Despite concerns, direct and indirect impacts of fishing on seamount ecosystems have been poorly quantified.

Studies have indicated that seamounts play a key role in supporting high biodiversity and high levels of endemism but interconnections between seamounts and other adjacent deep-sea ecosystems have not been investigated. Questions relating to the role of seamounts as centres for speciation, refugia or stepping-stones in trans-oceanic dispersal remain unanswered.

HERMIONE compared data from seamounts at different stages of exploitation to help understand the main effects of fishing activities on seamount communities. Anthropogenic impacts on the surrounding deep-sea benthic species were studied as were contamination and the responses to it in seamount organisms. Adaptations of organisms inhabiting seamounts and the adjacent deep-sea basins were studied in relation to their ecology to better understand the importance of biodiversity in the functioning of seamount ecosystems.

To provide stakeholders and policy-makers with scientific knowledge which will support ecologically sustainable governance of seamounts and their resources, HERMIONE also developed an Ecosystem Evaluation Framework for seamounts.

Seamount links

seamounts_mod_thumbTry out this interactive tutorial explaining more about seamounts and how they work

300px-rrs_james_cook_at_the_national_oceanography_centre_southamptonFollow this cruise blog from the RRS James Cook as it sets off to the southwest Indian Ridge to investigate seamounts in the area, the animals that live there, and how they are affected by deep-sea fishing.