Seamount science

Seamounts and the hydrothermal vents sometimes associated with them are highly significant areas of biodiversity and productivity. Found globally, seamounts are usually formed from volcanic activity and appear in a range of heights and depths and shapes. This habitat is one of the most extensive of all oceanic environments and occupies more area than any single land based habitat.

Estimated global seamount distribution

Image source: Yesson C., Clark MR, Taylor M, Rogers AD (2011). The global distribution of seamounts based on 30-second bathymetry data. Deep Sea Research Part I: Oceanographic Research Papers 58: 442-453. doi: 10.1016/j.dsr.2011.02.004. Data URL: http://data.unep- wcmc.org/datasets/41

Biodiversity Seamounts and hydrothermal vents have long been recognised as significant habitats for an important diversity of species. The vents function like chimneys for fissures in the Earth’s crust, funnelling leakages of mineral rich gasses and molten lava into the cooler ocean. Hostile though it is, this environment hosts unique animal communities that are not dependent on the sun and could be a possible origin of life. Seamounts and especially the vents are hotspots for elevated endemism relative to other habitats. As such they constitute an important genetic and scientific resource for the world.

One of the most important features of seamounts is their mountainous shape. Prevailing water currents carry nutrients up the steep slopes from the deep toward the ocean surface. This forms the basis for primary production of plankton which provides food for many species, both benthic (bottom-dwelling) and pelagic (free swimming).

Benthic species The dominant large fauna on many seamounts are benthic organisms (corals, sponges) that feed on food particles. The National Museum of Natural History (MNHN Paris) and Oxford University both specialise in the study of these communities. As the nutrients rise, they are sieved from the water currents by structures the animals have adapted for this function. Their structures in turn provide food and shelter for numerous other species of fish and crustaceans.

Pelagic species When the nutrients reach the surface waters, they become food for plankton and the basis of a complex food chain. Not only are the nutrients pushed up, but as water columns form above seamounts, many species (small fish, larvae and plankton) tend to aggregate here encouraging the hotspot trend. Our partners from IRD specialise in this area. Many of the fish are biologically important as they play major roles in the food web. Tuna and deep-water species, such as alfonsino and orange roughy, grow slowly and the latter can live for 150 years. The seamounts become feeding hotspots and many other animals like cetaceans (whales and dolphins), seabirds, sharks and seals depend on them.

Ecosystem services Plankton collects around these peaks and provides important ecosystem services like oxygen production and carbon storage. Over 50% of the oxygen in our atmosphere comes from plankton and phytoplankton, (for e.g. coccolithophores) one of the many organisms contributing to the mix of plankton species, play a significant role in sequestering carbon dioxide. These single-celled organisms are found in huge quantities in our oceans. Using photosynthesis, they take up the equivalent of half the CO2 produced by the burning of fossil fuels from the atmosphere and store it on the ocean floor when they die and sink. Scientists think this is more than the sequestering done by the worlds tropical rainforests and other terrestrial systems combined.

Protection Because of the diversity and richness seamounts are subject to human exploitation but benefit from no specific legal protection. This especially applies to those seamounts and hydrothermal vents in Areas Beyond National Jurisdiction (ABNJ). The fisheries industry has already had a significant impact on some seamount ecosystems, seriously depleting slow growing fish numbers and destroying valuable habitat by bottom-trawling for them. An increasing threat comes from future mining of the sea bed. Modern technology allows increasing access to these habitats, both for scientists as well as mineral mining companies prospecting for sulphides and cobalt crusts. If mining and fishing intensifies without a working governance framework in place, we could lose biodiversity and species before understanding their significance fully.

Knowledge gap Despite a recent increase in research on oceanic sub-surface features, many basic aspects (including species and ecological processes) of seamounts and hydrothermal vents remain unknown. Of over 200,000 found globally, fewer than 300 seamounts have been investigated.

Project location: ABNJ off the south east African coast

Project objectives (scientific):

1. Advance the state of knowledge of deep sea marine ecosystems connected to hydrothermal vents and seamounts including their relationship with fish populations.

1.1. Document the link between coastal and oceanic ecosystems of ABNJ towards increasing the involvement of coastal states in high seas governance.

Scientific actions planned during the project:

• Synthesis and analysis of knowledge and data so far. • Hydrology, biogeochemistry and environmental dynamics surveys. • Biological sampling on the Walter’s Shoal- zooplankton, seabirds and marine mammals surveys including acoustic survey along the ship's tracks. • Video camera for the pelagic fauna survey. • Bathymetric survey of a seamount south of Madagascar and deployment of ADCP moorings. • Identify sites of conservation interest towards their protection. • Evaluate the impact of threats linked to activities from fishing and mineral exploration/exploitation on biodiversity.