An integrated effort that documented and explained biodiversity patterns on gradient-dominated continental margins, including the potential interactions among their variety of habitats and ecosystems.
Myriam Sibuet, Ph.D., Institut Océanographique, Paris, France
Robert Carney, Ph.D., Lousiana State University, Baton Rouge, Louisiana, USA
Lenaick Menot, Ph.D., Institut Océanographique, Paris, France, & Ifremer, Brest, France
The continental margins are the ribbons of seafloor beginning at the edge of the continental slope and extending rapidly to abyssal plain depths. During the past few decades, our understanding of deep continental margin habitats has changed more than for any other large area of Earth. While it has been known for a long time that the ocean margins are a mixture of rugged mountainous scenery and sediment- covered slopes, it is only in recent times, with higher-resolution bathymetry and increased bottom sampling, that areas once envisioned as monotonous landscapes are now acknowledged to have a high degree of complexity and diversity. Continental margins furthermore support some of the ocean's strongest gradients (e.g. depth, pressure, organic matter flux, oxygen). Collectively, these processes create unique ecosystems, some only now being discovered and which we are just beginning to understand. As exploitation of living and mineral resources is advancing faster than ecological knowledge on continental slopes, a comprehensive analysis of species distribution, biodiversity patterns and processes on continental margins was needed.
Structural complexity of continental margins: A 3D bathymetry of the
Equatorial West African margin, cut by the Zaire canyon (© Ifremer - Zaiango project)
COMARGE was a field project of the Census of Marine Life launched in 2005. The project aimed to:
1. Describe biodiversity patterns of benthic and bentho-demersal communities on continental margins, with a focus on multiple habitats and spatial scales;
2. Identify the contribution of environmental heterogeneities to these patterns.
Variety of ecosystems on continental margins: Most continental margin fauna is fed by a rain or rather a drizzle of organic matter from the sunlit ocean but locally, the natural seepage of methane provides an alternative energy source for chemosynthetic ecosystems [from Sibuet M and Olu-Le Roy K (2002) in Wefer G, Billet D, Hebbeln D, Jorgensen BB, Schlüter M, van Weering T (eds) Ocean Margin Systems. Springer, Berlin, p 235-251].
To achieve its goals, COMARGE created a network of researchers to facilitate coordination among projects and cruises, to foster data sharing, to support data archiving through its database and, finally, to assure the maximum synergistic value for continental margin studies.
Interactions: Organic matter flux, faunal biomass and densities are enhanced at the edge of an Oxygen Minimum Zone (The Oman Margin, 3200 m depth - © National Oceanographic Center, Southampton, UK).
An objective of COMARGE was to turn basic advances in ecology into sound environmental advice. Fundamental patterns of species distribution first observed and explained in the context of monotonous slopes were re-evaluated in light of the newly recognized heterogeneity of continental margins. Multi-scale habitat definition and mapping provided basic geo-referenced information used to develop environmental sensitivity maps. Comprehensive cross-margin syntheses at the species level served to enlighten benthic species distributions in the deep-sea realm and helped refine estimates of how many species co-exist on continental margins. The scale of species distribution is a matter of debate among deep-sea ecologists and a basic requirement in conservation policies. Comprehensive cross-margin syntheses at the community level will allow local to global testing of controls on species diversity, will generate data inputs for food web models and will provide insights in theoretical ecology. A better understanding of biodiversity patterns and processes, ecosystem functioning and their inter-relationships as provided by COMARGE was acutely needed in order to forecast environmental risks on continental margins.
The deep-sea macrobenthos: We currently know about 250,000 marine species;
those small animals living in or near sediments may add up to 10 million species to the list.
Fascination with the unknown, and thus with the deep sea is high. The deep sea is the largest ecosystem on Earth but is one of the least understood environments. Its remoteness and difficulties encountered in its exploration excite human imagination. The deep sea is shrouded in a mystery that stimulates human desire for knowledge and invites us to conquer the last remaining frontier on Earth. Fortunately, submersibles and remotely- operated vehicles (ROVs) now offer access to hotspots on continental margins, where some of the best underwater mountain scenery on Earth can be found. Stunning photographs and videos produced by COMARGE partners offer a tremendous potential to enhance awareness of continental margins among the general public.
Rich and fragile: Either patchily distributed at the meter scale or forming km-wide and
thousand year-old carbonate mounds, deep-sea corals harbor 1300 known species in
the North East Atlantic (© Ifremer - Caracole - 2001).
By 2010, COMARGE had built a network of excellence, which fostered the emergence and dissemination of new ideas, generated an international research agenda designed to test the hypotheses that emerged from the COMARGE synthesis, and thus will guide ecological researches on continental margins for the next decade. The COMARGE network has the potential to remain a key partner:
* For the off shore oil and gas and fishing industries, where scientific expertise is needed to advise on environmental survey protocols, to provide a taxonomic clearing house and to forecast environmental risks.
* For the conservation stakeholders, enabling them to address conservation issues in the deep sea on a sound scientific basis.
* For national interests (governments) that wish to protect the biodiversity and natural resources within their Exclusive Economic Zones (EEZs).