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Biozaire

BIOZAIRE refers to the study of the benthic communities in the deep sea influenced by the Zaire canyon (now called Congo canyon) 

 

Project leaders: Myriam Sibuet, Institut Océanographique, Paris Joëlle Galéron, Ifremer, Plouzané

Objectives

The programme is conducted in the framework of a scientific and technical cooperation between Total and Ifremer and it focuses on the study of the benthic communities and the main physical and chemical characteristics of their environment in the Gulf of Guinea, off equatorial West Africa.

 

The studied area is characterised by contrasting environmental conditions mainly driven by the activities of one of the world’s largest and very active submarine canyons, the Congo canyon/channel system that extends westward off the Congo-Angola margin for 760 km down to the abyssal plain at 4900 m depth. The Congo channel has been shown to carry large quantities of particulate matter originating from the continent through intense turbiditic currents that were recorded down to 4800 m depth in the channel.

 

At 4000 m depth, the most active turbiditic events could overflow the flanks of the channel and affect the surroundings at least over several kilometres by carrying to the bottom large quantities of organic matter of terrestrial origin within a few days, able to double the annual organic input to the sediment interface.

 

Concerning the detritus based ecosystems, the aim of BIOZAIRE is to understand the dynamic of the energy inputs, their origins and their consequences on the biodiversity of the benthic communities on 4 stations: two stations (1350 m and 4000 m depth) under the pelagic and continental input, one (4000 m) under the influence of the Congo canyon, the last one (3500m) in the vicinity of a cold seep area.

 

Concerning the chemosynthetic based ecosystems, two areas are prospected on the Gabon margin, one at 800 m depth and the other one at 3500 m depth. The relation between the two types of ecosystems is also studied.

 

Several types of equipment are used to collect information on the environmental parameters and benthic communities, including the French ROV Victor that allows to work on the bottom at a very precise scale.

Results so far

A workshop was organised in June 2006 in Brest to present and discuss the results obtained by the scientists involved in the project. These results will be published in a special issue of Deep Sea Research II in 2008.

 

The study of the benthic communities at two sites at 4000 m depth, one next to the Congo channel, under influence of the Congo channel activities, and the other one 150 km in the southeast, out of influence of the turbiditic events, highlighted differences in terms of  community structure for the three main size classes (megafauna, macrofauna and meiofauna).

 

Megafauna seemed to respond to the influence of the Congo channel in terms of organic input by higher densities in the vicinity of the Congo channel, while macrofaunal and meiofaunal densities seemed driven by other factors as they were equivalent at both sites or even higher far from the channel.  Temporal variations were highlighted in density, taxonomic structure and vertical distribution of macrofauna at both sites which could suggest that the sediment communities were subject to changes in environmental parameters, particularly in trophic inputs, at regional scale beyond the Congo activity effects. One of the particularities evidenced during this study was the presence of some megafaunal species typically linked to the presence of methane or suphide at both sites (i.e. Vesicomya sp., Acharax sp.), while macrofaunal and meiofaunal assemblage structure seemed typical of abyssal sediment communities. 

 

The diversity and complexity of the deep sediment communities in the Gulf of Guinea, are probably linked to diversity in different environmental parameters such as the origin of the organic material fueling the communities (pelagic or terrestrial, through the Congo channel or along the continental margin), the quantity and regime of trophic inputs (erratic large inputs), and linked disturbances. Moreover this complexity is enhanced by the sporadic presence of chemosynthetic processes probably linked to the Congo paleochannels in a large area around the present Congo channel.

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