Sanctuaire Agoa

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Chapter 3. SITE DESCRIPTION

c - Biological features

Habitats

Brief description of dominant and particular habitats (marine and terrestrial)*: List here the habitats and ecosystems that are representative and/or of importance for the WCR (i.e. mangroves, coral reefs, etc):


 

1. Ecosystems features

The Caribbean Sea is a semi-closed basin between the Florida and the Bahamas in the North, and Central and South America in the West, and by the Antilles in the East. It is the second biggest sea of the world with a surface of 2 828 125 km2 (Costello, Coll and al ., on 2010) and is constantly fed by Atlantic waters and currents of Guyana.

These waters are seasonally enriched by the phytoplankton coming from the Guyana Shield. This exogenous supply comes to increase a coastal local primary production, mainly bound to the contributions of terrigenous nutrients, the level of which is still underestimated. Considered as the heart of the biodiversity of the Atlantic Ocean (Huggins, Keel and al ., on 2007; Spalding, Ravilious and al ., on 2001), the Caribbean sea is home to a multitude of species (117 types of sponges, 633 of mollusks, 378 of bivalves, 77 of stomatopodes, 148 of echinoderms, more than 1 400 species of fishes, 76 of sharks, 45 of shrimps and 28 of cetaceans) among which 13 % are endemic in the zone. Three types of major ecosystems are found : coral reefs, mangroves and seagrasses.

 

2. Physico-chemical features

"Battered by Atlantic swells, the windward coasts are currently protected in part by biological algae (barrier) constructions or algo-reef (fringing). This protection is dependent on the growth of organic buildings that are currently in decline. Maintaining that physical protection is of paramount importance for the preservation of coastal infrastructure, and mangroves which reduce erosion along this coast. Mangroves are the only bulwark against the discharge of terrigenous flux on other coastal ecosystems. The phanerogam seagrass is also involved in trapping coastal sediment and nutrients, thus providing to the communities some of the conditions necessary for growth.

 

Generally in the tropics and in the absence of nutrient enrichment phenomena, biological processes are mostly coastal. Each of the major coastal ecosystems is known to provide important primary production, habitat for communities living more or less specialized, shelter, feeding areas, and nurseries:
- The mangrove is an important source of primary production. The feet of mangrove tree also provide shelter for aquatic wildlife, resident or not, (mangrove crab, shorebird) and juvenile fish.
- The phanerogam seagrass provides shelter and feeding to a variety of wildlife resident or migrant (conch, white sea urchin, green turtles, corals, seagrass, gorgonians). It is also a nursery area.

 

- The coral communities offer, by their large spatial heterogeneity, multiple types of shelter and food sources allowing a very high biodiversity to live there (presence of fish, corals, mollusks and other many groups totally unknown , feeding area for hawksbill turtles). Their primary production is very high and they are also nursery grounds.
These biological functions (nursery, primary production ...) and physical (coastal protection) can be ensured only by functioning ecosystems, that is to say in good health (coral communities in good health and recrutantes , climax of seagrass beds, mangroves integrity) and whose functional relationships are preserved (exchange of matter and nutrients, migration of individuals at different time scales). "
- The intertidal habitats are rarely frequented by whales but they are very important because they provide breeding areas for fish and other prey.

 

- The continental shelf slopes gently from the shore at an average depth of 200 meters and is a rich food source for whales and other predators.
- The continental slope or bathyal zone which descends more abruptly ends at a depth of about 1100 meters or more and is frequented by some marine mammals like the sperm whale.
- The abyssal plain is itself extremely flat and occupies over 40% of sea area. Its depth varies by region but is generally 4000 meters.

Detail for each habitat/ecosystem the area it covers:

Marine / coastal ecosystem categories
Detail for each habitat / ecosystem the area covers
Size (estimate) Description and comments
unit Area covered
Mangroves
Antilles françaises ha 6083 Biodiversity in mangrove tree species in the Caribbean is low. Only four different species of mangrove trees have been identified, including three predominant: • The red mangrove - Rhizophora mangle L. (Rhizophoraceae) • The black mangrove - Avicennia germinans L. (Avicenniaceae) • The white mangrove - Laguncularia racemosa Gaertn (Combretaceae) There is, so scarce, the gray mangrove - Conocarpus erecta L. (Combretaceae), in sandy or rocky environments (edges of beaches). But these mangroves areas are home to significant biodiversity. For aquatic species, they are a safe haven and nursery for the juveniles.
Coral reefs
Antilles françaises (lagons et coraux) ha 30000 In the French Antilles (Martinique, Guadeloupe, St. Barthelemy, St. Martin), the situation has deteriorated since 1980: terrigenous sedimentation, nutrient pollution, fertilizers, pesticides and sewage led a coral degradation in favor of algae . Moreover, cyclones of 1980 and 1989 have greatly achieved corals (breakage and degradation by sedimentation), while the bleaching of 1998 resulted in a mortality of the order of 20 to 30%, as well as those of 2005.
Sea grass beds
sea grass ha 20000
Terrestrial ecosystems
Size (estimate)
unit Area covered