Tobago Cays Marine Park

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Chapter 3. SITE DESCRIPTION

a - General features of the site

Terrestrial surface under sovereignty, excluding wetlands:

5 sq. km

Wetland surface:

1 ha

Marine surface:

60 sq. km

Global comment for the 3 previous fields (optional):

These are estimate, there are are no exact figures. 

b - Physical features

Brief description of the main physical characteristics in the area:

The TCMP includes the four main islands of the cays (Petit Rameau, Petit Bateau, Jamesby and Baradal), Petit Tabac to the east and the larger island of Mayreau to the west. Three smaller islands are also found in the north of the park - Catholic Island, Jondall and Mayreau Baleine. The park includes the 4 km long Horseshoe Reef (the largest in the Southern Grenadines), Mayreau Gardens, World’s End and Egg reefs. The Horseshoe reef provides vital protection from incoming wave action from the open Atlantic and is the major reef complex within the Tobago Cays. The bank-barrier and fringing reefs of the Tobago Cays are dominated by the branching Elkhorn coral (Acropora palmata) in shallow water and by various head corals in the deeper fore-reef zones. All of the three major marine ecosystems are present within the Tobago Cays. Mangroves are located on the eastern side of Petit Rameau and large areas of seagrass beds lie in the centre lagoon sheltered by bank-barrier reefs to the east. 

Geology:

The Grenadines are geologically older than St. Vincent and are situated on an extensive shallow bank of volcanic origin – known as the southern Lesser Antilles arc platform (SLAAP). The SLAAP is a product of Miocene uplift (23–16 Ma) and characterized by Eocene to Pliocene extrusive to intrusive igneous rocks along with sedimentary rocks such as limestone, marl, and chert, and epiclastic arc-derived volcaniclastic units composed of mudstone, sandstone, and conglomerate. The islands are comprised of a variety of volcanic and sedimentary rocks. The area is an active subduction zone, and lies along the interface of the Caribbean and South American Tectonic plates. The shallow bank of the Grenadines extends from St Vincent to Grenada, and has a natural boundaries of the Tobago Trough to the east and the Grenada Trough to the west, where the depth increases rapidly. The shallow bank creates ideal conditions for the formation of productive seagrass beds, mangroves and coral reefs.

Topography:

The cays are very flat - Mayreau is the largest island within the park with a highest point of 99m above sea level. 

Bathymetry:

The TCMP lie on the shallow Grenadines shelf which extends up to three times further to the east of the Grenadines than to the west. This shelf is not uniformly shallow, but is marked by a ridge on its eastern margin of some relic reef system. The wide shallow shelf is conducive to the formation of many coral reefs, and bottom slopes away rapidly after the 50m depth contour. The Tobago Cays lies in shallow water, conducive to reef formation. 

Hydrodynamics:

The dominant ocean currents in the vicinity of St. Vincent and the Grenadines flow from the east-southeast. Some upwelling of deeper ocean waters is thought to exist along the eastern part of the insular shelf. Tides throughout the islands are semi-diurnal. There is a predominant current flow from east to west of up to 3 knots, which brings seasonal influxes of surface fresh water from the Amazon and Orinoco estuaries. This prevailing flow is reversed by a weaker, shorter duration west to east flow every day. Localised currents and topography significantly affect the tidal stream. Currents tend to suppress the eastgoing stream and enhance the west-going stream, while narrow channels strengthen the west-going streams. Due to the prevailing north easterly winds, the sea often breaks at depths of less than 8 m on the eastern side of the island chain. Strong tidal currents exist in the TCMP – for example tidal channels bisect areas of harder substrate within the Mayreau Gardens reef, and the strong currents result in high biodiversity along the channels.

Volcanic formations:

Geologically, the area lies along the interface of the Caribbean and South American Tectonic plates on the southern Lesser Antilles arc platform (SLAAP). The area is an active subduction zone with undersea volcanoes and seismic activity. Kick’em Jenny is an undersea volcano north of Grenada, and there is also another less active submarine named Kick’em Jack in the area. These volcanoes are important as their explosion may result in the creation of new land masses, and new marine life has been found by Northern Oceanic and Atmospheric Association in their vicinity.

Sand dunes:

There are very small sand dunes on some of the islands, but no major areas.

Underwater formations:

The Tobago Cays is renowned for its extensive coral reefs, including Horseshoe reef the longest bank-barrier reef in the Southern Grenadines (4 km long). Other major reefs include Egg, World’s End and Mayreau Gardens. There are also extensive fringing reef around the cays and islands. Additionally there are areas of sea grass beds which support endangered turtle populations.