Man O War Shoal Marine Park

Note: The data were entered in the language of the country of origin (English, French or Spanish) and there is no translation available yet.

Chapter 3. SITE DESCRIPTION

a - General features of the site

Terrestrial surface under sovereignty, excluding wetlands:

0 sq. km

Wetland surface:

0 ha

Marine surface:

31 sq. km

Global comment for the 3 previous fields (optional):

The Man of War Shoal Marine Park encompasses 31 sq Km of biologically diverse Coral Reef, Seagrass, Sandy Bottom and Open Ocean Ecosystems.

 

 

b - Physical features

Brief description of the main physical characteristics in the area:

Most reefs within the Man O War Shoal Marine Park are patch reefs, small isolated reef areas that develop from the substrate. The upper reef slopes have spur and groove features; coral ridges alternated by sand channels. The spurs are typically dominated by massive coral species. Algae, sponges and corals have established themselves on the spurs. The sandy groove areas support little coral or algae growths because of the mobile, scouring nature of the sand. The grooves often open out to an area of rubble and coarse sand.

 

 

Geology:

Very little is known about the specific geology of the Man O War Shoal Marine Park. However, there is more information about St Maarten and it's neighbouring islands, which are often described as having geologically evolved in similar ways. 

The islands of Saint Martin and Saint Bartholomew consist of andesitic tuffs and tuff-breccias of Middle and Late Eocene age, respectively, which have been intruded by hypabyssal basalt, andesite, and quartz diorite of a slightly later age. No older “basement rocks” are present as previously supposed. During the late Eocene and early Oligocene, these islands are believed to have been the sites of active volcanoes whose centers of activity shifted from east to west. The tuff series were tilted and faulted as a result of the volcanic activity and on St. Martin they were extensively metamorphosed.

By the end of the Oligocene, the area had been eroded to the roof level of the intrusive rocks and the Oligocene-Miocene limestone and marls were deposited unconformably on the tuffs. On Anguilla, limestone of a similar age covers the entire island except for two small outcrops of tilted tuffs and basalt.

At some later date, the limestones were gently folded, and, during the Pliocene and Pleistocene, the islands were probably connected to form one large island. The area is now submerged to form the Anguilla bank with the mountainous portions being the present islands.

R. A. Christman (1951), Geology Of St. Bartholomew, St. Martin, And Anguilla, Lesser Antilles, U. S. Geological Survey, Denver Federal Center, Denver, Colo. Princeton Investigation Of Caribbean Geology Number 6. Received June 15, 1951.

 

 

Soil:

N/A

Topography:

N/A

Bathymetry:

Man O War Shoal Marine Park is located on the edge of an undersea plateau, known as the Anguilla Bank, where depths generally do not exceed 36m. This is shared with St Barthélemy and Anguilla. The Southern edge of the Man O War Shoal Marine Park dips down into the St Barthelemy Channel, with depths within the boundaries of the marine park reaching down to 80m (Attachment 2).

The top of the Prosetylyte Reef Complex, known as Spanish Rock, is at 3m depth. Rock outcrops, spur and groove formations, canyons and sandy bottoms make for a varied topography around the reef.

Hydrodynamics:

 

St Martin and the neighbouring islands are affected by The Antilles Current. The Antilles Current was named in 1876, and flows northward east of the Antilles joining the Florida Current past the outer Bahamas. Its waters are concentrated into a strong northward Jet about 80-100 km wide centred at 400 m (Lee et al., 1996).

Mooring studies have indicated that the Antilles has mean transport speeds of 3.2 Sv northwards in the upper 800m of water. In addition there is deeper flow from the Deep Western Boundary Undercurrent below 800 m carrying 33 ± 10.9 Sv southwards (Lee et al., 1996). The influence of this deep flow results in a large, mean southward transport for the entire water column.

Deeper, colder waters of the St Barthelemy Channel are through to have some influence on the envrironment and ecology of the Man O War Shoal Marine Park.

Lee, T. N., Johns, W. E., Zantopp, R. & Fillenbaum, E. R. (1996). Moored observations of western boundary current variability and thermohaline circulation 26.5°N in the subtropical North Atlantic. Journal of Physical Oceanography , 962-963.

 

 

Volcanic formations:

The near-by island of St Maarten has some old volcanic features, the centre of the island being mountainous with isolated peaks reaching 400m height.

Little is known about the volcanic influences on the geology in the Man O War Shoal Marine Park.

 

Sand dunes:

N/A

Underwater formations:

The main underwater formations are best described in relation to their dive site names;

In the boundaries of Man O War Shoal Marine Park, shallow spur and groove reefs can be found at ‘Spanish Rock’ (3-8m). At ‘Molly BeDay’ dive site a large rock and smaller boulders show considerable coral cover at depths down to 20m.  ‘Hen and Chick’ is a series of rocks with a mini sub-marine wall dropping down 20+m to a sandy bottom, giving the area the appearance of a crater.

The Maze reef offers some mini-cave diving where turtles, rays and large French Angelfish are common. Long submarine canyons run parallel to each other at depths of 20m at a site known as Time Tunnels,. The 'Alleys' is a series of rock formations with a cave at their base. Further south is 'Cable Reef' with more caves and an abundance of fish life.

‘Fish bowl’ reef is a coral garden. ‘Little Sister’ is a reef formation lying in +/-30m of water, in the middle of a large sandy area. A deep reef – ‘Isabella Reef’ lying in 35+m of water, is the home to large stingrays, Garden Eels (Heteroconger halis), lobsters and giant tube sponges.

A dive site known as ‘One Step Beyond’ is one of the larger patch reefs of St Maarten. Staghorn Coral and many other coral species are home to fish in large quantities. At +/-30m depth, barracuda, moray eels, turtles, and lobster can be found.

Others:

The monthly average sea surface temperature ranges from 25°C in January-March to 29°C in August-November. Visibility ranges from 15m to 30+m. There are usually two high tides and two low tides every day in St Maarten, with about six hours between high tide and low tide. The average tidal range is around 45cm.

St Maarten lies within the Northeast Trade Wind zone, which causes wind swell for much of the year. Waves produced by the wind are generally highest from June to July and from December to March when the wind speeds are highest. Wave direction varies according to the time of year. Waves approach from a predominantly easterly direction. For this reason, the waves are highest on the east or windward coasts (Man O War Shoal Marine Park is on the south east of the island) where average wave height is more than 1 m (3 ft). On the leeward coasts, average wave height is usually less than 0.3 m (1 ft). Wave energy is diffused to some extent by the shallower parts of the Proselyte Reef Complex.

Waves, known as ground swell are produced by low pressure weather systems at sea. The majority of these form in the Western Atlantic and send waves towards St Maarten through winter months. A result of swell, large waves may be seen breaking on the coast even on calm, sunny days in winter. During each winter season, there may be from five to ten swell events, each lasting from one to eight days. Research has also shown that intense winter swell activity often runs in cycles, several active years being followed by several less active years. The height of swell waves on a usually calm leeward coast may vary between 1 m and 3 m (3–10 ft), although occasionally they may be as high as 5 m (16 ft).