Coral Rubble Flats, Algal & Gorgonian Pavements

DRAFTING…

“Coral Rubble Flats” existed in the shallower water at Bath in 1969, and were still present in, superficially at least, the same condition and location in subsequent years. Seagrasses are absent except for occasional occurrence of T. testudinum in tide pools within the Flats, hence  the Coral Rubble Flats were not identified  in the Bath seagrass maps of Patriquin (1971, 1975).. Nor were areas of “Algal Pavement”. The approx. areas of Coral Rubble flats and Algal Pavement are inserted as shown below:

Coral Rubble Flats similar tho those at Bath  occur elsewhere on the east coast of Barbados:    Lewis (1960) referred to them as “extensive reef flats”:

Extensive reef flats, 100 to 200 meters wide, front sand beaches and escarpments of the windward coast. These are formed of coral rock. They are covered by about a foot of water at mean low tide and are sometimes exposed along their inner edges at low water spring tides. A heavy cover of attached Sargassum sp. is present along the outer edge and the flats are subject to heavy wave action, for at high tide long “rollers” pour over it continuously.

A few species of corals are found on the flats. At the inner edge around the bases of holes and tide pools small colonies of Porites divaricata, Siderastrea radians, Favia fragum, and Porites astreoides occur. – from  p 1141 The Coral Reefs and Coral communities of Barbados, W.I., by J.B. Lewis in Canadian Journal of Zoology  38(6): 1133-1145, 7 Plates

Beyond the seagrass at Bath and leading out past “The Platform” (Rocks at MLW level and Rocks above HWS in Map 1 above), is hard bottom; it was mapped Bratwaite & Oxenford (2008, p. 36) who described it  as “Algal Pavement”  extending in deeper water to “Gorgonian Pavement“.

The powerful, rolling ocean waves and crashing breakers of the east coast provide a high energy and formidable undersea environment. These waves, coupled with continued re-suspension of eroded clays brought down by rivers from the Scotland District, mean that few corals exist anywhere offshore between Bathsheba and Gay’s Cove. At Cattlewash and Bathsheba huge boulders of Pleistocene limestone, the work of long dead corals, take a battering in the breaker zone. Further south at Bath and Conset, a shallow coastal lagoon is protected on its seaward side by a reef crest made up of coral rock boulders, supporting a few colonies of fire coral, brain corals and an abundance of macroalgae. Beyond this and stretching some distance offshore is an algal and gorgonian pavement.

The Algal Pavement extending in deeper water to Gorgonian Pavement of Bratwaite & Oxenford (2008) seems to correspond location-wise to benthic habitat classified as “Mixed Reef Hard Ground” by Baldwin et al., (2019):

Name: Mixed reef hard ground. Code: MRHG.  General Description: Usually on flat pavement with sand veneer or rubble. Diverse dense community – usually gorgonian or seafan dominated but other classes (hard coral, sponges, macroalgae) may be equally or almost as dominant.

Lewis (1960) provides this description”

Along the outer edge of the flats the water deepens to 8 to 10 ft or drops sharply to about 60 ft. Vertical sides are thus formed which face directly into the prevailing wind. Strong alongshore currents prevail and the water is heavily laden with sediment. Visibility is limited to less than 10 ft during most of the year. The vertical faces are deeply undercut with deep caves penetrating far into the rock and large block and debris falls are found at their bases. The most characteristic feature of the zone seaward of the reef flat is the complete absence of branching corals. Furthermore, the massive species I such as Montastrea, Siderastrea, and Diploria do not form rounded heads but are encrusting and flattened. At the outer edge of the reef, from depths of 8 or 10 f t to 60 ft, and 011the sides of the vertical walls, the following species occur: Less than 50% of the surface area of the reef rock is covered with living coral. Of the other invertebrate members in the community, Millepora forms low, stoutly branching colonies. The sea urchin, Diadema antillarum, is conspicuously absent. There are a number of alcyonarians present of which the commonest is the sea fan, Rhipidigorgia flabellum. It forms small colonies with a broad base.

This area of Algal Pavement in Map 1  is very turbulent and hard to visit/examine in detail most of the time. In relation to Lewis’s (1960) description, in 1994 I observed a large colony of Acropora palmata on the algal pavement at about 1.5 m depth at Low Water (see “X” in Map 1 above).  The area that is very roughly between 0.5 and 1 meter depth (MLW) in Map is where in 1968/9 I observed many rhodoliths. Closer to shore, over the outer seagrass bed area (of 1969), detached, healthy appearing sea fans are common.

Photos at Bath (Mar 2, 2025)
View Historical Imagery: Bath 2024 & 2025 for details.
Click on images for larger versions.

Map showing Photo Survey Route on Mar 2, 2025. Google Earth image is for June 9, 2021. The Coral Rubble flats occur in the sandy colored area. Pos’n 1(photo 113) is at approx the NNW limit and Pos’n 2 (photo 12o) 10-15 m from the NE limit of the Coral Rubble Flats.

113gps

114

117

Coral Rubble Flats: On their occurrence globally and the binding agents