The south-west coast of Curaçao (Netherlands Antilles) is lined by a rich fringing coral reef, the surface of which forms a submarine plateau mostly 30–100 m broad with a steep slope in front of it. Both plateau and slope are covered by rich living coral and algal communities. The zonation of coral, gorgonian, and algal species in two 5 m broad transects perpendicular to the coast line was investigated down to about 40 m depth (with a few observations down to 65 m), using a phytosociological method. Transect I (Figs. 1 and 2) was situated in a relatively sheltered bight, and transect II in front of a relatively exposed cape (Figs. 1 and 3). In transect II, water movement [as measured by Doty's (1971) diffusion factor] was appreciably higher than in transect I, at least down to a depth of about 20 m (Fig. 12). The following seven zonal communities were distinguished along both transects on the basis of cluster analysis and reef physiognomy: (1) the eulittoral Cyanophycean community; (2) the lower eulittoral community (characterized by algae such as Laurencia papillosa and Sargassum polyceratium); (3) the shallow reef community (depth c. 1–4 m, characterized by the corals Acropora palmata and Diploria clivosa); (4) the gorgonian community (depth c. 4–6 m, characterized by the gorgonians Pseudopterogorgia acerosa and P. americana); (5) the drop off community (depth c. 6–12 m, characterized by the coral Madracis mirabilis, the dominance of Montastrea annularis and the extremely sparse algal growth); (6) the roof shingle community on the upper part of the steep slope (depth c. 12–27 m, characterized by roof shingle-like corals such as Agaricia agaricites and the roof shingle-like forms of species such as Porites astreoides); (7) the deep algal community on the lower part of the steep slope (depth c. 27–c. 50 m, characterized by a conspicuous algal turf, possibly reflecting low grazing pressure at this depth, and by a more scattered growth of corals such as Agaricia lamarckii, A. grahamae and Madracis formosa). In the shallow reef, the crustose corallines Porolithon pachydermum, Lithophyllum daedaleum and L. intermedium were abundant. In the roof shingle community and the deep algal community, Hydrolithon boergesenii and Archaeolithothamnion dimotum abounded. An increasingly sparse algal turf occurred between 50 and 65 m, where it seemed to reach its lower limit. Light intensity amounted here to about 1% of the surface radiation. The lower limit of hermatypic coral and crustose coralline growth lies at c. 80–90 m, where light intensity is estimated to be c. 0.2% of the surface radiation, but this is also the lower limit of solid substrate which dips here into a sediment plain. Despite differences in water movement and the form of the profiles, the zonation patterns in both transects resembled each other to a high degree. The two transects differed mainly by differences in the quantitative development of structurally important corals in the upper 20 m of water which are more turbulent in transect II than in transect I. Thus, in transect II, the corals of the drop off community and the roof shingle community have developed impressive buttresses which are lacking in transect I. Such buttresses often occur in more exposed areas along the southwest coast of Curaçao.
SCUBA (open-circuit or unspecified)