MARINE BIOLOGICAL SURVEY OF THE PROPOSED DOCK SITE ...

-10sandy substratum. The genus ~olysiphonia (7% cover) was abundanton the coral rubbl~ interspersed among the sea-grasses. Microcoleuslyngbyaceus (3% cover), Halimeda opuntia (2% cover) and Caulerparacemosa (2 % cover) were the other conspicuous algae among the seagrasses.The sea-grasses also served as a substratum for severalof the filamentous-like alge, e.g .• Centroceras clavulatum, Champiaparvula, Spyridia filamentosa, Chondria sp., which grew epiphyticallyOn the blades.The only conspicuous alga in the San-Coral Zone (N = 55 tosses)was Polysiphonia (18% cover) which covered coral rubble. Although17 species of algae were recorded from this zone, the majority ofthe species were rare in this zone.The Lagoon Slope (N = 56 tosses) consisted primarily of coralrubble on which algal turf predominated. Polysiphonia spp. andMicrocoleus lyngbyaceus covered 21% and 4%, respectively, of therubble. In addition, the prostrate brown alga Lobophora variegata(2% cover) was evident.Among the live corals on a reef-flat platform across the studysite, six species of algae were observed - Caulerpa brachypus, ~.racemosa, C. verticillata, Halimeda macrophysa, Gelidiopsis intricataand Polysiphonia tepida. All species were previously observed inthe study site.Corals - The study area consists of a lagoon fringing reefsituated along the eastern side of Yap Island. The reef can bestructurally divided into a shallow reef-flat platform with relativelylittle surface relief and a lagoon slope which dips steeply downwardto the somewhat flattened lagoon floor of Tomil Channel. Based uponphysiographic origin and structure, substrate composition, andpresence of dominant floral and faunal elements the reef was dividedinto four zones as shown in Figure 1.The innermost part of the reef-flat platform consists of a sealevel erosional platform cut into metamorphic schistose rock. Theinner part is rather barren rock with a few scattered boulders hereand there and the outer part is thinly veneered by rubble and boulders.For the most part the zone is exposed during low tide and lacks coralgrowth.The central part of the reef-flat platform consists of a sandyflooredregion dominated principally by sea grasses, called theEnhalus-Thalassia zone. Corals are widely scattered and of smallsize in this zone with the total number of species observed on anytransect ranging from 3 to 4 (Table 2). The principal speciesencountered was Porites australiensis.