Science Diliman, Vol 17, No 2 (2005)

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Focal Benthic Mollusks (Mollusca: Bivalvia and Gastropoda) of Selected Sites in Tubbataha Reef National Marine Park, Palawan, Philippines

Roger G. Dolorosa, Sabine Schoppe

Abstract


The study was conducted at Tubbataha Reef National Marine Park from May 6-11, 2005. Seven preestablished stations with survey sites at 5 and 10 m depth and one intertidal area were assessed using 150 m permanent belt transects. Focal benthic mollusks found one meter to the left and right of transects were identified and counted. A total of 19 species belonging to eight families were recorded, of which 15 species are univalves. In the intertidal area a total of 12 species were noted, 13 species at the shallow (5 m) and five species at deeper (10 m) areas. Species belonging to the family Tridacnidae and Trochidae were the most abundant. Among the subtidal stations, the highest number of individuals was noted at a shallow reef flat (station VI). In terms of density, the intertidal area had the highest (213,310 ind. km-2) followed by the shallow (72,870 ind. km-2) and the deep with 5,720 ind. km-2.

The densities of Tridacna crocea (133,330 ind. km-2) and Hippopus hippopus (3,330 ind. km-2) at the intertidal area were found to be higher than in most other survey sites in Palawan but previous density records at the park indicate a stiff decline. On the contrary, the first record on the density of T. squamosa (950 ind. km-2) at the park is much lower compared to that from other parts of Palawan. Large and commercially valuable gastropods like, Trochus niloticus, Tectus maculatus and T. pyramis that are rarely encountered at the intertidal areas were abundant at the TRNMP. Other important species like Tridacna gigas, Charonia tritonis and Cassis cornuta were not encountered at the study sites. To fully assess the abundance of focal mollusks, permanent transects should be established in the same seven sites but in shallow reef flat of about 2 m deep, in the lagoon and in the intertidal of North and South Islets where species composition, density and growth could be monitored on an annual basis which could be used to evaluate the management effectiveness at the TRNMP.

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