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Tridacna gigas (Cardiidae: Tridacninae) is the largest extant reef-associated bivalves that occur abundantly in the Indo-West Pacific Region. However, unregulated exploitation had caused localized extinction in many parts of its distribution range. In Palawan, the species was considered virtually extinct in the 1980s, and since then, no study has been done to monitor their status in the wild. In the absence of updated studies about T. gigas, we gathered information through field reports, key informants, and field visits. Within five months of data gathering, we recorded 97 empty shells (14 in pairs and 83 single shells) with 65.86 cm (range: 42-112 cm) average shell length, which were estimated to be from 5 to >76 years old. Most (78.36%) of the empty shells were used for decoration and landscaping. On the other hand, 29 live individuals with 73.69 cm (range: 42-109 cm) average shell length were estimated to be 5 to >76 years old. Tubbataha Reefs Natural Park and some island resorts harbored the highest number of live T. gigas. The presence of live T. gigas in these areas reflects years of effective management and the resorts’ essential contribution to resource conservation. These remaining live individuals could be used in breeding and restocking programs to restore their lost populations.

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In this study of marine bivalves and gastropods of Tubbataha Reefs Natural Park (TRNP), Palawan, Philippines, we photo-document 96 species, including 17 species of bivalves (in seven families), and 79 species of gastropods (in 29 families). Of these, 64 species (eight bivalves and 56 gastropods species) were new recorded from the park. The list also includes the seven species of giant clams which are protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and three nationally protected gastropod species (Cassis cornuta, Charonia tritonis and Tectus niloticus). Thirty-six species that were previously reported at the park were not found in this study, which suggests that there are at least 132 species of gastropods and bivalves at TRNP. Our observations were limited at intertidal and shallow subtidal reefs in the park, suggesting that the number of species in the list may rise with an extensive survey.

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Intentional release of wild-caught individuals has been widely used to establish new populations of the commercially valuable but threatened reef gastropod Trochus niloticus in oceanic islands. Is this also a viable strategy to enhance depleted populations of this species and other marine invertebrates? We monitored growth and survival of 765 translocated individuals and 486 in their original habitat for 5-9 months. Individuals translocated to a severely overexploited reef (mainland Palawan) grew 2-3 times faster than those at Tubbataha Reefs Natural Park, Phillipines. Despite variations in growth between the three sites, survival probabilities were consistently high, ranging between 0.77 and 0.92. So translocation is feasible, and sites at which a species has previously been found are likely to be suitable for their growth and survival. If site management can control over-fishing, this approach is likely to be a valuable tool for enhancing field populations of a large invertebrates like Trochus that have a short lived planktonic larva.

Hippopus porcellanus is a rare and heavily exploited giant clam species with limited distribution range in the Indo-West Pacific Region. Overharvesting has resulted in the localized extinction of H. porcellanus in the Philippines, but its populations appeared to have recovered in Tubbataha Reefs Natural Park (TRNP) after more than 20 years of protection. As one of the least studied giant clam species, the shell dimension-live weight relationships were determined. In addition, the growth parameters of H. porcellanus in TRNP were monitored with the mark-recapture method. All three shell dimensions of H. porcellanus were good estimators of live weight. The von Bertallanfy growth parameters K (0.29) and L∞ (29.24 cm) were determined on the basis of 80 marked individuals recaptured twice within 2.5 years. Nearly 90% of marked clams survived at the end of the study. Studies on aspects of biology of other giant clams species at the park is suggested.