The paper describes the diversity and structural complexity of mangrove forest along Puerto Princesa Bay, Palawan Island, Philippines. Occurrence of 28 mangrove species and 11 floral associates were found, which identifies the entire bay as one of the most diverse mangrove forests in the country. Of the six coastal barangays surveyed, San Pedro had the highest diversity index, H′=0.912 while Sta Monica had the lowest, H′=0.349. Mangrove stands are structurally simple with two types of vegetation, fringe and riverine that further constitute five distinct mangrove zones named according to dominating species, Rhizophora-Sonneratia; Rhizophora-Sonneratia-Lumnitzera; Rhizophora-Lumnitzera-Xylocarpus; Rhizophora-Xylocarpus; and Rhizophora-Avicennia. Commonality among these zones is obvious as revealed in Bray-Curtis cluster analysis. Structural features differed across zones. Trees of larger dbh, 104.5cm and higher species richness, a total of 15 species, were found in zone 1 while those that comprised the highest basal area, 438m−2ha−1 and density, 8100ha−1 from zones 2 and 4, respectively. Zones 1 and 4 are fringing mangrove forests. Degrees of perturbations greatly depend on human access to mangrove areas. Garbage dumping, occasional cutting of trees, soil erosion, and encroachment of human settlers were identified as potential threats to mangrove forest along the bay

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.

The crocus clam Tridacna crocea, one of the seven known giant clam species in the Philippines (Poutiers 1998), is widely distributed in the IndoPacific Region but is possibly extinct in Guam and Northern Mariana Islands (IUCN 2014). In the Philippines, the exploitation of all giant clam species is prohibited under Fisheries Administrative Order No. 208, series of 2001 (DA 2001). However, illegal exploitation of giant clams in many parts of the country has greatly reduced natural stock populations (Gomez and MingoaLicuanan 2006; Gonzales et al. 2014; Picardal and Dolorosa 2014), and only in marine protected areas such as Tubbataha Reefs Natural Park (TRNP) where high densities (100-220 ind.100 m-2) of T. crocea (Calumpong and Cadiz 1993; Ozoa 1995; Dolorosa and Schoppe 2005) have been reported. Methods to quantify the abundance of this species involved the use of either belt transect with 1 x 1 m quadrat placed every 10 m or 2 x 100 m belt transect. No data are so far available on the density of T. crocea embedded in coral rocks exposed at low tide. To quantify the abundance of T. crocea in massive corals with heads exposed at low tide, some exposed corals near the vicinity of the Ranger Station of TRNP were randomly sampled in June 2010. The area of coral heads was measured by using a quadrat and then by measuring the shell lengths of T. crocea with calipers (Figure 1). Among the ten coral heads surveyed (area =40.75 m2), a total of 236 T. crocea was noted. The densities of T. crocea ranged from 200-2,200 ind.100 m-2 with an average (±sd) of 767 (±559) ind.100 m-2 (Table 1). The sizes of T. crocea varied between 10-135 mm with an average (±sd) shell length of 67.67 (±32.26) mm (Figure 2). Tridacna crocea can attain 150 mm maximum shell length but commonly 110 mm (Poutiers 1998). There is no available literature on the size at which T. crocea becomes sexually mature, however, if T. crocea begins to reproduce after attaining nearly 40% (60 mm) of its maximum shell length (150 mm) as recorded for Tridacna maxima by Jameson (1976), then at least more than half (57%) are sexually mature. About 14% of samples were very small (10-29 mm) and such may indicate a self seeding reef. These high densities of T. crocea could be due to the manner of survey which only accounted for the coral heads exposed at low tides. In 2009, a survey involving 40 transects (20 x 2 m) in the surrounding reefs within the Ranger Station of TRNP recorded an average density of 39.25 ind.100 m-2 (range: 3.13-126.25 ind.100 m-2 (Dolorosa unpublished data). Previous densities obtained along the transect lines at intertidal (13 ind.100-2m) and 5 m deep (3 ind. 100-2 m) areas of the park (Dolorosa and Schoppe 2005) were lower than the present data. Lower densities (31 ind.100-2 m) were also recorded using transect surveys in Apulit Island, Taytay, Palawan (Gonzales et al. 2014) and many other areas of the Philippines (see bin Othman et al. 2010). Much lower were the densities in Seribu Island (2.80 ind. 100 m-2) and Manado Waters, Indonesia (0.85 ind. 100 m-2) (Yusuf et al.2009), and in intertidal (0.037 ind. 100 m-2) and subtidal (0.027 ind. 100 m-2) reefs of Singapore (Neo and Todd 2012). Giant clams are important component of the reef ecosystems. Their ecological roles have recently been reviewed and quantified which include their capacity to promote a balanced reef ecosystem (Neo et al. 2015). Any reef restoration project should therefore at least include the revival of giant clam populations. The current higher abundance of T. crocea within the Ranger Station of TRNP therefore requires effective protection, as the park represents an important natural genetic bank and seed source for clamdepleted reefs within its vicinity and other reefs in the Sulu Sea.

The high demand for shells of the large reef-associated gastropod Trochus niloticus in the manufacture of mother-of-pearl buttons has resulted in a widespread decline of its population. As a consequence, juvenile mass production and restocking has been practiced as one of the many conservation measures. Trochus has long been successfully bred in captivity, but culturing of juveniles until ready for release is faced with many problems, including the shortage of natural food. Terrestrial plants have traditionally been used by fishermen as food in keeping wild trochus juveniles, but their potential use in intermediate culture of trochus has not been evaluated. We conducted four growth trials for 60–120 days, rearing hatchery-produced juveniles (10–28-mm shell diameter) at different stocking densities in indoor tanks and sea cages, with coconut leaves as the main or an additional substrate. An average growth rate of 4.4 mm mo⁻¹ (95% CL 4.0–4.7 mm mo⁻¹) for all stocking densities was achieved in growth trials using small cages deployed at 5–6 m on the reef slope, which was comparable to growth rates in the wild. This growth rate was three times higher than in trials using large metal cages on the reef slope, and 2 to 23 times higher than indoor trials using wooden tanks or small cages in concrete tanks. Survival rates were as high as 99%. Incidence of escape in sub-tidal cages was low except when some cages were damaged by strong waves. The results indicate that trochus juveniles can be successfully cultured at high density in sub-tidal cages with coconut leaves as substrate.

“For more than two decades, the Philippine government has protected the giant clams (Bivalvia: Cardiidae: Tridacninae) from exploitation and trade. However, there still is lack of information on the impact of these protective measures in conserving the species richness and density, especially in Palawan, the country’s last stronghold of these reef-associated bivalves. Hence, to assess the species richness and density of giant clams in Palawan, we conducted 57 photo-transect surveys in six sites covering 12,325 m ². Out of these transect, 15 measured 5 × 25 m and the rest measured 5 × 50 m. For historical trends in the population of giant clams in Palawan, we used six published papers obtained from online platforms, 13 reports, and five undergraduate theses archived in local libraries. Information derived from recent field surveys indicated high variations in species richness (2 to 5 species) and densities (0.1 to > 3.6 ind.100 m ^-2). Historical data starting from 1984, including recent fieldwork, indicated very low densities and a declining trend. The current status suggests that giant clam populations’ viability and the reefs’ health are threatened. Effective mechanisms are needed to safeguard and enhance the remaining giant clam populations.”

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.