Can giant clam (Tridacna squamosa) populations be restored on Singapore's heavily impacted coral reefs?

1. Giant clams have been a sustainable resource for millennia, but unregulated harvesting has led to local extinctions within the Indo-Pacific region. Giant clam mariculture can produce large numbers of juveniles for restocking wild populations where natural recruitment is low or absent. 2. Singapore is surrounded by more than 60 small islands, many with fringing reefs. These reefs, however, experience increased turbidity and sedimentation resulting from massive coastal development projects and regular dredging of shipping lanes. 3. Seven reefs off Singapore's southern islands were surveyed (9670 m(2)) for giant clams. Also, an experiment was conducted to determine the growth of Tridacna squamosa reared in aquaria under three light treatments: similar to 50% ambient photosynthetically active radiation (PAR); similar to 25% ambient PAR; and similar to 12% ambient PAR. Finally, 144 clams (T. squamosa) were transplanted to four reefs around Singapore to study survival and growth in a heavily impacted environment. 4. A total of 23 adult clams from three species were found during the survey, representing a mean density of 0.24 per 100 m(2). Most clams were found at Raffles Lighthouse, Singapore's 'best' reef. No juvenile clams were encountered. In the aquarium experiment, clam growth was significantly different among the three light treatments, with growth greatest in the similar to 50% ambient PAR treatment. Of the 144 transplanted clams, 116 (80.6%) were recovered after 7 months. All specimens had increased in size, with growth rates among reefs ranging from 3.3 mm month(-1) (SD = 1.3 mm) to 4.8 mm month(-1) (SD 1.6 mm). 5. Results suggest that, despite high levels of sedimentation and turbidity on Singapore's reefs, giant clams can survive and grow well. Restocking efforts using maricultured clams may be effective