Improving the quality of tridacnid clam juveniles through crossbreeding broodstock from different zones across the Spermonde Archipelago

Abstract

Tridacnid clam populations have declined, and they are considered as endangered. There is increasing concern over their status in the Spermonde archipelago, South Sulawesi, where some species can no longer be found, including larger species such as Tridacna gigas and T. derasa as well as the shallow-water clam Hippopus hippopus. This research aimed to produce high-quality juvenile tridacnid clams by crossbreeding distantly related broodstock from different zones as a contribution to the effective conservation of endangered species. The research was conducted in the Spermonde archipelago and at the Hasanuddin University Marine Station Hatchery in Barrang Lompo Island. Broodstock of T derasa and T. squamosa were collected from zones III and IV of the Spermonde Archipelago. Juvenile clam production followed established methods for inducing spawning and larval rearing through trocophore, veliger, and pediveliger stages to produce juveniles that were reared in land-based and ocean nurseries. Parameters measured were the juvenile survival rate and the quality of zooxanthellae (density, chlorophyll content, and mitotic index). Data were analyzed descriptively. The mean density of zooxanthellae in juvenile clams was 3.17 x 106 cells/ind (range 3.15x106 - 5.27x106 cells/in). The mean chlorophyll-a content of these zooxanthellae was 2.7 mg/m3 (range 1.1 mg/m3 - 4.1 mg/m3), which is consistent with the mean phaeopigment concentration of 5.5 mg/m3 (range 4.2 mg/m3 - 6.2 mg/m). The mitotic index peaked at 8.5% between 09:00 and 12:00.