Reduced salinities negatively impact fertilization success and early larval development of the giant clam Tridacna gigas (Cardiidae: Tridacninae)

Abstract The increasing frequency and intensity of precipitation attributed to global climate change, in combination with sewage disposal, agricultural runoff, and other anthropogenic sources, could lead to a reduction in the salinity levels of shallow water reefs. Given that many reef animals including the giant clam exhibit a bipartite life cycle wherein fertilization and larval development take place in the water column prior to settlement, tridacnine early life stages are susceptible to reduced salinity levels. To investigate the impacts of reduced salinities on the early life stages of the giant clam, we exposed the gametes, embryos, and larvae of Tridacna gigas to salinities of 18, 22, 26, 30, and 34 ppt. Fertilization occurred in all treatments but was significantly reduced at 18 ppt. Lower salinity conditions resulted in delayed embryonic development, with fewer trochophore and veliger larvae at 18, 22, and 26 ppt. No larvae survived more than two days of exposure at 18 ppt and four days at 22 or 26 ppt. Salinity did not have a significant effect on pediveliger larvae settlement rate or shell length. This study shows that reduced salinity affects both the fertilization success and survival of developing tridacnine larvae, suggesting that intensified precipitation events could further inhibit the survival of giant clams on the reef.