Toxicity of the water-accommodated fraction of diesel on veliger stage larvae of the fluted Giant Clam (Tridacna squamosa)

Abstract

The giant clams (Tridacnidae) found in tropical coral reef ecosystems of the Indo-Pacific are considered endangered, with declining populations throughout most of their range. One anthropogenic impact which could have adverse effects on giant clam populations is hydrocarbon pollution. We conducted an acute toxicity test to assess the effect of the water-accommodated fraction (WAF) of diesel on the mortality, morphology, and behavior of fluted giant clam (Tridacna squamosa) veliger phase larvae. The D-veliger larvae (ten per experimental unit) were exposed to different concentrations of diesel (control, 0.1, 1, 2.5, 5, and10 ml L−1) using a 24-hr static nonrenewal test with four replicates per treatment. The 24-hr LC50 of diesel was 1.14 ml L−1 (CI: 0.65- 1.98 ml L−1) based on Finney’s Probit Method. There were no morphological abnormalities (shell deformation) detected at the concentrations tested. However, the expulsion of zooxanthellae was observed at the higher concentrations (2.5, 5, and 10 ml L−1), and the severity of this phenomenon increased in line with diesel concentration. The decreased density of zooxanthellae detected in some living veliger larvae could weaken the larvae and lead to increased mortality.