Embryotoxic effects of dissolved okadaic acid on the development of Longfin yellowtail Seriola rivoliana.

In the context of global climate change where harmful algal blooms (HABs) might become more frequent and more severe, several studies have been conducted on the perturbation of embryonic development of marine animals by microalgal toxins. Okadaic acid (OA) and analogs (DSP toxins) produced by dinoflagellates of the genera Dynophysis and Prorocentrum are known to disturb embryogenesis. This study investigated the impact of dissolved DSP toxin (OA and Dinophysistoxin 1, DTX-1) exposure on embryo development of Longfin yellowtail Seriola rivoliana. Eggs were exposed to different concentrations of dissolved DSP toxins (low treatment: at 120μgl-1 OA eq; high treatment 175μgl-1 OA eq.). The first objective was to study the global toxic effect of DSP toxins with hatching percentages. Secondly, the effect of these toxins was investigated at molecular and functional level by measuring expression of responsible genes for bone morphogenetic protein (BMP) and proliferating cell nuclear antigen (PCNA) measuring phosphatase enzyme (serine/threonine and alkaline phosphatases) activities. Our results showed drastic mortalities induced by DSP toxins in both low and high concentration treatments. Activities of both protein and alkaline phosphatases were significantly inhibited by DSP toxin treatments, whose effects on gene expression were less evident, but levels of BMP expression in eggs treated with the lowest toxin concentration were significantly different from that in the control treatment. This work revealed an embryotoxic effect of DSP toxins resulting in high mortality of eggs. Phosphatase inhibition could have participated in part in these global effects by perturbing the regulation of pathways related to embryogenesis and resulting in a perturbation of gene expression.