Occurrence of okadaic acid in the feeding grounds of dugongs (Dugong dugon) and green turtles (Chelonia mydas) in Moreton Bay, Australia

Abstract

Okadaic acid (OA) is a diarrhetic shellfish poison (DSP) produced by a number of marine organisms including the benthic dinoflagellate Prorocentrum lima, which are often found on seagrass. As seagrass forms the basis of the diet of dugong (Dugong dugon) and green turtle (Chelonia mydas), these herbivores may potentially be exposed to OA through ingestion of P. lima found on the seagrass. In this study, the abundance of epiphytic P. lima, on seagrass, and the concentration of OA produced by these epiphytic dinoflagellates was measured in Moreton Bay, Queensland, Australia. P. lima and OA were found on all four species of seagrass collected. OA was detected in epiphytic material collected from seagrass, with a maximum of 460 ng OA/kg(wwtSG) found on Halophila spinulosa. From this information, the estimated maximum daily intake (DI) of OA by an adult dugong consuming 40 kg(wwtSG)/day was 18,400 ng/day, and an adult turtle consuming 2 kg(wwtSG)/day was 920 ng/day. Analysis by HPLC/MS/MS of 54 stranded dugongs and 19 stranded turtles did not yield OA above the detection limit of 10,000 ng/kg(animal tissue). OA was found on seagrass, however it was not detected in the tissue samples of dugongs and turtles.