Evaluation of Bioassays to Monitor Surface Microlayer Toxicity in Tropical Marine Waters

Abstract.

Bioassays were developed, using embryos of: coral, Montastraea faveolata; graysby, Epinephelus cruentatus; grouper, Epinephelus adscensionis x gruttatus (hybrid); queen conch, Strombus gigas; rock-boring urchin, Echinodermata lucunter; spotted seatrout, Cynoscion nebulosus; variegated urchin, Lytechinus variegatus; winged pearl oyster, Pteria colymbus; and yellowtail snapper, Ocyurus chrysurus. Relative sensitivities and precison of various species-endpoint combinations were evaluated using three reference toxicants: copper, sodium dodecyl sulfate, and Dibrom®. The 24-h P. colymbus embryo test had the best overall sensitivity and exhibited a high degree of precision. However, oyster embryos were difficult to obtain and did not aggregate at the air–water interface. Therefore, the P. colymbus embryo test was deemed unsuitable for use as a bioassay for monitoring sea-surface microlayer (SSML) toxicity. Tests based on normal development of L. variegatus to the early pluteus 3 stage and percent normal-live C. nebulosus larvae at 48 h were relatively sensitive and exhibited good replicability and repeatability. The L. variegatus urchin embryo test was also found to be highly reproducible. The results of this comparative study indicated that L. variegatus and C. nebulosus were suitable surrogates for coral-reef species in toxicity assessments of the SSML.