Echinoderm larvae as bioindicators for the assessment of marine pollution: Sea urchin and sea cucumber responsiveness and future perspectives

Echinoderms play a crucial role in the functioning of marine ecosystems and due to their extensive distribution, rapid response, and the high sensitivity of their planktonic larvae to a large range of stressors, some species are widely used as biological indicators. In addition to sea urchins, sea cucumbers have recently been implemented in embryotoxicity bioassays showing high potential in ecotoxicological studies. However, the use of this species is still hindered by a lack of knowledge regarding their comparative responsiveness. The present study aimed to investigate the responsiveness of different echinoderm species to environmental pollution in order to develop their integration in batteries of ecotoxicological bioassays. To this end, the embryos of two sea urchins (Paracentrotus lividus and Arbacia lixula) and two sea cucumbers (Holothuria polii and Holothuria tubulosa) were incubated with inorganic and organic toxicants (cadmium, copper, mercury, lead, sodium dodecyl sulphate and 4-n-Nonhyphenol) and elutriates from contaminated marine sediments, chosen as a case study model. The results obtained, expressed through the percentage of abnormal embryos and Integrative Toxicity Indices (ITI), indicated species-specific sensitivities to pollutants, with comparable and correlated responsiveness between sea urchins and sea cucumbers. More specifically, sea cucumber larvae exposed to elutriates appear to be more sensitive than sea urchins, especially when incubated with samples containing trace metals, PCB and TBT. These results indicate that toxic responses in embryos exposed to environmental matrices are probably modulated by interactions between different variables, including additive, synergistic and antagonistic effects. These findings suggest that performing a larval test using different echinoderm classes can integrate the interactive effects of bioavailable fraction of contaminants on various levels, providing sensitive, representative and all year-round batteries of bioassays to apply in ecotoxicological studies.