The Moon Jellyfish (Aurelia aurita): A Prospective Pelagic and Estuarine Bioindicator
Abstract
Due in part to the complexity of scyphozoan life histories, slight changes in environmental factors can have an effect on fecundity, growth & development and population fluctuations. Anthropogenic activities have been suggested as a major cause of increases in gelatinous communities. In addition, jellyfish, like other aquatic organisms, are exposed to a host of chemical contaminants in the ambient environment. Heavy metals, such as copper, are a major anthropogenic pollutant found throughout aquatic ecosystems. However, there are few accounts of copper contaminant effects on scyphozoans in terms of biochemical markers, or reported differences of responses between polyps, larvae, and adult medusa. Additionally, there are few accounts of contaminant effects coupled with environmental changes, such as temperature, salinity or pH fluctuations. We explored a variety of biochemical markers and behavioral endpoints to evaluate Aurelia aurita as a novel bioindicator species when exposed to a range of copper concentrations (5-50 ppb), for 48 hrs, temperature increases (18 to 24.5°C over two hours) for 48 hrs., Cu concentrations of 10 ppb coupled with temperature increase (18 to 24.5°C over two hours) for 48 hrs and differences between different life history stages (polyps, ephyrae and medusae) exposed to a range of copper concentrations (5-50 ppb). Acute toxicity (mortality) effects were observed at 50 ppb Cu in medusae but no significant mortalities were observed in animals exposed to lower Cu concentrations. Aurelia aurita was very sensitive to Cu. Lysosomal destabilization was observed at 5 ppb Cu; and high mortalities, 100%, were observed after only 48-hour exposures to 50 ppb Cu. Significant changes in behavior responses were also observed, and there was a significant correlation between behavior and lysosomal damage. Low baseline levels of GSH, an important antioxidant, were found in both oral arm and bell tissues; low GSH levels could contribute to their high sensitivity. The greatest effects of temperature were reduced GSH levels, which in and of itself is problematic, but can also increase susceptibility to pollutants and other stressors. Relative sensitivities of life history stages showed clear differences between polyps, ephyrae and medusae. A. aurita medusae were actually more sensitive than the ephyrae or polyp stages, further highlighting this species’ high sensitivity to low levels of a common anthropogenic contaminant and establishes a framework of knowledge for using cellular biomarkers for jellyfish.