Howe, PL 2013, 'Lethal and sub-lethal effects of contaminants on the zooxanthellate marine cnidarian Aiptasia pulchella', PhD thesis, Southern Cross University, Lismore, NSW.
Copyright PL Howe 2013
This study was conducted in response to the need for tropical marine species to be used in routine ecotoxicology and toxicological risk assessment. One group of organisms that is not currently represented in routine ecotoxicology is the ecologically- and economically-critical phylum, Cnidaria. The sea anemone Aiptasia pulchella is a zooxanthellate cnidarian found throughout tropical and sub-tropical oceans, and has frequently been used as a model organism in laboratory studies. However, this is the first study to investigate the sensitivity of A. pulchella and the associated zooxanthellae to a range of contaminants, determining the sensitivity of this species in ecotoxicological investigations.
Repeated 96-h lethal toxicity tests using cadmium, cobalt, copper, lead, nickel and zinc demonstrated good result repeatability and a high sensitivity of Aiptasia pulchella compared to many other tested marine species. ‘Severe’ tentacle retraction was identified as a common and rapid sub-lethal toxicological response and was further refined. Asexual reproduction by ‘pedal laceration’ was also observed and appeared to be inhibited by metal exposures. Subsequently, successful asexual reproduction was investigated as a potential chronic sub-lethal endpoint in 28-d static-renewal tests using cadmium, copper, cobalt, nickel and zinc. These tests showed that adult A. pulchella were able to asexually reproduce at metal concentrations where the offspring either did not survive, or where normal tentacle development was affected. Hence, ‘development to a juvenile stage’ was assessed as an additional sub- lethal endpoint in 14-d tests using the same metals as 28-d reproduction tests. Finally, zooxanthellate A. pulchella use in ecotoxicological testing allows investigations of contaminant effects not only on the animal host, but also on the associated zooxanthellae. This is important for toxicological risk assessment of contaminants such as herbicides that primarily affect photosynthetic organisms, including coral symbionts. The suitability of pulse amplitude modulated (PAM) chlorophyll a fluorometry for toxicological assessments of in-hospite zooxanthellae of A. pulchella was assessed in 48-h tests using the herbicides diuron and atrazine.
Overall, results show that Aiptasia pulchella and the associated zooxanthellae are sensitive to a range of contaminants relative to other tested marine organisms. Mortality and quantifiable sub-lethal effects occurred at relevant trace metal and herbicide concentrations in the context of the available marine toxicity data. Refinement and standardisation of the culturing and toxicity test methods for A. pulchella described throughout this thesis would make a valuable and much-needed contribution towards improving toxicological risk assessments and water quality guidelines for tropical marine ecosystems.