Adult Corals Are Uniquely More Sensitive to Manganese Than Coral Early-Life Stages

Bioindicator species of plastic toxicity in tropical environments

In French Polynesia, pearl farming represents the second economic resource of the country. The distinctive black pearls produced there are globally recognized and appreciated. However, pearl farms extensively use submerged plastic materials. Through gas chromatography coupled with tandem mass spectrometry detection (GC/MSMS) analysis, we were able to identify various POPs (Persistent Organic Pollutants) and additives released after 24 h of leaching into seawater from these "pearl plastics" composed of PE (Polyethylene) and PP (Polypropylene). Subsequently, we tested different concentrations of this plastic leachate on five tropical species commonly raised in the pearl and aquaculture sector in Polynesia: Pinctada margaritifera, Saccostrea cucullata, Holothuria whitmaei, Litopenaeus stylirostris, and Tripneustes gratilla. Monitoring the embryo-larval development of these organisms allowed us to establish a correlation between the decrease in the percentage of normal larvae and the plastic concentration. Through the use of regression models, the EC50 (Effective Concentration) of the plastic leachate for each species was determined, and demonstrated to range from 6.6 to 71.5 g/L, depending on the species. The most sensitive species was the black teatfish Holothuria whitmaei, a tropical sea cucumber used for the first time for ecotoxicological tests. The sensitivity of this species, its large distribution in tropical areas, and the various advantages presented by its cultivation make it an interesting bio-indicator species for monitoring plastic pollution in tropical lagoons.

Acute Toxicity Assays with Adult Coral Fragments: A Method for Standardization

Coral reefs are globally declining due to various anthropogenic stressors. Amongst those, chemical pollutants, such as pesticides from agricultural runoff, sewage or an overabundance of personal care products in coastal waters due to intense tourism, may be considered as a local stressor for reef-building corals. The extent to which such chemicals exhibit toxic effects towards corals at environmentally relevant concentrations is currently controversially discussed and existing studies are often based on varying and sometimes deficient test methods. To address this uncertainty, we adapted available methods into a reliable and comprehensive acute coral toxicity test method for the reef-building coral Montipora digitata. The toxicities of the four substances benzophenone-3 (BP-3), Diuron (DCMU), copper (Cu2+ as CuCl2, positive control) and dimethylformamide (DMF, solvent) were assessed in a 96 h semi-static test design. Endpoints such as maximum quantum yield, bleaching, tissue loss and mortality were evaluated with respect to their suitability for regulatory purposes. Overall, the endpoints bleaching and mortality yielded sensitive and robust results for the four tested substances. As the test method follows the principles of internationally standardized testing methods (ISO, OECD), it can be considered suitable for further validation and standardization. Once validated, a standardized test method will help to obtain reproducible toxicity results useful for marine hazard and risk assessment and regulatory decision making.

Acute and chronic toxicity of manganese to tropical adult coral (Acropora millepora) to support the derivation of marine manganese water quality guideline values

Adult corals are among the most sensitive marine organisms to dissolved manganese and experience tissue sloughing without bleaching (i.e., no loss of Symbiodinium spp.) but there are no chronic toxicity data for this sensitive endpoint. We exposed adult Acropora millepora to manganese in 2-d acute and 14-d chronic experiments using tissue sloughing as the toxicity endpoint. The acute tissue sloughing median effect concentration (EC50) was 2560 μg Mn/L. There was no chronic toxicity to A. millepora at concentrations up to and including the highest concentration of 1090 μg Mn/L i.e., the chronic no observed effect concentration (NOEC). A coral-specific acute-to-chronic ratio (ACR) (EC50/NOEC) of 2.3 was derived. These data were combined with chronic toxicity data for other marine organisms in a species sensitivity distribution (SSD). Marine manganese guidelines were 190, 300, 390 and 570 μg Mn/L to provide long-term protection of 99, 95, 90, and 80 % of marine species, respectively.