Recruits of the temperate coral Oculina arbuscula mimic adults in their resilience to ocean acidification

Ocean acidification has been investigated extensively in scleractinian corals, but studies on different life stages of the same species are lacking. We investigated the response of recruits of the temperate coral Oculina arbuscula to increased CO2 concentrations, a species whose adults show significant tolerance to elevated concentrations of CO2. Specifically, we exposed small colonies (5-12 mm diameter) to 475, 710, and 1261 ppm CO2 for 75 d in the laboratory to address the hypothesis that, like adults, the health of O. arbuscula recruits is not affected by increased CO2 concentrations. Calcification rates were monitored regularly during the experiment, while mortality, respiration rates, photosynthetic rates, algal symbiont densities, and soluble protein were quantified at the end. As predicted, CO2 concentration did not impact survival, algal densities, or soluble protein concentrations in O. arbuscula recruits. In contrast, both calcification rates and photosynthesis:respiration ratios tended to be lower at higher CO2. Comparing the results of this study on recruits with published studies on adults suggested that both life stages exhibit a similar non-linear response to CO2 concentration, whereby recruits may be unable to counter the increased energetic cost of calcification that occurs at the highest CO2. Based on these results and environmental monitoring showing that mean pCO2 is increasing by ~2.4% yr-1 in the waters off Georgia, USA, we conclude that O. arbuscula recruits may begin to exhibit depressed calcification rates within the current century if CO2 emissions are not reduced.

Patterns, dynamics and consequences of microplastic ingestion by the temperate coral, Astrangia poculata

Microplastics (less than 5 mm) are a recognized threat to aquatic food webs because they are ingested at multiple trophic levels and may bioaccumulate. In urban coastal environments, high densities of microplastics may disrupt nutritional intake. However, behavioural dynamics and consequences of microparticle ingestion are still poorly understood. As filter or suspension feeders, benthic marine invertebrates are vulnerable to microplastic ingestion. We explored microplastic ingestion by the temperate coral Astrangia poculata . We detected an average of over 100 microplastic particles per polyp in wild-captured colonies from Rhode Island. In the laboratory, corals were fed microbeads to characterize ingestion preference and retention of microplastics and consequences on feeding behaviour. Corals were fed biofilmed microplastics to test whether plastics serve as vectors for microbes. Ingested microplastics were apparent within the mesenterial tissues of the gastrovascular cavity. Corals preferred microplastic beads and declined subsequent offerings of brine shrimp eggs of the same diameter, suggesting that microplastic ingestion can inhibit food intake. The corals co-ingested Escherichia coli cells with microbeads. These findings detail specific mechanisms by which microplastics threaten corals, but also hint that the coral A. poculata , which has a large coastal range, may serve as a useful bioindicator and monitoring tool for microplastic pollution.