The suitability of Mytilus edulis as proxy archive and its response to ocean acidification

Past climate changes can be used as indicators of future scenarios, however past climatic changes can not be directly observed. Therefore, the reconstruction of past abiotic conditions can approximated using chemical or isotopic proxies. These proxies can be measured in natural archives (e.g. bivalve shells and coral skeletons). One aspect of current climate change is the acidification of the oceans, a phenomenon caused by the oceanic uptake of anthropogenic CO2 and a resulting shift in the marine carbonate system. As a result of this, a drop of mean ocean surface pH by ~0.3-0.7 units can be expected until the year 2100. In relation to geological timescales this drop occurs very fast (~0.1-0.2 units per 100 years) and causes species specific reactions which are not fully studied yet. For example, elevated [CO2] disturbs the acid-base status of extracellular body fluids and the degree of disturbances depends on animals metabolic rates. Especially marine calcifying organisms are influenced in their ability to form CaCO3-shells and skeletons by this decline in pH. The blue mussel (Mytilus edulis) is an important calcifier in many marine ecosystems and in aquaculture.

Intrageneric variation in antipredator responses of coral reef fishes affected by ocean acidification: implications for climate change projections on marine communities

Our planet is experiencing an increase in the concentration of atmospheric carbon dioxide (CO₂) unprecedented in the past 800 000 years. About 30% of excess atmospheric CO₂ is absorbed by the oceans, thus increasing the concentration of carbonic acid and reducing the ocean’s pH. Species able to survive the physiological stress imposed by ocean acidification may still suffer strong indirect negative consequences. Comparing the tolerance of different species to dissolved CO₂ is a necessary first step towards predicting the ecological impacts of rising CO₂ levels on marine communities. While it is intuitive that not all aquatic species will be affected the same way by CO₂, one could predict that closely related species, sharing similar life histories and ecology, may show similar tolerance levels to CO₂. Our ability to create functional groups of species according to their CO₂ tolerance may be crucial in our ability to predict community change in the future. Here, we tested the effects of CO₂ exposure on the antipredator responses of four damselfish species (Pomacentrus chrysurus, Pomacentrus moluccensis, Pomacentrus amboinensis and Pomacentrus nagasakiensis). Although being sympatric and sharing the same ecology and life history, the four congeneric species showed striking and unexpected variation in CO₂ tolerance, with CO₂-induced loss of response to predation risk ranging from 30% to 95%. Using P. chrysurus as a model species, we further tested if these behavioural differences translated into differential ability to survive predators under natural conditions. Our results indicate that P. chrysurus larvae raised under CO₂ levels predicted by 2070 and 2100 showed decreased antipredator responses to risk, leading to a five- to sevenfold increase in predation-related mortality in the first few hours of settlement. Examining ocean acidification, along with other environmental variables, will be a critical step in further evaluating ecological responses to predicted climatic change.