Anthropogenic CO2 emissions will lead to an increased ocean pCO2 level of possibly 1900 ppm in the year 2300. Previous studies depicted that bivalves might react very sensitively towards increased seawater pCO2 with decreased rates of calcification, metabolism and growth. In order to assess the impacts of simulated ocean acidification on a Baltic Sea M. edulis population, we simultaneously monitored heart rate variability, filtration and activity patterns, as well as extracellular acid base status and calcification.
Adult mussels were kept in flow through aquaria for two weeks at six different CO2 concentrations between 380 ppm and 4000 ppm. Mussels were fed continuously with a mixed phytoplankton concentrate. Measurements of heart rate, heart rate variability, valve and siphon opening revealed no effect of pCO2 on cardiac performance and activity, even though significant extracellular acid–base disturbances and decreases in calcification rate were recorded. Filtration rates, on the other hand, were significantly depressed at 4000 ppm. In an ongoing study, mussels are continuously being fed with Rhodomonas sp. at a concentration of 1000–4000 cells/ml in order to study filtration efficiency in more detail.
Physiological changes might not only affect the mussel’s health but the whole ecosystem, since filter feeding bivalves act as ecosystem engineers, not only changing the inorganic nutrient pool available to phytoplankton, but also producing faeces and pseudofaeces, which can reduce erosion by 10-fold in some areas. Being the dominant benthic invertebrate, dense mussel beds even provide an important settling ground for various other organisms.
Saphörster, J., Thomsen, J., and Melzner, F., 2009. Physiological performance of Baltic Sea blue mussels, Mytilus edulis, under CO2 induced stress: Cardiac performance, activity and filtration rate. Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology, 153(2): 59. Abstracts of the Annual Main Meeting of the Society of Experimental Biology, 28th June – 1st July, Glasgow, UK. Abstract.
