Intraspecific variation in the response of the estuarine European isopod Cyathura carinata (Krøyer, 1847) to ocean acidification.

In the present study the model isopod, Cyathura carinata were exposed to four pHNIST treatments (control: 7.9; 7.5, 7, 6.5) in order to determine the tolerance and pH threshold value this estuarine species withstand under future acidification scenarios. Seawater acidification significantly affected the lifespan of C. carinata, where population density was remarkably reduced at the lowest pH treatment. The longevity, survivorship and swimming activity (related to the acquisition of energy) of these isopods decreased with decreasing pH. Furthermore, to determine the possible metabolic plasticity of this species, the swimming activity, the Na+/K + -ATPase activity (relevant for osmoregulation process), and the RNA:DNA ratio (an indicator of fitness) were measure from two populations of C. carinata, one inhabiting a stable environment (pHNIST 7.5-8.0) and one inhabiting a fluctuating pCO2 regimes (pH 3.3-8.5) subjected to three pH treatments (7.9, 7.0 and 6.5). The population from high fluctuating pCO2 conditions showed capacity to withstand to pH 6.5, as well as higher longevity and metabolic plasticity, when compared with the population from the habitat with slight pCO2 variation. These results indicate that Cyathura population from stable environments could be vulnerable to ocean acidification because it could trigger detrimental effects on its survival energy budget, and growth. However, ocean acidification has limited effect on the energy budget and survival of C. carinata population from highly variable habitats, suggesting that they are able to cope with the elevated energy demand. The difference showed between populations is likely an indication of genetic differentiation in tolerance to ocean acidification, possibly attributable to local adaptations, which could provide the raw material necessary for adaptation to future conditions. In addition, our results suggest that when assessing marine crustacean responses to changing environments on a global scale, variability in population and metabolic responses need to be considered.

Lethal effects on different marine organisms, associated with sediment-seawater acidification deriving from CO2 leakage.

CO(2) leakages during carbon capture and storage in sub-seabed geological structures could produce potential impacts on the marine environment. To study lethal effects on marine organisms attributable to CO(2) seawater acidification, a bubbling CO(2) system was designed enabling a battery of different tests to be conducted, under laboratory conditions, employing various pH treatments (8.0, 7.5, 7.0, 6.5, 6.0, and 5.5). Assays were performed of three exposure routes (seawater, whole sediment, and sediment elutriate). Individuals of the clam (Ruditapes philippinarum) and early-life stages of the gilthead seabream, Sparus aurata, were exposed for 10 days and 72 h, respectively, to acidified clean seawater. S. aurata larvae were also exposed to acidified elutriate samples, and polychaete organisms of the specie Hediste diversicolor and clams R. philippinarum were also exposed for 10 days to estuarine whole sediment. In the fish larvae elutriate test, 100 % mortality was recorded at pH 6.0, after 48 h of exposure. Similar results were obtained in the clam sediment exposure test. In the other organisms, significant mortality (p < 0.05) was observed at pH values lower than 6.0. Very high lethal effects (calculating L[H(+)]50, defined as the H(+) concentration that causes lethal effects in 50 % of the population exposed) were detected in association with the lowest pH treatment for all the species. The implication of these results is that a severe decrease of seawater pH would cause high mortality in marine organisms of several different kinds and life stages. The study addresses the potential risks incurred due to CO(2) leakages in marine environments.

Improved sea-urchin embryo bioassay for in situ evaluation of dredged material.

Sediments usually contain many contaminants derived from human activities. In case of dredging activities, these sediment-bound contaminants arise following the excavation and remobilization of sediments. Previous studies have used different species of clam, crabs, lugworms, etc. for the evaluation of dredged material in situ, but there are not studies that use acute bioassays for these purposes. The sea-urchin embryo bioassay has been chosen to characterize biological effects in situ in two ports of the southwest of Spain, the Port of Huelva and the Port of Cadiz. The sea-urchin embryo bioassay has been adapted for in situ evaluation of seawater quality in coastal areas, however, they are necessary for further improvements to take into account differences of temperature between sites. This temperature variation is one of the principal reasons (other than pollution) of larval mortality and the slow down in the growth rate of the urchin. In the present study a bioassay was conducted in both field and laboratory conditions, in order to compare the effects in situ with the effects under controlled conditions of temperature, salinity and oxygen dissolved. Results showed a good correlation between samples obtained in situ and in the laboratory, but in the field the percentage of normal pluteus larvae is less than under laboratory conditions.