Reproduction, Growth and Biomineralization of Calcifying Marine Organisms and their Relationships with Environmental Parameters

Global climate changes, driven by increasing temperature and pCO2, negatively affect marine ecosystem and mainly calcifying organisms. The reproduction of the zooxanthellate coral, Balanophyllia europaea, varied significantly along a latitudinal gradient of temperature and solar radiation. The warmer populations showed a lower reproductive efficiency due to the inhibition of the zooxanthellae photosynthesis, leading less available energy for reproduction. On the contrary, the B. europaea population, naturally living along a pCO2 gradient, did not show differences in oocytes development, production and morphology, probably by reallocating additional energy due to increasing of photosynthetic efficiency of zooxanthellae under pCO2 conditions. Increasing pCO2 negatively influenced spermaries production and development in L. pruvoti, causing a delayed in fertilization process, probably due to the lack of zooxanthellae involving in a lack of additional energy available for coral. The effects of high temperature, pCO2 and their interaction were tested on two symbiotic tropical corals, Fungia granulosa (solitary) and Pocillopora verrucosa (colonial). F. granulosa showed negative effects only in interaction treatment, while P. verrucosa showed decreased photosynthetic efficiency, increased bleaching tissue and mortality in all treatments. The more sensitivity of P. verrucosa could be explained by lower tissue thickness, making it more exposed and vulnerable to external environmental conditions. To investigate the role of intra-skeletal organic matrix in coral biomineralization, four Mediterranean species with different trophic strategy and growth form were selected. B. europaea organic matrix presented stronger control and higher independence from the crystallization environment than the other corals. Shell features of clam Chamelea gallina varied along a latitudinal gradient of temperature and solar radiation. Shells from the warmest and the most irradiated population were ~30% lighter due to thinner and more porous shells. No variation was observed in shell polymorphism at the nanoscale level, indicating no effects of environmental parameters on its composition and crystallography.