Biomineralization control related to population density under ocean acidification

Abstract

Anthropogenic CO 2 is a major driver of current environmental change in most ecosystems 1 , and the related ocean acidification (OA) is threatening marine biota 2 . With increasing pCO 2 , calcification rates of several species decrease 3 , although cases of up-regulation are observed 4 . Here, we show that biological control over mineralization relates to species abundance along a natural pH gradient. As pCO 2 increased, the mineralogy of a scleractinian coral (Balanophyllia europaea) and a mollusc (Vermetus triqueter) did not change. In contrast, two calcifying algae (Padina pavonica and Acetabularia acetabulum) reduced and changed mineralization with increasing pCO 2 , from aragonite to the less soluble calcium sulphates and whewellite, respectively. As pCO 2 increased, the coral and mollusc abundance was severely reduced, with both species disappearing at pH < 7.8. Conversely, the two calcifying and a non-calcifying algae * Corresponding authors: Stefano Goffredo -s.goffredo@unibo.it, Tel. +39 051 2094244, Fax +39 051 2094286.; Giuseppe Falinigiuseppe.falini@unibo.it, Tel. +39 051 2099484 . Author Contributions S. G., Z. D., and G. F. conceived and designed research. S. G., F. P., E. C., and B. C. collected the samples and performed the diving fieldwork. L. P., S. F., M. R., and G. F. performed the lab experiments. S. G., F. P., E. C., B. C., L. P., P. F., M. R., and G. F. analysed the data. All authors wrote the manuscript and participated in the scientific discussion. Competing Financial InterestsThe authors declare no competing financial interests. Europe PMC Funders GroupAuthor Manuscript Nat Clim Chang. Author manuscript; available in PMC 2015 January 01. Published in final edited form as:Nat Clim Chang. 2014 July 1; 4(7): 593-597. doi:10.1038/nclimate2241. Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts (Lobophora variegata) showed less severe or no reductions with increasing pCO 2 , and were all found at the lowest pH site. The mineralization response to decreasing pH suggests a link with the degree of control over the biomineralization process by the organism, as only species with lower control managed to thrive in the lowest pH.Several studies on the influence of pH on crystallography and texture of calcified regions are ex situ, short-term experiments on isolated organisms 5 , providing important information, but unrepresentative of natural ecosystems and failing to assess long-term effects 6 . There is a great need of long-term analyses on OA effects on marine ecosystems acclimated to high pCO 2 , as found around CO 2 vents. Vents are not perfect predictors of future oceans, owing to pH variability, proximity of unaffected populations, and co-varying environmental parameters 7 . However, vents acidify seawater on sufficiently large temporal and spatial scales to integrate ecosystem processes 6 , acting as "natural laboratories". In Papua New Guinea vents, reductions in coral diversity, recruitment, abundance, and shifts in competitive interactions are found 8 . I...

Ocean warming and acidification synergistically increase coral mortality

“…(ii) The net calcification rate of the symbiotic B. europaea was not affected by decreasing pH, regardless of temperature, while for the two asymbiotic species L. pruvoti and A. calycularis it was negatively affected by decreasing pH and increasing temperature, suggesting that B. europaea may be more tolerant to increasing acidity compared to the other two species. Investigations at Panarea3031 and Ischia CO 2 vents2971 have shown that at pH TS 7.8, an ecological tipping point occurs as corals and mollusks disappear below this threshold. Our in situ transplant experiment is in agreement with this tipping point as in most cases we reported the highest mortality and the lowest calcification rates at mean pH TS  ≤ 7.7.…”

“…Gross calcification rate (CaCO 3 production by the coral) of B. europaea transplanted at CO 2 vents off Ischia, decreased with increasing acidity when the water was warmest29. Moreover, B. europaea naturally occurring at a CO 2 vent off Panarea, under long-term exposure to acidic conditions, shows a significant decrease in population density and net calcification rate, accompanied by an increase in skeletal porosity, with increasing acidity3031. This suggests that OA could likely exacerbate the mass benthic mortality events already recorded in the warming Mediterranean Sea, making it crucial to study the possible interactive effects between increasing sea temperature and acidity on coral mortality and growth rates.…”

Ocean acidification bends the mermaid's wineglass

“…A previous study has shown A. acetabulum growing under high CO 2 lose their orderly aragonite crystalline structure and shift to amorphous carbonate [10]. We observed pitted imperfections on stems at elevated CO 2 levels, which could create microcracks that concentrate stress and lower a material's strength and stiffness [17].…”

“…Here, we used volcanic CO 2 seeps to assess the effects of chronic exposure to low calcium carbonate saturation on the calcified green alga Acetabularia acetabulum that persists across CO 2 gradients in the Mediterranean, albeit with changes in its biomineral composition [10]. Its common name, the mermaid's wineglass, aptly describes its morphology of a cup atop a long slender stem (figure 1a).…”

Historical baselines and the future of shell calcification for a foundation species in a changing ocean

“…All of these factors probably contribute to how a species modulates calcification internally (e.g. [14]). In general, available data suggest that considerable variation exists within and among taxa in their ability to calcify and/or survive under changing CO 2 regimes, but the causes of that variation remain poorly understood.…”