Ocean Acidification Reduces Growth and Calcification in a Marine Dinoflagellate

Abstract

Ocean acidification is considered a major threat to marine ecosystems and may particularly affect calcifying organisms such as corals, foraminifera and coccolithophores. Here we investigate the impact of elevated pCO2 and lowered pH on growth and calcification in the common calcareous dinoflagellate Thoracosphaera heimii. We observe a substantial reduction in growth rate, calcification and cyst stability of T. heimii under elevated pCO2. Furthermore, transcriptomic analyses reveal CO2 sensitive regulation of many genes, particularly those being associated to inorganic carbon acquisition and calcification. Stable carbon isotope fractionation for organic carbon production increased with increasing pCO2 whereas it decreased for calcification, which suggests interdependence between both processes. We also found a strong effect of pCO2 on the stable oxygen isotopic composition of calcite, in line with earlier observations concerning another T. heimii strain. The observed changes in stable oxygen and carbon isotope composition of T. heimii cysts may provide an ideal tool for reconstructing past seawater carbonate chemistry, and ultimately past pCO2. Although the function of calcification in T. heimii remains unresolved, this trait likely plays an important role in the ecological and evolutionary success of this species. Acting on calcification as well as growth, ocean acidification may therefore impose a great threat for T. heimii.

Constraints on the vital effect in coccolithophore and dinoflagellate calcite by oxygen isotopic modification of seawater

“…leptoporus (Ziveri et al, 2012;Van de Waal et al, 2013). The magnitude in 13 C/ 12 C fractionation is in agreement with the extremely light carbon isotope compositions observed by Zonneveld et al (2007).…”

Stable carbon isotope fractionation of organic cyst-forming dinoflagellates: Evaluating the potential for a CO2 proxy

“…For instance, based on culturing experiments, Burkhardt et al (1999a) investigated the effects of growth rate, CO 2 and cell size on 13 C fractionation in one dinoflagellate species and found a clear CO 2 -sensitivity. Similarly, CO 2 -dependent 13 C fractionation has been found in other both non-calcareous (Rost et al, 2006) and calcareous dinoflagellate species (Van de Waal et al, 2013). It has furthermore been shown that dinoflagellates possess effective carbon concentrating mechanisms (CCMs), including active uptake of both CO 2 and HCO 3 À .…”

A transcriptomic analysis of the response of the arctic pteropod Limacina helicina to carbon dioxide-driven seawater acidification

“…Moreover, it could drive reduced growth or the death of marine calcifiers in harsh acidic environments (Miles et al 2007; Van de Waal et al 2013). In particular, shelled pteropods have been considered to be sensitive to acidified seawater because of their highly soluble, thin, fragile, aragonitic shells.…”