Comparative effects of seawater acidification on microalgae: Single and multispecies toxicity tests

Highlights

• Different responses were observed depending on the species.
• In this work N. gaditana was the most sensitive species to low pH.
• Effects of competence among species were observed in the multispecies control (pH 8.0).
• Effects of competence were eclipsed by the CO2 effects on cultures exposed to pH 6.0.

Abstract

In order to gain knowledge about the potential effects of acidification in aquatic ecosystems, global change research based on microalgae as sentinel species has been often developed. However, these studies are limited to single species tests and there is still a knowledge gap about the behaviour of microalgal communities under this environmental stressor. Thus, the aim of this study was to assess the negative effects of CO2 under an ecologically realistic scenario. To achieve this objective, two types of toxicity tests were developed; i) single toxicity tests and ii) multispecies toxicity tests, in order to evaluate the effects on each species as well as the interspecific competition. For this purpose, three microalgae species (Tetraselmis chuii, Phaeodactylum tricornutum and Nannochloropsis gaditana) were exposed to two selected pH levels (7.4, 6.0) and a control (pH 8.0). The pH values were choosen for testsing different scenarios of CO2 enrichment including the exchange atmosphere-ocean (pH 7.4) and natural or anthropogenic sources of CO2 (pH 6.0). The effects on growth, cell viability, oxidative stress, plus inherent cell properties (size, complexity and autofluorescence) were studied using flow cytometry (FCM). Results showed that T. chuii was the most resistant species to CO2 enrichment with less abrupt changes in terms of cell density, inherent cell properties, oxidative stress and cell viability. Although P. tricornutum was the dominant species in both single and multispecies tests, this species showed a higher decrease in cell density under pH 6.0. Effects of competence were recorded in the multispecies tests (pH 8, control) but this competence was eclipsed by the effects of low pH. The knowledge of biological interactions made by different microalgae species is a useful tool to extrapolate research data from laboratory to the field.

Bautista-Chamizo E., Sendra M., de Orte M. R. & Riba I., in press. Comparative effects of seawater acidification on microalgae: Single and multispecies toxicity tests. Science of the Total Environment. Article (subscription required).

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Ocean acidification in the IPCC AR5 WG II

OUP book