Abstract
Abstract. An increasing number of studies are now reporting the effects of ocean acidification on a broad range of marine species, processes and systems. Many of these are investigating the sensitive early life-history stages that several major reviews have highlighted as being potentially most susceptible to ocean acidification. Nonetheless there remain few investigations of the effects of ocean acidification on the very earliest, and critical, process of fertilization, and still fewer that have investigated levels of ocean acidification relevant for the coming century. Here we report the effects of near-future levels of ocean acidification (≈−0.35 pH unit change) on sperm swimming speed, sperm motility, and fertilization kinetics in a population of the Pacific oyster Crassostrea gigas from western Sweden. We found no significant effect of ocean acidification – a result that was well-supported by power analysis. Similar findings from Japan suggest that this may be a globally robust result, and we emphasise the need for experiments on multiple populations from throughout a species' range. We also discuss the importance of sound experimental design and power analysis in meaningful interpretation of non-significant results.
Highlights
It is accepted that increasing atmospheric CO2 is causing reductions in oceanic pH – a process widely referred to as “ocean acidification”
Mean sperm swimming speeds were very similar at both pH levels
Power analysis showed that these tests had >80% power to detect a 5% change in percent motility
Summary
It is accepted that increasing atmospheric CO2 is causing reductions in oceanic pH – a process widely referred to as “ocean acidification”. Global ocean pH has fallen by an average of 0.1 pH units since the onset of the industrial revolution and several estimates show that oceanic pH could fall by ≤0.4 pH units by the year 2100 (Caldeira and Wickett, 2003; Raven et al, 2005; Blackford and Gilbert, 2007; IPCC, 2007) This results in decreases in the saturation states of calcite and aragonite, the two common crystalline forms of biogenic CaCO3. Extensive field observations from the US west coast have already found seasonal upwelling of undersaturated waters reaching the surface (Feely et al, 2008) The extent of this process in other parts of the world is currently unknown
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