Abstract
Abstract. As a result of high anthropogenic CO2 emissions, the concentration of CO2 in the oceans has increased, causing a decrease in pH, known as ocean acidification (OA). Numerous studies have shown negative effects on marine invertebrates, and also that the early life stages are the most sensitive to OA. We studied the effects of OA on embryos and unfed larvae of the great scallop (Pecten maximus Lamarck), at pCO2 levels of 469 (ambient), 807, 1164, and 1599 μatm until seven days after fertilization. To our knowledge, this is the first study on OA effects on larvae of this species. A drop in pCO2 level the first 12 h was observed in the elevated pCO2 groups due to a discontinuation in water flow to avoid escape of embryos. When the flow was restarted, pCO2 level stabilized and was significantly different between all groups. OA affected both survival and shell growth negatively after seven days. Survival was reduced from 45% in the ambient group to 12% in the highest pCO2 group. Shell length and height were reduced by 8 and 15%, respectively, when pCO2 increased from ambient to 1599 μatm. Development of normal hinges was negatively affected by elevated pCO2 levels in both trochophore larvae after two days and veliger larvae after seven days. After seven days, deformities in the shell hinge were more connected to elevated pCO2 levels than deformities in the shell edge. Embryos stained with calcein showed fluorescence in the newly formed shell area, indicating calcification of the shell at the early trochophore stage between one and two days after fertilization. Our results show that P. maximus embryos and early larvae may be negatively affected by elevated pCO2 levels within the range of what is projected towards year 2250, although the initial drop in pCO2 level may have overestimated the effect of the highest pCO2 levels. Future work should focus on long-term effects on this species from hatching, throughout the larval stages, and further into the juvenile and adult stages.
Highlights
The increase of anthropogenic CO2 emissions since the industrial revolution has lead to an increase of carbon dioxide (CO2) concentration and a decrease in pH in the oceans termed as ocean acidification (OA)
The variation inpCO2 values given as the coefficient of variation (CoV), increased with increasingpCO2 levels, and was higher between days for replicates than between replicates on any day (Table 1)
The shell deformities we found in our control group may at least partly be a result of an already elevated CO2 level; future studies on P. maximus should include experimental groups kept in pre-industrial CO2 conditions to elucidate whether the ongoing OA already may have an impact on scallop larvae
Summary
The increase of anthropogenic CO2 emissions since the industrial revolution has lead to an increase of carbon dioxide (CO2) concentration and a decrease in pH in the oceans termed as ocean acidification (OA). Within less than 250 yr the ocean surface pH may drop as much as 0.7 units, which may be the lowest pH value experienced during the last 300 million years (Caldeira and Wickett, 2003). Depending on their distribution and habitats, marine organisms are exposed to various levels of pH fluctuations. In areas with natural high CO2 supply (upwelling of deep-sea CO2-rich water and volcanic CO2 vents) marine organisms are exposed to seawater CO2 values as high as 2000 ppm, corresponding to a pH of 7.4–7.5 (Hall-Spencer et al, 2008; Thomsen et al, 2010).
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