Abstract
Ocean acidification is causing severe changes in the inorganic carbon balance of the oceans. The pH conditions predicted for the future oceans are, however, already regularly occurring in the Baltic Sea, and the system might thus work as an analogue for future ocean acidification scenarios. The characteristics of the Baltic Sea with low buffering capacity and large natural pH fluctuations, in combination with multiple other stressors, suggest that OA effects may be severe, but remain largely unexplored. A calcifying species potentially affected by low pH conditions is the bivalve Macoma balthica (L.). We investigated larval survival and development of M. balthica by exposing the larvae to a range of pH levels: 7.2, 7.4, 7.7 and 8.1 during 20 days in order to learn what the effects of reduced pH are on the larval biology and thus also potentially for the population dynamics of this key species. We found that even a slight pH decrease causes significant negative changes during the larval phase, both by slowing growth and by decreasing survival. The growth was slower in all reduced pH treatments compared to the control treatment. The size of 250 µm that is considered indicative to imminent settling in our system was reached by 22% of the larvae grown in control conditions after 20 days, whereas in all reduced pH treatments the size of 250 µm was reached by only 7–14%. The strong impact of ocean acidification on larvae is alarming as slowly growing individuals are exposed to higher predation risk in response to the longer time they are required to spend in the plankton, further decreasing the ecological competence of the species.
Highlights
Anthropogenic emissions of carbon dioxide (CO2) are causing severe changes in the global inorganic carbon balance of the oceans [1]
Predicting the impact of OA on the early life stages is essential for estimating the true consequences of future and ongoing ocean acidification [15]
Our aim was to learn what the effects of reduced pH are on the larval biology and potentially for the population dynamics of M. balthica
Summary
Anthropogenic emissions of carbon dioxide (CO2) are causing severe changes in the global inorganic carbon balance of the oceans [1]. One third of the atmospheric CO2 is absorbed in the oceans due to the pCO2 difference in ocean surface and atmosphere This removal of CO2 from the atmosphere will help moderate future climate change [2], the reaction of excess CO2 in the seawater has severe effects on marine ecosystems [3,4]. A direct consequence of CO2induced ocean acidification (OA) is the reduction in carbonate ion concentration (CO322). This makes calcification, the building of calcium carbonate structures, one of the biological processes most sensitive to ocean acidification. Predicting the impact of OA on the early life stages is essential for estimating the true consequences of future and ongoing ocean acidification [15]. A reduced performance of the early-life stages is alarming as larvae are crucially important for sustaining viable populations, and a failure in their recruitment might lead to negative effects on the population
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