Effects of Reduced pH on Macoma balthica Larvae from a System with Naturally Fluctuating pH-Dynamics

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.

Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

“…In the natural environment, in coastal regions of mussel cultures such as the Baltic Sea, pH is highly variable (Jansson et al. 2013). The survival and development of the bivalve Macoma balthica (L.) is reduced when grown under severe reductions in pH (pH 7.2, 7.4, and 7.7) fluctuating in the natural Baltic Sea environment.…”

“…Although naturally subjected to highly variable temperatures, pH, and salinities, the additional impact of ocean acidification has severe implications for reduced survival and growth of M. balthica larvae (Jansson et al. 2013). Similarly, ocean acidification conditions impact shell shape and thickness of the M. edulis shells in this study.…”

“…In the natural culture environment of Loch Fyne and the Baltic Sea, salinity is highly variable due to freshwater input (Jansson et al. 2013). Salinity was relatively static with high salinities throughout the duration of the experiment.…”

“…The Baltic Sea and Loch Fyne have similar variability, as freshwater inputs into the catchments reduce the total alkalinity, pH, and carbonate concentrations, providing conditions consistent with early‐onset ocean acidification (Jansson et al. 2013). It has been reported that ocean acidification will impact not only growth but also the ultrastructure of mollusk shells (Dickinson et al.…”

Early Development of the Threespine Stickleback in Relation to Water pH

“…The current ocean acidification and change in the equilibrium of the seawater chemistry are so rapid that they will most likely lead to major changes in marine ecosystems and impact marine life (Pelejero et al, 2010). For more than a decade, the biological responses of phytoplankton (Lohbeck et al, 2012), foraminifera (Bijma et al, 2002), pteropods (Bednaršek et al, 2017), bivalves (Jansson et al, 2013), crustaceans (Vehmaa et al, 2013) and fish (reviewed by Clements and Hunt, 2015;Esbaugh, 2017) have been studied under different ocean acidification scenarios. Research suggests that mobile species, such as crustaceans and fish are less sensitive to acidification than sessile species, possibly due to their high metabolic rates and active regulation of internal pH (reviewed by Kroeker et al, 2013).…”