An Investigation of the Effects of Ocean Acidification on Larval Development, Juvenile Settlement and Mortality, Growth, Onset of Egg Production, Shell Integrity and Feeding Activity in the Common Barnacle Amphibalanus amphitrite

Abstract

Ocean acidification is of great concern among the scientific community and is caused by the anthropogenic release of CO₂ from the burning of fossil fuels. Higher levels of atmospheric CO₂ are anticipated to cause a decrease in oceanic pH. Recent studies have shown that this can have adverse effects on a variety of marine organisms; calcified organisms are predicted to be the most heavily affected and of these types of organisms, barnacles have received little attention.

The barnacle Amphibalanus amphitrite was utilized to examine the effects of Ocean acidification across various life history stages. No adverse effects of reduced seawater pH (7.4) were found upon larval condition, cyprid size, cyprid attachment and metamorphosis juvenile-to-adult growth, and egg production. However, barnacles exposed to acidified water had significantly larger basal shell diameters than those developing in ambient pH (8.2) seawater, suggestive of compensatory hypercalcification. Furthermore, the force required to remove the barnacles from their substrate was significantly greater in the acidified than in the non-acidified group. Comparisons of ash content in basal shells show significantly more ash in the acidified group, further confirming our observation of compensatory calcification. Despite this finding, penetrometry revealed that the central wall plates of barnacles exposed to acidified seawater were significantly weaker than individuals in ambient seawater. Thus ecologically, weaker shells could reduce the resistance of barnacles to crushing predators. Prey feeding rates of near adult sized barnacles were significantly lower for those in acidified seawater versus those held in ambient seawater and an analysis of the mechanism behind reduced prey capture determined that cirral beat frequency when feeding did not differ significantly between the two treatment groups. Overall, these findings indicate that reduced energy acquisition and dissolution of shells under reduced pH may play an important role in the lack of wall shell maintenance observed under conditions of ocean acidification.

Keywords: Ocean acidification barnacle life history feeding behavior