Sour times: seawater acidification effects on growth, feeding behaviour and acid–base status of Asterias rubens and Carcinus maenas

Abstract

The impact of seawater acidification on calcifying organisms varies at the species level. If the impact differs between predator and prey in strength and/or sign, trophic interactions may be altered. In the present study, we investigated the impact of 3 different seawater pCO 2 levels (650, 1250 and 3500 µatm) on the acid -base status or the growth of 2 predatory species, the common sea star Asterias rubens and the shore crab Carcinus maenas, and tested whether the quantity or size of prey consumed is affected. We exposed both the predators and their prey, the blue mussel Mytilus edulis, over a time span of 10 wk and subsequently performed feeding experiments. Intermediate acidification levels had no significant effect on growth or consumption in either predator species. The highest acidification level reduced feeding and growth rates in sea stars by 56%, while in crabs a 41% decrease in consumption rates of mussels could be demonstrated over the 10 wk experimental period but not in the subsequent shorter feeding assays.Because only a few crabs moulted in the experiment, acidification effects on crab growth could not be investigated. Active extracellular pH compensation by means of bicarbonate accumulation was observed in C. maenas, whereas the coelomic fluid pH in A. rubens remained uncompensated. Acidification did not provoke a measurable shift in prey size preferred by either predator. Mussels exposed to elevated pCO 2 were preferred by previously untreated A. rubens but not by C. maenas. The observed effects on species interactions were weak even at the high acidification levels expected in the future in marginal marine habitats such as the Baltic Sea. Our results indicate that when stress effects are similar (and weak) on interacting species, biotic interactions may remain unaffected.

Salinity dependence of recruitment success of the sea star Asterias rubens in the brackish western Baltic Sea

“…Other stressors that will concomitantly increase pressure on marine organisms, such as warming and ocean acidification (e.g. Appelhans et al 2012), might additionally impact the fitness of A. rubens in the area.…”

Predicting the Effects of Ocean Acidification on Predator-Prey Interactions: A Conceptual Framework Based on Coastal Molluscs

“…This may serve to increase the predation rates across a range of consumer types. In contrast, OA could also result in metabolic depression in those predators that are unable to regulate intracellular pH, which could lead to decreased feeding rates among some species (Rosa and Seibel, 2008;Appelhans et al, 2012). Generally, highly active, mobile species are more capable of regulating their acid-base balance (e.g., fishes, brachyuran crustaceans, but see Rosa and Seibel, 2008) than more sedentary species (Pörtner, 2008;Melzner et al, 2009).…”

Ammonia excretion in mytilid mussels is facilitated by ciliary beating

“…At the same time, this water flow provides transport of aerated high P O2 and low P CO2 and P NH3 water to the animal. Furthermore, fish and crustaceans exposed to high environmental TAM or elevated P CO2 attempt to actively maintain blood and haemolymph TAM concentrations and pH despite changing external conditions (Claiborne and Evans, 1988;Appelhans et al, 2012;Martin et al, 2011;Hans et al, 2014). Nevertheless, long-term exposure to high environmental TAM or elevated P CO2 can affect the performance of crustaceans, resulting in increasing extracellular TAM concentration or lowered TAM excretion (Martin et al, 2011;Hans et al, 2014).…”