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Environmental Change and Potential Trophic Mismatches

Reference
Appelhans, Y.S., Thomsen, J., Pansch, C., Melzner, F. and Wahl, M. 2012. Sour times: seawater acidification effects on growth, feeding behavior and acid-base status of Asterias rubens and Carcinus maenas. Marine Ecology Progress Series 459: 85-97.
Changes in environmental conditions are often looked upon with a high degree of negativity, due to the possibility that there may be consequent "mismatches" across different trophic levels in many of Earth's natural ecosystems. On land, global warming is usually of greatest concern in this regard, while at sea an additional parameter of major concern is ocean acidification; and a most interesting example of the latter is described in the study of Appelhans et al. (2012).

Noting that "two of the main benthic predators in the western Baltic are the common sea star Asterias rubens and the shore crab Carcinus maenas," and that "a large portion of their prey consists of the highly abundant blue mussel Mytilus edulis," the five German researchers studied the impacts of three different seawater pCO2 levels (650, 1250 and 3500 ppm, which were all higher than that prevailing in the atmosphere: ~380 ppm) on the two predator-prey relationships. This they did by exposing the two predators and their common prey to these three degrees of ocean acidification - which resulted in aragonite saturation state (Ωarag) values of 0.96, 0.53 and 0.20, respectively, and calcite saturation state (Ωcalc) values of 1.64, 0.91 and 0.34, respectively. And they did it over a period of ten weeks, after which they performed a number of different feeding experiments (of the mussel to the sea star and crab).

As a result of their experimental findings, Appelhans et al. report that "even though the seawater was under-saturated in aragonite in all treatment levels and in calcite in the two higher pCO2 levels, both predator organisms were able to survive under acidified conditions." And they state that "these observations are in line with recent acidification studies on crabs and echinoderms (Dupont and Thorndyke, 2008; Wood et al., 2008; Gooding et al., 2009; Dupont et al., 2010a, 2010b; Whiteley, 2011)." In addition, they indicate that "no significant responses of feeding rate and/or growth were observed under moderate (1250 ppm) seawater acidification scenarios."

At the highest level of acidification [3500 ppm], however, the five researchers report that "all three species show a shift in certain traits," noting that "mussel shells become more brittle, sea stars grow slower, and both sea stars and crabs feed less under strong acidification." And as a result, they state in the conclusion of their paper that "the enhanced vulnerability of mussels seems to be neutralized by the decreased consumption of the predators under high acidification," which allows them to conclude - in the final sentence of their paper's abstract - that "when stress effects are similar on interacting species, biotic interactions may remain unaffected," providing, thereby, a fine example of ocean acidification-induced trophic non-mismatches.

Additional References
Dupont, S. and Thorndyke, M. 2008. Ocean acidification and its impact on the early life-history stages of marine animals. In: Briand, F. (Ed.). Impacts of Acidification on Biological, Chemical and Physical Systems in the Mediterranean and Black Seas, Book 36. CIESM Monographs, Monaco.

Dupont, S., Lundve, B. and Thorndyke, M. 2010a. Near future ocean acidification increases growth rate of the lecithotrophic larvae and juveniles of the sea star Crossaster papposus. Journal of Experimental Zoology B 314: 382-389.

Dupont, S., Ortega-Martinez, O. and Thorndyke, M. 2010b. Impact of near-future ocean acidification on echinoderms. Ecotoxicology 19: 449-462.

Gooding, R.A., Harley, C.D.G. and Tang, E. 2009. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. Proceedings of the National Academy of Sciences USA 106: 9316-9321.

Whiteley, N.M. 2011. Physiological and ecological responses of crustaceans to ocean acidification. Marine Ecology Progress Series 430: 257-271.

Wood, H.L., Spicer, J. and Widdicombe, S. 2008. Ocean acidification may increase calcification rates, but at a cost. Proceedings of the Royal Society of London B 275: 1767-1773.

Archived 24 October 2012