Author: Jesus C. Compaire
We have all have heard about how ocean acidification has an important impact on marine ecosystems (if you don’t know what ocean acidification is, our colleague Jon Sharp tells you in his entry about pH onboard GOMECC-3). One of the most known effects is coral bleaching in tropical areas, but this phenomenon does not only affect the sessile organisms (who cannot run looking for better areas for their growth). At different scales, the rest of plants and animals in the ocean can also be affected by ocean acidification since this reduces the calcification in many organisms (Orr et al., 2005). Species affected include planktonic calcifiers (coccolithophores, foraminifera, pteropods), and also other animals like echinoderms, bryozoans, molluscs, crustaceans, fish, and a long etcetera.
But, what exactly does “reduce the calcification” mean, you might ask yourselves, and why is this a negative impact? To try to understand this phenomenon let’s see a few cases in different animals. For example it has been documented that elevated pressure of CO2 (i.e. high concentration of carbon dioxide) reduces the growth of molluscs and sea urchins, which means that compared to normal levels of CO2, the animals that grew in high CO2 conditions had smaller sizes and body weights (Shirayama & Thornton, 2005). In other experiments with crabs, the combination of increased temperature and lower pH reduced the energy for reproduction (Paganini et al., 2014). Now let’s talk about fish, and in particular about the ichthyoplankton (the eggs and larvae of fish found mainly in the upper 200 meters of the water column) of the marine coastal species. The survival of their larvae depends on them being able to find a suitable adult habitat at the end of an offshore dispersive stage that can last weeks or months. The way that they may return to adult habitats is with their ability to detect olfactory cues from these adult places. However, under experimental ocean acidification conditions it has been noted that this ability was disrupted. So if acidification continues unabated, the impairment of the sensory ability may reduce the population sustainability of many marine species, with potentially profound consequences for marine diversity (Munday et al., 2009) and impacts to wide sections of the population whose economies depend on these species.
It is for all these reasons that we are taking zooplankton samples throughout the Gulf of Mexico in this cruise (if you are not sure about what the zooplankton is, please check out this blog entry from July 29th where our colleague Lucio Loman explains this in detail). We aim to study the species composition and their abundances, and their relationships with the physical and chemical characteristics of the water column. The long-term study of the communities composition in the Gulf of Mexico will allow for the monitoring of changes and impacts due to increased sea surface temperature and ocean acidification, which in turn, will help managers to reduce this impact.
– Munday, P. L., Dixson, D. L., Donelson, J. M., Jones, G. P., Pratchett, M. S., Devitsina, G. V., & Døving, K. B. (2009). Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proceedings of the National Academy of Sciences, 106(6), 1848-1852.
– Orr, J. C., Fabry, V. J., Aumont, O., Bopp, L., Doney, S. C., Feely, R. A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., et al. (2005). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681-686.
– Paganini, A. W., Miller, N. A., & Stillman, J. H. (2014). Temperature and acidification variability reduce physiological performance in the intertidal zone porcelain crab Petrolisthes cinctipes. Journal of Experimental Biology, 217(22), 3974-3980.
– Shirayama, Y., & H. Thornton (2005) Effect of increased atmospheric CO2 on shallow water marine benthos. Journal of Geophysical Research, 110, C09S08, doi: 10.1029/2004JC002618.