Linkages between Ocean Acidification and Marine Organisms

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.

coral infographic

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.

References:

– 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.

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Zooplankton, Pteropods, and their importance in a changing ocean

Author: Lucio Loman Ramos

Finally, we get into the biology of the macro zooplankton in this blog. My colleague Jesús Cano Compairé and I are involved in research of these tiny creatures that live in the oceans all over the world called Zooplankton. We are each interested in some specific group within this categorization.

Zooplankton (from the Greek: Zoon, animal; and planktos, wandering) are myriads of diverse floating and drifting animals with limited power of locomotion. The majority of them are microscopic, unicellular or multicellular forms with sizes ranging from a few microns to a millimeter or more.

Picture 1
A brief view of the enigmatic Zooplankton

Talking about their role in the oceans, zooplankton are very important when studying the faunal bio-diversity of aquatic ecosystems, their ecology and also, they give us clues about their surrounding environment. They include representatives of almost every taxon of the animal kingdom and occur in the aquatic environment either as adults (holoplankton, which live all their life in the water column) or as larvae (meroplankton, which live part of their life at the bottom, attached to something and the other part in the water column). By sheer abundance of both types and their presence at varying depths, the zooplankton are utilized to assess energy transfer at secondary trophic levels. They feed on phytoplankton (microscopic plants) and facilitate the conversion of plant material into animal tissue and in turn constitute the basic food for higher animals including fishes, particularly their larvae.

One of the reasons why we are interested in collecting zooplankton here on GOMECC-3 is because certain planktonic organisms are capable of building hard structures of calcium carbonate, concentrating it as shells and thus can act as indicators of the chemistry of the water, they can tell us how they can be affected by environmental changes such as CO2 increase.

We are employing tow nets for zooplankton collection. The plankton nets we use are the Bongo type, called like this because they look like those big musical instruments. We are towing these nets with a steel cable attached to the NOAA ship Ronald H. Brown in a hauling type technique denominated oblique hauls, which allow us to collect zooplankton from a certain depth through all the water column to the surface. These plankton nets are conical in shape and consist of a ring (rigid and round), the filtering cone and the collecting bucket for collection of organisms. After the catch, we need to fixate them with some chemicals and then add preservatives to make them last many years. If we do this step carefully, years from now organisms will look almost the same as if they were caught the previous day, allowing us to make further qualitative and quantitative studies on them.

Picture 2
Preparing and waiting for the deployment of the net
Picture 3
Deploying and towing the nets. Image credit: Lucio Loman Ramos
Picture 4
Left: Fresh samples just after washing the net. Right: Zooplankton just treated with a fixative. Image credit: Lucio Loman Ramos

Our group from ECOSUR Campeche, Mexico, is interested in Pteropods from the Gulf of Mexico. We are looking to have an extended database of pteropod communities and to use it as indicator of the extension of acidification in the Gulf of Mexico. Pteropods are a group of holoplanktonic heterobranch gastropod mollusks (related to seashells), in other words, tiny mollusks that have a shell and live in the water column, they are widespread and abundant in the marine zooplankton. They have been proposed as bioindicators to monitor the effects of ocean acidification because their calcium carbonate shells are exceptionally vulnerable to rising levels of CO2 in the global ocean. It is expected that anthropogenic carbon input into the ocean may affect marine life more severely than in the past, because it is happening much faster than, for instance, at the Paleocene-Eocene thermal maximum (PETM) ~56 million years ago. During the PETM, massive amounts of carbon were released into the atmosphere and ocean, leading to ocean acidification and warming, a situation that persisted for tens of thousands of years (Zachos et al., 2005). This resulted in major shifts in marine planktonic communities. So, we know what happens to some members of the plankton community when CO2 rises and we are interested to know if the anthropogenic activities are involved today in the alteration of plankton organisms with calcareous shells like pteropods in the Gulf of Mexico.

Picture 5
Group: Pteropods, Suborder: Thecosomes. Commonly known as Sea butterflies.

References:

Zachos JC, RoÈhl U, Schellenberg SA, Sluijs A, Hodell DA, Kelly DC, et al. Rapid acidification of the ocean during the Paleocene-Eocene Thermal Maximum. Science 2005; 308: 1611-1615.