ecology

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Ocean Acidification: Problems & Solutions

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A blog post written by students in Bodega Marine Laboratory's Biological Oceanography Class:  Alex, Siena & Chelsey (see more about them below!)

Ocean acidification (OA) is a process in which ocean chemistry is altered due to the carbon dioxide (CO2) generated through fossil fuel burnging. Our ocean absorbs around 33% of all CO2 put into the atmosphere (Sabine et al. 2004). Once CO2 is absorbed into the ocean, it reacts with water to form a weak acid. In doing so the release of hydrogen ions creates more acidic water. Current research has shown that the changing ocean chemistry is inflicting highly stressful conditions for larvae and juvenile calcifying organisms, stunting their growth and even causing death. Other organisms experience behavioral changes that can impact their ability to find food or escape predators.

Conch snail, Wikimedia Commons

Conch snail, Wikimedia Commons

Many marine organisms use chemical cues around them to understand their environment, including predator/prey presence, wayfinding, and mating. However, multiple studies have indicated that OA most likely interferes with the function of neurotransmitter receptors responsible for processing these cues (Hamilton et al. 2014, Leung et al. 2015, & Watson et al. 2014), leaving marine animals less able to sense them and exhibit a response. For example, when conch snails detect the presence of predators through chemical signals, they will jump away from the predator. In a study of conch snails and their response to a cone shell predator, conch snails in acidified water took longer to start jumping away from the predator than those under normal pH conditions. The snails in acidified water also moved at an angle closer to the predator, exposing them to the predator for a longer period of time and decreasing their chance of survival (Watson et al. 2014). Snails can also induce other responses to predators, such a growing a thicker shell. However, this response may be compromised with more acidified waters because the water will be more able to dissolve minerals (Bibby et al. 2007). This means snails will be less able to gather the calcium carbonate required to thicken their shell in response to predators.

Snails can respond and adapt to acidified water to a certain extent. In a study of the nassa mud snail, Nassarius festivus, snails exposed to acidified waters responded both by retracting into their shells within the mud and by reducing their oxygen consumption. However, these responses only work for a short time, as longer-term acidity will inhibit their ability to hunt for carrion (Leung et al. 2015). In another study, snails collected from acidified sites took 4 times less to start moving, spent twice the amount of time moving, and crawled out of the acidified water in much higher numbers than gastropods from non-acidified sites, indicating that snails often exposed to lower acidity have adapted to respond to and avoid acidified waters (Amaral et al. 2014). See interesting and related work from UCD scientists on this topic here. 

Tomales Bay, CA (Wikimedia Commons)

Tomales Bay, CA (Wikimedia Commons)

OA is not only a direct threat to marine organisms’ ability to detect chemical cues, but also a threat to marine fisheries. In 2004, an oyster hatchery in Oregon lost approximately 80% of their larvae used to supply 75% of the juvenile oyster spat for west coast oyster farmers (Kelly et al. 2014). This was a huge economic loss for the west coast oyster industry and an alarm signalling OA impacts on oyster farmers. We have also started seeing these effects in local waters such as Tomales Bay, a pristine 15 mile long estuary that is home to several local oyster farming companies. The companies supply the rural West Marin community with fresh, sustainable, and ecologically beneficial oysters. Oysters require no fertilizers and they deposit nitrate-rich waste material onto surrounding sediments, fueling the growth of helpful bacteria (Newell et al. 2005). These filter feeders help to maintain the water quality of the estuary by trapping phytoplankton and other particles. In some cases, oysters have been shown to reduce the number of harmful algal blooms due to their filtration system (Cerrato et al. 2014). Tomales Bay oyster farmers are now facing a threat to their livelihood due to OA. 

But how can we tackle an issue as big as OA? One way may be through the utilization of carbon sequestration, a series of processes through which carbon could be stored away over the long term. Plants and other similar living things can take CO2 out of their surroundings through photosynthesis, turning it into larger molecules that they can store within their bodies. In the ocean, there are many different ecosystems that have the potential to play a role in sequestration of some kind: coral, kelp, seagrasses, salt marshes, mangroves, and even phytoplankton (small plant-like creatures). But not all photosynthesizers are made equal: for example, coral puts out as much carbon as it takes in on average (Ohde and van Woesik 1999), and kelp forests do not transfer carbon into any long-term storage (any carbon stored within their bodies will be released as they decompose), so neither are strong candidates for sequestration research.

A Godwit feeding within a seagrass meadow. Photo: Wikimedia Commons

A Godwit feeding within a seagrass meadow. Photo: Wikimedia Commons

Currently, most sequestration research is focused around seagrass meadows, because they can both take in a lot of carbon as well as have a means to store it under the sandy sediment they live within. It’s currently estimated that 4.6-9.3 billion tons of CO2 are stored within seagrass meadows globally, with some estimates going as far as 21 billion tons (Fourqurean et al 2012). As a bonus, because they pull the excess carbon out of the water, they can restore local pH conditions to their former alkalinity, making seagrass beds good areas for oysters and other calcifying organisms to grow their shells. But human impacts such as erosion and dredging can release those carbon stores earlier than anticipated, hindering our efforts.

Indeed, most of the issues with marine carbon sequestration stem from human impacts on these photosynthesizers, such as coral bleaching, increased storm activity hurting kelp, and deforestation of mangroves. Therefore, we need to work on restoring and protecting these marine habitats so that they can help us in turn. OA will continue to be an issue for our local communities and for our entire planet. It is necessary to act now in order to minimize the damage to our ocean.

About the authors:

Alexander is a second-year student in the Joint Doctoral Program in Ecology between UC Davis and San Diego State University. His research focuses on the role that kelp forest ecosystems play in the carbon cycle.

Siena is an undergraduate student in the Marine and Coastal Science major at UC Davis. She recently conducted research at Bodega Marine Lab on the indirect and direct interactions of snails with non-native and native crab predators.

Chelsey is an undergraduate student in the Pharmaceutical Chemistry major at UC Davis and a Tomales Bay native. She recently conducted research at Bodega Marine Lab related to the carbon content found in seagrass meadow sediments.

 

References:

  • Amaral, V., Cabral, H.N. and Bishop, M.J., 2014. Prior exposure influences the behavioural avoidance by an intertidal gastropod, Bembicium auratum, of acidified waters. Estuarine, Coastal and Shelf Science, 136, pp.82-90.

  • Bibby, R., Cleall-Harding, P., Rundle, S., Widdicombe, S. and Spicer, J., 2007. Ocean acidification disrupts induced defenses in the intertidal gastropod Littorina littorea. Biology Letters, 3(6), pp.699-701.

  • Cerrato RM, Caron DA, Lonsdale DJ, Rose JM, Schaffner RA. 2004. Effect of the northern quahog Mercenaria mercenaria on the development of blooms of the brown tide alga Aureococcus anophagefferens. Marine Ecology Progress Series 281: 93–108

  • Fourqurean, J.W., Duarte, C.M., Kennedy, H., Marbà, N., Holmer, M., Mateo, M.A., Apostolaski, E.T., Kendrick, G.A., Krause Jensen, D., McGlathery, K.J., and Serrano, O. 2012. Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience 5: 505-509.

  • Hamilton, T.J., Holcombe, A. and Tresguerres, M., 2014, January. CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning. In Proc. R. Soc. B (Vol. 281, No. 1775, p. 20132509). The Royal Society.

  • Kelly, R. P., Cooley, S. R., & Klinger, T. (2014). Narratives can motivate environmental action: The Whiskey Creek ocean acidification story. Ambio, 43(5), 592-599.

  • Leung, J.Y., Russell, B.D., Connell, S.D., Ng, J.C. and Lo, M.M., 2015. Acid dulls the senses: impaired locomotion and foraging performance in a marine mollusc. Animal Behaviour, 106, pp.223-229.

  • Newell RIE, Fisher TR, Holyoke RR, Cornwell JC. 2005. Influence of eastern oysters on nitrogen and phosphorus regeneration in Chesapeake Bay, USA. Pages 93–120 in Dame RF, Olenin S, eds. The Comparative Roles of Suspension Feeders in Ecosystems. Springer.

  • Ohde, S; van Woesik, R. (1999) Carbon dioxide flux and metabolic processes of a coral reef, Okinawa. Bulletin of Marine Science 65(2): 559-576.

  • Sabine, CL; Feely, RA; Gruber, N; Key, RM; Lee, K; Bullister, JL; Wanninkhof, R; Wong, CS; Wallace, DWR; Tilbrook, B; Millero, FJ; Peng, T-H; Kozyr, A; Ono, T.; Rios, AF. 2004. The Oceanic Sink for Anthropogenic CO2. Science 305(5682):367-371.

  • Watson, S.A., Lefevre, S., McCormick, M.I., Domenici, P., Nilsson, G.E. and Munday, P.L., 2014. Marine mollusc predator-escape behaviour altered by near-future carbon dioxide levels. Proceedings of the Royal Society of London B: Biological Sciences, 281(1774), p.20132377.

 

For more blogging from UC Davis Bodega Marine Laboratory students, see below!