Protecting Ocean Ecosystems

The Catch of Climate Change: OA Presents a Threat to Fisheries

Nancy Shrodes is a volunteer for the Ocean Conservation Program at the Conservation Law Foundation. She recently graduated from Tufts University (class of 2011), majoring in Environmental Science with a focus in marine biology.

The Catch of Climate Change is an exclusive Talking Fish series that will look at the potential impacts of ocean acidification from climate change on New England’s oceans and fisheries. This post is the second in the series. Read the first post here.

There are many threats our oceans face today, including coastal pollution, oil spills, overfishing, and ocean acidification (OA), which has recently entered the equation as a direct threat to many marine species with consequences that may likewise threaten the fishing-based economies that depend upon them. Here is a look at how climate change, by contributing to warmer and more acidic oceans, could have dire consequences for fisheries.

Two clownfish seek shelter in purple sea anemone (Photo credit: Nick Hobgood)

As ocean acidification is a fairly new subject of study, very little is known about its direct effects on various species of fish. However, larvae of clownfish reared under acidic conditions were much less likely to survive as those reared under control conditions because they were unable to locate safe habitats to grow and therefore were more likely to be eaten by predators.[1] Even more alarmingly, two separate studies demonstrated that juvenile clownfish exposed to increased acidification had damaged sensory abilities, rendering them unable to discern the scent and sound of predators.[2],[3] With these key behavioral defenses impaired, clownfish were less likely to detect and swim away from death threats, thus lowering their chances for survival.

While the studies mentioned above are discouraging, not much is known about how increased acidification directly affects the commercially valuable fish we like to eat, such as tuna, salmon, or haddock. Indirectly, fish such as cod, herring, mackerel, and salmon could struggle to feed as their plankton prey, called pteropods, suffer major shell dissolution due to OA.[4] Nevertheless, the scientific community recognizes the need for more information about the ecological consequences of OA (how it affects species-to-species relationships within marine communities) and the inevitable economic costs of any adverse impacts. In fact, there is currently a study underway investigating the effects of OA on coral trout, a species that has significant commercial value in Australia.

However, there is an abundance of information regarding the effects of OA on calcifying species, which are organisms that use calcium carbonate to build skeletal structures and protective shells.  OA decreases the concentration of calcium carbonate in the water, hindering the ability of species such as corals and shellfish to calcify.[5] In addition, the more acidic water can directly dissolve and damage these structures. Corals and shellfish are often very important to coastal economies and their high sensitivity to OA concerns many scientists, rendering them the focus of much research.

Evidence of coral bleaching found in the Great Barrier Reef in 2002 (Photo credit: Ray Berkelmans, Australia Institute of Marine Science)

The stresses of climate change threaten corals, the very foundation of reef ecosystems, through a process known as coral bleaching. This devastating process occurs when, in reaction to both higher temperatures and acidification, sensitive corals expel from their tissues the photosynthetic algae that give them their vibrant colors, eventually killing the corals and leaving only their white calcium carbonate skeleton behind. This is detrimental to coral-based marine communities that rely on reefs for shelter, nutrients, spawning, and protection. Members of such communities include commercially valuable fish, and if these fish populations decline due to coral bleaching, coastal economies will be hurt.

Moreover, CNN reported ocean acidification as a threat to food security, since “[t]ropical reefs provide shelter and food for around a quarter of all known marine fish species…[and] over one billion people rely on fish as a key source of protein.”[6] This is an economic threat not to be taken lightly.

OA also hinders the growth, development, and survival of many types of shellfish larvae, which could rapidly diminish entire populations.[7] As mentioned above, OA causes the degradation of shells and can inhibit calcification, resulting in weaker, if not deformed, shells.[8] And while some species surprisingly increase calcification in response to OA, it is at the metabolic cost of less muscle production.[9]

These impacts of ocean acidification will be felt in New England, since shellfish are an important source of revenue to the region.  In 2007, mollusks (such as scallops) made up 19% of total U.S. ex-vessel revenues, and fish that prey directly on calcifiers made up 24% of total U.S. ex-vessel revenues.[10] We love our clams, oysters, mussels, and scallops here in New England. It would hurt our seafood-hungry palate, as well as the coastal economies that rely on this income, to sit by idly as waters become increasingly acidic at record-breaking rates.

In my next post, I’ll explore further how top-earning New England ports such as New Bedford would be directly affected by OA.

[1] Munday, P.L., D.L. Dixson, J.M. Donelson, G.P. Jones, M.S. Pratchett, G.V. Devitsina, K.B. Doving. 2009. Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. PNAS 106(6): 1848-1852.

[2] Munday, P.L., D.L. Dixson, M.I. McCormick, M. Meekan, M.C.O. Ferrari, D.P. Chivers. 2010. Replenishment of fish populations is threatened by ocean acidification. PNAS 107(29): 12930-12934.

[3] Simpson, S.D., P.L. Munday, M.L. Wittenrich, R. Manassa, D.L. Dixson, M. Gagliano, H.Y. Yan. 2011. Ocean acidification erodes crucial auditory behavior in marine fish. Biol. Lett. 10.1098.

[4] Feely, R.A., C.L. Sabine, K. Lee, W. Berelson, J. Kleypas, V.J. Fabry, F.J. Millero. 2004. Impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science 305(5682): 362-366.

[5] Gazeau, F., C. Quiblier, J. M. Jansen, J.-P. Gattuso, J. J. Middelburg, C. H. R. Heip. 2007. Impact of elevated CO2 on shellfish calcification. Geophys. Res. Lett., 34(L07603): 1-5.

[6] Knight, Matthew. 2 December 2010. “Ocean’s failing the acid test, U.N. says.” CNN World News.

[8] Feely, R.A., C.L. Sabine, K. Lee, W. Berelson, J. Kleypas, V.J. Fabry, F.J. Millero. 2004. Impact of anthropogenic CO2 on the CaCO3 system in the oceans. Science 305(5682): 362-366.

[9] Wood, H.L., J.I. Spicer, S. Widdicombe. 2008. Ocean acidification may increase calcification rates, but at a cost. Proc. R. Soc. B 275(1644): 1767-1773.

[10] Cooley, Sarah R. and Scott C. Doney. 2009. Anticipating ocean acidification’s economic consequences on commercial fisheries. Env. Res. Lett. 4(2) doi:10.1088/1748-9326/4/2/024007.


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