Are New Englanders more tolerant than Southerners? A test of latitudinal variation in Atlantic sea urchins

Kaelyn* Lemon, Macalester College/ Dr. Bob Podolsky and Grice Marine Lab

If you’re not a climate change denier, you know that global climate change, mainly driven by the increasing amounts of carbon dioxide that humans release into the atmosphere, has been raising the Earth’s average temperature and will continue to do so for the near future. If you are particularly well-versed in your environmental science, you know that these increasing amounts of carbon dioxide are also causing the oceans of the world to become more acidic (see: coral bleaching) (1). Unless you are a marine or climate scientist, though, you probably don’t know why climate change is causing ocean acidification or how this will affect ocean animals besides probably not being the best thing ever for them.

Our oceans actually absorb around 30% of the carbon dioxide we release into the air (2). This CO2 hangs around as a gas mixed into the water and goes through a series of chemical reactions that both release hydrogen ions (the H in pH), therefore lowering the pH of the water and making it more acidic, and reducing the amount of carbonate available in the water for ocean animals and other organisms to use (2). Animals like sea urchins that build shells or skeletons out of calcium carbonate (the main ingredient in limestone) find this task more difficult when there is less carbonate around.

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Ocean acidification due to greater amounts of carbon dioxide in the atmosphere leads to less carbonate in the water (from http://www.i-fink.com/ocean-acidification/)

While the thought of sea urchins will bring to mind their hard, spiny exterior, these animals (yes, there are body tissues inside those aquatic pincushions) are actually most affected by ocean acidification during their larval stage of life, when they build a skeleton that allows them to swim around and eat (3) (urchin larvae are like insect larvae in that they behave and look very different from the full-grown animals they will eventually become). When oceans become more acidic and less carbonate is available, urchin larvae are smaller, which makes it harder for them to eat at the same time as they are more at risk of being eaten themselves (3). Unfortunately, a world with a lot fewer urchins would be a world where seaweed would easily overgrow ocean habitats and predators of urchins (like the adorable fuzzy otters that lay on their backs in the ocean and hold hands- google it) might have more difficulty finding food.

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One of the sea urchins from South Carolina with some of the seaweed they like to eat (photo credit: Kaelyn  Lemon)

I’m looking into whether sea urchins (specifically the species Arbacia puntulata, which is found in the Atlantic ocean) from Massachusetts and South Carolina will react differently in higher acidity. If one group of urchins can produce larvae that maintain a larger body size under more acidic conditions than the other group, then we will know that there is some degree of variability within the species. This would be a positive result for the sea urchins (and therefore for oceans in general) because it would mean that these urchins may be able to adapt to acidified waters more easily than we can currently expect.

Sources:

1. IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

2. Clark D, Lamare M, Barker M. 2009. Response of sea urchin pluteus larvae (Echinodermata: Echinoidea) to reduced seawater pH: a comparison among a tropical, temperate, and a polar species. Marine Biology. 156: 1125-1137.

3. Sheppard Brennand H, Soars N, Dworjanyn SA, Davis AR, Byrne M. 2010. Impact of ocean warming and ocean acidification on larval development and calcification in the sea urchin Tripneustes gratilla. PloS One. 5:1-7.

Funding from the NSF and support from the College of Charleston

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