On the front lines of ocean acidification | Healthy Oceans | David Suzuki Foundation
Photo: On the front lines of ocean acidification

Just how does one deposit a pH meter in extremely cold sea water under a thick layer of sea ice? Very carefully, of course! (Credit: Henry Kaiser)

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Carin Bondar is a biologist, TV host and science communicator with a PhD in population ecology from the University of British Columbia. She blogs for Scientific American and Huffington Post and has appeared in a scientific capacity on various international television networks. Her writing has been featured online at National Geographic Wild, Jezebel, Forbes, The Guardian, The Daily Beast and the Richard Dawkins Foundation. Find Dr. Bondar online, on twitter or on her Facebook page. Look for her blogs on science topics in the coming weeks on the David Suzuki Foundation website.

In my first piece on ocean acidification, I gave a brief overview of the processes involved and the potential for disastrous consequences to oceanic food webs. I'd like to spend the next few posts discussing some of the diverse ways that scientists are approaching the topic. The bulk of the expected drop in ocean pH hasn't happened yet, so researchers have had to get creative to design environmentally relevant experiments.

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Looking to Antarctica

Gretchen Hofmann is a professor at the University of California at Santa Barbara who has been working on the topic of ocean acidification for seven years. Most of Hofmann's work takes place in the polar environments of the Arctic and Antarctica. These areas are expected to be the first to experience acidification-related events because of their extremely cold ocean temperatures (-1.8°C) and naturally low carbonate saturation levels. Scientists expect that as early as 2040, the waters around the coast of Antarctica will not support calcification of the organisms now living there. Hofmann and her team recently returned from a field expedition, and she presented some of her findings at the recent meeting of the American Association for the Advancement of Science.

Hofmann has two Antarctic research sites where MacGyver-inspired pH meters are continuously deployed to monitor the normal levels and fluctuations that occur. Just how does one deposit a pH meter in extremely cold sea water under a thick layer of sea ice? Very carefully, of course! Untethered scuba divers must find their way back to one small exit hole after securing the device, a task that is certainly not for the faint of heart. Divers collect specimens of Hofmann's main research organism, the sea urchin Sterechinus naumayeri. The urchins are a key member of the bottom-dwelling community in this area, and understanding how they react to changes in pH is critical to predict changes to ecosystem function.

In Hofmann's most recent experiments, urchins were spawned and raised at increasing levels of acidification from a baseline dictated by the pH meters in the field. Results confirm that calcification occurs early in development and that a decrease in pH directly affects the ability to calcify. During normal development urchin larvae form long, calcareous spines that act as feeding structures. In the acidified environment the urchins developed shorter feeding arms, which interfered with their ability to feed and resulted in a smaller overall body size.
The obvious question that comes to mind is: Do smaller larvae develop into smaller adults? Since these results are so recent, Hofmann does not yet have data on the adult sizes of specimens from acidified treatments. However, she provided me with resources for several other species where a positive relationship has been found between larval size and adult size. In other words, it is likely that smaller larvae will become smaller adults.

Is it bad to be small?

The trend toward smaller body size could have massive effects on the benthic ecosystems of the Antarctic. First of all, there are direct implications for fecundity of females (the number of eggs an individual is able to carry). A smaller body size naturally leads to a smaller number of eggs that can be carried within it. Second, a smaller adult body size can translate into increased susceptibility of the urchins to smaller predators. According to Hofmann, these ecosystems are prone to invasion by crushing predators like crabs and bony fishes. Not only are these urchins smaller, their shells are likely to be much more brittle due to a lack of useable carbonate in the water. So overall the urchins will be less fecund, have an increased number of potential predators and a decreased ability to protect themselves within their calcium carbonate shells. This sounds like bad news to me.

Looking Ahead

Next week I'll detail the work of Jason Hall-Spencer of the University of Plymouth, who studies biodiversity of ecosystems near naturally occurring CO2 vents. Do these areas support diverse communities? Stay tuned...

March 14, 2012
http://www.davidsuzuki.org/blogs/healthy-oceans-blog/2012/03/on-the-front-lines-of-ocean-acidification/

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