Temperature Rise and Ocean Acidification Impacts Physiological Processes of the Brittlestar Ophiocten sericeum

The Arctic is considered one of the most threatened areas on the planet. Climate change has already greatly impacted the oceanic landscape of this region. Further increases in temperature and acidity are believed to affect the Arctic more strongly than any other region on Earth. Ocean acidification has been shown to negatively affect the calcification and growth of many marine organisms. Temperature increases have placed organisms under great thermal stress and narrowed the habitat range of species, especially in the Arctic. Wood et al. (2011) examined the physiological effects of temperature and acidity increases on the Arctic brittlestar Ophiocten sericeum. The authors found that high temperature had no effect on metabolic rate, but resulted in a decrease in muscle density. The results also suggest that a lower pH increased metabolism. Taken together, the authors found that increased temperature and acidity due to climate change could result in decreased survival over the long term.––Emily Putnam
Wood, H., Spicer, J., Kendall, M., Lowe, D., Widdicombe, S., 2011. Ocean warming and acidification; implications for the Arctic brittlestar Ophiocten sericeum. Polar Biology 34, 1–12.

Wood and colleagues at the Plymouth Marine Laboratory tested the effects of increased temperature and increased acidity on the physiology of O. sericeum. Six experimental setups were used––three with ambient temperature seawater and three at a higher temperature. The setups at each temperature were further broken down by pH––current ocean pH, the mid-level pH predicted for the year 2100, and the extreme pH level predicted for the year 2100. Some of the brittlestars were chosen for amputation and 25% or 70% of an arm was removed. All brittlestars were then randomly placed into one of the experimental setups, where they remained for twenty days. After this time, brittlestars that had been left complete were placed into a metabolic chamber for 2 hours. The amount of oxygen respired was measured. These brittlestars then had one complete arm amputated for examination under microscope of the size and density of muscle cells, changes in calcium content, and the thickness of the outer layer of tissue. Previously amputated brittlestars were measured for the amount of arm regenerated following exposure to acidified and/or heated water. Regeneration was measured by comparing the length of the arm after twenty days to the length just after amputation.
Metabolic oxygen uptake increased under conditions of increased acidity, but not increased temperature. Higher temperatures resulted in a decrease in muscle density and lower calcium contents. Regeneration was affected by both increased acidity and temperature, though pH had a greater effect. Functional regeneration was greater at the more basic pH and greater in all of the high temperature setups.
The increase in metabolic rate at lower pH indicates a highly stressful environment for this species. The brittlestars compensate for the low pH with an increased energy demand. Temperature was expected to have an effect on metabolic rate, but no increase was detected. The authors posit that the temperature used in this study was not sufficiently high to find a significant effect on metabolism. The decrease in muscle at high temperatures suggest that pre-existing muscle may have provided an additional energy source for the brittlestars. Wood et al. concluded that increased acidification resulted in an increase in energy demand. This energy demand created additional stresses for the brittlestars, forcing them to use reserve energy. This idea was further supported by the faster regeneration in acidified and hotter waters. The brittlestars use energy faster and require more energy than can be adequately taken in from their surroundings. The authors conclude that O. sericeum may be able to survive short-term increases in temperature and acidity, but long-term survival may not be possible under the current predictions.

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