Predicting Coastal Algal Blooms in Southern California

McGowan, J. A., Deyle, E. R., Ye, H., Carter, M. L., Perretti, C. T., Seger, K. D., de Verneil, A. and Sugihara, G. (2017), Predicting Coastal Algal Blooms in Southern California. Ecology. Accepted Author Manuscript. doi:10.1002/ecy.1804

• Bottom line: A 2017 study has found that “red tides”—blooms of marine algae that can be toxic to marine life and humans—can often be predicted in Southern California using an approach known as empirical dynamic modeling (EDM). Previous attempts to predict them in coastal settings have been unsuccessful.  This technique could lead to early warning systems for red tides and other “harmful algal blooms,” which also occur in Florida, the Great Lakes, and around the world.
• Background: Red tides, like many natural phenomena, can appear suddenly and seemingly at random. But instead of being random, they may be the result of nonlinear interactions. In other words, they have multiple causes whose impacts change depending on the situation. For example, nutrients in the water might promote algal blooms on calm days but have no effect on windy days. Such interactions can confound traditional prediction methods, which generally assume that causal factors have the same impact regardless of the conditions. 
• Methods: EDM is a forecasting method that tries to uncover the rules of how a system operates using only patterns found in the data. The researchers applied EDM to 24 years of twice-weekly measurements taken at the Scripps Institution of Oceanography pier in La Jolla, California. They considered several possible causes of red tides, including nutrient levels, wind speed, and ocean conditions such as temperature and water density. As a proxy or indicator of red tides, they used the concentration of chlorophyll—the primary pigment in the algae responsible for red tides.
• Findings:
  • The study found that red tides are more likely when the water is calm and nutrient concentration near the surface is low. Such conditions are known to favor a type of algae known as dinoflagellates, the main cause of red tides.
  • It predicted chlorophyll concentration with a “forecast skill” of 0.63—the rough equivalent of correctly predicting a coin toss 80 percent of the time.
  • EDM was unable to predict all instances of red tides. This suggests that the environmental variables used in this study may be indirect measurements of the true cause of red tides, or that different red tides have different causes.
  • Investigators are exploring further improvements to the models, and including more data from throughout Southern California, with the end goal of predicting red tides to warn fishermen and beachgoers of the presence of dangerous algae. It could also aid in the planning of naval training exercises and guide temporary shutdowns of power plants and desalination plants, where algal blooms can cause operational problems.

The full publication is available here: http://onlinelibrary.wiley.com/doi/10.1002/ecy.1804/full.