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Pathogen Pressure on Seagrass: Helped or Hindered by Warming?

Paper Reviewed
Olsen, Y.S., Potouroglou, M., Garcias-Bonet, N. and Duarte, C.M. 2015. Warming reduces pathogen pressure on a climate-vulnerable seagrass species. Estuaries and Coasts 38: 659-667.

In studying Posidonia oceanica, which they describe as "a climate-vulnerable Mediterranean seagrass," Olsen et al. (2015) "tested the impact of warming on infection by Labyrinthula sp.," which they describe as "the causative pathogen of wasting disease," along with the combined effect of elevated temperature and disease on the photobiology of the seagrass. This they did by incubating infected and control shoots of P. oceanica at temperatures between 24 and 32°C, "encompassing maximum summer seawater temperatures projected for the Mediterranean Sea during the twenty-first century." And what did they thereby learn?

The four researchers report that "warming reduced the occurrence and severity of the disease," while "temperatures greater than 28°C inhibited cell division and growth of Labyrinthula," so that the photochemical efficiency of the seagrass was not significantly affected by either the short-term warming or Labyrinthula infection. And these results further suggest, as they state in the concluding sentence of their paper's abstract, that "unlike what has been predicted for the majority of pathogen-host relationships, warming may lead to a reduced risk of wasting disease in P. oceanica and relieve pathogen pressure from this species."

But it is not only in the case of seagrass and its nemesis that this phenomenon occurs, for Olsen et al. write that much the same has been observed for certain "coral diseases (Ward et al., 2007), soil pathogens (Roy et al., 2004), and disease in coldwater salmonids (Holt et al., 1989)." And they also note that "a cythrid fungus that causes infections in amphibians leading to dramatic declines and population extinctions of frogs, ceases growth at temperatures above 28°C," and that "frogs living in water bodies with elevated temperatures (e.g., thermal springs) were shown to have a lower prevalence of cythrid infection, suggesting that thermal refugia may offer significant protection from this disease," as has been reported by Forrest and Schlaepfer (2011).

References
Forest, M.J. and Schlaepfer, M.A. 2011. Nothing a hot bath won't cure: Infection rates of amphibian cythrid fungus correlate negatively with water temperature under natural field settings. PLoS ONE 6: e28444.

Holt, R.A., Amandi, A., Rohovee, J.S. and Fryer, J.L. 1989. Relation of water temperature to bacterial coldwater disease in coho salmon, chinook salmon and rainbow trout. Journal of Aquatic Animal Health 1: 94-101.

Roy, B.A., Gusewell, S. and Harte, J. 2004. Response of plant pathogens and herbivores to a warming experiment. Ecology 85: 2570-2581.

Ward, J.R., Kim, K. and Harwell, D. 2007. Temperature affects coral disease resistance and pathogen growth. Marine Ecology Progress Series 329: 115-121.

Posted 27 May 2015