Rock size mediates thermal stress in the rocky intertidal

Marine scientists at Brown University have determined that the size of rocks in rocky intertidal areas is important to the survival of a common marine animal, the acorn barnacle. The bigger the rock, the less its temperature fluctuates during hot spells. That’s better for the barnacle, which needs rock temperatures to not exceed a certain range to survive.

In field tests, the scientists learned that air temperature peaks were far more prominent in southern New England, meaning that rock, or substrate, size plays an even larger role in barnacle habitat.

The research is important for many reasons. First, it shows that the survival of barnacles, described as the popcorn of the sea for its status in the marine food chain, can depend on the size of the rock on which it attaches itself. In southern New England intertidal zones, where smaller rocks predominate and summertime temperatures can spike, this has clear consequences.

Secondly, climate projections show mean air temperatures continuing to rise in New England, which could affect barnacles’ habitat, especially in southern waters. Thirdly, it opens a window into another aspect of the marine intertidal environment – the size of substrates – that influences the viability and perhaps variety of animals living there.

As Keryn Gedan, lead author of the paper in Ecology who earned her doctorate at Brown and is now a postdoc at the Smithsonian Research Center in Maryland, put it: “Hot spots and cold spots occur naturally due to variations like rock size and orientation. It’s important to understand where these hot and cold spots occur in order to predict the ecological effects of climate change and the temperatures that organisms experience.”

Heather Leslie, a marine ecologist and a co-author on the paper, said the study suggests that “all rocky shores are not the same. Physical characteristics like rock size can dictate how (animal) communities can function.”

Gedan, Keryn B., Joanna Bernhardt, Mark D. Bertness, and Heather M. Leslie. 2011. Substrate size mediates thermal stress in the rocky intertidal. Ecology 92:576–582. [doi:10.1890/10-0717.1]

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