Barnacles Don't Fight Over Dropping Temperatures

Barnacles are important and popular models for ecological research and they are very sensitive to temperature. Given these facts, researchers studied the effects of temperature change on competition in a community of two barnacle species in Chile, expecting to find profound insights into the impacts of climate change. They found no significant effect of temperature on competition at all.

The study, which will appear in an upcoming issue of Journal of Experimental Marine Biology and Ecology, may lead to important implications despite its "non-findings."

"The dominant if somewhat dated narrative in marine ecology, and ecology more broadly, is that competition is a major structuring force in natural communities," said co-author Heather Leslie, assistant professor of environmental studies and biology at Brown University. "We know it's a more nuanced story, but to find cases where it's a bit of a draw is really unusual."

What's more, it was temperature, of all factors, that was found to not be competition-inducing.

"Temperature wasn't the beast that we often think of it being, which in itself is surprising," Leslie said.

Other studies of barnacles - the authors mentioned a specific example of North Atlantic barnacles - have found that temperature is indeed the differentiating factor. In the example, the "little gray barnacle" could only survive high up on the rocks where it is hottest and driest, whereas the competing "northern rock barnacle" thrived farther down.

The Chile study, led by Emily Lamb, a research assistant at the Estación Costera de Investigaciones Marinas (ECIM) in Chile, wanted to clarify the competition between two southern hemisphere barnacle species.

The two species, Jehlius cirratus and Notochthalamus scabrosus, show preference for different areas of the tidal zone, but do blend in some areas of the rocky cliffs. Lamb and her colleagues built 100-square-centimeter shade canopies and installed them at 10 sites along the rocks. They also selected 10 similar patches of rock to watch as controls, according to the press release announcing the research.

The team visited the experimental sites from February to August of 2010 to collect data. Overall, they found the shaded sites did not impact the competition between the two species or favor one species over the other.

The shade, and subsequent temperature drop, did lead to more growth on the part of both species, but both species tended to benefit equally.

"Finding a pair of species that exhibit vertical zonation but do not strongly compete is unusual," Lamb said.