A San Francisco State University student who spent nearly three years analyzing dime-sized sea snails along the Tiburon shore has compiled data indicating global warming could affect not only the species but other sea life critical in the food web.

Brittany Bjelde, 27, who just graduated with a master’s in marine biology, worked at the university’s Romberg Tiburon Center for Environmental Studies closely monitoring the temperatures and even heartbeats of fingered limpets — a tiny mollusk.

“My goal was to assess how these animals might fair under climate change,” said Bjelde, standing inside a lab at the Romberg Center along the bay. “I wanted to look at how vulnerable they are right now to the temperatures they experience.”

She theorized the findings could be applied not only to the snails but other invertebrate and intertidal organisms that form a food web essential to marine and bird life along Marin’s coast and in the Bay Area.

The snails — which attach themselves to rocks — were of particular interest to Bjelde because they live both in and out of the water as tides ebb and flow. Research has been done on the species in the water, but not outside, when they are much more vulnerable to temperatures.

“The limpet’s foot is in contact with the rock, so whatever temperature the rock is, that’s their body temperature,” said Bjelde, a Central Valley native whose curiosity in the oceans was sparked by scuba diving.

Bjelde was able to reproduce those rock temperatures in the lab and measure the mollusk’s body heat.

What the young researcher found was astonishing: the limpets’ temperatures could climb as much as 24 degrees in one day.

“It’s a lot variability,” she said. “It’s thought these animals have already stretched their physiology to the maximum to live in such a hard, variable environment. So the question is, do they have the capability to acclimate and push their physiology any more, or are they at their limit?”

There is now evidence it’s the latter. As outside temperatures climbed past 90 degrees, it proved fatal for some of the limpets, the Romberg researcher showed.

“At some point their heart flat-lines. What we found is that these animals are really vulnerable right now,” she said. “There are already temperatures that are exceeding their break point, so a die-off in the future with climate change could occur.”

The research, published in the Journal of Experimental Biology, determined that limpets have a narrow safety margin for heat outside the water and experience multiple days when summer temperatures potentially can prove fatal.

“This is groundbreaking work that is showing how a lot of different organisms are going to react to changes in temperatures,” said Toby Garfield, director of the Romberg Center. “Nature is going to adapt, but we want to understand how that happens.”

Contact Mark Prado via email at mprado@marinij.com