Hot Stuff on Mussel Beach

Elizabeth Turner
NOS Center for Sponsored Coastal Ocean Research

February 20, 2009 — It is a good idea to warm up your muscles before you exercise, but for marine animals such as mussels, warming up may prove to be hazardous. Mussels and other species living in the intertidal zone, between the high and low tide marks on ocean shores, can be especially sensitive to temperature changes since they are covered with seawater at high tide and exposed to the air at low tide. Their body temperatures already change dramatically over the course of a day and long-term climate changes may produce conditions that will place them at risk.

A project supported by NOAA’s Center for Sponsored Coastal Ocean Research is determining how warming temperatures may affect animals that live in the intertidal zone. Understanding the influence of long-term temperature changes on these species will allow us to predict changes in their distributions and provide information for the management of coastal environments in a changing climate.

"As humans, we tend to have a very biased view of the world. We forget that changes in air temperature, which tend to have only very small direct effects on us, can have huge effects on other species," says project co-investigator Brian Helmuth, associate professor of biological sciences at the University of South Carolina.

Helmuth notes that, "this is especially true for species that have temperatures driven primarily by the sun, wind, and air temperature, much as the way your car heats up on a sunny day." In many cases, these animals and plants have temperatures that are very different from the surrounding air, and two species living under the same environmental conditions can have very different body temperatures due to their shape, color, size, and behaviors.

Study areas for this project include National Estuarine Research Reserves sites on the East and West coasts of the U.S. The NERR system is a partnership between NOAA and coastal states that provides a network of protected areas for long-term research, education, and stewardship. The NERR sites provided ideal locations for this project, because of their wide geographic range and the long-term monitoring of temperatures and species present at the sites.

Species targeted for study include mussels and barnacles on rocky shores, in addition to worms, burrowing shrimp, and sea urchins on sandy and muddy beaches. Because these species have a big influence on the structure of the ecosystem, understanding how they react to temperature changes can help predict what will happen to the larger system.

The project staff compares temperatures collected by the “robomussels” against the results of a computer model that uses NOAA and NASA weather data, as well as information on the animals themselves, to predict patterns of animal temperature. Results have shown that the predictions of animal internal temperatures line up well with the model predictions. More importantly, the model results help to explain observations over the last 100 years that have shown shifts in where species live.

"Unfortunately, from what we can tell so far, California mussels are likely already pretty close to the edge of their distributional range, at least at some places along the West Coast. Our study suggests that climate change may start to kill marine animals in certain areas,” Helmuth says.

The ability to explain past patterns gives the researchers confidence that they may be able to forecast changes in the habitat range of species. By combining predictions of temperature with temperature tolerances of different species, they hope to provide resource managers and other scientists with “maps” of the probability of temperature stress at sites around the globe. This will help managers plan for changes in coastal ecosystems and help them to interpret species changes that may occur.