Marine Organisms

Global Warming: Lessons Taught By Snails And Crabs
Science Daily, November 23, 2000

If you think that global warming is some far-off problem for future generations to worry about, consider what George Somero has to say. As acting director of Stanford's Hopkins Marine Station, Somero has to walk only a few dozen steps from his lab to the waters of Monterey Bay, where he and other marine biologists have found disturbing signs that higher ocean temperatures have transformed wildlife populations in the Pacific. "The effects of global warming already seem evident," says Somero, the David and Lucile Packard Professor in Marine Science at Stanford. "The vast majority of scientists regard continued warming of the Earth as inevitable," he adds, "and some of the best information we have on the potential effects of climate change comes from data collected right here at Hopkins." Somero points to a three-year study conducted in the 1930s, when Stanford graduate student Willis Hewatt counted and identified all of the marine invertebrates living in a 95-square-yard section of intertidal shoreline near the marine lab located in Pacific Grove, Calif.

The study was all but forgotten until 1993, when researchers decided to re-survey the same area to determine if the types of invertebrate species present at Hopkins had shifted during the past few decades. Scientists counted everything from limpets to crabs and discovered that marine populations had changed dramatically in just 60 years. "There was a significant decrease in northern species - those that tend to occur to the north of Monterey Bay, but eight out of nine southern species increased in abundance," says Somero. "The overall message in these data," he notes, "is that cold-loving species tended to move out, and warm-loving species moved in." Could this shift in species distribution have been caused by a change in climate?

To answer that, researchers needed to determine if the temperature of Monterey Bay had changed since the 1930s. Fortunately, notes Somero, Hopkins Marine Station personnel have been meticulously recording seawater temperatures every day for nearly 80 years, and a review of those records showed that, indeed, Monterey Bay had gotten warmer. "The data showed that, during the 60-year interval between the two animal surveys, annual mean water temperatures increased on average by about 1.3 F [0.7 C]," says Somero. More significantly, he adds, peak summer temperatures in August rose nearly 4 F (2.2 C). Although these temperature increases seem relatively small, Somero believes they may have been substantial enough to push some species over the edge of what he calls their thermal tolerance range. "When thermal stress pushes body temperatures to values that are unnaturally high or low, biochemical structures and the physiological processes they support - such as the heart and nervous system - may be severely, and perhaps lethally, upset," Somero observes. Climatologists predict that, if global warming continues at its current pace, the average temperature of the Earth could increase another a 6 F (3.3 C) in the next 50 years.