In 1931 a Stanford student named W.G. Hewatt marked out a narrow strip of shoreline, 108 yards long, on a rocky outcrop called Cabrillo Point in Monterey Bay. Over the next two years, Hewatt surveyed this intertidal strip, meticulously recording every countable marine creature he saw - starfish, limpets, snails, barnacles, anemones - you name it, he counted it. At the time, this laborious exercise provided a biological inventory for the Hopkins Marine Station, located in Monterey Bay, not to mention a doctoral dissertation for Hewatt. But beyond that, you might well ask, why bother? Who cares how many limpets cling to Cabrillo Point? It turns out, more than 60 years later, that we should all care. It has to do with global warming.
While it is well established that the world's temperatures are rising, almost certainly due to humans and their greenhouse gases, little is known about how plant and animal communities will respond to the change. Scientists have studied a variety of ecosystems, from the redwood forests, to the Gulf Stream waters, but most of this work can offer only predictions of what might happen as temperatures rise. The reason for the uncertainty is simple: so few studies have been detailed enough or long enough to accumulate the data required to link ecological changes with climate shift. Such work is labor-intensive and time consuming and tends to be met with questions like, "who cares how many limpets cling to Cabrillo Point?"
When ecology student, Sarah Gilman, now at UC Davis' Dept. of Evolution & Ecology, wanted to examine how a shoreline community might respond to rising temperatures, she needed a study site where 1) a detailed census had been conducted previously and 2) water temperatures had been regularly collected . She and her colleagues, Rafe Sagarin, Chuck Baxter and Jim Barry from the Hopkins Marine Station and the Monterey Bay Aquarium Research Institute turned to Hewatt's study site from 1931. Using his original maps and photographs, they located the metal bolts he had hammered into the rock to mark his transect. Replicating his exact methodology, they re-sampled the area in 1993 and 1994 and came up with dramatic results.
Ten out of 11 "southern" species, that is, those creatures who prefer warmer waters, had increased significantly in numbers since Hewatt's count. On the other hand, 6 out of 8 cold-loving "northern" species had declined sharply. These included species of starfish and crab. The 28 "cosmopolitan" species who aren't fussy about temperature, showed no particular trend. Among the more dramatic changes to the neighborhood was a warm-water snail that had not been recorded at all by Hewatt, but now clings to the rocks in aggregates as dense as 229 snails per square yard.
The landscaping too was different. From Hewatt's general descriptions of the underwater flora, it was clear that various species of algae (seaweed) had changed in abundance and distribution according to warm-cold preferences. In summary, it looks as if warm-water organisms have moved in Cabrillo Point, while cold-lovers have moved out.
Meanwhile, what has the water temperature been doing? Continuous records at Hopkins Marine Station show that the annual mean temperature of shoreline water has increased by 1.3 ° Fahrenheit (0.75 ° C) since 1931, while maximum summer temperatures have climbed by about 4 ° F (2.2 ° C). It appears that even this modest rise in water temperature has caused fundamental changes to the community of plants and animals in Monterey Bay.
Ecosystems throughout the world are likely to be responding in similar ways to global warming. The changes will almost certainly affect human activities, for example, our agriculture and fisheries. If we want to be prepared, we need to keep track of Mother Nature.
A distinction is often made, especially by funding agencies, between
"pure" research - that which has no discernible practical
value, and "applied" research - that which influences
human society. It's becoming clear that the line between the two
is a fine one at best. I doubt that even W.G. Hewatt in 1931 would
have guessed that his census of Cabrillo Point might have such
wide-reaching application.
© Kelly Stewart
Department of Anthropology, UCD, Davis, CA 95616.
email: kjstewart@ucdavis.edu