Waves of Change
Global warming drives some marine animals north up the Central Coast.
Thursday, December 27, 2007
As global warming tweaks weather patterns – contributing to more droughts, hurricanes, wildfires and floods – it’s prompting some people to move to more environmentally hospitable places. After Hurricane Katrina, for example, a reported 14,000 evacuees fled to California. This fall’s wildfires drove thousands more away from their Southern California homes. Greenpeace predicts that by 2040, global warming will cause 200 million people to relocate.
Some marine animals are doing the same thing.
Scientists at Stanford’s Hopkins Marine Station were the first to pick up on the trend in the early 1990s. Chuck Baxter, who was a Stanford lecturer at the time, was surprised to find creatures along Hopkins’ Pacific Grove shoreline that he was used to seeing in warmer waters. It was like shirtless beach studs from Malibu tossing a Frisbee in chilly Monterey.
“I had noticed these changes in the intertidal that were reminiscent of what I had seen in Southern California,” he says.
Baxter knew that, in the early 1930s, Hopkins scientists had counted marine invertebrates within a 108-yard band of rocky intertidal habitat behind the PG lab. He convinced two of his undergraduate students to repeat the experiment six decades later, when the average annual shoreline temperature had warmed by 1.35 degrees Fahrenheit.
The students’ findings confirmed their prediction: As global warming heats up the sea, some of Monterey Bay’s temperature-sensitive species are moving north to cooler waters.
Eight of nine southern species that were absent or scarce in the 1930s transect were common in the 1990s. Five of eight northern species became scarcer or disappeared entirely. Some plant communities also shifted in the rocky tidelands, becoming more dominated by low-growing turf algae characteristic of warmer waters. The study made such a splash that it was published in the prestigious journal Science.
Since then, research and observation have supported the notion that global warming is changing our marine neighborhood.Hopkins scientists are currently studying an invasive Mediterranean mussel that looks identical to a native mussel, but has mixed with – and in some cases entirely replaced – the native population. Likewise, according to Hopkins Director George Somero, a southern finger limpet appears to be moving up the Central Coast and taking over its native look-alike in the Monterey Bay.
Tidal species native to the Central Coast may be vulnerable to takeover by invaders better equipped for the heat, Somero says, with ripple effects up the food chain. For example, if mussels displace barnacles covering rocks in the tidal areas, sea otters and sea stars may get extra munchies – while exclusive barnacle-eaters go hungry.
“Climate change is going to work in favor of the invasive species,” he says.
In the past decade, fishermen and scientists have also noticed more giant Humboldt squid gliding through local waters, gobbling up whatever hapless creatures they can fit in their knife-sharp beaks.
The Humboldt squid, unlike the limpets and anemones of the transect study, is a very temperature-tolerant creature. It does just fine in cold and warm waters alike. So it probably hasn’t been lured to Monterey Bay by warmer surface waters – at least not directly. But the web of nature works in indirect ways.
Squid can tolerate low-oxygen waters that would suffocate most other organisms. And those “hypoxic” waters, which tend to occur about 600 to 800 meters deep off the coast of California, are expanding and moving closer to the surface, according to Hopkins professor and Humboldt squid expert William Gilly.
The opportunistic squid appear to be taking advantage of the low-oxygen waters that keep out competitors, giving them easy access to a buffet of sea creatures closer to the surface. “They can hang out in this hypoxic netherworld all day, if they want,” Gilly says.
Scientists don’t know exactly why that netherworld is expanding. It could be related to agricultural runoff that causes oxygen-depleting algal blooms, he says. Or it could be that surface waters heated by global warming have changed plankton productivity, causing consequent effects through the complex marine food web.
“There’s something going on in the ocean that is causing a problem that may or may not be linked to the temperature directly. Probably indirectly,” Gilly says. “It may be another manifestation of global climate change. That’s what I don’t think anyone knows.”
Whale-watchers have noted the presence of more Risso’s dolphins and other predators that may be drawn by the higher numbers of squid. “These animals are following food and productivity,” Gilly says, “not the temperature per se.”
Hopkins scientists strongly suspect that climate change is a major influence on the shifting demographics of Monterey’s underwater neighborhood. But they need good historical data to prove it, and that’s hard to come by.
“It’s tough to try and interpret the things that are going on,” says Jim Watanabe, an invertebrate biologist and Hopkins lecturer. “The big problem is the lack of long-term information that’s been gathered in specific locations over a long enough time so that you can see the long-term trends. It’s the sort of data that nobody thinks is sexy and is a heck of a job to go out and collect, but there’s no substitute for it when you need it.”
Somero adds a typical scientist’s disclaimer: Not all temperature-sensitive marine species are marching northward up the Central Coast. As noted in the transect study, two northern snails became more abundant in the 1990s than they were in the 1930s – a result that bucks the trend.
“That speaks to the complexity and unpredictability of climate change,” he says. “There will be changes. You can’t put a ‘good’ or ‘bad’ on that. It’s gonna be different.”