A snail can tell us a lot about global warming

Green Acre: A study at the University of Washington's Friday Harbor Marine Lab takes an unusual approach to studying climate change.


An experiment at the Friday Harbor Marine Lab

Green Acre: A study at the University of Washington's Friday Harbor Marine Lab takes an unusual approach to studying climate change.

The star of a scientific study about how marine life will adapt to global warming is usually thought of as a garden pest. But an experimental study at the University of Washington’s Friday Harbor Marine Lab is giving the pest some notoriety. What is it? Hint: rhymes with whale.

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It may seem counterintuitive to study how marine ecosystems will adapt to global warming in Western Washington. But come to the University of Washington Friday Harbor Marine Lab on San Juan Island and you’ll learn the inter-tidal shoreline is a West Coast "hot spot." Long low midday tides from April to September, coupled with sunny days in July and August make it perfect testing ground. Add a simple predator/prey relationship, the snail and the barnacle, and you have the perfect test subjects. “Predator-prey systems are all over the world," says UW Biology Professor, Emily Carrington. "They’re really important for structuring any community as well as our marine one.” Carrington is lead researcher in a multi-year study about global warming’s impact on the ubiquitous marine snail.

First step: predict the body temperature of snails under current weather conditions. Carrington points to a specially designed tower with wires and instruments that measure wind velocity, UV radiation. “So with these inputs we can predict the body temperature of organisms that live on the shore. If we know where they are exactly.”

But how do you track a creature averaging 3 cm in length? Study its foraging behavior. How often and when do snails leave the cool comfort of underwater crevices to feed on exposed barnacles? “What we’re looking at is not any specific day, but what their temperature is, what the pattern is over the scale of weeks, seasons or ever year to year during the lifetime of these organisms.” This is where the wires come in. Thermal couple wires measure the temperature of just about anything, says Carrington. They’re draped over rocks and crevices, likely snail habitats. “So if they’re high on the rock we know what the snail temperature would be. If they’re in a crevice we know what it would be.”  What’s been discovered is snails seek food when tides are low in the evening or early dawn to avoid thermal exposure. If tides are low at midday, a few days later, they return to hiding. In contrast, their immobile prey, the barnacle, is stuck on rocks for life. Carrington says, “So in this particular case we would predict barnacles don’t do so well. Snails have a behavior that looks like they could adapt but then they won’t have any food to eat.”

To gain a better understanding of how snails and barnacles respond to climate change researchers brought them into the lab. Large tanks replicate the inter-tidal coastline: There are snails, barnacles, rocks and even the rhythm of tides timed to the real thing. Dawn Vaughn, a post-doc, increased the tanks aerial temperature during low tide over the course of a month by placing heat lamps over barnacles and rocks positioned on clay pots. “So the snails in order to feed had to crawl up this pot all the way to the top. If they were going to eat they were going to be hot. We gave them no choice.” Vaughn says they could have chosen not to feed and that’s what’s most interesting about the experiment.

Males fed less under high temperatures but females, who’d recently laid eggs, foraged on. It was initially thought snails would notice when it was hot and stop feeding or choose another time in the tidal cycle. “They continued to feed as if they were hard wired to feed approximately every 14 days despite what the temperature is.” Four days on, 10 days off, just as they feed on the inter-tidal shore. Again Professor Carrington: “So this tells us that air temperature alone isn’t the environmental cue they respond to directly. We didn’t know that when we started.”

The next lab study will test the effect of heat on reproductive output. The study of “free range” snails hopes to get a better sense of when they move up and down the shore. For that, graduate student Hilary Hayford, devised an ingenious method. A small cylinder with a radio frequency ID will be attached to the back of each snail. “We’ll put a little nub of marine epoxy around the radio tag and then stick it on the back of the snail like a little back pack.” Then she can monitor snails all over San Juan Island. “So if I’m clever about how I set this up I can know who exactly is crawling upshore and who is crawling downshore and if they’re doing this as the tide comes in and out or only at certain points in the lunar cycle,” Hayford says. So far in this three-year-long study researchers predict the lunar tidal cycle is a more important driver than temperature variation on any given day. The snails are so slow moving that deciding not to crawl up to feed because it was hot yesterday may not be a strategy that pays off energetically compared to basing their behavior on a predictable time of month when the temperature is likely to be favorable.

Green Acre Radio is supported by the HumanLinks Foundation. Engineering by Moe Provenchar. Produced in the Jack Straw Productions studios and broadcast by KBCS.


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A snail can tell us a lot about global warming