Investigating Ocean Toxicity with Evan Tjeerdema, Marine and Coastal Sciences Undergrad
A red abalone perches atop an algae-covered rock. The sea snail’s spindly tentacles wriggle in the water, spilling from beneath its brick red shell as it feeds. The ocean current is light; the scene seems peaceful—if just for a moment.
Suddenly, an intruder emerges. A sea star is on the hunt, clambering across the rocky ocean bottom. After closing within the abalone’s range, it stretches out an arm lined with twitching, tubular feet and grasps the abalone’s shell.
To survive, the red abalone must act quickly. Fortunately, its tentacles have already chemically detected the sea star’s presence.
In defense, the abalone raises its shell high and shakes it back and forth vigorously, attempting to dislodge the sea star’s powerful arms. The sea star soon loses its grip, and the red abalone skitters away, moving much more quickly than expected for a snail. It disappears into the ocean blue. Safe, for now.
Such predator-prey interactions fascinate UC Davis undergraduate student Evan Tjeerdema, a senior Marine and Coastal Sciences major and Environmental Toxicology minor.
“What I’m interested in is seeing how these anti-predatory behaviors might be impaired in future ocean conditions,” said Tjeerdema. “A lot of the reading that I’ve done and the work I’ve done seems to show that ocean acidification may impair a red abalone’s ability to detect chemicals exuded by predators in the water.”
Exploring adaptation to ocean acidification
Over the summer, Tjeerdema recreated this scenario in an experimental setting at the Bodega Marine Laboratory. Using red abalone (Haliotis rufescens) and sea stars (Pisaster ochraceus), he tested the predator-prey interaction in ambient and acidified waters.
“There was a pretty marked difference with the acidified abalone, in that it responded in the same way but not quite to the same degree,” he said. “No one has looked at this with abalone before, and doing this type of work with such a commercially and culturally important species in California, I think it’s an important thing.”
Tjeerdema spent the entire summer at the Bodega Marine Laboratory, participating in both of the facility’s summer sessions. The opportunity to work continuously near the ocean for an extended period of time was a dream come true for him.
“As long as I can remember, I wanted to be a marine biologist,” said Tjeerdema. “The Bodega Marine Lab is just beautiful, the marine reserve is fantastic. There’s just something about being this close to the ocean all the time.”
The impact of environmental toxins
As part of the Bodega Marine Laboratory’s summer sessions, Tjeerdema took various marine science courses, including one on environmental toxicology. His research on red abalone anti-predatory behaviors is one of two independent research projects he conducted over the summer.
For his first project, he focused on a different shelled organism—the crab.
“I wanted to study some pollutant that adversely affects marine organisms and eventually, I settled on investigating creosote,” Tjeerdema said.
Creosote—an oily, black substance—is a preservative that can be found coating the wood of piers and marinas. It’s also toxic to marine life. Previously, the Bodega Marine Lab Toxicology Group showed creosote-treated pilings were harmful to the embryos of herring, which sometimes spawn on the pilings.
“While [creosote] is stuck in the wood pilings, some fraction of it is able to essentially diffuse out and mix with the water,” Tjeerdema said. “That’s what can affect swimming organisms, like fish or aquatic larvae of crabs or snails.”
The toxic effects of UV light
Tjeerdema tested the effects of creosote on lined shore crabs (Pachygrapsus crassipes). One can find adults of this species scuttling around the tide pools of Horseshoe Cove, a stone’s throw from the Bodega Marin Laboratory. In their juvenile form, lined shore crabs look dramatically different from their adult counterparts. With a bulbous head and a curved tail, the larvae somewhat resemble chestbursters from the Alien film franchise.
Tjeerdema wanted to see if creosote adversely affected the larvae’s swimming behavior. Using juveniles, he exposed one group to creosote-infused water and another group to ambient water for a 20-hour period. He found that it took only 1 part per million of creosote to adversely affect half the population of his crab larvae. “One liter of creosote in an Olympic-sized swimming pool is about the equivalent of 1 part per million,” he said.
Tjeerdema also studied the phototoxic effects of creosote by exposing his crab larvae to ultraviolet light in the lab.
“Certain chemicals get more toxic when they’re exposed to sunlight,” Tjeerdema said. “In particular, ultraviolet light.”
“So you have your chemical in the water and it gets hits by ultraviolet light and some of the chemical bonds in the molecules start to break,” he continued. “They interact with surrounding oxygen molecules and water molecules to form what are known as reactive oxygen species.”
While creosote is harmful in and of itself, the reactive oxygen species are also toxic. The combination of the two increases the overall toxicity of creosote-contaminated water. When treated with ultraviolet light, creosote became three times as toxic to the crab larvae, according to Tjeerdema.
This same process occurs in the creosote accumulated in the animals’ tissues. When crab larvae that have taken up creosote are exposed to ultraviolet light, the creosote in their cells breaks down and becomes even more toxic.
But recovery wasn’t out of the question.
“After 10 hours of removal from the ultraviolet source, the number of impaired individuals ceased to be statistically different from that of the samples which had no ultraviolet exposure,” said Tjeerdema. “This suggests that over time, after ultraviolet light is removed, the phototoxic effects dwindle leaving only the effects of creosote alone.”
Making a contribution to ocean knowledge
For Tjeerdema, the Bodega Marine Laboratory’s summer sessions are a way for undergraduates to contribute to humanity’s growing knowledge of the ocean and its inhabitants.
“Having 30-something undergraduates come out every summer and do their own project is huge because that’s like 30 extra researchers generating 30 pieces of new information that’s never been done before,” he said.
Each summer, a new cohort of UC Davis students continues this tradition of contribution. Like Tjeerdema, these students explore the unknowns of the ocean, finding new ways to usher in discovery.
“It kind of illustrates how much we don’t know about something like Bodega Bay, which is right here,” Tjeerdema said. “There’s a lot that’s happening that we don’t entirely understand.”