larvae are a critical stage in the life cycles of marine invertebrates, we need to understand what happens to larvae in the ocean and how these larvae get back to shore.”

He continues, “We would ultimately like to develop predictive models that may be usefully applied to commercial fisheries. Further, we’re trying to predict possible responses of marine organisms to global climate change and El Nino events.”

Project members studied the distribution and transport of larvae and patterns of ocean currents. Now, mathematical biologists are processing the collected data in order to develop the larger model.

Jarrett’s findings to date? “I compared two sites and found barnacle mortality was much higher and growth rates much lower at the site in Mexico compared to La Jolla,” he concludes. “What was really interesting was that at the Mexico site, barnacles were either narrow or bent in their morphology, and at La Jolla, all the barnacles had an oval operculum (opening). I thought there’s something strange here! They are the same species, Chthamalus fissus, but they look very different.” Jarrett’s findings will appear in the January 2008 issue of Journal of Crustacean Biology.

Further Research Has Yielded More

One day Jarrett was observing snail predators. To feed on barnacles, the snail rams its long pointy spine into the barnacle’s operculum. “I got to thinking if the barnacle had a narrow operculum or if the opening were on the side of the barnacle, it would be harder for the predator to kill it,” remembers Jarrett. “I also observed that the snail population is much larger at the Mexico site and practically non-existent at La Jolla. I wondered if what I was seeing was an example of phenotypic plasticity whereby exposure to the predator at the Mexico site was inducing an adaptive change in morphology.”

To test his idea, Jarrett transplanted juvenile barnacles among the two study sites and monitored their morphology over nine months. “Sure enough! Regardless of where the juveniles originated, the juveniles in Mexico became narrow or bent; the juveniles in La Jolla developed the oval morphology,” he exclaims.

Subsequently, Jarrett has done predator exposure experiments in the field. Data support the conclusion that mucous from the predatory snail induces the change in morphology. One outcome of this research, he says, “There’s recent evidence that the snail predator population is expanding further north due perhaps to an increase in water temperature.” 

Bemused, he smiles. “The big question in studying plasticity is why barnacles do not just develop the adaptive morphology (either bent or narrow)? It ends up that the bent and narrow forms can better survive predation, but grow much slower and produce fewer offspring. So by being plastic, barnacles can develop the oval morphology when the predator is absent, but in the presence of predators, barnacles can develop the adaptive morphology and at least improve their chances of survival and reproduction.”
 

Two New Projects

Jarrett is now studying whether individuals in barnacle populations further north are capable of developing adaptive morphologies. “The concern is if the barnacles don’t have this adaptive capacity, their populations may be decimated by the predator. If that’s the case, marine reserves and conservation directors should keep a close eye on this predator, because barnacles are an important food source for a variety of marine organisms,” he explains.

He lauds his CCSU students who currently are culturing barnacles from several different populations in Southern California and exposing them to the predator to see if the barnacles can alter their morphology. “This research could definitely not have progressed to where it is today without the work of so many dedicated undergraduate and graduate students involved!” he declares.

This summer Jarrett journeyed to southwest Ireland on an exploratory trip looking for evidence of phenotypic plasticity in related species of barnacles. “Looks like there’s a different mechanism that results in the plastic response of these barnacles from southwest Ireland. I wonder why?” he muses.

“That’s what’s exciting about studying biology. There are always new questions to be answered!”