The barnacle, a key thread in the marine food web, was thought to be missing along rocky coasts dominated by upwellings. Now a research team headed by Brown University marine ecologist Jon Witman has found the opposite to be true: Barnacle populations thrive in vertical upwelling zones in moderately deep waters in the Galapagos Islands.

Working at an expansive range of underwater sites in the Galapagos, marine ecologist Jon Witman and his team found that at two sub-tidal depths, barnacle larvae had latched onto rock walls, despite the vertical currents. In fact, the stronger the vertical current, the more likely the barnacles would colonize a rocky surface.

The researchers also documented the presence of whelks and hogfish, which feast on barnacles. This predator-prey relationship shows that vertical upwelling zones are “much more dynamic ecosystems in terms of marine organisms than previously believed,” Witman said.

Scientists who study coastal marine communities had assumed that prey species such as barnacles and mussels would be largely absent in vertical upwelling areas, since the larvae, which float freely in the water as they seek a surface to attach to, would more likely be swept away in the coast-to-offshore currents. Studies of the near-surface layer of the water in rocky tidal zones confirmed that thinking. But the field work by Witman and his group, in deeper water than previous studies, told a different tale: Few barnacles were found on the plates in the weak upwelling zones, while plates at the strong upwelling sites were teeming with the crustaceans. Flourishing barnacle communities were found at both the 6-meter and 15-meter stations, the researchers reported.

The scientists think the free-floating larvae thrive in the vertical-current zones because they are constantly being bounced against the rocky walls and eventually find a tranquil spot in micro crevices in the rock to latch on to.

Further Reading
Coupling between subtidal prey and consumers along a mesoscale upwelling gradient in the Galápagos Islands. Jon D. Witman, Margarita Brandt, Franz Smith. Ecological Monographs 2010 80:1, 153-177
Brown University News, Barnacles Prefer Upwelling Currents, Enriching Food Chains in the Galapagos