By Gail Gallessich

A tough early life turns out to be a good thing for a fish, according to scientists at UC Santa Barbara.

They discovered that marine fish larvae that survive a long, rough journey eventually arrive at a near shore reef in good condition, and that they thrive afterwards.

In contrast, locally produced young have a relatively easy life and they arrive on the reef (near where they were spawned) in a variety of conditions––from poor to good. Only the young that are in good condition survive the first month on the reef.

“This research delves into one of the major questions of how populations are connected through dispersal,” said Scott Hamilton, a postdoctoral fellow in the Department of Ecology, Evolution, and Marine Biology. “We want to know where the young of many marine organisms are coming from and going to, and what factors determine whether they survive.”

Hamilton is the first author of the report on the team’s findings, published last month online in the Proceedings of the National Academies of Science. The results point to significant policy implications for the planning of marine protected areas, a topic of worldwide concern.

“It turns out that not all settlers arrive equally prepared for the rigors of the reef, and the probability that a new recruit will reproduce successfully may depend on where it came from,” said Robert Warner, professor of ecology, evolution, and marine biology.

Scientists analyzed the bluehead wrasse in this study, a fish that is common in the Caribbean Sea. Warner has studied the bluehead wrasse since the late 1970s. “We have been measuring ‘connectivity’ –– the proportional contribution of different sources to the population in any particular place –– by the numbers arriving,” said Warner. Survival may also depend on where the fish originated, he explained.

They used chemical analysis of the ear bones of the fish to extract information. The ear bones, also called otoliths, are hard, calcium carbonate structures located behind the eyes and below the brains of the fish. The otoliths grow a ring every day from birth and, like tree rings, these rings tell much about the life of the fish. For example, the spacing of the rings indicates how quickly the fish grew at different periods in its life.

The results surprised the scientists. “This information went against our expectation,” said Hamilton. “We expected near shore fish to get back and do well, particularly because they are in nutrient-rich waters, which is a good place to be.”

The otolith reveals the history and location of the fish during its life. Each ocean area has a particular chemical “signature” that is incorporated into the ring of the otolith as the fish pass through. The chemical composition of the ring indicates the type of water in which the fish swam on a particular day.

A fish traveling near a populated shoreline collects a higher amount of trace metals, like lead, in the rings of its otolith.

James Regetz, a programmer with UCSB’s National Center for Ecological Analysis and Synthesis, is a co-author.