A new study published this week in Proceedings of the National Academy of Sciences (PNAS), confirms the importance of eddies in the growth and development of larval fish. Researchers found that young fish reared in nutrient-rich eddies in the Straits of Florida grew faster, and had a survival advantage compared to their counterparts outside eddies.
The research team from Oregon State University and the University of Miami, collected larval fish both inside and outside of eddies, focusing on three species – bluehead wrasse (Thalassoma bifasciatum), bluelip parrotfish (Cryptotomus roseus) and bicolor damselfish (Stegastes partitus). They found that both T. bifasciatum and C. roseus grew faster than larvae outside of eddies, and they were subsequently more likely to populate nearby reefs.
The team first investigated the daily growth rates of each fish by examining the otoliths, or ear stones, finding that fish from the eddies had substantially higher growth rates than fish caught outside the eddies. To confirm their survival rate, researchers sampled young juveniles which had settled to nearby reefs. And again using otoliths to chart daily growth rates, they were able to determine that almost all the fish had growth patterns similar to larvae from eddies.
The researcher theorized that fish which begin life outside an eddies either die from starvation, or become more susceptible to predators then fish from inside the eddies. “Eddies upwell nutrients and provide a high-productivity environment that gives larval fishes growing there a head start on survival,” said Su Sponaugle, a marine biologist and principal investigator on the study who is affiliated with both Oregon State University and the University of Miami.
In cooler springtime waters, when larval fish are growing slowly, there is only a slight difference between fish raised inside or outside of eddies. However by the late summer, when warm waters increase fish growth rates and food becomes scarce, eddies act as oasis in the dessert providing larvae a steady supply of nutrients, and a fighting chance for survival on the reef. [Phys.org]