Warm Water and El Niño Effect Killing Off Young Coral Reef Fish

yellow Tang fish nips at corals

Migrated Image / Joel Kramer / Flickr

Baby fish are getting the short end of the stick with warmer ocean temperatures, and populations of coral reef fish species could see a significant decline. A team of biologists looking at the arrival of young fish along the Rangiroa coral atoll in French Polynesia has found that fish populations are suffering. The young fish struggle as plankton, a major food source, collapses with the warmer temperatures.

Science Daily reports that young coral reef fish grow up in the open waters off the reef, feeding on plankton and hiding from predators. They make their way back to the reef as they grow up. However, without plankton, they lack a food source. Researchers used a crest net -- a large net facing out to sea along the edges of a barrier reef. Biologists monitored the number of fish that return to the reef from the open ocean over the course of four years. The target years included the 1997-1998 El Niño. What they found is worrying.

"Analysis of satellite images around Rangiroa suggested that plankton, the food supply for many baby and adult reef fishes, declined dramatically during the warm waters of El Niño. As a consequence, adults struggled to produce offspring and young fishes were likely to starve when in open waters off reefs, Just one to two months after the onset of the warm conditions, the next generation of young fish stopped arriving so that adult stocks were no longer being re-supplied."--Steve Simpson, The University of Bristol

Because ocean temperatures are expected to continue to increase, as is the frequency of El Niño events, the findings are worrying not only for the health of coral reef ecosystems but also the coastal economies that rely on fish for food, exports, and tourism.

We know that coral reefs are worth upwards of $172 billion to the global economy, and a loss of the colorful, vibrant species that draw the attention of humans could be devastating, let alone the fact that the survival of coral reefs depends on an abundance of hundreds, even thousands of different species.