Unseasonal warm temperatures caused by El Niño have a profound effect on the fish populations of coral reefs in the South Pacific, scientists have found.  An international team of biologists studied the arrival of young fish to the atoll of Rangiroa in French Polynesia for four years and compared their results with satellite and oceanographic data.  They found that the El Niño event caused a sudden collapse in the plankton community and this led to a near absence of the young fish that are required to replenish adult stocks.

Coral reef fishes are bad parents.  Rather than caring for their young, they disperse them into the open waters off the reef where they drift with the currents while they grow and develop into small juveniles, at which point they make their way back again to the reef.  This process allows these baby fish to feed on plankton and escape the predators that would consume them if they had to grow up on the reef with adults.  But in a changing climate, this dispersal into the haven of open water could now become an Achilles’ heel for coral reef fishes.

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