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El Nino threatens South Pacific reef fish

BRISTOL, England, Dec. 1 (UPI) -- Unseasonably warm temperatures caused by El Nino have had a disastrous effect on fish populations in South Pacific coral reefs, British researchers say.

An international team of marine biologists studying the arrival of young fish at the atoll of Rangiroa in French Polynesia for the last four years, said the El Nino event caused a sudden collapse in the plankton community that led to a near absence of the young fish that are required to replenish adult stocks, a University of Bristol release said.

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Coral reef fish, rather than caring for their young, disperse them into the open waters off the reef, where they drift with currents while growing into small juveniles before making their way back to the reef. This process allows the baby fish to feed on plankton and escape predators that would consume them if they had to grow up on the reef with adults.

In a changing climate, this dispersal into the of open water could spell doom for coral reef fishes, the researchers say.

"Near to the equator, fish arrive throughout the year to replenish adult populations," Steve Simpson from Bristol's School of Biological Sciences said. "In contrast, during the El Nino event at Rangiroa, when temperatures climbed up to 3.5°C (6.3 degrees F.) above the seasonal average, we found that the young fish virtually disappeared.

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"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 Nino," Simpson said.

"Just 1-2 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."

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