While coral bleaching is a well-known result of unusually warm ocean water, it turns out that sea anemones can also be bleached, which in turn affects the clownfish that live in and around the anemones.
In fact, the fish show much higher stress levels and a dramatic decrease in offspring — as much as 73% less — when their home sea anemones are bleached in warmer waters, the study found.
“While no effects on adult anemone survival were observed, the effects of bleaching on reproduction and population demography were likely even greater than demonstrated here,” study lead author Suzanne Mills of the French university Ecole Pratique des Hautes Etudes told the Daily Mail.
She added that the finding is alarming, since man-made stressors and the rate of change in environmental conditions are expected to multiply in the coming decades, “with bleaching and habitat degradation becoming more frequent.”
Using the natural El Niño warming phenomenon as a stand-in for what future man-made warming might bring, researchers visited 13 pairs of clownfish and their host anemones in the coral reefs near Moorea Island in French Polynesia from October 2015 to December 2016.
Scientists capitalized on that opportunity to measure the fishes’ stress and reproduction before, during and after their host anemone underwent bleaching. (Half of the anemones monitored in this study bleached.)
It turned out that the clownfish couples from bleached anemones spawned far less frequently and produced far fewer viable young than those that were not bleached.
This study, which appeared in the peer-reviewed British journal Nature Communications, underscores the numerous cascading effects of warming oceans on the residents of coral reefs.
The clownfish are not an isolated case: In all, 12% of the coastal fish in French Polynesia depend on anemones or corals to feed or to find protection from predators.
In cases of prolonged bleaching, like that of the Australian Great Barrier Reef in 2016 and 2017, the renewal of all of these populations could be affected, and with them the stability of the ecosystems, the scientists said.