New Publication: October 2017 (Beldade et al)

It Takes Three to Tango : Global Warming Puts Clownfish Future in Hot Water
10 October 2017 | Contact: SUZANNE MILLS | Nature Communications

New research has found that high sea temperatures that bleach anemones disrupt reproduction in wild clownfish. Scientists at CRIOBE from the École Pratique des Hautes Études (EPHE), the Centre National de la Recherche Scientifique (CNRS), France, and from the University of Ulster, Northern Ireland, showed that high temperatures by bleaching anemones could affect the future survival of clownfish.

Researchers and students monitored wild clownfish and their anemones in Moorea, French Polynesia, every two days over 14 months before, during and after the 2016 global warming event that bleached coral reefs worldwide. Half of the anemones bleached, and in those that did the clownfish living in them became stressed and stopped laying eggs until the anemone recovered 4-5 months later, long after the temperatures had returned to normal.

Lead author Dr Ricardo Beldade, CRIOBE, CNRS, said, “Elevated sea temperatures cause the small algae living in a symbiosis inside the anemone’s tentacles, and which also renders them golden in colour, to be expelled and anemones lose their colour or “bleach”; clownfish that also live in symbiosis with the bleached anemones suffer an immediate reproductive depression. It clearly takes three to tango in this three-species interaction and high sea temperatures / climate change stop/s the music.” Dr Beldade adds, “In coral reef ecosystems not only anemones but also corals bleach, and as a direct consequence fish associated with them may not reproduce either. Such strong indirect but immediate impacts of elevated sea temperatures will certainly disrupt the functioning of coral reef ecosystems.”

Figure 1 Monthly temperatures in Moorea lagoon from 2007-2015 (black lines) and September 2016 to August 2016 (red lines). The vertical and red lines are the period of the heating anomaly in 2016.

ERASMUS exchange student from the University of Ulster, Northern Ireland, Rory O’Donnell, said “When the water temperature increased the golden coloured anemones remained alive but they dramatically turned bright white. The clownfish had no option to move elsewhere as they would have been predated upon outside their anemone, so their way of coping was to reduce reproduction. We photographed over 500 nests and counted over half a million eggs, one by one, and the impact of bleaching on reproduction was striking.”

EPHE Masters student Agathe Blandin at CRIOBE, added, “We took small blood samples from the clownfish and found that their levels of cortisol, a stress hormone, were elevated and their reproductive hormones, similar to testosterone in males and estradiol in females, decreased. I was most relieved when the clownfish started spawning again once the anemones had recovered.”

“Clownfish are long-lived fish and as they don't move from their host anemone, we are monitoring individual fish to see how they cope with a second warming-induced bleaching event. We will see if their response is the same as after the first time, or whether they can refine their response to impact their reproduction less dramatically. We are exploring if fish can cope with climate change via small modifications in their physiology, namely their stress hormone response,” explains Associate Professor Suzanne Mills, from EPHE at CRIOBE.

These results highlight the indirect effect of coral reef bleaching and emphasise the need to halt and/or reverse climate change.

Beldade R., Blandin, A., O’Donnell, R., Mills S.C. 2017. Cascading fitness effects of thermally-induced anemone bleaching on associated anemonefish hormonal stress response and reproduction. Nature Communications.

Dr Suzanne Mills (Moorea, French Polynesia)