Bleached Anemones and the Devastating Effect on Anemonefish

We recently saw something sad in Moorea: the anemones are bleaching, and the Anemonefish who live there are struggling.

It turns out the bleaching of the reefs in Moorea is not restricted to corals. The anemones are bleaching, too.

We’ve been returning to a particularly beautiful anemone garden for more than a year, in about 15 meters of water. Recently we found all the anemones at shallow depths were a ghostly white, instead of their standard golden color.

We’ve never seen Nemo’s coral garden look like this before, and it was concerning.

We wondered what affect this would have on the anemonefish. It turns out the fish are under a lot of stress due to the bleaching of their anemone homes.

CRIOBE conducted an intensive study in Moorea in 2016 during a similar ocean warming event. They found the bleached host anemones had devastating effects on the reproductive abilities of the Anemonefish.

The Anemonefish has a commensal relationship with its anemone and stays near it for protection. The study found the bleaching of the anemone causes high stress for the fish.

This increased stress resulted in a 73% decrease in the viable eggs the fish were able to produce in the bleached anemone.

“Over the 5-month bleaching period, anemonefish associated with bleached hosts spawned less frequently, initially laid 64% fewer eggs, experienced 38% higher egg mortality during incubation, and ultimately produced 73% fewer viable pre-hatch eggs compared to before the bleaching period.

Why anemonefish should exhibit a stress response to host bleaching is not known, but may be in response to a perceived increased risk of predation either from the shrinking of the anemone, or a reduced neurotoxicity of venom from bleached anemones.”

Fortunately, the study also suggests the anemones can recover when ocean temperatures drop. The ocean is colder now, so this anemone garden might have a chance to heal. But I am concerned about the future stress on these anemonefishes as ocean temperatures continue to rise. We will continue to find animals affected by rising ocean temperatures, like these anemonefishes.

Information credit: Cascading effects of thermally-induced anemone bleaching on associated anemonefish hormonal stress response and reproduction. CRIOBE, Moorea, October 10, 2017