Warming oceans, one of the effects of climate change, may reduce the fertility of clownfish living in sea anemone.
Coral bleaching is also a known effect of climate change. Corals have a symbiotic relationship with a type of algae called zooxanthellae. This algae is what gives the corals their vibrant colors, as well as the nutrients that corals need. When ocean waters get too warm, the corals get stressed and expel their zooxanthellae. When this happens, the corals turn bone white. While corals can survive a bleaching event, they'll definitely be in danger of dying.
Sea anemone, where clownfish reside, also experience the same kind of bleaching as corals. Clownfish protect themselves from predators by hiding in the tentacles of sea anemone, and the anemone also serve as a nursery for the clownfish's eggs.
The sea anemone also lose the algae that give them their vibrant colors when the rising ocean temperatures stress them out. When this happens, the clownfish get stressed as well.
Bleached anemone [Photo by Justin Marchall/coralwatch.org/UQ]
The stress caused by the sea anemone's bleaching makes the clownfish simply stop producing and laying eggs. According to a new study, clownfish may not be the only species that get affected by bleaching. Other species of marine life that live in anemone and corals also may get affected. Thus, just the stress of bleaching may dramatically impact fish populations.
Researchers monitored 13 pairs of clownfish and their anemone from October 2015 to December 2016. The monitoring began before the 2016 El Niño event that triggered a global bleaching event and continued after the El Niño ended. Half of the anemones the researchers were studying experienced bleaching, and the clownfish living in these anemone drastically reduced the number of viable eggs they laid.
According to the findings, the fish living in the bleached anemones began laying eggs less frequently, and each time, they laid fewer and fewer viable eggs. However, the clownfish living in anemone unaffected by bleaching showed no changes in the frequency of egg laying as well as the number and viability of the eggs they produced.
So how was sea anemone bleaching affecting the clownfish's fertility? The answer may lie in the hormones that regulate a clownfish's bodily functions.
A clownfish withtending to its eggs [Photo by David Doubilet]
Researchers took blood samples from 52 pairs of clownfish, including the 13 earlier included, and noticed something about the hormone cortisol as well as the fish's sex hormones. The samples revealed that cortisol levels increased in the fish, while sex hormone levels dropped significantly. As sex hormones go down, so does the fertility of the fish.
Fortunately, the sea anemone and the fish they were hosting did recover from the bleaching event. However, they definitely took their time. When the anemone and the fish regained their health, the temperatures in the ocean had been down for months.
Now, the researchers wonder how the coral, anemone, clownfish, and other fish will fare during the next El Niño. What if the next one would be more intense, or would last longer? The researchers intend to continue studying the same clownfish in their research, since clownfish live relatively long lives and hardly ever swim far from home.
Get weekly science updates in your inbox!