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Ocean warming impacts the development of clownfish

A recent experimental study led by the Okinawa Institute of Science and Technology (OIST) in Japan has found that future ocean warming and marine heatwaves may impact the growth and development of clownfish (Amphiprion ocellaris) during their earliest life stages, with the larvae growing faster, having higher metabolic rates, and showing changes in the activity of certain genes in warmer temperatures.

During the first 20 days of their lives, clownfish pass through several developmental stages, marked by important environmental and behavioral changes in the wild. Soon after hatching, clownfish larvae are carried from their home reef to the open ocean where, after roughly ten days, they start to develop their iconic orange-white colors. Around day 14, they find a new reef where they seek out and settle into an anemone host. 

To assess how warmer temperatures may impact this developmental timeline, the experts reared clownfish in captivity at water temperatures of either 28°C (the current summer ocean temperature in Okinawa) or 31°C (the estimated seawater temperatures triggered by global warming by the end of the century). The experiment revealed that the larvae reared at higher temperatures hit their developmental milestones around two days earlier than those reared at current temperatures, and exhibited higher metabolic rates, most likely driving their faster growth rates. 

In addition, at each stage of their development, clownfish reared at 31°C showed either increased or decreased activity in over 450 genes, with several genes associated with heat-stress being more active from the earliest developmental stages, while genes involved in neurotransmission decreasing their activity at later stages, meaning that higher temperatures could lead to changes in clownfish cognition and behavior.

However, predicting how these metabolic and genetic modifications will impact the survival of clownfish under increased heat stress remains a major challenge. “On the one hand, the majority of clownfish do not survive the larval period due to predation, so shortening this time could increase their chances of survival and settlement. On the other hand, faster development may mean the clownfish disperse to new reefs less effectively, and the larvae may not be able to take in sufficient food to meet their increased energy demands,” explained lead author Billy Moore, a doctoral student in Marine Biology at OIST.

Finally, the experiments also revealed changes in the epigenome (the set of chemical compounds which modify the genome in ways “telling” it what to do, where to do it, and when to do it) of clownfish raised in warmer temperatures. 

“We are now beginning experiments to study how the epigenome differs between clownfish raised at 31°C compared to 28°C. This could have really important implications as epigenetic changes laid down in the early stages of development impact how individuals respond to changes and stresses in the environment during their adult life,” Moore concluded.

The study is published in the journal Science of the Total Environment.

By Andrei Ionescu, Staff Writer

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