As global temperatures rise and the oceans heat up, a huge question is how fish that are adapted to one set of temperatures will survive this upheaval. Now we know at least one species could adapt fast enough to survive.
Generally speaking, fish require very precise temperatures to survive in a way, leaving them far less margin for ecological error than their land animal counterparts. As temperatures continue to rise, that means many fish species will have to move further away from the equator in order to compensate, but scientists don't know whether many fish species will be able to migrate fast enough to keep pace with the changing water temperatures. Indeed, how fish and other species will be able to acclimatize to these changing conditions remains one of the biggest mysteries of climate science.
Now, a team of Australian scientists have a bit of good news. They examined the damselfish, which is found throughout the world's tropical coral reefs. Lead researcher Jennifer Donelson explains:
"When we exposed damsel fish to water temperatures 1.5 degrees and 3 degrees above today's, there was a marked decline in their aerobic capacity as we'd expected. This affects their ability to swim fast and avoid predators. However when we bred the fish for several generations at higher temperatures, we found that the second generation offspring had almost completely adjusted to the higher temperatures. We were amazed… stunned, even. It shows that some species can adjust faster than the rate of climate change."
What exactly is driving this adaptation is unknown. This doesn't appear to be a simple case of natural selection - indeed, team leader Professor Philip Munday comes surprisingly close to invoking Lamarck and acquired characteristics to explain this adjustment:
"When one generation of damselfish experiences high temperatures their whole life, the next generation is better able to cope with warmer water. We don't yet fully understand the mechanisms involved, but it doesn't seem to be simple Darwinian selection over a couple of generations. Instead, there has been a transmission of information between the generations that enables damselfish to adjust to higher water temperatures."
While this is a bit of much-needed good news, the overall context still isn't that great. This only applies to a single tropical fish species, and we can't know how widespread this ability to acclimatize actually is. Also, even if the fish can survive warming temperatures, it's an open question how well the generally more fragile coral reef habitat will fare. Finally, these heat-adjusted fish seem to be born somewhat smaller than their parents, which may be a trade-off for their ability to survive the heat.
Still, it appears that at least one fish has the tools in place to survive a century's worth of warming temperatures...and that is hardly bad news.