Climate Change May Make Fish Commit Predator-Assisted Suicide
Remember the tale of Nemo (the juvenile clownfish that was fish-napped by a dentist) and Marlin (Nemo’s dad)? Marlin braves the open ocean to find Nemo, meeting a whale-speaking blue tang and a few non-piscivorous sharks along the way. Of course, Marlin and Nemo are reunited (it’s a Disney movie), but could a little clownfish really survive such an adventure without getting eaten?
It depends on the conditions. Scientists at James Cook University in Australia found that settlement-stage orange clownfish larvae raised in an aquarium with normal water conditions* had mad predator avoidance skills. To test the larvae’s ability to detect and avoid predators without killing their test subjects, the scientists used a flow chamber with two parallel streams of water moving at identical flow rates. One stream of water came from a tank with clownfish predators and the other came from one with non-predatory fish. When the scientists released the larvae into the flow chamber, the fish (which had never been exposed to predators) immediately swam away from the predator-tainted stream of water.
This innate survival skill is just as critical for an itty-bitty fish looking for a home on a coral reef as it was for an animated fish looking for his son. Ya see, larval fish typically settle on a reef at night during a new moon when there is very little light. They can’t rely on their vision to identify safe places to settle, so they have to sniff out a safe place to park instead.
That sounds easy enough for a critter hard-wired to sniff out and avoid predators…or not. The scientists raised another set of settlement-stage orange clownfish larvae in an aquarium with more acidic water (7.8 pH and 1000 ppm CO2) designed to mimic the conditions that could occur by 2100 under a business-as-usual scenario. These fish didn’t exhibit the mad predator avoidance skills of their normally-raised counterparts. In fact, the larvae raised in the more acidic water displayed stellar predator-assisted suicide skills, swimming towards both streams in the flow channel.
If ocean acidification does occur as predicted and clownfish respond to the increasingly acidic conditions as they did in this experiment, boy, are they screwed. It’ll be a miracle if Nemo’s great-great-great-great-great-great grandchildren survive long enough to claim a spot on a reef, let alone survive a Disney-esque adventure.
Of course, ocean acidification isn’t the only side effect of our little CO2 problem. We’ve got climate change to worry about too. And climate change, as it warms our oceans, may make fish pissy. Who cares about a hot pissy fish? Well hot pissy fish get eaten. And if all the fish are pissy and they all get eaten, well, there goes the neighborhood.
In a recent study, scientists studying personality traits in two species of juvenile damselfish from the Great Barrier Reef found that aggressiveness, boldness and activity rate varied with small changes in water temperature. With just a 1-2°C increase in water temperature, some fish became up to 30 times more aggressive, bold and active while the personality of other fish barely changed. The fish that get pissier in warmer water may be on to something, the scientists theorize. In warmer water, fish have to expend a lot of energy to stay cool, leaving them with less energy to grow. The scientists suggest that the pissier fish may be increasing their rate of food intake to give them enough energy to maintain their growth rate in the warm water.
These 1-2° temperature fluctuations occur naturally throughout the day, but more dramatic fluctuations may occur as the oceans heat up. Toss in an inability to smell a predator and we’re destined for an ocean full of reckless, hyperactive fish. Just what our fisheries need.
*The normal water had a pH of 8.15, the current average pH of ocean water near the surface.
Dixson, D., Munday, P., & Jones, G. (2010). Ocean acidification disrupts the innate ability of fish to detect predator olfactory cues Ecology Letters, 13 (1), 68-75 DOI: 10.1111/j.1461-0248.2009.01400.x
Biro, P., Beckmann, C., & Stamps, J. (2009). Small within-day increases in temperature affects boldness and alters personality in coral reef fish Proceedings of the Royal Society B: Biological Sciences, 277 (1678), 71-77 DOI: 10.1098/rspb.2009.1346