FISH SEEKING TO BEAT THE HEAT MAKE LOUSY NEIGHBORS
Invasive species can cause serious problems — divers don’t need to look further than the Caribbean’s lionfish infestation for proof. As the ocean heats up — with the potential to rise 37.4 degrees F by 2100 under the Intergovernmental Panel on Climate Change’s highest emissions scenario — other animals will find their way into new locations in search of cooler waters. The marine life we are diving with today could well be the invaders of tomorrow.
Corals rely on a precarious balance of environmental conditions to thrive. NOAA states that the optimal temperature for coral growth is between 73 and 84 degrees F. (Corals also require appropriate ph levels and a host of other considerations.) Reef fish play a part in maintaining this environment — herbivores like parrotfish and rabbitfish scrape away algae that would otherwise smother the reef and clear space for new corals to colonize. But what happens when you can’t take the heat? You get out of the kitchen.
A 2014 paper in the ICES Journal of Marine Science by Miranda Jones and William Cheung of the University of British Columbia estimated that marine fish and invertebrates will shift with a median rate of 16 miles per decade; these tropical vagrants already have started appearing throughout the world. And when the new kids roll into town, there’s often a clash.
When these tropical grazers find their way to temperate regions, they do what they’ve always done — eat the green stuff. This can have a devastating effect on kelp forests and sea-grass beds, and disrupt local ecosystems. According to National Geographic, examples can already be found in Japan, Australia, the Mediterranean and the Gulf of Mexico. The barren landscape also acts as a potential beachhead for coral and an invasion of reef-dependent life. Without the kelp, temperate critters lose shelter and food, facing a crisis of their own. This mix of endemic and invasive species will lead to increased competition, and not everyone will swim away a winner.
Jones and Cheung’s model estimates that under the highest emissions scenario, an average of 6.5 species will become locally extinct for every 0.5 degree of latitude between 10 degrees north and 10 degrees south between 2000 and 2050. Those that survive will do so by pushing into new territory or by adapting to the new normal. What will remain when the bubbles settle is the question scientists are trying to answer.
“We’re still trying to understand which species will be the winners with all this environmental change and which won’t do as well,” say Malin Pinsky, an ecologist from Rutgers University studying marine communities. “Even from a coral perspective, there are some out there that do surprisingly well when the water is really hot.”
What species will continue to thrive, and where will they be located in the not-so-distant future? Whether corals adapt to heated waters or head for cooler climes, one thing seems certain: The underwater realm we explore tomorrow could look quite different from the one we know today.