Article: Donelson, Jennifer M. “Development in a warm future ocean may enhance performance in some species.” Journal of Experimental Marine Biology and Ecology 472 (2015): 119-125.
Climate change is on a lot of people’s minds these days. Right now, world leaders have gathered in Paris to talk climate and talk solutions. One of the major components of global climate change is warming. We know that our oceans are already warming and that temperatures are only going to continue to rise over the next 100 years. For marine species, there are only a few options when facing threats of warming: you move, you adapt, or you die.
There have been many studies highlighting the poleward movement of many marine populations who can’t handle the heat and seek out colder waters. There is a lot less known, however, about the acclimation and adaptation ability of marine organisms. Think about it: although the oceans are warming at a quick rate, it’s not like they are heating up overnight. This gives species a small window of time (or a few generations) to figure out a way to handle the heat.
Acclimation, and ultimately adaptation, will be especially critical for tropical species (Fig. 1). For species living near the equator, temperatures are high year round as there is really no difference in seasons. For species living in higher latitudes, seasonal changes in water temperature can be quite big, and this variability gives these species a little bit more wiggle room when it comes to dealing with ocean warming. Many tropical species already live close to their thermal maximum, meaning the temperature at which it is too hot to continue most physiological processes. If tropical oceans warm as projected (Fig. 2), this would put tropical species in peril, likely pushing them beyond their tolerance limit.
However, tolerance limits are correlated with temperatures individuals are exposed to. Think about taking a New Englander and putting them in Florida for a few months in the summer, they would be miserable and would have a tough time acclimating (most likely complaining about heat and humidity). But if you take someone from Georgia, they likely won’t have any trouble acclimating to Florida weather since they were raised in a pretty warm environment. So, maybe if young individuals are exposed to higher temperatures early on, they will have acclimated and can withstand warming waters. To investigate this further, researchers at James Cook University in Australia decided to test if this acclimation was a possibility for reef fish.
With the aim of testing the ability of reef fish to undergo developmental acclimation, breeding pairs of the Spine Cheek anemonefish (Premnas biaculeatus) (Fig. 3) were collected from the Great Barrier Reef and brought to a lab facility. Breeding pairs were allowed to acclimate to their lab surroundings, which included water set to average summer water temperatures (28.5°C). Offspring from the breeding pairs were collected and moved to new tanks until the age of larval settlement (14 days). Once at settlement age, larval fish were then separated into three temperature treatments: +0.0°C (control), +1.5°C, and +3.0°C. Fish were kept in these treatments for 1 year before being tested for temperature acclimation.
After one year, resting metabolic rate and maximum metabolic rates (collected when fish were forced to swim) were determined by oxygen consumption within a swim chamber. The critical thermal limit was also tested for these fish by slowly increasing water temperature until fish started exhibiting signs of losing equilibrium. At that point, fish were euthanized and measurements of their size, weight, and health were collected.
It was found that the fish grown in the warmest waters (+3.0°C) were actually the largest in both weight and length; these fish were also the healthiest (Fig. 4)! When testing the metabolic rates, it was found that fish grown at +1.5°C and +3.0°C were able to increase their aerobic capacity and increase their overall metabolism (Fig. 5). This was evident particularly with maximum metabolic rates. This increase in metabolism likely resulted in these fish being larger at the end of treatment. The factor of thermal maximum however, did not appear to be influenced by the temperature treatment.
This study has shed light on the ability of tropical marine fish to acclimate to warming waters. Certain physiological traits within these fish appear to be plastic, meaning they can be changed based on the environment (such as metabolism), but other metrics, like thermal tolerance, appear to be more hardwired. However, this study shows that fish do have the ability to acclimate and respond positively to warming water if they are given an opportunity to acclimate to temperature at the right developmental stage. If we are to truly understand how climate change will impact organisms, we need to look into acclimation and adaptation, because it seems as though some species will be able to handle the heat!