If you’ve been reading UNdertheC for while, then you know that I study coral reefs (specifically those in the Caribbean). If this is your first time here, welcome! Tell your friends 🙂
As the 4th year of my PhD dawns here at UNC, the first chapter of my dissertation work has finally been published in a peer-reviewed journal! It focuses on how temperature regimes impact the structure of coral communities in Belize. I’ve written about some of the field and lab components of this research before so check out the following links for more info 1 2 3 4.
The question guiding my research is the title of this post: does temperature dictate which corals can survive on a reef?
To rephrase: Does the historical temperature record in an area impact which corals can survive in that area? The obvious answer to this question is yes. However, the extent of the impact is what I wanted to identify. To do that I looked at a bunch of satellite temperature data and was able to classify the Belize Mesoamerican Barrier Reef System into 3 thermal regimes (see below).
The thermal regimes are defined by maximum average annual temperatures as well as annual temperature range. Areas with the highest average temp and largest range (annual variation in temp) are labeled “High” in red (areas with the lowest of both are in blue, if they were in between low and high they are green or “Moderate”).
So what kinds of corals do we see at each of these thermal regimes? Both “Low” and “Moderate” reefs look like this (diverse corals, lots of 3D structure).
Reefs at “High” sites looked like this (low coral cover, low diversity, low 3D structure- you may also notice murky water, likely due to proximity to shore–the impact of nutrients was not measurable in this study but they may have played a role in defining the patterns we saw).
As you can see, these reef areas are not the same. The “High” sites experience warmer summer temperatures and more thermal variation than the “Low” and “Moderate” sites. Elevated temperatures and larger magnitudes of variation can be stressful to corals and if they are prolonged they can lead to bleaching or death. This is likely what is occurring here (along with some other factors such as current and nutrients). Certain corals are more tolerant of stress than others and these corals are the ones who can survive in the “High” sites. Our research has revealed that both large, mounding “stress-tolerant” species such as the one below and small, fast-growing, weedy species can survive in these stressful environments.
As the oceans continue to warm sites that are currently classified as “Low” and “Moderate” will start to see elevated summer temperatures and potentially more thermal variation (similar to what “High” sites see now). That means that these more diverse reefs may shift to look like present day “High” sites (low diversity, less 3D structure). This would have significant impacts on both the fishing and tourism industries in the Caribbean and could be very detrimental to the people who depend on the reef for jobs, money, and/or food. It also means that some already endangered corals (like the beautiful Acropora below) are at risk of extinction.
However, all hope is not lost. We have published several articles in the past about how corals may be able to cope with a changing climate (1, 2). This research supports the idea that some corals have already adapted or have the ability to adapt or acclimate to changing conditions. The corals that are currently living in “High” sites (hot, variable, and potentially impacted by nutrients and other local stress) appear to be surviving and reproducing. Perhaps these corals are already prepared to cope with changing temperatures and it is possible that they can produce larvae that will distribute throughout the Caribbean and help seed reefs with more resilient corals!
Only time will tell, in the meantime you can help! Reduce your carbon footprint, spread awareness, cut your plastic usage, etc…
The original article can be located here free of charge.
Feel free to comment with questions!