Warmer Ocean Temperatures Increasing Coral Growth Rates?
In the past few years, all the talk about warming ocean waters is typically associated with coral bleaching. While it is true that coral bleaching is the main negative side effect warming waters are having on coral reefs, there are many factors that affect coral growth and health. When you single out the global change in temperature that is occurring, you can see that water temperature boundaries in the ocean are also changing. It appears from a study done by scientists from the AIMS research institute and published in the journal Science that we are seeing negative effects on some coral populations and positive effects on others . What does this data mean in the big picture though?
How is warming water affecting coral growth rates?
Simply put, coral grows well within a range of temperature, generally from the low 70’s to the low 80’s though there are exceptions on either side through a process called calcification. Within this range with all other factors that affect coral health constant, corals will grow more as you move temperature up towards the low 80’s. The study that was done by the researchers at AIMS clearly shows that corals in tropical waters that are in the maximum growth range will die if the temperatures rise much above where they are today. However corals in the lower range of temperature that are now experiencing warmer surroundings are naturally showing increases in their growth rates.
Have we seen this before in our Reef Tanks?
In our reef tanks here at Reefnation, we run our temperature on an annual cycle that replicates the conditions at 15 degrees north latitude. In addition to that, we have the lighting tuned to simulate day length and lunar conditions found at this same latitude. This is controlled by a Neptune Apex controller that runs our tanks. From a water temperature perspective, this gives us a winter temperature that dips down to about 75.5F degrees and a summer temperature that we let max out around 81.5F. While we create these conditions to best replicate conditions on a tropical reef, it is interesting to note that we too have observed coral growth rates being visibly faster in summer than they are in winter with certain acropora and echinopora species in general. Now while our tanks offer us a place to observe and on a small scale run some experimentation, I do want to point out that in no way are we controlling all other variables like would be done in an actual study, albeit an interesting correlation.
What results will this have on coral reefs?
Its both interesting and a little scary to ponder what the AIMS experiment is showing may happen in the coming decades. Perhaps if the changes happen slow enough, corals would be able to slowly migrate through sexual reproduction into what will become a more suitable thermal environment for them. Perhaps this warming will occur too quickly and there will be some species loss at the warmest areas, while the more temperate corals of today will begin to dominate these new sub tropical reefs that start to spread poleward. Its hard to know what other factors might be in play as we are just singling out temperature for this conversation.
Have you had any experience seeing growth affected by temperature change in your reef tank?