Long Term Temperature Monitoring

Why monitor temperature?

Corals are highly sensitive to even small temperature changes and can react through bleaching, reduced growth rates, reduced reproduction, increased vulnerability to diseases, and die-offs. Corals have a mutually beneficial, or symbiotic, relationship with a type of algae known as zooxanthellae. Zooxanthellae live inside the coral and provide them with energy derived from photosynthesis, and the coral provides the algae with shelter. However, corals can tolerate only a relatively narrow temperature range and prefer water between 73-84 degrees, and water temperatures over 86 degrees or under 64 degrees can become stressful and eventually fatal for coral. When the water gets too warm, zooxanthellae release compounds to deal with the heat stress that are harmful to the coral, causing the coral to expel their zooxanthellae and become bleached. Although the coral is still alive, just colorless, they will eventually die from starvation if the zooxanthellae does not return.

Recently, massive, region-wide bleaching events have become more common on the Florida Reef Tract. Six extensive coral bleaching events have affected the entire Florida Reef Tract since 1987, with substantial mass coral mortality occurring during the global bleaching events of 1997/1998 and 2014/2015.  Even beyond these major bleaching episodes, some level of bleaching is occurring nearly every year in the Florida Keys. On the other hand, corals at the northern end of their range - such as those found on the Florida Reef Tract - are also vulnerable to cold winter temperatures. A severe cold snap in 2010 resulted in high mortality of certain coral species on shallow-water patch reefs throughout the Florida Reef Tract (see Colella et al. 2012, “Cold-water event of January 2010 results in catastrophic benthic mortality on patch reefs in the Florida Keys”).

Therefore, long-term temperature monitoring, in conjunction with coral health and population surveys, is key to providing scientists and coral reef managers a better understanding of how temperature stress is affecting corals in the Florida Keys.  CREMP has one of the longest running active bottom temperature datasets for the region and has records going back 20 years for certain reefs in the Florida Keys. By closely monitoring water temperatures, we can determine when coral mortality and stress is most likely due to temperature, and when it may be due to other factors. Anthropogenic climate change is altering water temperatures and resulting in extreme fluctuations which well exceed the normal temperature ranges of corals, and our data has shown that both hot and cold water temperature stress events are increasing in frequency.

What we do

CREMP has been monitoring temperature along the Florida Reef Tract since 1996. We are deploying temperature loggers at every active CREMP site, and currently have 52 loggers recording water temperatures on sites ranging from just south of Biscayne National Park to the waters surrounding Dry Tortugas National Park. See a map of the Florida Reef Tract with our monitoring sites here. This is an ArcGIS map with multiple layers - to turn on the layer showing the temperature monitoring sites, click the “Show Contents of Map” icon on the left above “Unified Florida Coral Reef Tract Map”, then check the box next to “FRT Temperature Monitoring – CREMP Sites”.  We monitor water temperatures on a variety of different reef types and depths, including hardbottom habitats, shallow fore reefs, deep fore reefs, and patch reefs.

We record water temperatures using the HOBO Water Temp Pro v2 loggers (model U22-001; Onset Corporation). These loggers are set to record the temperature every hour, giving us a high resolution, continuous temperature record. Loggers are attached to the metal stakes drilled into the reef used in the CREMP coral surveys using zip ties (see picture).

Data requests

Please direct temperature data requests to Katy Cummings at katy.cummings@myfwc.com with the sites and time frame you are interested in.