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Long Term Temperature Monitoring

Why monitor temperature?

A close up of the ridges, valleys, and prominent septa of a grooved brain coral. The bleaching coral is white and yellow on the right side of the photo but retains some brown coloration on the left side.

A bleaching Colpophyllia natans, boulder brain coral. Bleached corals are not dead, but are lacking critical zooxanthellae algae in their tissues, seen in the brown tissue on the left. 

Corals are highly sensitive to even small temperature changes. Changes from normal temperature patterns can cause bleaching, reduced growth, reproduction problems, increased vulnerability to diseases, and even death. Corals have a mutually beneficial relationship with a type of algae called zooxanthellae. Zooxanthellae live inside coral tissues and provide them with energy from photosynthesis. In return the coral gives the zooxanthellae shelter. Corals and their zooxanthellae prefer water that’s not too hot, but not too cold - water temperatures over 86° F or under 64° F can be harmful. When water gets too warm, zooxanthellae release compounds due to the heat stress which inadvertently harm the coral. The coral expels their colorful zooxanthellae, leaving their tissues clear. As you can see their white skeleton through their now see-through tissue, scientists call this “bleaching”. Although the coral is still alive, just colorless, they will eventually die from starvation if the zooxanthellae does not return. 

It's getting hot in here...

Region-wide bleaching events have become more common on Florida’s Coral Reef. Six mass coral bleaching events have affected the entire Reef since 1987. High coral mortality occurred during the global bleaching events of 1997/1998 and 2014/2015.  Even beyond these major bleaching events, 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 – like here in Florida - are also vulnerable to cold temperatures in the winter. A severe cold snap in 2010 resulted in high coral mortality on shallow-water patch reefs (see Colella et al. 2012, “Cold-water event of January 2010 results in catastrophic benthic mortality on patch reefs in the Florida Keys”). 

Long-term temperature monitoring, paired with coral surveys, is key to providing scientists a better understanding of how temperature stress is affecting corals.  CREMP has one of the longest running bottom temperature datasets for the region, with records going back to 2002 for certain reefs. By closely monitoring water temperatures we can determine when coral death and stress is most likely due to temperature and when it may be due to other factors. Climate change is altering water temperatures and resulting in extreme fluctuations which exceed the normal temperature range of corals. Our data has shown that both hot and cold-water temperature stress events are increasing.

A metal stake is embedded in reef bottom, with a black temperature logger wrapped in silver duct tape with

An offshore CREMP stake with temperature logger attached.

What we do:

CREMP has been monitoring corals along Florida’s Coral Reef since 1996. Every active CREMP monitoring site is now paired with a temperature logger. We currently have 77 loggers recording water temperatures from Martin County to the waters of Dry Tortugas National Park - 22 in Southeast Florida, 44 in the Florida Keys, and 11 in the Dry Tortugas. See a map of Florida’s Coral Reef with our monitoring sites on the Unified Florida Reef Map. 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 forereefs, deep forereefs, 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 zip tied to the metal stakes drilled into the reef used in the CREMP coral surveys.

Data requests

For all Southeast Florida, Florida Keys, and Dry Tortugas temperature data, please direct requests to with the sites and time frame you are interested in.  

Please cite our temperature data using the following citation: 

FWC Coral Research Program. (2022). CREMP Long-term Temperature Dataset [data files]. Florida Fish and Wildlife Conservation Commission-Fish and Wildlife Research Institute [producer]. <> 

Site Table

Refer to the CREMP sites with temperature loggers table for a full listing of monitoring sites with long-term temperature data.