Using Data to Identify Hot Spots and Predict Bleaching Events

Part D: The Florida Keys Reef Tract

Satellite image showing the location of Sombrero Reef (red star), the midpoint of the Florida Keys island chain. Click image for a larger view. Image source: Google Maps.

The Florida Keys Reef Tract is the third largest living coral barrier reef system in the world behind the Great Barrier Reef in Australia and the Mesoamerican Barrier Reef System off the coasts of Mexico, Belize, Guatemala, and Honduras. It is also the only extensive reef system in the continental United States. Several state parks and sanctuaries were established in different parts of the Florida Keys to protect coral reefs starting in 1960. In 1990, the Florida Keys National Marine Sanctuary was established, incorporating the preexisting Key Largo and Looe Key sanctuaries. The Florida Keys NMS currently protects 9947 km² of coastal and ocean waters through several protective measures, including prohibiting oil exploration, mining, or activities altering the seafloor, restricting large shipping traffic, and restricting anchoring on, touching, and collecting coral.

In this part of the lab, you will examine data from the Florida Keys to determine if and how bleaching has affected this reef. You will then compare data from several other coral reef sites.

1. Go to NOAA's Coral Reef Watch home page. Click on the Virtual Stations icon in the left-hand navigation bar to view a map of the 213 "Virtual Station" sites around the world.
   Show me what a virtual station is
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   Locations of the 213 NOAA regional virtual stations. The color of each station balloon indicates the level of heat stress experienced on that day. Image source: NOAA.

   
   
   Along with the worldwide data, NOAA also focuses in on several representative coral reef locations around the world. Even though the temperature measurements at these locations are based on satellite measurements, honing in on a specific region is like having a temperature sensor in the water next to a reef, hence the term "Virtual Stations". Data from these stations update daily.
2. In the map, zoom in to the Caribbean area using the "Select a region" drop-down list in the lower right below the map. Once you have zoomed in enough to see the Florida area and the Virtual Stations more clearly, click the station indicator for the Florida Keys. You will see an image of current gauge data. Click the link for Alert Gauges & Outlook to see a map of this location and graphs of the data.
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   This page shows the current, 4-, 8-, and 12-week bleaching outlooks. Just below is a time series graph for the SST at the Florida Keys virtual station for the most recent 2-year period. The graph can display two-year ranges of data from January 1985 through the most current measurement.
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   These graphs show the time series data at a particular station. This particular example shows data from the U.S. Virgin Islands station. The left axis of each graph shows temperature in °C. SST is plotted with a dark blue solid line overlaid on the gray minimum and maximum SST range. The mean SST for each month is plotted as a light-blue cross, and the maximum monthly mean (MMM) is indicated by a light-blue dashed line. There is a bleaching hot spot any time the SST goes above the MMM (dashed light-blue line). The bleaching threshold temperature, equal to 1 °C higher than the MMM, is a solid light-blue line. Whenever the temperature goes above the bleaching threshold, corals experience thermal stress.

   

   
   
   DHWs are shown at the bottom of each graph as a separate trace , and the right axis shows the DHW scale.

   

   Images courtesy of NOAA.

   

   
   
3. Select the 2-year range 2006-2007 to view its graph, and compare the summer seasons.
   
   

   Checking In

   Use the Florida Keys graphs to answer the following questions.
   
   

   • Which month is the warmest on average?
     Show me the answer
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     August
   • What is the maximum monthly mean?
     Show me the answer
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     29.6264°C
   • What is the bleaching threshold temperature?
     Show me the answer
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     30.6264°C
   • What was the highest alert level for the Virtual Station at the Florida Keys in 2006 and 2007?
     Show me the answer
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     Alert Level 2 (in early September 2007)

   Stop and Think

   4: Over what time period, if any, do you think significant bleaching occurred? Explain.

Bleaching Rates Over Time

In 2018, a research study, publishing their findings in the journal Science, stated that the number of years between severe bleaching events had diminished steadily in the four decades between 1980 and 2016. In the early 1980s, the rate of severe bleaching events was once every 25 to 30 years but had become once every 6 years by 2016. The study looked at 100 reefs in 54 countries and used both published research and direct observations. This article Severe Coral Reef Bleaching Now 'Five Times More Frequent' Than 40 Years Ago is based on the findings. Your teacher may ask you to read this article.

The study found:

• The risk of bleaching (moderate & severe) has increased at a rate of 4% per year -- in the 1980s, 8% of reef locations were affected by bleaching yearly; in 2016, the number of reef locations affected was 31%.
• The difference in a bleaching event being of moderate or severe impact is determined by a range of factors, including SST, sea level, and human activities, including pollution.
• The mass bleaching event of 2015-2016 was the most severe on record, affecting 75% of the examined 100 reefs.
• The highest number of bleaching events occurred in the western Atlantic, which included 2 to 3 times more events than other regions.
• 58% of severe bleaching events have been recorded during strong El Niño periods, but average tropical sea surface temperatures are warmer today under La Niña conditions than they were under El Niño events only three decades earlier.

1. Look at the Bleaching Alert data for the Florida Keys from 1985 to 2016 and take note of the different alert levels during that time.

2. Compare the bleaching alert data for two more of the following sites that you learned about in Lab 5:

• Belize
• Guam
• Bali - the Virtual Station is East Java & Bali
  
• Great Barrier Reef - choose one of the following GBR Virtual Stations: Northern GBR or Central GBR
  

Stop and Think

5: Looking at the Florida Keys, does the data demonstrate an increase in frequency of severe bleaching events over the four decades between 1985 and 2016? Why or why not?

6: What two other sites did you compare? Did these two sites also show an increase in frequency of severe bleaching events between 1985 and 2016? Why or why not?

7: Do the Coral Reef Watch virtual stations do an adequate job of indicating all possible global bleaching events? Explain.

Optional Extensions

More about Florida Keys National Marine Sanctuary

Scientific paper The 2014-2017 global-scale coral bleaching event: insights and impacts