Coral Bleaching

A sample activity where the “Coral Bleaching” module of NOAA Data in the Classroom is used, in combination with other resources, to assess one of the current threats to coral reef ecosystems and to examine humanity’s role in the fate of reefs in the future.

Introduction

Coral reefs are some of the most biodiverse ecosystems on this planet and thanks to this role have been dubbed the “rainforest of the sea” (NOAA, 2019). In addition to providing shelter for many marine organisms, coral reefs offer coastal protection, job and recreational opportunities, and food for a large proportion of humans (NOAA, 2019). However, coral reefs face many threats because of human activities. In turn, these threats undermine the ecological services that reefs provide. Thus, protecting the well-being of coral reefs is vital to not only maintaining the stability of these marine ecosystems, but also to the benefits that humanity draws from healthy coral reefs.

Objectives

In this activity, you will explore the importance, as well as the biology and ecology, of reef corals. You will examine the role thermal stress has on coral bleaching, by determining how bleaching is measured and monitored. You will examine how different species respond to bleaching and consider the significance of this variation for conservation purposes. You will apply what you have learned to determine the well-being of reefs in the Florida Keys. Finally, you will forecast the fate of reef corals based on future temperature projections and recommend conservation strategies to protect reef corals and thus preserve the valuable services these ecosystems provide.

What to do:

Step 1: Background information on the importance of coral reefs.

• To learn more about the ecological and human significance of coral reefs see NOAA’s Ocean Today – “The Coral and the Algae”.

Step 2: Coral biology and ecology. Knowledge of reef biology and ecology is critical in understanding why reefs may experience stress due to changes in their physical environment (e.g., heat exposure) that are outside of the normal temperature range that results in bleaching.

• Please watch NOAA’s Ocean Today “The Coral and the Algae” to learn about the animals of coral reefs, how corals gain most of their energy for survival thanks to a symbiotic relationship with algae, and why the corals experience bleaching.  A descriptive format (supported with images) to illustrate the process of bleaching is also available in LEVEL 3, “Background” section, of NOAA Data in the Classroom “Investigating Coral Bleaching Using Data in the Classroom”.
• To better understand reef ecology, its geographic range and ideal habitat requirements such as depth and sea surface temperature, click on and complete all activities in NOAA Data in the Classroom, LEVEL 1, “Investigating Coral Bleaching Using Data in the Classroom”.

Step 3: Measuring heat stress and reef sensitivity to estimate severity of coral bleaching events.

• To learn about the temperature threshold that causes bleaching, to determine how heat stress is measured from sea surface temperature data and used to estimate bleaching severity, please complete all activities in LEVEL 2 of the “Investigating Coral Bleaching Using Data in the Classroom”. Please note that the last activity in this module is a video that features multiple threats that coral reefs are facing. This video is also available via NOAA’s Ocean Today: “Corals Under Threat”. This video will be helpful when evaluating conservation options for reefs.
• Heat stress impacts different coral species in various ways. To determine how reef corals vary in their sensitivity and response to bleaching events analyze Figure 2 from a research paper by Hughes, T.P., et al. (2017). This activity will provide some insight into potential conservation options for reef corals.
• In addition to loss of color, a characteristic effect of coral bleaching, other changes to reef ecosystems occur because of thermal stress. In LEVEL 3 of NOAA’s Data in the Classroom scroll down to the section on “Identifying the Effect of Bleaching on Coral Reefs”. Use the images of 4 geographic regions to identify characteristics of healthy and unhealthy reefs by examining the visuals before and after bleaching, respectively.
• Apply this knowledge of reef characteristics to determine the quality of reefs at Cheeka Rocks, Florida; Cozumel, Mexico; Goff’s Caye, Belize and Batu Rufus, Raja Ampat, Indonesia via “virtually swimming” at the sites. This activity is the last in the LEVEL 3 NOAA’s Data in the classroom (i.e., optional: Surveying Coral Reefs).

Step 4: Apply what you have learned to analyze the bleaching event in the Florida Keys (by completing LEVEL 4 in NOAA’s Data in the Classroom). Use the student worksheet for LEVEL 4 to support the completion of this exercise.

Step 5: Assess the fate of reef corals given the temperature projections from the Intergovernmental Panel on Climate Change’s (IPCC) most recent report (IPCC, 2021) and your knowledge about heat stress threshold. For this activity a range of temperature projections (based on various carbon dioxide emission scenarios associated with different levels of human activity, see Figure SPM.8 in Summary for Policymakers) are used. Discuss what the likely impact is on coral reefs based on the projected temperature for each scenario by 2050.

Reflection

In Steps 1 through 5 you have learned about

• the role of coral reefs,
• their biology,
• ecology, and
• the stresses these ecosystems experience because of continued human activities.

You also learned how different pathways humanity chooses to take in the future would either reduce or increase the stress on natural environments. As a global citizen and a beneficiary of ecosystem services that coral reefs provide, decide on the pathway that we should take to preserve coral reef ecosystems. Propose strategies that would help humanity achieve this pathway and, in the process, maintain the health and increase the resilience of coral reefs.