Most people are familiar with the concept that compares coral reefs to underwater rainforests. Coral reefs form the most biodiverse habitats in the ocean, and their presence is essential to the survival of thousands of other marine species - many of which we rely on for food.
Hard corals are the reef-building corals, and their stonelike structures are composed of calcium carbonate, the same substance found in the shells of many marine organisms including oysters, clams and snails. Like these mollusks, corals must have access to available calcium in the seawater in order to build their hard skeleton. This is especially important in the early stages of a coral polyps's life, when it settles onto a hard substance and starts "building" its skeleton. Some studies have shown a 52-73% decline in larval settlement on reefs that are experiencing lower pH levels. Scientists can also measure the calcification rates of hard corals, and ocean acidification has had a negative impact on the rate at which corals calcify. This means that coral colonies in the future may be more brittle and less resilient to other factors influencing their survival.
Ocean acidification is just one more threat to the success of hard corals. Coral reefs are already being affected by many other pressures, some human-related and some natural. Warming ocean temperatures are contributing to coral bleaching and making them more susceptible to diseases. Nutrient and chemical pollution coming into the oceans from rivers is also making suitable coral habitat very scarce. Natural threats impacting coral reefs include predation from urchins and a variety of fishes, and also tropical storms. Coral reefs are naturally very resilient to many of these threats, but now their ability to recolonize and grow sturdy structures is being compromised by ocean acidification. Sometimes, coral habitat is gradually being replaced by non-calcifying organisms, like seagrass, once the coral has been killed off.
The resources included in this lesson will describe many of these processes, and will also provide suggestions for how to protect coral habitats. Protecting oceans as a whole will help corals maintain resiliency in the face of these threats.
- PBS created a 7-minute documentary titled "Coral Reefs Die as Ocean Temperatures Rise, Water Acidifies". This is a great video to watch because it shows scientists researching corals in lab conditions, and trying to "forecast" how corals will respond to acidity changes in their water.
- The majority of the 30-minute talk "Ocean Acidification: Coral Reefs in the Balance" deals with the impacts of OA on coral reefs. Much of this information goes beyond what we need to interpret for general audiences, but it may be good to know if you want to be prepared for anything! Pages 15-35 of the powerpoint focus on coral reefs. The coral reef topic is covered in the video from 6:00-25:45.
- "Climate Training Activities" shows Aquarium interpreters explaining why ocean acidification is detrimental to hard corals, and how suitable coral habitat is shrinking in the near future.
- The short animation shows the past, present and future of suitable coral reef habitat. It only plays for 16 seconds, so you may need to pause it or slow it down to catch what's happening.
The stony structures of hard corals are composed of calcium carbonate. In order to create this material, corals rely on a specific pH balance to extract calcium from the seawater. Ocean acidification will have a negative impact on the ability of corals to develop, and on their ability to recover from damage. Reef-building corals form the most biodiverse habitats in the ocean, their success is essential to everyone!
This is a lengthy pdf document of a powerpoint presentation that accompanies a talk by Dr. Dwight Gledhill with the Cooperative Institute of Marine and Atmospheric Science. It is a good resource for background information about ocean acidification because it covers chemistry, carbon cycles, CO2 emmission, and focuses on the impacts of ocean acidification on coral reefs. If you are looking to fully understand these concepts, check this out.
As we add more carbon dioxide (CO2) to the atmosphere, the ocean absorbs about a quarter of it. This changes the basic chemistry of the ocean, shifting it towards the more acidic end of the pH spectrum. Ocean acidification makes it more difficult for shelled organisms to make their shells. This activity takes the complex chemistry of ocean acidification and makes it physical. It is designed for any age, with pictures and graphs to make the science deeper, richer, and easier to grasp.
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This very short animation (16 seconds) from NOAA's Environmental Visualization Library shows a map of suitable coral reef habitat over time, and how that habitat shrinks as we move into the latter part of this century.
A short (16-sec) animation of past, present and future Aragonite Saturation Levels as it relates to coral reef habitats. This can be used as supplement to OA classroom presentations, it provides a good and colorful visual.