20th November: Answers to School Kids’ Questions – Corals and Climate

This is the second part of the questions asked by school children from London.

2)   Corals and Climate

  • What kinds of coral are there?

This question could take a long time to answer so I will try my best to keep it short! The word coral actually covers a few different groups of creatures. They are all part of one large group (phylum) called Cnidaria (pronounced ny-dairy-a), which also includes jellyfish. Then you have the hard corals and soft corals (including big sea fans) which are the most common types and make up coral reefs. You can find them living alone or in big colonies. These are a particular kind of Cnidarian called Anthozoa. Other types of Anthozoan include gold corals, black corals, bamboo corals and sea anemones. They can live in warm or cold water and from the very surface of the ocean to some of the deepest places. You can even find them around the south coast of England! On this cruise we are looking mainly at hard corals because we can analyse their hard skeletons to work out what the ocean was like in the past. There are other types of coral (fire coral and lace coral) that belong to a kind of Cnidaria called Hydrozoa. Some of these also have hard skeletons that we can analyse when we get home.

Pete Spooner

  • I would like to know how many corals you predict to find.

We have already found a huge amount. I was surprised at how many there can be in the deep-sea. We are aiming for areas where we think they might live (like seamounts) in the hope that this will mean we will find more. However, we have already seen big differences between the first two seamounts we have visited, with different species and amounts of creatures. We are some of the first to thoroughly explore these areas so it is difficult to predict exactly what we will find, but that is part of the fun!

Pete Spooner

  • How many corals have you seen so far?

Thousands! Corals are really prolific here. They like the habitats that you can find on a seamount (underwater mountain), because there are fast currents to provide food and sweep away sand that would otherwise cover up the delicate corals. Sometimes the currents are so strong that they can sweep the ROV along! The ones that live in colonies usually live on rock faces or big boulders, and the ones that live on their own seem to like to grow where the sea floor is a bit sandy. We have seen lots of both types.

Pete Spooner

  • What have you found out about coral so far?

It has been really interesting to see where the corals live! When we are watching the screens in the ROV control room we can get a good idea about where the corals like to live best. For example, the big fan-shaped ones like to live on big rocks or cliffs, but some of the small solitary corals live in the sand. We have also seen that some species of coral like to live only at certain depths, but we haven’t worked out why yet!

Most of our investigations will happen when we get back home though, because we can’t bring entire labs on the ship with us. I will be testing the chemistry of the coral skeletons; in particular how much magnesium is present compared to lithium (two kinds of metal that can be found in small amounts in the skeletons). We think that this is related to the temperature of the water that the skeleton grew in. If it is, we will be able to work out how warm the deep-sea was thousands of years ago by measuring the skeletons of fossil corals. This could help us understand how climate has changed in the past, as well as in the future.

Pete Spooner

  • Have you been to the Seychelles? If you haven’t you better go because Seychelles has the 2nd largest amount of coral in the world.

Neat! I haven’t been to the Seychelles but I have been to the Great Barrier Reef in Australia which also has a lot of coral. In both the Seychelles and the Great Barrier Reef most of the corals you see while snorkelling are shallow water corals that only live in warm water. On this cruise we’re actually looking at deep water corals. Otherwise we would have loved to go to the Seychelles!

Allison Jacobel

  • In your studies have you found out what happens to the corals due to climate change?

Most studies so far have focussed on how climate change may affect shallow water corals. Climate change is likely to affect these corals in two main ways:

1)     Ocean warming: Corals that live in warm water have algae that live inside them that can photosynthesize like plants. These help to give the coral energy. If the water gets too warm these algae don’t like it and leave the coral. This is known as coral bleaching. If it happens too much the algae don’t return to the coral and it will die.

However, the deep sea corals that we are studying don’t have these algae, because there is no light in the deep sea for them to use for photosynthesis. Also, the temperature of the deep sea will get warmer much more slowly than the surface water, because it takes a long time for the heat to get down into deep water. So it is unclear how much effect ocean warming will have on deep-water corals.

2)     Ocean acidification: This happens when we burn fossil fuels and add carbon dioxide to the atmosphere, because carbon dioxide can dissolve in water, making the water more acidic (you can do this experiment yourself by blowing through a straw into water and measuring the change in pH). Coral skeletons are made of calcium carbonate, which dissolves in acid. Most people think that if the ocean becomes more acidic corals will find it harder to make their skeletons. However, this is likely to affect different species in different ways, so it is very difficult to predict what will happen to whole coral ecosystems, especially for the deep-water ones because we know much less about them.

From studying deep sea fossil corals from around Antarctica we know that as the Earth got warmer after the last Ice Age and the oceans changed, certain species of coral completely changed where they lived. We hope to do the same studies for the corals we find in this cruise to see what happened to the corals in the Atlantic Ocean as well.

Pete Spooner

  • What kind of affect does the coral have on the sea to change the climate?

This is a very interesting question! Mostly we think about the effect of climate change on corals but you’re right that corals can affect the climate too. The chemistry involved can be quite complex and would take a long time to describe here, but the basic idea is that when corals grow they use up some elements carried by the seawater to make their hard skeletons. This slightly changes the chemistry of the seawater, which can affect how much carbon dioxide the seawater contains. Because the concentrations of carbon dioxide in the ocean and in the atmosphere are linked, this means that coral growth or death can affect the level of carbon dioxide in the atmosphere. Carbon dioxide is an important greenhouse gas so changing how much there is in the atmosphere can change the climate.

One of the best known scientific hypotheses about this is called ‘The Coral Reef Hypothesis’. During the last Ice Age, sea level was about 120m lower than today, because lots of water was stored in ice sheets on land rather than in the ocean. This meant that there was much less warm, shallow ocean floor area for coral reefs to grow. Because there were fewer corals, the chemistry of the ocean may have changed allowing more atmospheric carbon dioxide to be absorbed by the ocean. This may have helped to cause the low atmospheric carbon dioxide levels and cold temperatures of the Ice Age. It is known as a feedback process which made cold ice age temperatures even colder (see below).

Coral reef hypothesis feedback process:

Colder temperatures -> Ice sheets grow -> Sea level falls -> Less area for coral reef -> Fewer corals -> Less carbon dioxide in atmosphere -> Even colder temperatures.

However, we don’t know how much effect changing sea level would have had on deep sea coral, or how deep sea coral populations changed during the Ice Age. This is something we can start to discover from the fossil corals we are collecting on this cruise.

Pete Spooner

  • How long did you practice for?

 You could say that being at sea is unlike any other experience and that none of us practiced for the cruise! However, all of us have been going to school for a very long time and ‘practicing’ science every day.

Allison Jacobel



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