Underwater Forests

Imagine walking through a forest full of trees, and seeing all the plants and animals that call the forest home. What you are imagining is an ecosystem created by the trees. Now, hold your breath and imagine a similar forest under the ocean. Not just any ocean—the icy-cold Arctic Ocean. You can stop imagining because these underwater forests exist. They are commonly found along the coasts of oceans all over the world, including the Arctic!

Underwater forests are similar to forests on land but, instead of trees, there are large, brown marine algae that can be several meters tall. They are called kelp (Figure 1). Like trees, kelp make their own food using sunlight, carbon dioxide, water, and nutrients found in the water. This is called photosynthesis.

Kelp create an environment like trees do on land: they generate shade and soften not the wind, but the waves. Kelp forests provide a safe, protected place for animals to hide and reproduce. These forests are a perfect home for fish, crabs, and sea urchins.

The same way you can find many kinds of trees in a forest, you can find many kinds of kelp in kelp forests. Lots of kelp species have been described in the Arctic Ocean. Understanding these species is important, because it tells scientists how healthy the forest ecosystem is [1].

A Changing Arctic Ocean

Before we discuss the kelp that are found in the Arctic Ocean, it is important to understand the environment and conditions that they live in. Kelp forests have adapted to the temperatures and light found in the areas of the world where they live. In the Arctic Ocean, kelp forests have adapted to live in freezing temperatures and long periods of darkness in the winter. They can even grow underneath the sea ice! Today, all the northern conditions that Arctic kelp have adapted to are changing.

What is changing in the Arctic? As a result of climate change, temperatures are getting warmer. The air temperature in the Arctic rose by 3°C over the last 50 years. This is three times higher than the rise in temperatures seen in the rest of the world! Ocean temperatures have also risen. The sea-surface temperature of the Arctic Ocean has warmed twice as fast as the sea surfaces in the rest of the world [2]. This warming has a dramatic impact on the sea ice. In the summer, Arctic sea ice is melting more quickly than we have ever seen before. The ice is also freezing more slowly in the winter. Taken together, these changes mean that there is less sea ice in the Arctic than there used to be—up to 40% of the sea-ice cover has been lost. The glaciers and permafrost in the Arctic are melting, too. This makes the coastline more fragile.

These changes in the Arctic kelp’s environment affect how they grow and even whether they survive. The warmer temperatures cause other environmental factors to change too—which you will soon see, if you keep reading.

How Climate Change Affects Arctic Kelp Species

So far, you know that underwater kelp forests are real and that they are important for Arctic life. You also know that climate change is changing the Arctic Ocean. Now we will tell you what we know about how kelp species are affected by the changes in the Arctic.

Let us start with temperature. Like temperatures on land, the ocean temperature is very important for underwater life. It also changes with seasons. In the winter, water temperatures in the Arctic Ocean average 0°C. In summer, water temperatures average 5°C, but can reach 10°C in the southern parts of the Arctic Ocean where it is warmer. Scientists that study Arctic kelp found that many species grow best between 10–15°C. So, the increasing temperatures in the Arctic Ocean are good for some kelp, helping them to grow well [3]. Other kelp species grow better in lower temperatures and might not survive as well as the waters warm. The kelp species that prefer colder temperatures and are only found in the southern region of the Arctic Ocean today may even start growing in the northern regions of the Arctic Ocean where the water temperature is slightly colder. Even kelp species that are usually found in the Atlantic Ocean are being found more frequently in the Arctic Ocean. This is because the Arctic waters are warming enough to be suitable for them, and this may result in a lot of changes to the kelp species found in the Arctic kelp forests. Warming waters might also change which animals live in in those forests.

The amount of salt in seawater, called its salinity, is important as well. When ice melts on land, freshwater flows into the Arctic Ocean and dilutes the salt, therefore decreasing the salinity. The opposite happens when water freezes and salinity increases again. In the Arctic Ocean, salinity changes naturally due to the freezing and melting of ice with the seasons. But as more ice melts due to climate change, the salinity of the Arctic Ocean is decreasing. Just like with temperature, kelp species have ranges of salinity that are best for their growth. Studies have found that the growth of some kelp species can decrease if there is a strong decrease in salinity.

Use your imagination again: pretend that the sea ice is a lid that covers the water below. When there is less ice, or when the lid is no longer there, more light can reach into the water. Because kelp need light, a loss of sea ice could be good news for kelp forests. Scientists believe that the loss of ice in the Arctic will open up new areas for kelp to grow.

Turbidity is the last factor to consider. Turbidity describes the clarity of the water, or how see-through it is. The turbidity of water is determined by the number of particles present. The more particles, the higher the turbidity, and the more light is blocked from traveling through the water. This is not a good thing because, as you know, kelp need light to grow. The melting of glaciers and permafrost in the Arctic region is increasing the turbidity of the water in coastal regions, by bringing more soil particles, called sediment, into the ocean. Sediments block light from reaching kelp forests [4]. Therefore, as temperatures continue to increase and melting continues, increasing turbidity could make survival tough for Arctic kelp species.

Kelp Forests of the Future?

As you can see, when it comes to kelp forests, there are positive and negative outcomes of climate change in the Arctic Ocean. The impact that climate change will have also depends on the species, the specific region of the Artic, and the elements of the environment that are affected. Many ideas have been proposed to describe what the kelp forests of the Arctic might look like in the future. One idea is that kelp species that can handle the higher temperatures and lower salinities will dominate in the region, and the other kelp species will disappear from the forests. The animals that depend on the kelp species will likely follow the same trend (Figure 2).

It is important to understand that all the environmental elements are connected, so kelp may face many changes at the same time—like changes in temperature and salinity. We call this the cumulative effect of climate change, and it is difficult to predict. For example, scientists did an experiment on one kelp species that does not like high temperatures or low salinities, and when the two negative conditions were combined, the kelp grew even slower and struggled to photosynthesize [5]. Understanding the cumulative effect of climate change on kelp is a big challenge for scientists studying kelp today.

Glossary

Ecosystem: ↑ A set of organisms that interact with each other and with their environment.

Marine Algae: ↑ Plants that grow in saltwater environments like oceans, seas, and estuaries. The plants come in different shapes, sizes and colors.

Kelp: ↑ A type of large seaweed that belongs to the brown marine algae family.

Glacier: ↑ A large mass of ice, snow, rock, sediment, and often liquid water that starts on land.

Permafrost: ↑ A thick layer of soil underneath the ground surface that remains frozen throughout the year in polar regions.

Salinity: ↑ A measure of how salty water is, so the amount of salt that is dissolved in water. The higher the salinity, the more salt there is in the water.

Turbidity: ↑ A measure of how murky water appears to be because of small particles that are suspended in the water. The higher the turbidity, the more particles there are in the water.

Cumulative Effect: ↑ Changes to the environment that are caused by more than one effect, like the effects of changes in temperature, salinity, and turbidity on the kelp forests.

Acknowledgments

This work is a contribution to the ORCA (Benthic organisms and communities in a changing Arctic) project (3051) funded by Foundation Prince Albert II de Monaco (www.fpa2.org).

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.