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How Algae is Both Good and Bad for Marine Ecosystems

How Algae is Both Good and Bad for Marine Ecosystems

We’ve all heard about algae during our botany classes. If you remember, they’re basically plants that come in many different shapes, forms, sizes, and colors. They’re considered to be an important part of the ocean, although not many understand the role that they play in marine ecosystems. In fact, many think they do nothing but pollute the waters, such as when beach water turns murky green.

But before we explain how marine algae benefits and harms marine ecosystems, let’s first define what algae really is.

What is Algae?

patches of washed up algae on the sand

The term algae refers to many different types of organisms that may be found in a marine ecosystem. Some species of algae are microscopic, unicellular organisms that grow in groups while other types are much bigger, such as seaweed and giant kelp. Varieties include blue-green algae, green algae, red algae, and brown algae.

An example of a unicellular, plant-like alga is known as phytoplankton. Phytoplankton occurs near the surface of a body of water, where it is exposed to sunlight and is the base of the marine food chain.

Simply put, algae are an essential part of a healthy marine ecosystem because they capture and use energy from sunlight, carbon dioxide, and water to produce organic compounds. This cycle helps maintain the balance of life in the ocean. We’ll explain more about how they benefit and sometimes harm the ocean and the surrounding environment.

How Does Algae Help the Ocean Environment?

red algae at the bottom of the ocean

As previously mentioned, the presence of algae in the ocean—usually near the surface where they can absorb the sun’s energy—helps contribute to a healthier ocean. One way that they do this is by using up the carbon dioxide from the atmosphere to produce and release oxygen back into the atmosphere. Of course, we already know that oxygen is necessary for many living things, including mammals that live in the ocean.

Another way that algae makes itself useful is by maintaining symbiotic relationships with other organisms. For instance, some sea sponges coexist with green algae. The algae live near the sponges’ surface, where it metabolizes and produces sugar and oxygen that sea sponges need in order to grow. In return, the sponges help protect the green algae from predators of the ocean.

A coral reef is a marine ecosystem that is also often dependent on algae. A coral reef needs to exist in equilibrium, with coral growth balancing with marine erosion. Certain species of algae can speed up the metabolism of the invertebrates that form coral. These invertebrates make use of the algae’s sugar and oxygen. Without the algae, the reef would gradually deteriorate.

Finally, some forms of algae are the primary source of food for marine animals at the bottom of the food chain, even in the coldest parts of the ocean. One marine life form that feeds on algae is shrimp-like organisms called krill, which serve as a vital food source for whales, seals, penguins, and even seabirds.

There are times when environmental conditions cause cold, denser water to sink from the surface and other water to rise and replace it. When this upwelling happens, nutrient-rich waters reach the top and trigger an increase in algal density, called algal blooms. This is actually a good thing, as algal blooms increase productivity in areas where they occur. And when there’s more algae, more organic compounds are produced for higher organisms, like oysters, clams, mussels, and ultimately, humans.

How Does Algae Harm the Ocean Environment?

green algae washed up on the shore

While certain algae are necessary for a functioning marine ecosystem, other species can be damaging. A small percentage of algae species naturally produce toxins, which can be harmful to animals that consume them. When algal blooms take place, it can trigger the increase of toxic algae species.

Harmful algal blooms can have significant negative effects on marine species. These incidents have led to the deaths of large numbers of fish, sea turtles, and marine mammals. The toxins sometimes lead to human illness when seafood becomes contaminated. And when deaths cause organisms to fall to the bottom of the ocean, they decay and release bodily compounds that can deplete the oxygen in the water.

Then again, the benefits truly outweigh the risks presented by the algae ecosystem, as less than 1% of algae blooms actually produce toxins.

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