What Are Kelp Forests And Why Are They in Danger?

Imagine an underwater forest where many types of fish, sea urchins, and mollusks live among macroalgae, which you might know as seaweed. These ecosystems are called kelp forests. Kelp is a type of seaweed that grows in cold waters near coastlines worldwide. Kelp forests provide many benefits, such as producing some of the oxygen we breathe, absorbing carbon pollution from the atmosphere, protecting coastlines by slowing down waves so they do not wash the land away, and serving as food sources for coastal communities [1].

In a kelp forest, all living things are connected through a food web—a system where animals and plants depend on each other to eat and survive.

Off the coast of Baja California, Mexico, there is an important kelp forest that is dominated by the species of macroalgae called giant kelp. These kelps are like underwater trees that can reach up to 30 m high. Small animals, like purple sea urchins, eat the kelp, and in turn, larger fish, like the California sheephead, eat the sea urchins (Figure 1). Each species has an important role—if one disappears, the entire food web can be affected. Sadly, kelp forests around the world are shrinking because of threats like ocean pollution [2].

What Are Microplastics And How Do They Reach The Ocean?

Microplastics are one major type of pollution affecting kelp forests. Microplastics are tiny pieces of plastic, smaller than 5 mm, which is about the length of a grain of rice [3]. Microplastics can be sorted into different groups depending on their shape, size, color, or where they come from. You might think that microplastics are round, but they often look like fibers or broken pieces—some even thinner than a strand of hair!

Microplastics are not found naturally in the environment. They come from plastic products made by humans, like plastic bottles, shoes, and toothpaste tubes. Many objects that we use every day contain plastic. Because plastic items can be difficult to recycle, microplastics frequently end up in the environment.

Microplastics are everywhere: in the air, on land, in the ocean, and even in animals and people! When we eat food, we also eat microplastics without knowing it. It is the same for many marine animals—they accidentally eat microplastics, which can be harmful to their health.

The damage microplastics cause to marine animals, like fish or sea urchins, depends on several factors, including the size and amount of microplastic particles and the size of the organism that ingests them. For example, if a fish eats too many plastic particles, microplastics can block its stomach and intestines. Microplastics can also make sea animals think they are full. When their stomachs fill with plastic instead of real food, they stop eating even though they are not getting the nutrients they need to stay healthy.

Microplastics can also be harmful because they often contain dangerous chemicals that were added to make the plastic stronger or more flexible. When sea animals accidentally eat microplastics, the chemicals can leak into their bodies and make them sick.

How Do We Study Microplastics In Kelp Forests?

To find out how many microplastics are inside animals living in kelp forests, divers working with marine scientists swam through the underwater kelp forests to collect samples that could be studied in the lab. The divers visited three kelp forests in Todos Santos Bay, Mexico, between August and October 2021. They collected pieces of giant kelp blades, purple sea urchins, and California sheephead fish.

Back in the laboratory, scientists used special microscopes to look for microplastics, because these tiny pieces are too small for human eyes to see. To make sure the tiny particles they found were really plastic—especially the fiber-like ones that can easily be confused with natural materials—they used a special machine that acts like a plastic “fingerprint reader”. Every type of plastic has its own unique fingerprint, so the machine can tell exactly what kind it is (Figure 2B). To figure out how much microplastic is inside a kelp forest animal, the scientists counted all the tiny plastic pieces they found and then compared that number to how much the animal weighed.

What Did We Find?

Microplastics were found in all the kelp forests we studied! They were present in giant kelp, purple sea urchins, and California sheephead fish.

The most common shape of microplastics was fibers, followed by much smaller amounts of tiny chunks. The main colors we found were black, blue, and red (Figure 2A).

Polyester, which is often used to make clothes, was the most common material—it made up almost half of everything we found. Other materials included acrylic (a type of plastic that can feel like wool when used in clothes), rayon (another type of plastic used to make soft clothes like t-shirts), polyethylene (plastic shopping bags), and polypropylene (ropes and fishing lines; Figure 3).

When we compared the amount of microplastics to the weight of the sea organisms, we noticed that the giant kelp contained the most microplastics. Sea urchins had an intermediate amount, and the California sheephead fish had the least.

Even if microplastics are present in ocean organisms, they do not always reach us directly when we eat seafood. For example, in fish, microplastics are mostly found in organs such as the stomach and intestines. These organs are usually removed before the fish is eaten, so they are not typically consumed. However, for other types of seafood, the situation can be different because they may be eaten with their digestive organs, such as mussels and oysters. In these cases, people could ingest microplastics.

Research is still underway to determine how many microplastics may be ingested through the consumption of these organisms and what potential effects they could have on human health.

Where Do Microplastics In Kelp Forests Come From?

One of the biggest challenges in studying microplastics is figuring out where they come from and how they travel through the environment. This research is not easy, but one of our best clues is the material and shape of the microplastics we find.

Think about your clothes. Many of them are made of polyester, one of the most common materials in the world [4]. About half of all clothes today contain polyester! So, could the polyester fibers we found in kelp forests have come from clothing? It is possible! When we wear, wash, and even throw away clothes, they shed tiny fibers. Millions of these fibers are flushed down the drain every time you do laundry. The wastewater from washing machines usually passes through cleaning systems called wastewater treatment plants, but these systems cannot remove all microplastics, so some of them eventually reach the ocean. We believe this is one of the main ways microplastics, such as polyester fibers, end up in kelp forests.

However, laundry is not the only way microplastics can reach kelp forests. Another way is through the air—a process called atmospheric transport. Tiny fibers shed from clothing can be carried by the wind for hundreds of kilometers before settling into the ocean and eventually reaching kelp forests.

Our study shows that even kelp forests, which are super important ocean habitats, have a microplastic problem. We need more research like this to understand the dangers of microplastics and find ways to protect marine biodiversity.

Glossary

Macroalgae: ↑ Large seaweeds that grow in the ocean, attach to rocks, and provide food and shelter for many marine animals.

Food Web: ↑ How plants and animals depend on each other for food and survival.

Microplastics: ↑ Tiny plastic particles with a size less than 5 mm.

Atmospheric Transport: ↑ Is the wind-driven movement of tiny particles through the air, carrying them from one place to another, sometimes across very long distances.

Acknowledgments

The original research was financed by the project “Fuentes, Concentraciones, Impactos y Destinos de Microplásticos (MP) en Dos Bahías de Baja California, México”, which was submitted in the “Convocatoria 2016 Investigación Científica Básica (CB-SEP/ CONACYT)” [grant number 11521] and Universidad Autónoma de Baja California internal founds [grant number 11397].

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Conflict of Interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.