Nutritious Mussels

Have you ever eaten mussels? Mussels belong to a group or organisms called bivalve mollusks. The word “mollusk” means soft, a very specific body characteristic, and “bivalve” means it has two valves, also known as shells (Figure 1). Bivalve mollusks include other edible creatures like oysters and scallops. Mussels are tender, tasty, and nutritious (Figure 2)! They are rich in protein, nutrients that keep our muscles healthy, and they are a good source of vitamins including D and B₁₂, as well as minerals including iron, phosphorus, and calcium. In addition, they have the types of fats that are considered healthy [1]. Some researchers also argue that mussels could help to reduce hunger in the world [1]. As the world’s population increases, more and more food is required to feed everyone, and producing all this food uses up fresh water and costs a lot of money, particularly for animal feed and medicines. The costs of growing mussels are lower, since mussels feed on nutrients from the environment and they do not need fresh water.

Mussel Environmentally Friendly and Economically Important

Mussels feed on very small plants called microalgae, which are present in seawater. As they feed they filter the water, which helps to clean out any substances suspended in it. Filter feeders like mussels help sunlight to penetrate deeper into the water. This is important for organisms that perform photosynthesis, which produces the oxygen needed to keep the water healthy for other organisms. Mussels are also a very important food for fish, birds, starfish, octopuses, and many other animals (Figure 2). Mussels live attached to the rocks, through a very thin, strong structure called the byssus. Many mussels can grow close together, creating an environment for other species to live in (Figure 2).

Mussels can teach us a lot! The byssus is composed of materials that, although very thin, can attach the mussels to a surface so firmly that not even the ocean currents and waves can remove them. Based on the properties of the byssus, some researchers are conducting tests to develop medical materials such as surgical glues, which can be used to help wounds heal [2]. Mussel shells have also been studied to assess their usefulness in drug production [3] and pet food.

Because they are filter feeders and remain in the same place for a long time, mussels can accumulate contaminants from the environment, so studying them can help researchers understand the health of the environment (Figure 2).

Mussels are very important for many families that live close to the sea and make a living by selling them—either as food or as art made from mussel shells (Figure 2). Mussels can be taken directly from the natural banks where they grow, or they can be grown in marine (ocean) farms. Marine farms are a good option for growing mussels because there are no feed costs, since mussels feed on microalgae in seawater, and no electricity is needed. No medicines are needed to treat mussels grown in marine farms, so this saves money, too [1]. Marine farms also use very little fresh water, do not generate much waste, and have very low CO₂ emissions.

Global Warming is a Threat to Mussels

Although mussels help us in many ways, we are not helping them in return. Today, the results of human activities threaten mussels in several ways (Figure 3), including the effects of global warming.

Global warming is the term used for the increasing temperature of our planet. Many researchers believe that humans are responsible for global warming because we emit greenhouse gases from burning fuels and from certain industries. Wildfires are increasing due to climate change, and they also release greenhouse gases. Recently, many mollusks have been dying due to the overheating of ocean water. When large numbers of these animals die, the bad smell can also attract disease-transmitting insects, which makes the problem even worse.

Pollution Can Harm Mussels

If the water coming through sewers from homes and industries is not treated properly, it can contain an excess of nutrients such as phosphorus and nitrogen. If this water makes its way into rivers, ponds, and seas, it can speed up the growth of algae and other aquatic plants because the nutrients feed them. Overgrowth of algae turns the water into a greenish, cloudy broth. With so many algae, sunlight can no longer penetrate into the water to help photosynthetic organisms produce oxygen. Without oxygen, all the organisms in the water can die [1]. Some algae can also release poisonous substances, called phycotoxins, which do not harm mussels but can cause poisoning in humans that eat them. Symptoms include nausea, vomiting, paralysis, and even death. To verify if mussels are contaminated, authorities must examine the water for the presence of phycotoxins and ban the capture of animals when phycotoxin levels are high.

In addition, untreated sewer water can contain dangerous bacteria present in human feces (poop). These bacteria can be bad for the health of mussels and the people who consume contaminated mussels.

Certain metals, such as lead, have been discovered in high concentrations in mussels [4]. Eating too much lead-containing seafood can cause lead to accumulate in the body, leading to problems with the nervous system and even death. Mercury, another metal that has been found in mussels and other seafood, can also cause nervous system problems if too much is eaten. In pregnant women, mercury can also interfere with the proper development of their unborn babies.

Emerging Pollutants Have Unknown Dangers

Emerging pollutants are fairly new contaminants, for which we do not fully understand the environmental impacts. For example, tiny particles of plastic—or microplastics—have gotten a lot of attention in recent years plastics reach the oceans due to improper disposal of bottles, bags, cups, and other objects. Once in the ocean, plastic objects are broken down into small pieces due to the action of waves, and the resulting microplastics can be taken up by organisms like mussels—and then eaten by humans and other animals that eat the mussels. Studies have already found microplastics in humans [5].

Chemicals that come from plastics have also been found in mussels and, although the harm to humans is still unknown, it is suspected that these chemicals can damage the reproductive systems of animals and humans [6].

Other emerging pollutants, including medicines like antibiotics and hormones, have also been found in mussels [7]. Incorrect disposal of medicines in sinks or toilets is concerning because the effects of these substances can be severe. For example, antibiotics in water can cause the bacteria naturally found in the environment to become antibiotic resistant. This means that humans and other animals could develop bacterial infections that are very difficult to treat or that might not even be curable at all with current antibiotics. Studies on hormones are just beginning, but researchers believe that hormones consumed in food can unbalance the functioning of the body, possibly causing diseases of the reproductive system, including infertility.

Helping Mussels: Knowledge is Key!

Are you worried about the threats to the lives of mussels, and the consequences for the lives of all of us? Do you know how you can help? It is easy! Avoid using plastics, and do not throw old medicines out in the garbage—dispose of them properly. And most importantly, talk to your parents and friends about what you have learned here. By doing these simple things, you will contribute to the health of the ocean environment, which is so necessary for the life of the planet. Speaking of which, we are in Ocean Decade (2021–2030)! This period was established by several countries of the world as a time to focus on taking care of the marine environment. You have already taken the first step toward contributing, by learning about mussels!

Glossary

Bivalve Mollusks: ↑ A group of organisms with soft bodies protected by shells formed from two pieces, called valves. They include mussels and oysters.

Microalgae: ↑ Small plants that live in water.

Filter Feeders: ↑ Animals that eat by filtering the water to remove particles of food.

Photosynthesis: ↑ Process carried out by plants to produce energy from sunlight, water, and carbon dioxide.

Byssus: ↑ Thread-like structures used by mussels to attach to rocks or other objects in the water.

Phycotoxins: ↑ Toxic chemicals produced by algae.

Antibiotics: ↑ Medicines used to treat diseases caused by bacteria.

Hormones: ↑ Chemicals produced by the body’s glands that have many functions, including growth and sexual development.

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.

Acknowledgments

This study was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES)—finance Code 001—and Departamento de Inovação da Universidade do Estado do Rio de Janeiro (inovUERJ). We would like to thank the 23 students of Kite Montessori School in Poland who read this article, and especially Bogdan, Janek, Mikołaj, Stasiu, and Florek, who decided to spend more time and discuss this article in depth. We would also like to thank the other anonymous students who also participated in this review. You helped us to make the article better for a young audience, which makes us!