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Mussels are filter animals that can concentrate contaminants that are present in their habitat.

Image: from Anonymous in Unsplash

The mussel is a bivalve mollusk, protected by two bluish-black shells, that lives near marine shores and rocky surfaces of oceans and freshwater surfaces. They are filter animals that feed on microscopic algae and suspended materials. Therefore, they can concentrate contaminants that are present in their habitat. Like oysters, mussels also have the ability to produce pearls.

Consumed since prehistory, mussels were considered by Greco-Roman cultures as a noble food, served at parties and special occasions. The cultivation of mussels, called Mitiliculture, has its beginning attributed to the Irish Patrick Walton, who was shipwrecked in the bay of Aguillon, in France, where he laid out a net to capture birds. However, the hammocks became a place of great fixation for mussels, which started to serve as food for him. Since then, mitiliculture has been developing in various parts of the world, contributing to the commercial activity of several countries.

In Brazil, the cultivation of mussels began in the 1970s by researchers from the University of São Paulo, the São Paulo Fisheries Institute and the Navy Research Institute. Currently, the state of Santa Catarina is the largest producer of oysters and mussels, accounting for over 90% of national production. The most abundant species of mussel in Brazil is the Perna perna.

Natural habitat

Mussels inhabit rocky shores in the intertidal region and can be found at a depth of up to ten meters. They live attached to rocks by means of a very resistant filamentous structure - the byssus - forming dense colonies. They are found more often on shores more exposed to wave action than in sheltered places.

As they inhabit the intertidal region, mussels are adapted to spend most of the time exposed to the air. However, in the case of cultivation, the most used strategy is to keep them constantly submerged, providing uninterrupted feeding and accelerating the rate of growth.

In addition to being able to live exposed to the air, mussels can populate polluted places, settling in pilasters of ports, boat hulls, buoys and any submerged or floating material that serves as substrate. Because they have the characteristic of filtering water, mussels can accumulate pollutants in their tissues. Thus, they are used in experiments as indicators of chemical or biological contamination of marine environments.

Mussels that huddle on reefs can ingest three times as much plastic

According to data released by the UN, 80% of all marine waste is made of plastic. Each year, eight million tons of the material ends up in ocean waters, causing 100,000 marine animals to die. Researchers from several universities analyze how mussels can be affected by plastic pollution in marine ecosystems.

Research by scientists at the University of Plymouth investigated how the tendency of mussels to form reef structures can affect the uptake of plastic waste. For this, they carried out several experiments that consisted of placing mussel aggregations in water gutters and submitting them to waves of different speeds. In addition, the team added microplastic particles throughout the tests, noting how water fluxes influenced the ingestion risk for mussels.

With this series of experiments, the researchers found that when mussels were grouped together in the laboratory to form reef-like structures, they were able to slow down the water flowing over them, as well as increase turbulence. The result of this was a threefold increase in plastic intake.

This is not the first time that the harmful effects of plastic on mussels have been analyzed. A study published in 2019 concluded that exposing these animals to microplastics could induce a strong immune response. Contact with the material causes the mussels to secrete less adhesive fibers, which they depend on to stick to the rocky shores.

Occupying about 70% of our planet, the oceans are of fundamental importance for the maintenance of life on Earth. They contribute to climate stability, regulate humidity and harbor a vast portion of biodiversity. Therefore, they must be preserved and protected.

external morphology

Externally, mussels are made up of two limestone shells or valves, which vary according to the habitat in which they live. Due to the constant crash of waves, marine mussels have thick, worn valves and less height than mussels from crops, which remain submerged.

Breathing

The respiratory apparatus of a mussel is composed of gill blades and a heart. Oxygen absorption is carried out by the gill laminae and membranes existing on the entire inner surface of the mussel. The heart is located in the middle dorsal portion of the body, resting on the intestines.

food

The digestive tract of mussels is made up of an anterior mouth, a short esophagus and a stomach, with a stylet-shaped structure, the end of which, in contact with another structure of the stomach - the gastric shield - dissolves, releasing digestive enzymes .

Mussels are exclusively filter-feeding animals, that is, they take their food from the water used in the breathing process. The gill blades, in addition to absorbing oxygen, act in the selection of food particles, consisting of microscopic algae, bacteria and organic debris. Feeding is a continuous process, being interrupted only when the mussels are exposed to air or remain subject to any other unfavorable environmental condition, such as low salinity.

reproduction

Mussels are animals of separate sexes, with rare cases of hermaphroditism. The sex glands are spread throughout its internal structure. During sexual maturation, these glands transform into gametes, produced by the gonads. When mussels are sexually mature, gametes are emitted, stimulated by physical or climatic factors. Fertilization takes place in the aquatic environment, external to the animal's body.

To conclude, mussels are of great ecological importance. As they are filter animals and feed on microscopic algae, bacteria and suspended particles, mussels can accumulate pollutants that are present in their habitat. Thus, they are considered indicators of pollution.