Bioturbation

Walrus (Odobenus rosmarus) resting in a crowd on Wahlbergøya, Svalbard (3)

Arenicola marina 2010

Goby fish with shrimp

Camas pocket gopher mounds

Chironomidae

Bioturbation refers to the process by which organisms living in the soil or sediment at the bottom of bodies of water, such as lakes, rivers, and oceans, rework the structure of the sediment by their activities. These activities can include burrowing, ingestion, and defecation of the sediment particles. The organisms responsible for bioturbation are known as bioturbators and include a wide range of animals such as worms, bivalves, crustaceans, and other invertebrates. Bioturbation plays a critical role in ecosystems by affecting sediment properties, nutrient dynamics, and the distribution of organisms and pollutants.

Effects of Bioturbation

Bioturbation has several significant effects on sedimentary environments and ecosystem functioning:

• Sediment Mixing: Bioturbators mix the sediment layers, leading to homogenization of the sediment column. This mixing can affect the sediment's physical and chemical properties, including texture, porosity, and oxygen distribution.
• Nutrient Cycling: By moving sediments, bioturbators help in the cycling of nutrients, making them more available to other organisms in the ecosystem. This process is crucial for the productivity and health of aquatic environments.
• Gas Exchange: The activities of bioturbators enhance the exchange of gases between the sediment and water, influencing the levels of oxygen and other gases within the sediment. This can have significant implications for the metabolic processes of sediment-dwelling organisms.
• Pollutant Redistribution: Bioturbation can also affect the distribution and fate of pollutants within sediments. By mixing sediments, bioturbators can either dilute or concentrate pollutants, impacting their bioavailability and toxicity.

Types of Bioturbation

Bioturbation can be classified based on the behavior of the organisms involved:

• Gallery and Burrow Construction: Many organisms construct galleries and burrows within the sediment. This type of bioturbation can significantly alter the sediment structure and facilitate the exchange of water and gases.
• Ingestion and Defecation: Some bioturbators ingest sediment as they burrow, later excreting it at the surface or within the sediment column. This process contributes to sediment mixing and nutrient cycling.
• Surface Grazing: Organisms that feed on the sediment surface can also disturb and redistribute sediment particles, affecting the sediment's surface characteristics.

Bioturbators

A wide variety of organisms are involved in bioturbation, including:

• Worms: Many species of worms, such as polychaetes and oligochaetes, are active bioturbators.
• Bivalves: Clams and other bivalves can burrow into sediments, affecting sediment structure and chemistry.
• Crustaceans: Certain crustaceans, like some species of crabs and shrimp, are known to significantly alter sediment properties through their burrowing activities.
• Echinoderms: Sea stars and sea cucumbers can also contribute to bioturbation through their feeding and movement.

Impact on Human Activities

Bioturbation can have both positive and negative impacts on human activities. In aquaculture, for example, bioturbation can be beneficial by improving water quality and nutrient cycling. However, it can also be detrimental by resuspending sediments and pollutants, potentially harming cultured species.

Research and Conservation

Understanding bioturbation is crucial for managing and conserving aquatic ecosystems. Research in this field focuses on quantifying the effects of bioturbation on sediment dynamics, nutrient cycling, and pollutant fate. Conservation efforts aim to protect key bioturbator species and their habitats to maintain healthy and productive aquatic environments.