Tardigrades, often called water bears or moss piglets, are microscopic invertebrates renowned for their remarkable resilience. These tiny creatures, typically less than a millimeter in length, inhabit diverse environments from mountaintops to deep-sea trenches. Understanding their diet is central to comprehending their survival and ecological roles. This article explores the varied diet and feeding strategies that allow tardigrades to thrive in such a wide array of habitats.
Common Dietary Items
Tardigrades exhibit a diverse diet, consuming a range of microscopic organisms and organic matter. Many species primarily feed on the fluids of plant cells, such as algae and mosses. Terrestrial tardigrades often extract nutrients from the cells of mosses and lichens, which are abundant in their microhabitats.
Beyond plant matter, some tardigrade species are detritivores, meaning they feed on decaying organic material. This detritus can consist of dead plant cells, bacterial colonies, or other decomposing biological matter. These species play a role in nutrient cycling within their tiny ecosystems.
A significant number of tardigrades are carnivorous or omnivorous, preying on other small invertebrates. They consume rotifers, nematodes, and even other smaller tardigrades. This predatory behavior highlights a more active hunting strategy compared to the passive consumption of plant fluids or detritus.
How Tardigrades Eat
Tardigrades possess a specialized feeding apparatus designed for piercing and sucking. This mechanism includes a buccal tube, and a pair of sharp, protrusible stylets. These stylets are located at the front of the mouth and can be extended and retracted.
When feeding, a tardigrade uses its stylets to puncture the cell walls of plants, algae, or the outer cuticles of smaller invertebrates. After piercing, a muscular pharynx located behind the buccal tube contracts. This creates a powerful sucking action that draws internal fluids or cellular contents from the prey item into the tardigrade’s digestive system.
The rhythmic pumping of the pharynx allows the tardigrade to efficiently extract nutrients from its food source. This method of feeding is highly effective for obtaining the liquid contents of cells, whether from a plant, an algal filament, or the internal tissues of a small worm.
Dietary Adaptations and Flexibility
The diet of a tardigrade can significantly vary depending on its species and the specific habitat it occupies. For instance, aquatic tardigrades found in freshwater ponds might predominantly consume different types of algae or protozoa compared to terrestrial species living in moss cushions, which rely more on moss cells and associated microorganisms. This adaptability allows them to exploit available resources.
Tardigrades also exhibit remarkable flexibility in their feeding strategies, adapting to periods of food scarcity. When food becomes unavailable, many species can enter a state of cryptobiosis, significantly slowing their metabolism and suspending most biological functions. This allows them to effectively “wait out” unfavorable conditions until food sources reappear.
While some tardigrade species are specialized feeders, others are more generalist or omnivorous. This dietary breadth contributes to their widespread distribution and ability to survive in diverse environments. Their capacity to switch between different food sources or endure periods of starvation underscores their robust survival mechanisms.