Fairy shrimp are small, freshwater crustaceans belonging to the order Anostraca, immediately recognizable by their habit of swimming upside-down. These translucent organisms thrive in temporary bodies of water, such as vernal pools, where they spend their short lives suspended in the water column. Their existence is centered on rapid growth and reproduction before their temporary habitat dries out, a feat largely dependent on their efficient and non-selective feeding strategy. This strategy allows them to process the diverse array of microscopic particles available in their unique, fleeting ecosystems.
Primary Dietary Components
Fairy shrimp are suspension feeders, meaning their diet consists of tiny particles suspended throughout the water column. The bulk of their food comes from phytoplankton, which includes various forms of algae like diatoms and filamentous green algae. Fairy shrimp are sometimes referred to as algivores, reflecting the high proportion of algae in their natural diet.
Beyond algae, their diet includes other microscopic life forms such as bacteria and protozoans like amoebae. They consume fungal spores and minute metazoans, or small invertebrates, that drift in the water. A significant part of their sustenance comes from non-living organic matter known as detritus, often consisting of decaying plant material.
Fairy shrimp are non-selective feeders, consuming nearly any particle that falls within an acceptable size range. Their gut contents have been found to include flatworm eggs and the shells of organisms like Arcella, a type of amoeba. The color of the fairy shrimp is often a direct indicator of the specific types of algae and carotenoid pigments they have been consuming.
The Filter Feeding Process
Fairy shrimp accomplish suspension feeding using their numerous thoracic appendages, or thoracopods. These leaf-like limbs extend downward from the body as the shrimp swims on its back. There are typically 11 pairs of these appendages, and they beat rhythmically and synchronously, creating a metachronal wave.
This continuous beating motion serves two functions: propelling the animal through the water and generating the water currents necessary for feeding. The movement of the limbs creates a filter chamber and draws suspended food particles toward the midline of the body. Specialized setae, or fine bristles, on the limbs act as a filtering mesh, capturing the microscopic food items.
Once captured, the food particles are transferred into a ventral food groove that runs along the underside of the body. Muscular action then moves the concentrated food mass anteriorly, toward the mouthparts. Larger or unsuitable particles, such as sediment or oversized detritus, can be actively rejected before or after entering the food groove, maintaining the efficiency of the filtering mechanism.
Influence of Ephemeral Habitats on Food Availability
Fairy shrimp inhabit ephemeral habitats, such as vernal pools, which fill seasonally and then dry out completely. This temporary nature dictates a highly variable food supply that changes dramatically throughout the pool’s life cycle. When the pool first fills with cold winter rains, the environment is typically rich in organic detritus and decaying matter from the previous dry season.
As the water remains, light increases, and temperatures rise slightly, a succession of phytoplankton populations emerges. This shift means that fairy shrimp must be flexible omnivores, first relying on bacteria and detritus, and later capitalizing on blooms of algae and protozoans.
This efficiency ensures they can reach maturity and lay their dormant eggs, or cysts, before the pool evaporates, completing their life cycle.