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Fairy Shrimp (Eubranchipus species are most common) Fairy shrimp are small crustaceans restricted to vernal pools and are widely distributed throughout the United States. Though widespread in spatial distribution, fairy shrimp are greatly restricted seasonally. Their temperature tolerance is limited to 40 to 60°F. They appear soon after spring thaw and disappear with the onset of warm, summer weather leaving behind resistant eggs that carry the species over to the next favorable period. The resting egg (actually a developing embryo) has a dark covering and is able to survive drying, extreme heat, freezing, and ingestion by birds. Re-flooding the following spring stimulates hatching. Adult fairy shrimp may persist into the summer but are usually hard to find after May. Fairy shrimp usually have one generation per wet episode. Fairy shrimp do not occur in all vernal pools. Even within one pool, shrimp may occur regularly for many years only to disappear in others, even under seemingly favorable conditions. The habitat requirements for fairy shrimp are not well known. Studies in Maine were not able to explain why fairy shrimp are found in some pools and not in others. Potential factors affecting their distribution include water chemistry, hydrology, depth of unfrozen water, and presence of algae in spring. Description: The different species of fairy shrimp vary in size, color, and shape. All swim upside down, waving 10 pairs of leaf-shaped limbs, with which they feed. The two major eyes are on stalks. Most have a long tail, sometimes with "neon" spots near the tip. Colors generally white or brownish, with orange or red marks; egg sacs carried by female may be bright blue. Strikingly large among the swimming invertebrates. From a distance may look like a small fish. Size is one half to one inch. Distribution and Status: Probably found in vernal pools throughout Maine. Eggs: Very small (pinhead size), brownish and laid in clumps. Breeding Pools: Fairy shrimp occur only in waters that are free of fish—primarily temporary and semi-permanent vernal pools. The habitat requirements for fairy shrimp are not well known. To see the next species common to vernal pools, click Next. To return to the overview of four species common to vernal pools, click Overview. To go to the previous page, click Back. |
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