These pages are not comprehensive. The current literature on Anostraca is too voluminous and too inaccessible. What follows is based partly on physical publications I read and copied decades ago. Most online journal articles are behind pay or registration walls. Even so, I have included information from more than about 100 works from 1921 to 2024 that are Open Access or otherwise available to the public. I have also used some abstracts that had useful information even when the article was inaccessible. My hope is to help non-specialists, like me, who are interested in fairy shrimp to better appreciate their remarkable lives.
The citations are given on the References page.
Synopsis
Fairy shrimp live in puddles, ponds, and lakes. They don’t live in the oceans or in flowing water. Different species are adapted to different salinity ranges, from as pure as rainwater to 6 times saltier than sea water. Those that inhabit water saltier than sea water are commonly referred to as brine shrimp. Fairy shrimp populate alpine, tundra, forest, sagebrush steppe, Asian steppe, prairie, rock pool, saline lake, desert playa, and other environments.
Adult fairy shrimp are generally 7-30 mm (0.3-1.2″) long. They are crustaceans (Order: Anostraca) with no shells or exoskeletons and with 22 flexible legs attached to 11 thoracic segments, with rare exceptions. The abdomen is thin and tubular and about as long as the thorax. It lacks legs and looks like a tail. Fairy shrimp have small heads with 2 compound eyes on short stalks and 2 pairs of antennae.
The legs, which are all similar, are the most distinctive feature of fairy shrimp. They have been likened to leaves because each consists of flat lobes of various shapes and sizes, sort of like a lobed leaf. The legs have bristles for straining small items from the water for food, principally algae. Fairy shrimp absorb oxygen through their legs. The legs move with rippling wave-like motions for simultaneous swimming, breathing, and eating.
Fairy shrimp commonly glide gracefully through the water. Their swimming is more steady than the sprint-pause swimming of most copepods, cladocerans, and aquatic insect larvae and adults and slower than the zipping of amphipods and many ostracods. They occasionally make jerky motions. They never stop swimming.
The fairy shrimp life strategy is to go for less popular waters in order to avoid voracious, fast-swimming, visual predators like fish. Consequently, they find homes in ephemeral ponds that may last for days to months, in shallow ponds that freeze solid in winter, and in permanent ponds and lakes that are too salty for, or are inaccessible to, fish.
Fairy shrimp produce resting eggs that survive drying, extreme temperatures, and space travel and, less commonly, live eggs that hatch soon after release by the mother. Resting eggs remain viable for several years. Most resting eggs remain on the dry or wet bottoms of the parents’ ponds. Eggs that don’t hatch one year may hatch in a subsequent year under similar or different conditions. Some eggs are carried off by wind or in the fur, feathers, or guts of animals or in mud stuck to their bodies. Fairy shrimp have hatched from eggs in bird and amphibian feces. Transported eggs may colonize new ponds or contribute genetic diversity to other existing populations.
Fairy shrimp are distributed from the Arctic and Antarctic to the tropics and can be found on all continents and many islands. Their distribution has been greatly reduced by agriculture, urbanization, infrastructure, and fish-stocking for recreation but has been increased with ponds for watering livestock, roadside ditches, gravel pits, bomb craters, and other unmanaged excavations that can fill with rain or snow. Although some species which live in only a few ponds are at risk of extinction, the Anostraca order has survived 2 mass extinction events over the past 300 million years and has the resilience to withstand future heedless human disturbances, including nuclear war.
Resting Eggs of Fairy Shrimp and Their Hatching