Invertebrates
Shrimp
Caridea and Dendrobranchiata · also called shrimps, prawn
“Shrimp” is a shape, not a family. Slender body, long antennae, a fan tail for flicking backward out of danger — that outline has been arrived at by several separate branches of the crustaceans, and shrimp of one kind or another now live in nearly every wet place on Earth, from hydrothermal vents to desert rain pools.
Overview
The animals called shrimp span several crustacean groups, chiefly the caridean shrimp and the dendrobranchiate prawns, plus the unrelated mantis shrimp and the brine and fairy shrimp. Most are small, swimming crustaceans of the sea floor and water column, and most are omnivores — scavenging, grazing, filtering, or hunting small invertebrates. The cleaner shrimp pick parasites off fish.
Tricks of the trade
A startled shrimp snaps its abdomen and fan tail to shoot backward in a fraction of a second. The pistol shrimp fires a claw so fast the water boils into a bubble whose collapse makes a snap that can stun small prey — and, from whole colonies, a crackle loud enough to interfere with sonar. Many shrimp start male and turn female as they grow, since a large female carries more eggs.
Feeding the ocean, and being farmed
Wild shrimp feed almost every fish, and krill feed whales, seals, and penguins. Farmed shrimp — mostly whiteleg and giant tiger prawns — is one of the largest aquaculture industries in the world, though coastal ponds have cleared vast areas of mangrove and intensive systems can pollute and spread disease.
Status
Shrimp as a group are Not Evaluated. Most are abundant and fast-breeding, but some cave and spring species have tiny ranges, and wild stocks are heavily trawled, which also produces large amounts of bycatch.
Shrimp: common questions
What is the difference between a shrimp and a prawn?
In everyday use the two words are largely interchangeable, and which one people prefer depends on the country, with prawn more common in Britain, Australia, and India and shrimp more common in North America, often for the same animal or just for larger versions. There is a loose biological distinction, since true prawns belong to the dendrobranchiate crustaceans and true shrimp to the carideans, and they differ in gill structure and in how the body segments overlap, with prawns lacking the sharp bend in the body that shrimp have. But the culinary and common names do not follow that split at all, so a dish of shrimp and a dish of prawns may contain animals from either group.
Are mantis shrimp really shrimp?
No, despite the name. Mantis shrimp are stomatopods, a separate order of crustaceans that split from the true shrimp and other decapods hundreds of millions of years ago. They are best known for two things. Their front limbs are modified into clubs or spears that strike with the speed of a bullet, one of the fastest movements in the animal kingdom, fast enough to crack aquarium glass and shatter snail shells with a shock wave. And their eyes are among the most complex known, with up to 16 types of colour receptor against a human's three, and the ability to detect polarised light. They are called shrimp only because of their general body shape.
Is shrimp farming bad for the environment?
It can be, and historically much of it was. The rapid growth of coastal shrimp farming from the 1980s onward cleared very large areas of mangrove forest in Southeast Asia, South Asia, and Latin America, and mangroves are among the most valuable habitats there are, for fish nurseries, coastal protection, and carbon storage. Intensive ponds also concentrate waste, are prone to disease outbreaks that lead to antibiotic use and abandoned ponds, and can salinise surrounding land and water. Against this, farmed shrimp takes pressure off wild stocks, and there is real progress through mangrove replanting rules, certification schemes, polyculture, and inland closed systems that recirculate water, so the footprint varies enormously between operations.
How do pistol shrimp make such a loud noise?
A pistol shrimp has one greatly enlarged claw with a hinged upper part that it cocks open against a latch. When it releases the latch, powerful muscles snap the claw shut so fast, in under a millisecond, that a jet of water shoots out at around 100 kilometres an hour. The pressure in the wake of that jet drops so low that the water vaporises into a bubble, a process called cavitation, and when the bubble collapses an instant later it releases a sharp pressure wave, a flash of light, and briefly temperatures approaching those of the sun's surface in a microscopic volume. The snap can stun or kill prey a few centimetres away, and the collective sound of many pistol shrimp is one of the loudest ambient noises in the ocean.