The order Decapoda encompasses nearly all of the crustaceans that are used for human consumption, and supports many large and valuable fisheries. In addition, penaeid shrimps and crayfish are extensively cultured for food in many parts of the world.
A number of human fatalities have been caused by the consumption of poisonous crabs. Several reef-dwelling species of Indo-Pacific crabs appear to acquire toxins from their food; since toxicity varies with the crab's diet and location, it can be very difficult to determine whether one of these crabs is safe to eat. In other areas, decapods are often host to such schistosome parasites as lung flukes, which can infect humans who eat raw or poorly cooked freshwater crabs or crayfish.
In some rice farming areas land crabs are considered serious pests, both because they eat the plants and because they dig burrows that drain water from the fields. The burrowing activities of thalassinid shrimps have had serious effects on oyster culture; when present in large numbers they loosen the substrate to such an extent that the oysters sink into it and are smothered.
The intentional and unintentional introduction of some decapods to new areas has caused a number of detrimental effects. For example, the accidental introduction of the European green crab (Carcinus maenas) to the eastern coast of the United States has resulted in serious population reductions in the clam fisheries there. Various intentional introductions of freshwater crayfish have resulted in crop damage and threats to native species of crayfish.
1. Yellowline arrow crab (Stenorhynchus seticornis); 2. Pea crab (Pinnotheres pisum); 3. Harlequin shrimp (Hymenocera picta); 4. Sand fiddler crab (Uca pugilator); 5. Banded coral shrimp (Stenopus hispidus); 6. Pacific sand crab (Emerita analoga); 7. Sevenspine bay shrimp (Crangon septemspinosa). (Illustration by Jonathan Higgins)
1. Spanner crab (Ranina ranina); 2. Giant tiger prawn (Penaeus monodon); 3. Chinese mitten crab (Eriocheir sinensis); 4. Common hermit crab (Pagurus bernhardus); 5. Mangrove crab (Scylla serrata); 6. Flathead locust lobster (Thenus orientalis); 7. Red swamp crayfish (Procambarus clarkii); 8. Red king crab (Paralithodes camtschaticus). (Illustration by Jonathan Higgins)
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