Shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some are found in freshwater. In addition, a few species of land crabs are eaten, for example Cardisoma guanhumi in the Caribbean. Shellfish are among the most common food allergens.[1]
Not to be confused with selfishness.
Despite the name, shellfish are not fish. Most shellfish are low on the food chain and eat a diet composed primarily of phytoplankton and zooplankton.[2] Many varieties of shellfish, and crustaceans in particular, are actually closely related to insects and arachnids; crustaceans make up one of the main subphyla of the phylum Arthropoda. Molluscs include cephalopods (squids, octopuses, cuttlefish) and bivalves (clams, oysters), as well as gastropods (aquatic species such as whelks and winkles; land species such as snails and slugs).
Molluscs used as a food source by humans include many species of clams, mussels, oysters, winkles, and scallops. Some crustaceans that are commonly eaten are shrimp, lobsters, crayfish, crabs and barnacles.[3] Echinoderms are not as frequently harvested for food as molluscs and crustaceans; however, sea urchin gonads are quite popular in many parts of the world, where the live delicacy is harder to transport.[4][5]
Though some shellfish harvesting has been unsustainable, and shrimp farming has been destructive in some parts of the world, shellfish farming can be important to environmental restoration, by developing reefs, filtering water and eating biomass.
Toxic content[edit]
Some shellfish, such as whelk, contain arsenic. A sample of whelk was found to have a total content of arsenic at 15.42 mg/kg of which 1% is inorganic arsenic.[18]
Shellfish caught in Alaska can cause paralytic shellfish poisoning (PSP).[19]
PSP is caused by toxins namely Saxitoxins released by dinoflagellate, a type of protista (also considered algae), which are extremely poisonous (1000 times more potent than cyanide) and can lead to death by paralyzing the breathing muscles.
Due to warming oceans, algae blooms have become more widespread,[20] thereby increasing the likelihood of intoxications of various types.
Ecosystem services and reef-building[edit]
Shellfish of various kinds contribute to the formation of reefs, such as when millions of oysters or mussels aggregate together. Reefs provide habitat for numerous other species, bury carbon, contributing to climate change mitigation,[21] and defend the shore against erosion, floods and waves.[22][23] Conversely, when they are destroyed or exploited, carbon can be released into the atmosphere, simultaneously increasing the likelihood of severe weather while removing the natural defence against its consequences.[21][24] In addition, some shellfish are known for filtering water, removing suspended particles and contaminants, which contributes to both quality and clarity.[25] These benefits cascade to other species that are helpful to humankind such as seagrasses.[25]