Crangon franciscorum
From Wikipedia, the free encyclopedia
| Crangon franciscorum | |
|---|---|
 | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Caridea |
| Family: | Crangonidae |
| Genus: | Crangon |
| Species: | C. franciscorum |
| Binomial name | |
| Crangon franciscorum Stimpson, 1856 | |
Crangon franciscorum is a species of shrimp in the family Crangonidae which is endemic to the brackish estuaries of California,[1] and found from Puget Sound in the north to San Diego, California in the south.[2] The species is especially abundant in San Francisco Bay, despite population fluctuations due to environmental stresses. Its common names include bay shrimp, sand shrimp, common shrimp, grass shrimp, black shrimp, California shrimp and black tailed shrimp.[2] The species has been commercially fished from 1869 to the present.
This shrimp species is "an important part of the estuarine food web" in the greater San Francisco Bay.[3] It feeds on bivalves, amphipods and foraminiferins, and is prey for various fish,[3] including striped bass, white sturgeon, Pacific tomcod and shellfish such as Dungeness crab.[2] Its diet is "heavily influenced by predator size, temperature-salinity preferences, and prey availability."[3]
Lifecycle
The shrimp are short-lived, with a lifespan ranging up to 18 months for males and 30 months for females. The males spawn once, while longer-lived females spawn twice. Some evidence indicates the species may be protandrous hermaphrodites, which means that surviving males are transformed into females after one year of life. This may account for the longer lifespan of females.
The two most important natural environmental factors affecting the health of the shrimp population are water temperature and salinity. The shrimp thrive in brackish water, with a preferred salinity of 14 parts per thousand (ppt) when young to 24 ppt when ready to spawn.[4] In contrast, open ocean waters have a salinity of about 35 ppt. The species prefers a water temperature of about 18 °C, or 65 °F.[4] Because these factors vary within the bay, based on the seasons each year, and the variations in the inflow of fresh water in heavy rainfall years as opposed to drought years, the shrimp migrate around the bay, seeking optimal conditions, and their population levels fluctuate dramatically. When heavy flows of fresh water enter the bay, mature females migrate to the saltier parts of the central bay, or out the Golden Gate to the Gulf of the Farallones.[4] There, they mate with males which prefer a slightly saltier environment. The females then incubate from 2,000 to 8,000 eggs[2][4] and when hatched, the young shrimp migrate back to the shallower and less salty estuaries around the bay.[4] As the newly hatched shrimp develop and mature, they gradually migrate to "deeper, cooler and more saline water".[5]