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Hemigrapsus nudus

Hemigrapsus nudus (Varunidae), commonly known as the purple shore crab, is found along the Pacific coast of North America, ranging from Yacobi Island, Alaska to Bahia de Tortuga, California (Oliver and Schmelter 1997). Hemigrapus nudus typically inhabits the rocky shore areas of the mid to low intertidal zones, preferring locations with larger rocks and stones overlaying sand. These areas provide an abundance of shelter and allow for more adequate drainage of water (Kundsen 1964; McGaw 2003). Purple shore crabs prefer water temperature ranges from 14.6 °C to 26.9 °C. Their preferred salinity ranges between 22 PSU and 32 PSU, but H. nudus will tolerate lower salinities in order to find shelter (McGraw 2001, McGraw 2003). Hemigrapsus nudus is typically purple in color, but individuals can vary from greenish-yellow to reddish-brown. Purple shore crabs are characterized by the reddish-purple spots located on their claws and the lack of hair on their legs. The shell, or carapace, of males can measure up to 36.2 mm wide, while the carapace of females can measure up to 34 mm wide (Oliver and Schmelter 1997). Mating occurs annually, generally beginning in November and extending into early April, with eggs hatching from May to early June. The number of offspring produced by a female is positively correlated with her size. Females can lay from 441 to 36,400 eggs at a time; on average, females lay around 13,000 eggs (Kundsen 1964, Oliver and Schmelter 1997). Purple shore crabs are considered to be omnivorous with a diet consisting mainly of diatoms, desmids, and green algae. They are also known to occasionally eat small animals such as snails and barnacles and consume dead organic matter (Kundsen 1964, Lewis et al. 2007, Oliver and Schmelter 1997).


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