Color Phase—Specific Ion Regulation of the European Green CrabCarcinus maenasin an Oscillating Salinity Environment

PopulationDynamics of Green Crabs (Carcinus maenas) -- A Review

“…In some locations they migrate into deeper water during the cold winter months but in other areas many appear to remain in the shallow subtidal throughout the year, although numbers are reduced [76,87]. Following a colder than normal winter the density of the population is reduced [76,88] and many crabs can be found dead inside their Spartina bank burrows [89], evidence that they did not migrate.…”

“…The lower temperature limit for feeding is generally considered to be 7°C [29], although Ropes [65] concludes that at temperatures as low as 7°C crabs from Massachusetts do not suppress feeding but activity and presumably feeding probably cease at some temperature below 7°C. In most populations, adult crabs migrate offshore when the water temperature drops below 8°C in winter and then return as the water warms in the spring [1,82,87,[103][104][105][106][107][108][109][110]. Audet et al [111] report that C. maenas in Prince Edward Island waters may feed at temperatures below 6°C but only in the fall, not in the spring, and Eriksson et al [63] indicates that feeding may occur below 7°C but almost ceases below 3-4°C for crabs in Sweden.…”

“…Green phase crabs are known to be more tolerant of low salinity than red phase crabs and males are generally considered to be more tolerant than females [106,110,117,118] although Himes et al [87] found that females were more tolerant than males. These differences in tolerance to low salinity as well as to oscillating salinities result from greater expression of the osmoregulatory genes behind ion transport (Na+/K+-ATPase, cytoplasmic carbonic anhydrase) in green phase and female C. maenas, making green more tolerant than red, and females more tolerant than males [87]. In the native range, green crabs are more common in estuarine and intertidal habitats while red crabs are more common in the more saline waters of open shore and subtidal environments [1,119,120].…”

“…Furthermore, red females are more abundant than red males at estuarine sites [1,106,110,120]. These different distributions were not seen, however, in the nonindigenous population in southern Maine, where there was an even distribution of green phase crabs across sex in the intertidal and red phase crabs of both sexes were present in the intertidal throughout the year and at nearly the same abundances as green phase crabs during the summer months [87]. Adult C. maenas can tolerate short-term exposure to high salinities of up to 54‰ [29,63,91,121] but the preferred salinity range based on laboratory choice experiments performed with Isle of Man crabs is reported to be 27-40‰ [77,122], and Broekhyusen [91] indicated that crabs are rarely found in salinities >31‰.…”

“…Four of the most commonly used methods are discussed here; a review of additional methods can be found in [64]. Individuals can be counted directly along a transect or within quadrats (see for example [37,87,90,109,134]) but this method is practical only for the intertidal zone at low tide where mostly juveniles will be found or in very shallow water. Extremely high densities of small juvenile crabs ranging from 200 -2000 m -2 have been estimated using this method [72,[135][136][137].…”