The blue crab's carapace (or shell) is about 7 inches (17.8 cm) wide and 4 inches (10.2 cm) long. Blue crabs have been introduced to various international waters such as in Black Sea, Mediterranean Sea, Baltic See, European Water and Japanese water. As larvae, they are vulnerable to fishes, jellyfish and other planktivores. This may be an adaptation to low oxygen levels, since the scarlet crab lives at 1000 m, near the oxygen minimum zone. Seasonal appearance: Early spring to late fall. Females have red-tipped claws. The first pair is modified as pinchers and the last four pairs are walking legs. More information about adaptation strategies. They are mobile predators whose salinity requirements change at different stages in their lives. Blue Crab (Callinectes sapidus)Color: Olive green carapace, with brilliant blue claws. Additional Resources. Size: Up to 9 inches long from point to point, and 4 inches from head to tail. Blue crabs are subject to predation throughout their life cycle and are particularly susceptible when they are soft during the molting process. Description. Blue crabs live in estuaries along the United States' Atlantic and Gulf coasts. These crabs enter estuaries as juveniles and grow quite quickly, maturing after one year. Facts about Blue Crabs 8: the natural predators. If the crab is flipped over, the shape of the folded surface of the belly (the apron) reveals the animal's approximate age and sex. It weighs 1 to 2 pounds (0.45 to 0.9 kg) when fully grown. Adult male crabs live in the low-salinity waters upstream, while adult female crabs live in the higher-salinity waters near the mouth of the estuary. Crabs are crustaceans with five pairs of legs. Monitoring blue crab population levels and range shifts to gain knowledge on how changing conditions may be impacting crab populations is a useful first-step adaptation strategy for this species. During this time females migrate to the mouths of estuaries so that larvae may be released into high salinity waters. They drink water from dew and the ground, they get it from food, and even from water vapor. The blue crab's incubation time is 14-17 days, which is when the eggs are brooded. The sharks, striped bass, eels, drum, whiptail stingrays, conose rays, and trout are considered as some of the natural predators of blue crabs. Thinner legs require less oxygen, hence less energy. Land crabs have even more adaptations to prevent drying out. Blue crab larvae are part of the Bay’s planktonic community, serving as food for menhaden, oysters and other filter feeders. The megalopae and juvenile crabs are consumed by various fishes and birds, as well as other blue crabs. There, however, the crab is invasive. The Blue Swimmer Crab is a popular food in Australia and is targeted and caught in large numbers by professional and recreational fishers. Juvenile and adult blue crabs serve as food for fish, birds and even other blue crabs. There are many crab behavioral adaptations for survival that this shellfish do since they need to be able to fight their predators and live in their natural habitat. Habitat: Shallow and brackish waters, eelgrass beds, muddy bottoms. Stowaway blue crabs on ship ballasts have even showed up in the Mediterranean. Blue crabs are sexually dimorphic.Males are slightly larger than females and have bright blue claws. Blue crab larvae have a salinity requirement of at least 20 ppt, and show poor survival below this threshold. It was first seen off Egyptian waters in the 1940s, but reports of blue crab sightings in Italy, Israel, Greece, and Turkey have been made, too. Blue Crabs. The scarlet king crab lives even deeper than the golden king crab, and has legs that are much thinner in respect to their length. They also store water in their bladder, blood, and specialized pockets throughout their bodies. 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