Decapods exhibit many complex and even spectacular behaviors. The Caribbean spiny lobster Panulirus argus sometimes migrates toward deeper water in long lines or queues of as many as 65 individuals. The reason for these migrations is not entirely clear, but seems to be associated with avoidance of winter storms. Juvenile red king crabs (Paralithodes
camtschaticus) often gather together into mounds that may contain thousands of individuals, possibly to deter predators.
Many decapods use visual and even auditory signals to communicate with one another. Sounds are usually produced with some type of stridulating surface, and this means of communication is most common in terrestrial and semiterrestrial species. Stridulation refers to sounds produced by rubbing body parts together. Communication using pheromones appears to be common in aquatic species, especially in conjunction with mating. Pheromones are released in the urine via the antennal gland; when crayfish fight they literally blow pheromone-laden urine into the face of their opponent.
Experiments have demonstrated that crabs and lobsters are capable of such complex learning as navigating a path through a maze. Crabs that are offered novel items of prey quickly learn the most effective way to feed on them, and decapods have been taught to respond to a specific cue or to discriminate among colors.
The activity patterns of intertidal species are often synchronized with the tidal cycle. For example, a crab may emerge to feed only during nighttime high tides, and this pattern becomes set in the animal's own biological clock. When the crab is placed in captivity away from all tidal influence, its set rhythm of activity can persist for days or even weeks.
Many marine decapods form symbiotic associations with other organisms. Some shrimp set up cleaning stations where fishes line up to be picked over for parasites. Others may live full-time with a fish, building and maintaining a shared burrow while the fish watches for predators. Far more have established less formal associations with larger organisms that offer protection from predators, such as the many kinds of shrimps that associate with sea anemones.
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