Red and green Carcinus: how different?
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Carcinus maenas is, arguably, the most extensively studied intertidal crab in the world and can be found in a variety of habitats, from rocky intertidal, subtidal, in many areas of the world. Because of its range of habitats, it can tolerant a wide range of salinities and other environmental stressors like hypoxia and desiccation. Some individuals go into a prolonged state of intermoult when they reach a certain size, and turn red in colour. This means that C. maenas exhibits colour polymorphism, there being a green colour morph and a red colour morph due to different levels of expression in CYP enzymes. These colour morphs have various behavioural, physiological and biochemical differences which result in them occupying different habitats; the green morphs exhibiting tidal migrations up and down the shore, whilst the red morphs stay in the subtidal. Thus although red morphs are better competitors and are more likely to win fights over mates or prey, green morphs are more tolerant to a wide range of salinities and other stressors and so can exploit a wider range of habitats. Recent studies have suggested that green morphs may also be pre-adapted to deal with anthropogenic stress. Most experiments have involved mainly male samples; however, suggesting future research into female C. maenas colour morphs could give a wider picture of the differences between colour morphs.
Lewis, J. (2011) 'Red and green Carcinus: how different?', The Plymouth Student Scientist, 4(1), p. 423-431.