Red and green colour forms in the common shore crab Carcinus maenas (L.) (Crustacea: Brachyura: Portunidae): theoretical predictions and empirical data

Abstract

The shore crab Carcinus maenas (L.) is known to exhibit a range of carapace colours from green through orange to red. Recent studies have demonstrated that the different colours reflect increasing lengths of intermoult duration, with clear physiological and ecological differences between red and green crabs. It was hypothesized that these different colour forms represent different ‘life-strategies’. However, to date, there has been no study on population dynamics which attempts to account for these differences in colour. In order to test the red/green hypothesis, theoretical predictions were made about the occurrence of red males within a population, and the occurrence of different male colour forms was investigated in a population of shore crabs in the German Wadden Sea. The general differences in size and the coverage of epibionts and the seasonal changes in abundance between red and green males were investigated. These empirical data were compared with the theoretical predictions about red males which supported the hypothesis that red and green forms represent separate phases with different ‘life-strategies’ in the life cycle of Carcinus maenas.