COLOR POLYMORPHISM IN RELATION TO SPATIAL-DISTRIBUTION IN SOME INTERTIDAL ISOPODS IN NORTHERN SPAIN

The hypothesis that the level of chromatic polymorphism in intertidal isopods is related to their distribution and seasonal fluctuations in abundance was examined in northern Spain. Four species were used, Dynamene bidentata, Dynamene magnitorata, Cymodoce truncata and Cymodoce emarginata. Only for Dynamene species were results consistent with initial hypothesis. The most common colour morph in Dynamene bidentata was uniformis which is the most flexible phenotype, allowing effective concealment in most of the environments where the species occurs. Dynamene bidentata is the most abundant species of isopod in northern Spain, where it is abundant along the shore and throughout the year. Distribution of D. magnitorata, Cymodoce truncata and C. emarginata is restricted to macroalgal assemblages at low tidal levels. Seasonality is also important in D. magnitorata and C. truncata. The number of colour morphs and phenotypic diversity was larger in D. magnitorata than in D. bidentata. Only one colour morph was found in C. truncata and four in C. emarginata.