Life cycles and growth rates of two morphotypes of Cystodytes (Ascidiacea) in the western Mediterranean

The reproductive cycles, growth and survival of the 2 most abundant color morphs (blue and purple) of the colonial ascidian Cystodytes occurring in the western Mediterranean were studied over a period of 20 mo. Previous reports have assigned the 2 morphotypes to the nominal species C. dellechiajei. A seasonal pattern emerged, in which larval release occurred in late spring and summer, followed by a period of active growth. Significant differences between morphotypes were also detected: the cycles of both reproduction and growth rates of the purple morph lagged 1 to 2 mo behind those of the blue morph. Within morphotypes, the time course of reproductive activity and growth rates also displayed a temporal lag that suggests partitioning of resources to either reproduction or growth. In particular, the growth rates of the 2 morphotypes peaked when reproductive activity was at its lowest. There were no significant differences in mortality between these forms, and in both cases a significant negative correlation was found between mortality and size. In the blue morph, maximal growth rate was negatively correlated with size, whilst no significant relationship between growth rate and size was detected in the purple morph. There were no significant differences in growth between colonies of the purple morph that were in contact with the toxic sponge Crambe crambe and those that were not. The differences found in the reproductive cycles of these 2 morphotypes match previously reported genetic and chemical divergences.