MEPS 244:125-137 (2002)  -  doi:10.3354/meps244125

ABSTRACT: Clavelina lepadiformis is a colonial ascidian found in harbour and rocky littoral habitats. The populations of these 2 habitat types in the Western Mediterranean showed marked genetic differences in mtDNA sequence data in previous works. However, no morphological differences between the forms inhabiting the 2 habitat types have been found. Here, we compared the biology and accumulation of heavy metals in populations of both habitats in NE of Spain. Abundance and seasonal cycles showed contrasting trends in the 2 habitat types: harbour populations reached densities of ca. 3900 zooids m^-2 and active colonies were found all year round. Abundance in the rocky littoral environment was 1 order of magnitude lower and showed a clear seasonal pattern, with the disappearance of zooids during summer (aestivation). Reproductive cycles also differed, as larvae were present in the harbour population from November through June, with several sexual cycles during this period. In contrast, in the open littoral, larval occurrence was restricted to 2 to 3 mo during winter-spring, with only 1 gonadal cycle yr^-1. The zooids and larvae of the harbour were significantly larger. However, neither the total reproductive effort, tunic production (in weight ratios) nor fecundity significantly differed between these habitats. The harbour population accumulated significantly more Cu and Pb, and heavy metal concentrations showed a seasonal cycle with minima in summer. On the other hand, both populations accumulated a similar amount of V, a metal involved in ascidian metabolism. The production of secondary metabolites and the toxicity of polar extracts were higher in the open littoral form. These results, however, did not correlate with the outcome of palatability tests carried out with specialist and generalist predators, in which no preference was observed. Experimental juvenile transplantation between habitats showed that newly settled individuals from the rocky littoral habitat can survive in both environments (with survival rates of 30 to 50% during the first 4 wk), while those from harbours show low survivorship when moved out (ca. 5% survival after 4 wk). We conclude that there was a marked ecophenotypic variation between populations of both habitat types.

KEY WORDS: Ascidians · Harbours · Ecophenotypic variation · Genetic divergence · Sub-lethal pollution · Reproductive investment · Biological cycles