MORPHOLOGICAL VARIATION IN FUCUS-VESICULOSUS POPULATIONS ALONG TEMPERATURE AND SALINITY GRADIENTS IN ICELAND

Geographical morphological variations in Fucus vesiculosus populations were studied along the coast of Iceland. Principal component analysis (PCA) based on 11 morphological characters clustered the 26 sampling sites into four different morphological types as follows: (1) a morpho logical type found along the S-SW-W coast; (2) an intermediate form co mprising only two populations in the NW; (3) a type found along the N- NE-E-SE coast; and (4) a type found independent of geographical area, in estuaries and at sites influenced by large freshwater outflows. Pop ulations influenced by low salinity had significantly (P less than or equal to 0.001) shorter thalli, a shorter distance from the holdfast t o the oldest dichotomy, smaller fronds, narrower stipes and midrib wid th compared to the morphology of all other more saline populations. No significant difference in frond width was found between the S-SW-W an d the N-NE-E-SE populations. However, significant (P less than or equa l to 0.001) morphological differences between them were observed, the former having shorter thalli, a greater distance from the holdfast to the oldest dichotomy, narrower stipes and smaller midrib width compare d to the latter. These differences between populations along the S-SW- W and the N-NE-E-SE coasts are suggested to be due to combined effects of rare, long distance dispersal of reproductive fronds by the warm-t emperate Irminger Current and the cold, Arctic East Icelandic Current respectively and the short dispersal range of Fucus gametes. Thus, ove r the years, the East Icelandic Current may have transported reproduct ive fronds from the northernmost F. vesiculosus populations on the Gre enland coast and the Barents Sea to the eastern coast of Iceland while the Irminger Current has carried thalli from the more southerly distr ibution of Fucus on the North American east coast to the southwestern part of Iceland. Excluding the populations affected by reduced salinit y, the comparatively similar morphology within these two areas, may be explained by the restricted dispersal of the short lived F, vesiculos us gametes.