Phenotypic variation of Fucus spiralis was examined in terms of morphology and chemical composition, as determined by pyrolysis mass spectrometry (PyMS). After discriminant analysis both techniques revealed the existence of two morphotypes which were subsequently designated as F. spiralis and F. spiralis forma nanus. The nanus plants differed from the nominate spiralis in that they were shorter, narrower and had fewer branches, but had more units of growth from a single holdfast. F. spiralis f. nanus was consistently higher on the shore than F. spiralis, but the two morphotypes overlapped in terms of shore exposure level. We suggest that the formae exist within a mosaic of stable phenotypes representing populations specifically adapted to the local environment. PyMS data were in agreement with morphological descriptions showing that gross morphology can be correlated with chemical composition.

Exposure of Fucus spiralis germlings to precise copper concentrations (0 to 844 nM Cu2+) in chemically defined medium demonstrated a relationship between ultrastructural changes and growth retardation with increasing copper concentration. Electron-translucent vesicles, present in ova, which normally disappear after fertilization, accumulated in germlings exposed to Cu2+ above 10·6 nM, suggesting that copper may inhibit a metabolic pathway involved in cell wall formation which is initiated by fertilization. No membrane damage was observed during the exposure period. During a post-exposure period in copper-free medium, recovery occurred (rhizoid extension, apical hair formation) in germlings previously exposed to concentrations below 106 nM Cu2+ and electron-translucent vesicles became granular and disappeared. It is proposed that the electron-translucent vesicles contain a cell wall precursor and that copper inhibits its incorporation into the cell wall, preventing growth and development of the zygote.