Date of Award

Fall 1982

Project Type


Program or Major


Degree Name

Doctor of Philosophy


Growth rates, reproductive phenology, and longevity of Fucus distichus ssp. edentatus and F. distichus ssp. evanescens were evaluated in natural populations in New England. Both subspecies exhibited maximum growth during early summer, a slight decline in late summer, and a brief resurgence in the early fall. The maximum growth rates (in terms of elongation) for ssp. edentatus and ssp. evanescens was 3.5 cm/mo and 3.7 cm/mo, respectively. Populations of both subspecies showed a distinct bimodal reproductive periodicity, with maximums in the spring and fall. Individuals within natural populations were reproductive in either the spring or fall but never both seasons. After the reproductive period receptacles dehisced and plants were vegetative or died. Increased rates of plant attrition were observed during periods of reproduction.

The sources of morphological variation of Fucus distichus ssp. edentatus and F. distichus ssp. evanescens were evaluated in natural populations in New England. Variation of characters (width and length of receptacles, width of fronds, etc.) were shown to be of a continuous nature by frequency distribution plots. On the other hand, individuals from different populations were morphologically distinct as judged by population means and analysis of variance. A correlation between the plant's form and its habitat has been established by field observation. The broadest material grows in calm estuarine habitats, while the narrowest plants occur in exposed, open coastal areas. Major differences in morphology also appear seasonally. In addition, microhabitat factors such as exposure to wave action and elevation explain some morphological variation. Cultured germlings from distinct populations of "evanescens-type" and "edentatus-type" plants have been outplanted to experimental gardens in order to ascertain whether the variation is heritable or environmentally induced. Results of the garden experiments indicate that major differences in morphology are genetically based.

Morphological, ecological, and genetic distinctions of a dwarf, non-tide pool member of the Fucus distichus complex were assessed at an exposed site in southern Maine. Variation in plant stature from typical F. distichus ssp. edentatus to the dwarf form is continuous. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.