Date of Award

Fall 1983

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The reproductive phenology, growth and variation of chemical composition of Gracilaria tikvahiae from the Great Bay Estuary, N.H. were evaluated. A major objective was an analysis of the chemical composition, particularly agar content and properties, of plants separated into reproductive categories. The net photosynthetic responses of G. tikvahiae to several irradiance, temperature and salinity regimes were determined.

Gracilaria tikvahiae plants from the Great Bay Estuary were vegetative throughout most of the year. However, discrete maxima of tetrasporic and spermatangial plants occurred during June-July and for cystocarpic plants during July-August. The in situ growth of Gracilaria tikvahiae was highest during June-September, with maximum rates of 11%/day. The growth cycle of G. tikvahiae plants was most strongly correlated with water temperature. Seasonal variations of surface irradiance and dissolved inorganic nitrogen were not related to the growth cycle of G. tikvahiae.

Gracilaria tikvahiae had annual cycles of ash, dry weight, carbohydrate, agar, carbon, nitrogen and phycoerythrin contents. In contrast, little variation in protein, phosphorus or chlorophyll occurred. The changes in tissue carbon, nitrogen, carbohydrate and agar had summer minima and winter maxima. However, the ash content was maximal in summer and lowest during winter. The total tissue nitrogen of G. tikvahiae did not decrease below 2% of dry weight. No significant differences in chemical composition were noted between reproductive stages. The agar content of Gracilaria tikvahiae varied between 7% (summer) and 23% (winter). The gel strengths and 3,6-anhydrogalactose content of G. tikvahiae agar were highest in the summer. There were no significant differences in 3,6-anhydrogalactose, sulfate, ash content, gel strength or viscosity between agar, extracted with hydroxide pretreatment, from cystocarpic or tetrasporic plants.

The net photosynthesis of Gracilaria tikvahiae was light-saturated at 200-600 (mu)E(.)m('-2)(.)s('-1), but it was not inhibited at 1440 (mu)E(.)m('-2)(.)s('-1). G. tikvahiae had increasing net photosynthetic rates from 5(DEGREES) to 25(DEGREES)C. Maximum net photosynthesis occurred between 25(DEGREES) and 35(DEGREES)C, while rates decreased at 37.5(DEGREES)C. The net photosynthetic responses at 25(DEGREES) and 30(DEGREES)C were stable after acclimation times of one to four days, but declined after three days at 35(DEGREES)C. G. tikvahiae has a euryhaline net photosynthetic response between 5 g/kg and 40 g/kg.