The most southerly populations of benthic marine algae occurring anywhere in the world are found in McMurdo Sound. There is considerable divergence of opinion amongst phycologists as to the suitability of polar seas for the growth of autotrophic seaweeds. Some consider the exceptional clarity of the open ocean waters to be ideal for good deep growth whereas others postulate the need for partially ... heterotrophic nutrition to account for growth under very poor photic conditions. In order to determine the physiological adaptations of these plants, it is also important to know their overall tolerances of extremes of illumination and increased water temperature. To determine whether the two dominant red seaweeds, Iridaea cordata and Phyllophora antarctica, found at Cape Evans show any physiological adaptation to the prevailing environmental conditions, a series of experiments was undertaken to quantify rates of photosynthesis and respiration under a range of irradiances and at water temperatures between -1°C and 25°C. All measurements of photosynthesis and dark respiration were made using the Winkler chemical method to determine changes in dissolved oxygen caused by the metabolic activities of pieces of algal tissue inside sealed glass bottles. The incubation apparatus was designed so that temperatures down to -2°C could be attained. The specific experiments were as follows. 1) To assess the metabolic response of P. antarctica and I. cordata at a range of irradiance levels and ambient sea temperature, bottles containing homogenous portions of plant tissue were incubated for 1 hour under a range of irradiance levels. At the end of incubation, changes in dissolved oxygen were measured and converted to rates of photosynthesis and respiration. 2) To assess the metabolic response of P. antarctica and I. cordata to elevated temperatures plants were exposed for 1 hour to temperatures ranging between -1°C and 25°C. Respiration rates were measured. The effect of longer exposure to elevated temperatures was also investigated. 3) To assess the chlorophyll content of Antarctic seaweeds, the chlorophyll a content was determined. 4) To assess the growth in situ of P. antarctica and I. chordata individual plants were attached to a rope at different depths and changes in weight monitored over a four week period. In addition, material was brought back to New Zealand for chemical analysis for chlorophyll, total carbon, nitrogen and phosphorus content, inorganic ion composition and cell wall polysaccharides. An ecological survey using a non-destructive harvesting technique was also carried out. Information was obtained on the distribution of then benthic communities and the relative quantities of the 2 dominant species present at Cape Evans.