Benthic algal ecology and primary pathways of energy flow were considered on the Squamish River delta at the head of Howe Sound, a fjord-type estuary. The study elucidated the structure and function of major autotrophic components of the estuarine ecosystem. Benthic algae were investigated with regard to species composition and distribution and the capacity for energy conversion, input to the system and storage. Comparisons were made with existing information on the vascular plant component of the ecosystem. The benthic algal community was studied by regular field sampling of major macroalgae and microalgal associations with a monitoring of physical-chemical environmental factors. Presence of an alga in the estuary was a function of its osmoregulatory capabilities. Establishment and temporal-spatial distribution patterns were controlled by substrate-habitat preference and availability and the interaction of light, interspecies competition, desiccation, temperature and salinity, light being of greatest importance. Carex lyngbyei Hornem., the dominant vascular plant, had a significant effect on distribution of benthic algae through light restriction during Its summer growth period and action as a substrate during the winter. Total species diversity, biomass and distributional area of benthic algae were greatest at the latter period. The effect of ecosystem structure on function was investigated by analysis of energy flux through major benthic algal producers. Comparisons were made of the total amount of energy input attributable to benthic algae and vascular plants. The importance of an algal producer to energy flux•m⁻² was a function of either high primary productivity, photosynthetic efficiency and caloric content, or in the case of diatom dominated micro-algal associations, high caloric content alone. Distribution, reflecting the presence of suitable substrate-habitat, modified this pattern. Macroalgae having high energy input•m⁻² (Monoetroma oxyapermum (Kutz.) Doty, Pylaiella littoral-is (Lyngb.) Kjell.) were of minimum importance to total energy input. Two microalgal associations (Association E, diatom dominated, Association G, Ulothrix flaoca (Dill.) Thur. dominated), each with low energy input-m but with wide distribution and high photosynthetic efficiency and caloric content contributed a total of 8H% of available energy attributable to benthic algae. Benthic algae account for a maximum of ca. 7% of total energy input to the delta ecosystem compared to ca. 90$ by vascular plants and 3% by addition of organic matter. The majority of energy for the detrital based ecosystem comes from vascular plants and becomes available after a lag period allowing decomposition. Benthic algae are significant to the ecosystem as a readily available, continually present energy source requiring little or no breakdown for utilization and not for total energy input. Energy is available as either dissolved or particulate organic matter. Of the latter, ca. 49$ is removed to the estuary, 33% incorporated into the sediments of the delta and 18$ used by consumers in the delta ecosystem. / Science, Faculty of / Botany, Department of / Graduate