Effects of Environmental Disturbance on the Distribution and Primary Production of Benthic Algae on a British Columbia Estuary

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Abstract
Construction of a river training dyke at Squamish, B.C., has resulted in strong salinity, water transparency, and sedimentation gradients across the estuary face which have significantly affected the distribution and primary production of benthic algae. The estuary west of the dyke is now a very unstable habitat for algal colonization and growth. During river freshet, heavy sedimentation and salinities less than 3‰ make algal survival difficult. At other times of the year, a salinity range of up to 25‰ is common over a tidal cycle. Algae in this area are generally strongly euryhaline, the dominant species being Enteromorpha minima, Rhizoclonium riparium, and Vaucheria dichotoma; mean production is 0.6 g Cm−2 day−1. The eastern portion of the estuary has a more stable benthic environment; lower sedimentation and higher salinity result in greater species diversity, biomass, and primary production. Dominant species are E. minima, Ulva lactuca, Pylaiella littoralis, and a variety of diatom communities. These algae tend to be weakly euryhaline, with optimum salinities between 15 and 30‰. Mean production is 2.2 g C m−2 day−1. Recent intrusion of Fucus vesiculosus strongly indicates that the eastern estuary is developing into a more marine habitat.Primary production of benthic algae is maintained by the wax and wane of low light and high light favoring species. Annual production estimates of 215 g C m−2 approximate those for estuaries at similar latitudes.