Composition and structure of algal communities in a tributary stream of Lake Ontario

Abstract

The composition and structure of epipelic and planktonic algal communities in Shelter Valley Creek, Ontario, was studied for 1 year. The overall assemblage consisted of 388 taxa of which 321 were Bacillariophyceae. On the sediments, seasonal succession and community structure was, with some exceptions, typical of a hard-water stream in the northern temperate zone. Taxa that occurred frequently throughout the year were Achnanthes minutissima Kütz., Cocconeis placentula var. euglypta (Ehr.) Cl., Gomphonema olivaceum var. balticum Cl., and Navicula tripunctata (O. F. Müller) Bory. The planktonic community was, for the most part, derived from the benthos. Herbivorous grazing by larval sea lamprey, Petromyzon marinus (Pisces: Cyclostomata) did not noticeably affect algal numbers in either the plankton or sediments.Sixty-six taxa are reported as new occurrences in southern Ontario.