Estuarine, Coastal and Shelf Science, 24(1987), 47-68

I.P. MARTINI¹ and R.I.G. MORRISON²

1Department of Land Resource Science, University of Guelph, Guelph, Ontario,Canada, N1G 2W1
²Canadian Wildlife Service, 1725 Woodward Drive, Ottawa, Ontario, Canada, K1A 0E7

The distribution of Macoma balthica and Hydrobia minuta was studied regionally along a 1000 km stretch of subarctic coast from latitude 52°N to 57°N in western James Bay and Hudson Bay, Ontario. Macoma balthica is widely distributed, but absent from estuaries of major rivers and from intertidal transects periodically inundated by fluvial waters. The frequency of occurrence of Macoma balthica is highly correlated with fine to very fine sand and silt. It thrives in the lower and middle parts of the tidal flats. The high tidal flats and lower marshes have fine silt deposits: they may however, develop anoxic conditions due to decomposition of algal mats, and they are toxic environments for the survival and development of Macoma spats. The frequency of occurrence of Hydrobia minuta does not correlate closely with the average grain size of the substratum. Hydrobia is found in large numbers where clay drapes develop in sheltered locations and where relatively low-salinity and higher-temperature environments occur, as in southern James Bay. Hydrobia minuta reaches the northern limits of its range in James Bay, very few specimens having been found north of Akimiski Island (latitude 53°15'N).