Autotrophic and heterotrophic production in the Mackenzie river/Beaufort Sea estuary

Summary Productivity studies in the Mackenzie estuary and Beaufort Sea have confirmed the existence of two food chains based either on autotrophic marine diatoms or on organic material derived from the river. From ¹³C and ¹⁵N isotope studies, it appears that autotrophic production, which reached surface values of 10 mgC/m³/h, was largely responsible for maintaining the herbivorous copepods and a number of important predators including jellyfish, chaetognaths, hyperiid amphipods and some marine fish. The heterotrophic food chain largely supported a population of gammarid amphipods and some anadromous fish. In the summer of 1987, bacterial populations of>10⁶ cells/ml were encountered in the estuarine waters. These values were much higher than in 1986. It is suggested that this difference was caused by advective processes due to on-shore winds in 1987; other differences between 1986 and 1987 fish populations, near shore temperatures and ice cover were also noted.