Seston Ecology of the Surface Waters of Hudson Bay

Abstract

The planktonic biomass variables, chlorophyll a, ATP, particulate organic carbon, and nitrogen have been measured in surface waters throughout Hudson Bay for the first time. On the basis of these variables Hudson Bay can be regarded as oligotrophc during the summer months. Clear inshore–offshore gradients of biomass were evident showing significant correlations in transects to salinity, temperature, depth, and distance from shore. Chlorophyll a values were always low, averaging 0.09 mg m−3 offshore and 0.28 mg m−3 inshore. ATP averaged 0.072 mg m−3 offshore and twice as high inshore. Biomass ratios also demonstrated clear inshore–offshore gradients; carbon:nitrogen ratios ranged from 4.9:1 inshore to 12.5:1 offshore indicating nitrogen limitation of offshore waters. Chlorophyll a: phaeopigment ratios decreased and biocarbon:chlorophyll a ratios increased offshore indicating an increased proportion of heterotrophs and possibly higher relative grazing pressure offshore. For the inshore areas, biomass and probably productivity were highest and significantly correlated to runoff with the exception of the Southampton–Coats–Mansel islands area, which is influenced by waters from Foxe Channel and Hudson Strait. While Hudson Bay meets most of the criteria for arctic classification, its character is sufficiently different to warrant special status.Key words: Hudson Bay, seston ecology, chlorophyll a, biomass ratios, phaeopigments, plankton