FACTORS CONTROLLING THE TIMING OF THE SPRING BLOOM IN THE STRAIT OF GEORGIA ESTUARY, BRITISH-COLUMBIA, CANADA

We present a conceptual model to illustrate how wind events and the an nual migration and grazing of the dominant copepod Neocalanus plumchru s interact and affect the development of the spring bloom. The model w as supported by observations made during 1988, 1992, and 1993. For exa mple, in 1992, an El Nino year, the annual freshet of the Fraser River and probably the spring bloom started 1 month earlier. The bloom was interrupted by a wind event in late March. A few days later, its full recovery was interrupted by the peak in zooplankton grazing, and ambie nt ammonium concentrations increased. In contrast, in 1988, the annual freshet started later (mid-April), and winds remained strong througho ut the same period, hindering the development of the spring bloom. The spring bloom was further suppressed by large numbers of zooplankton d uring April, resulting in a prolonged spring bloom. These observations indicate that interannual variations in winds and the timing of the a nnual freshet determine the timing and duration of the spring bloom, w hich in turn, determine the matching of phytoplankton to zooplankton i n the Strait of Georgia. The matching or mismatching bears significant implications for food availability for juvenile fish.