A 1D ecosystem model, driven by surface heat and wind forcing and relaxed toward observed salinity profiles, was applied to simulate the interannual and decadal scale variability of phytoplankton blooms and plankton production from 1984 to 2007 in the Nova Scotian Shelf (NSS) and Gulf of Maine (GoM) region. The model captured the mean observed timing and magnitude of the spring (SPB) and fall phytoplankton bloom (FPB) in both systems, as well as observed interannual variations in SPB peak timing. Model simulations for both the GoM and NSS exhibited marked interannual variability in SPB and FPB timing (± 2 to 3 wk) and magnitude (up to ~1 mg chlorophyll m -3 ). Earlier SPBs and delayed FPBs are linked to enhanced water column stability generated by less saline surface water or sharper salinity gradients over the top 50 m of the water column. The modeled variation in annual primary productivity, mesozooplankton productivity, and particle export flux was modest (<10% of the mean). Years with high primary production were weakly associated with early SPBs (GoM: r = -0.205; NSS: r = -0.51), but there was no significant relationship with water column stability. This suggests that variation in annual productivity in the GoM and NSS reflects a combination of variation in light limitation (which is alleviated by increased water column stability) and nutrient limitation (which is exacerbated by increased water column stability) that offset and are of near equal importance when averaged over the year. Interannual variations in fisheries production due to changes in annual productivity are thus likely secondary to profound shifts in fisheries recruitment and production that have been linked to variations in SPB and FPB timing.
KEY WORDS: Phytoplankton bloom · Interannual variability · Modeling · Nova Scotian Shelf · Gulf of Maine
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 426: [105][106][107][108][109][110][111][112][113][114][115][116][117][118] 2011 related environmental change might have caused significant decadal shifts in the state of the pelagic ecosystems in the NSS-GoM region (e.g. Durbin et al. 2003, Frank et al. 2005, Greene & Pershing 2007, Ji et al. 2007), presumably through a bottom-up process. Understanding phytoplankton bloom dynamics and its relationship with environmental factors has long been the focus of ecosystem studies in the Gulf of Maine and adjacent regions (e.g. Bigelow 1926, Bigelow et al. 1940, Cushing 1959, Townsend & Spinard 1986, Thomas et al. 2003, Ji et al. 2006. In recent years, interannual variations of phytoplankton bloom dynamics have been better detected with the help of field surveys (e.g. Durbin et al. 2003) and advances in technology such as remote sensing (e.g. Thomas et al. 2003, Ji et al. 2007) and continuous plankton recorders (e.g. Sameoto 2001, Greene & Pershing 2007. Most of these recent studies have focused on the spring phytoplankton bloom (SPB). There has been little analysis of the potential impacts of c...