Bottom-up and Top-down Controls

Spatial Considerations | Bottom-up/Top-down Controls of Zooplankton | Impacts of Sea-ice on Bering Sea

LCZ are a critical link between lower trophic levels and higher predators in the eastern Bering Sea. It has been proposed that LCZ standing stocks are controlled by physical forcing through lower trophic level production: cold years are characterized by higher abundances of large copepods and euphausiids, while warm years favor smaller zooplankton at their expense (Baier and Napp, 2003, Coyle et al., 2008, Hunt et al., 2008, 2010, In Press). Both springtime primary production associated with sea ice retreat (Baier and Napp, 2003) and the amount and timing of summertime primary production (Coyle et al., 2008) have been invoked as possible explanations for this pattern, but the exact mechanism remains uncertain. It has also been argued that tight top-down trophic coupling between LCZ and predators such as pollock can lead to control of the standing stock of LCZ (Springer, 1992) such as euphausiids (Smith, 1991). Sea ice and water temperature are important factors that structure the spatial distribution of LCZ predators such as pollock (Wyllie-Echeverria and Wooster, 1998, Kotwicki et al, 2005). Pollock generally avoid the coldest water (< 2°C) which may thereby mediate the impact of predation on LCZ. The relativeimportance of bottom-up and top-down controls on LCZ standing stock has not been established. We will test the data gathered during the recent BEST-BSIERP program for consistency with hypotheses about these two competing factors.