West Coast of Vancouver Island - Ecology

Productivity of the WCVI ecosystem depends upon interactions between physical and biological processes. Key physical processes include summer upwelling and the timing of the spring transition to upwelling, as well as episodic events, such as El Nino. The intensity of summer upwelling, as well as the timing and transition to upwelling in spring affects the abundance and distribution of animals in the WCVI area (McFarlane et al. 1997, Ware and McFarlane 1995, Jamieson et al. 1989). Warm water events, such as El Nino events, have been associated with increased Pacific hake abundance and have corresponded to strong sablefish and rock sole year classes (Ware and McFarlane 1986, McFarlane and Beamish 1986, Fargo and McKinnell 1988). Key biological processes in the WCVI ecosystem include the timing of the peak zooplankton biomass and the duration of that peak, and interannual variations in the dominant zooplankton taxa that are present (McFarlane et al. 1997). For example, zooplankton biomass anomalies are correlated with salmon marine survival, sablefish recruitment, herring growth and sardine production (Mackas et al. 2007, Tanasichuk 2002). Interactions between physical and biological processes can result in changes in community composition, predation and competition. Predation and competition are biological processes that may play a role in the WCVI ecosystem for some species, such as Pacific herring (Schweigert et al. 2010, McFarlane et al. 2009). For example, warm years resulting in increased hake abundance can negatively affect herring year class strength, since hake are predators of herring and also competitors for euphausiid prey (Mysak et al. 1982, Ware and McFarlane 1986). Overall, bottom-up processes, appear to be dominant drivers in this ecosystem, since resident fish yield has been found to be correlated with phytoplankton and zooplankton production in BC (Ware and Thomson 2005); however, competition or top-down processes such as predation may also be important for some species, such as herring (Schweigert et al. 2010).