Climate Change, Ecosystem Variability and Fisheries Productivity

Climate-driven variation on the timing and location of phytoplankton blooms has profound effects on the number of larval fish and invertebrates surviving and recruiting each year, and ultimately on the structure and dynamics of marine ecosystems. The spring phytoplankton bloom is the only source of food for many fish and invertebrate larvae. The degree of spatial and temporal overlap of the spring phytoplankton bloom with the timing and spatial distribution of the spawning of eggs into the surface warters has a strong influence on larval fish survival (Hjort, 1914; Cushing, 1990; Mertz and Ayers, 1994; Platt et aL, 2003). Eggs and larvae develop in the planktonic zone of the water column for 1 to 2 months before descending to the seabed habitat. Fish and invertebrate larvae have sufficient yolk stores to survive for only a small fraction of the total time spent developing in the surface waters. Larvae starve and die unless they are spawned into, or transported into, a patch of phytoand zooplankton that is sufficiently large and productive enough to sustain their development. The variable pattern of fish and invertebrate recruitment to juvenile stages is modulated by physical forcing of phytoplankton and ultimately, this environmental variability has a measurable effect on recruitment of new individuals to exploited stocks and the productivity and biomass of higher trophic levels. Remote sensing of ocean colour has finally provided data at the resolution in time and space necessary to elucidate the linkages between climate-driven changes in the marine environment and the dynamics of fish and ecosystem productivity. In this chapter we focus on large-scale year-by-year variability in the physical environment and consider how this influences fish and invertebrate production. In particular we consider the likely effect of climate change on ocean temperature and productivity and highlight emerging approaches toward understanding the consequences for global fisheries yields.