CLIMATIC WARMING AND THE DECLINE OF ZOOPLANKTON IN THE CALIFORNIA CURRENT

Since 1951, the biomass of macrozooplankton in waters off southern Cal ifornia has decreased by 80 percent. During the same period, the surfa ce layer warmed-by more than 1.5 degrees C in some places-and the temp erature difference across the thermocline increased. Increased stratif ication resulted in less lifting of the thermocline by wind-driven upw elling. A shallower source of upwelled waters provided less inorganic nutrient for new biological production and hence supported a smaller z ooplankton population. Continued warming could lead to further decline of zooplankton.