DARK-SEASON SURVIVAL STRATEGIES OF COASTAL ZONE ZOOPLANKTON IN THE CANADIAN ARCTIC

For herbivorous zooplankton. surviving the arctic winter requires that sufficient energy be stored in summer to enable ten months or more of possible starvation. Energy and materials for reproduction may also b e totally derived from stored lipid and bodily protein. The predominan t storage products are wax esters, often visible as translucent drople ts or a fusiform inclusion in the tissues. Lipid may constitute more t han 50% of dry weight at the end of summer. Reproduction is synchroniz ed with season and environmental conditions to enable offspring to exp loit the brief period of intense primary production. So far as we know , fertilization occurs only once in the copepods studied here, which m ake up more than 98% of the total zooplankton by numbers, and males ar e short lived, but in one species (Calanus hyperboreus) females may su rvive into a second productive season, thereby storing sufficient rese rves to spawn a second time. Several planktonic species, including lar val invertebrates, start growth early by utilizing algae that develop on the under-ice surface several months before the pelagic phytoplankt on bloom. The minimum water temperature (-1.8-degrees-C) is constant a nd much warmer than the atmosphere, so overwintering should be less st ressful for aquatic species than for terrestrial forms. Additional ada ptations used by zooplankton in winter include seeking deeper water to escape predation, reducing swimming costs by regulating buoyancy, and further lowering metabolic rates by limiting synthesis of enzymes and increasing the fraction of lipid used in respiration.