Chapter 9 Zooplankton Processes in Arctic and Antarctic Polynyas

There are various similarities and differences in zooplankton processes between Arctic Ocean (AO) and Southern Ocean (SO) polynyas, many of which are due to fundamental differences in their respective ecosystem properties. The composition of zooplankton communities in AO and SO polynyas is largely dependent upon advection from local, ice-covered waters, with little evidence of an endemic, polynya zooplankton fauna. While copepods are common in both systems, a major difference is the predominance of euphausiids in the SO and appendicularian tunicates in the AO. The same genera of small copepods occur in both the AO and SO and appear to derive little benefit from the higher primary productivity and extended growing season of polynyas. In contrast, larger calanoid copepods appear to derive recruitment and life cycle benefits from the diatom production and heat in polynyas, with higher egg production rates and shorter generation times. Most large calanoid copepods overwinter in diapause in AO polynyas, while some proportion of SO populations remain in surface waters. Grazing impact by copepods in AO polynyas accounts for about 20% of primary productivity d−1, with appendicularian tunicates accounting for another 20% d−1. The few estimates of community impact in the SO are variable. In both regions, individual zooplankton feeding rates are high and equivalent to boreal ocean values; thus, grazing impact depends primarily on the biomass of zooplankton and phytoplankton. SO zooplankton contribute to the vertical particulate flux through faecal pellets from euphausiids, copepods and pteropods, while the contribution in AO polynyas is primarily through appendicularian tunicate faecal pellets and shed houses and copepod faeces. Maximum pellet flux in both the AO and SO occurs at times of high biomass of diatoms. The primary benefits of polar polynyas to zooplankton processes results from the greater production of diatoms and extended productive period, with few differences in individual daily rations or food web transfer efficiencies relative to temperate and boreal systems