Climate change causes contrasting trends in reproductive performance of planktivorous and piscivorous alcids

1. Eight years of observations on seabird reproductive success and oceanogr aphic change in Tauyskaya Bay (Okhotsk Sea, north-western Pacific) were use d to evaluate the hypothesis that interannual climate change causes opposit e trends in reproductive performances of planktivorous auklets (Aethia cris tatella and Cyclorhinchus psittacula) vs. piscivorous puffins (Lunda cirrha ta and Fratercula corniculata). 2. The climate change was assessed by examining changes in sea-surface temp erature (SST), time of permanent ice disappearance (ID), wind (WV) and curr ent vectors (CV). Changes in the distribution of zooplankton biomass in the study region were used to assess changes in prey communities. Bird reprodu ctive success was determined as the number of chicks fledged per nest occup ied. 3. There were two distinct sets of oceanographic conditions in the study re gion, as reflected in the SST, ID, WV and CV. Strong northerly winds in the spring produced a late ice disappearance in the study region, whereas east erly winds determined an early ice disappearance. The patterns in ice disap pearance were significantly correlated with SST anomalies during the summer . A negative SST anomaly (- 1.2 degrees C) defined a 'cold' regime, whereas a positive SST anomaly ( + 1.2 degrees C) defined a 'warm' regime. 4. Reproductive success of planktivorous auklets was negatively correlated with the SST in the western part of Tauyskaya Bay, whereas reproductive suc cess of piscivorous puffins was positively correlated with the SST. The 'co ld' season in 1988 was characterized by a strong in-flow of water masses in to the bay area. The 'warm' season in 1989 was characterized by well-mixed warm water inside the bay that were separated from colder water masses outs ide the bay. Macro-zooplankton, which were the main prey of planktivorous a uklets, were more abundant during the 'cold' regime of the ecosystem. Meso- zooplankton, a potential prey of juvenile pelagic fish, were more abundant during the 'warm' regime of the ecosystem. 5. Interannual oceanographic change probably impacts alcid reproductive per formances by affecting food accessibility to planktivorous auklets and pisc ivorous puffins in opposite ways.