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

1. Eight years of observations on seabird reproductive success and oceanographic change in Tauyskaya Bay (Okhotsk Sea, north-western Pacific) were used to evaluate the hypothesis that interannual climate change causes opposite trends in reproductive performances of planktivorous auklets (Aethia cristatella and Cyclorhinchus psittacula) vs. piscivorous puffins (Lunda cirrhata and Fratercula corniculata). 2. The climate change was assessed by examining changes in sea-surface temperature (SST), time of permanent ice disappearance (ID), wind (WV) and current vectors (CV). Changes in the distribution of zooplankton biomass in the study region were used to assess changes in prey communities. Bird reproductive success was determined as the number of chicks fledged per nest occupied. 3. There were two distinct sets of oceanographic conditions in the study region, 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 easterly winds determined an early ice disappearance. The patterns in ice disappearance 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 success of piscivorous puffins was positively correlated with the SST. The 'cold' season in 1988 was characterized by a strong in-flow of water masses into 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 outside the bay. Macro-zooplankton, which were the main prey of planktivorous auklets, 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 performances by affecting food accessibility to planktivorous auklets and piscivorous puffins in opposite ways.