Jan van Franeker, Bram Feij, André Meijboom
Transcription
Jan van Franeker, Bram Feij, André Meijboom
IMARES Wageningen The importance of sea ice - the predators Jan van Franeker, Bram Feij, André Meijboom, Michiel van Dorssen & Hauke Flores Postbus 167 1790 AD Den Burg (Texel) The Netherlands +31 222 369 724 [email protected] IMARES is a partner of the Alfred Wegener Institute (AWI) in the Antarctic ‘Lazarev Sea Krill Study’ (LAKRIS). Our contribution focuses on the biology in the upper water layer in the seasonal sea ice zone. Birds, seals and whales indicate that the sea ice ‘fuels’ the Antarctic foodweb. In a ‘top down’ approach we specify the food requirements of top predators and the availability of prey under the sea ice. Understanding the role of sea ice in sustaining the Antarctic krill stocks and associated foodweb is vital to the assessment of ecological impacts of climate change. Density estimates of birds, seals and whales are made by surveys from both ship and helicopter. Densities can be translated to daily food requirements of the combined community of top predators. Preliminary data shown here are from ship observations 2004, 2006 and 2007-08. LAKRIS Food from the seasonal sea ice Throughout the year the seasonal sea ice zone of the Lazarev Sea south of 55°S meets food demands from birds and mammals that are higher than those in the permanently open water further north. food requirement kg/km2/day Food requirements of birds and mammals in the sea ice zone and open water seasonal sea ice zone (south of 55°S) open ocean (35-55°S) 14 12 10 8 6 4 2 0 AUTUMN WINTER 2004 ANT-21-4 2006 ANT-23-6 SUMMER 2007-08 ANT-24-2 Seasonal changes in the food requirements of predators in the LAKRIS study area 327 25 10 5 AUTUMN WINTER SUMMER 2004 - ANT-21-4 2006 - ANT-23-6 2007-08 - ANT-24-2 -60 -60 -60 kg food -61 -61 -61 per km2 per day -62 -62 -62 -63 -63 -63 -64 -64 -64 -65 -65 -65 -66 -66 -66 -67 -67 -67 -68 -68 -68 -69 -69 -69 -70 -70 -70 -71 -71 -71 open water sea ice -9 Area average -6 -3 0 3 6 -9 2.5 kg km-2 day-1 Netherlands AntArctic Programme -6 -3 0 4.8 kg km-2 day-1 3 6 LAKRIS has shown that even in midwinter top predators are attracted deep into the heavy pack ice. Recently formed young ice in autumn and winter appears less attractive. However, after winter the melting of the older ice apparently releases such abundant food that migrator y animals move in from 1000’s of km’s away. Animal populations of a wide area depend on the continued existence of the Antarctic seasonal sea ice. -9 -6 -3 0 3 14.6 kg km-2 day-1 LNV 6 9