Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
LONG-TERM CHANGE
IN LIMNOLOGY, INVERTEBRATES, AND AVIAN PREDATORS IN
ALASKAN BOREAL WETLANDS
Robin Corcoran¹, James R. Lovvorn¹, and Patricia J. Heglund²
¹Department of Zoology, University of Wyoming, Laramie, WY 82071; robin_corcoran@fws.gov
²Patricia J. Heglund/USGS-Upper Midwest Environmental Sciences Center, 2630 Fanta Reed
Climate change is more pronounced at high northern latitudes, and may be affecting the physical,
chemical, and biological attributes of the abundant wetlands in boreal forests. On the Yukon
Flats, located in pristine boreal forest of northeast Alaska, we re-sampled water chemistry and
macroinvertebrates in summer 2001-2003 from 9 wetlands where similar data were collected during
1985-1989. These wetlands lost an average 19% of surface water area between decades, results very
similar to other studies over much larger areas. Total nitrogen and most metal cations (Na, Mg, and
Ca, but not K) increased between these periods, while total phosphorus (TP) and chlorophyll a (Chl
a) declined. These changes were greater in wetlands that had experienced more drying (decreased
surface area). Compared to 1985-1989, densities of cladocerans, copepods, and ostracods in both June
and August were higher in 2002-2003, while densities of amphipods, gastropods, and chironomid
larvae were generally lower. The latter taxa (especially amphipods) are thought to be critical prey for
lesser scaup (Aythya affinis), a diving duck that nests mainly in the boreal forest and whose numbers
have been declining for over 20 years. In comparisons among wetlands in 2002-2003 only, amphipod
biomass was lower in wetlands with lower Chl a, which might help explain the decline of amphipods
since the late 1980s when Chl a was higher. The long-term decline in Chl a corresponded to greatly
increased zooplankton density in June, suggesting a shift in carbon flow from scrapers/depositfeeders
that are eaten by scaup to water-column grazers that are not. In 2003, the density of lesser
scaup ducklings among wetlands was positively related to total macroinvertebrate biomass collected
in sweep and core samples. Declines in benthic and epibenthic deposit-feeding invertebrates, that are
key prey for lesser scaup, suggest important foodweb effects of climate change in otherwise pristine
wetlands of the boreal forest. Changes in boreal wetlands may also be a factor in scoter (Melanitta
sp.) declines, which are tightly correlated to scaup declines. These taxa largely overlap on northern
staging and breeding areas but winter in ecologically and spatially different areas.
76 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005