Chlorophyll-a concentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake
- Lough Neagh is one of the most important non-estuarine sites in the British Isles for overwintering wildfowl. A change in the waterbird assemblage following the winter of 2000/2001 was driven mainly by a rapid decline in the population of overwintering diving ducks. Sudden and discrete changes in resident as well as migratory waterbirds may suggest an intrinsic cause.
- We compared the density and biomass of benthic macroinvertebrates, the food of overwintering diving ducks, in 2010 (following the diving duck population decline) with values from a baseline survey conducted in 1997/1998 (before the decline in diving ducks).
- The mean total density of macroinvertebrates declined significantly by c. 65% from 15 300 m−2 in 1997/1998 to 5136 m−2 in 2010. There was a concomitant c. 70% decline in mean macroinvertebrate biomass from 15 667 mg m −2 to 5112 mg m−2. In terms of taxonomic composition, the relative contribution of Tanypodinae, Glyptotendipes spp. and Tanytarsini declined, while the relative contribution of Chironomus spp. increased.
- We describe a shift in chlorophyll-a concentration, a proxy of phytoplankton biomass, in the largest freshwater lake in the British Isles coincident with a significant reduction in macroinvertebrate density and biomass, with potential implications for ecosystem processes and ecologically and economically important consumer populations, including waterbirds and fishes.