Influence of macroalgal mats on abundance and distribution of dunlin Calidris alpina in estuaries: A long-term approach

Abstract

Estuaries used by shorebirds during the non-breeding season face many types of human pressure, including eutrophication and consequent occurrence of macroalgal blooms. The impact of this phenomenon on the abundance of dunlin Calidris alpina in the Mondego estuary, Portugal, was explored using long-term, monthly time series, between 1993 and 2003. The data series included total macroalgal cover, macroinvertebrate biomass and dunlin abundance. We observed an increase in dunlin abundance during this period that matched the decrease in macroalgal cover, especially since the promotion of management actions in 1998. We suggest that this increase was related to the increase of some of its main prey species, the polychaete Hediste diversicolor and the bivalve Scrobicularia plana. At smaller scales, no effect of macroalgae was observed on the proportion of dunlin that chose to feed in alternative habitats (salinas) during the low tide period. However, there was a small effect of the level of algal cover on the proportion of birds recorded on macroalgae at intermediate levels of coverage (around 25 % of total mudflat area). © Inter-Research 2006.