Figure 1.

Host abundance (solid line) and parasite prevalence (dotted line) over the first 4 months of the years 2008–2010 at 5 m depth in Lake Maarsseveen. The sampling events for population genetic diversity samples (n=1 or 2 for each subpopulation) are indicated for early bloom (black circles) and peak bloom (empty circles). In 2008 (a), Asterionella population density and parasite prevalence in spring remain low, and winter and spring surface water temperatures remain relatively high. In 2009 and 2010 (b and c), the Asterionella spring-blooms show more typical time courses and are followed by high prevalence parasite epidemics. Winter and spring surface water temperatures start off cooler but increase over time. Light extinction shows no particular pattern over the observed time period.