Lost in the dark: estimation of the akinete pool for the recruitment of Nostocales populations (cyanobacteria) in a temperate deep lake

Akinetes (resting stages), as key elements in the life cycle of Nostocales, ensure the persistence of species and invasion of new habitats. Information about the sedimentary akinete pool is required to predict blooms of Nostocales. We studied the akinete abundance in the surface sediment of a deep stratified lake in NE Germany to determine which part of the akinete pool is potentially able to germinate under the underwater light, temperature and oxygen conditions present. Akinetes increased in abundance significantly with depth (R-2 = 0.86). They accumulated below 12 m (214 x 10(6) akinetes m(-2)), where temperatures of 8-12A degrees C could support germination, but light supply a <= 0.1 mol photons m(-2) d(-1) and anoxia in the summer prevent germination. Assuming a light supply of 0.5 mol photons m(-2)d(-1) and oxic conditions suitable for germination, only 10% of the total akinete pool deposited in littoral areas of 0-8 m depth can contribute to the recruitment. The sediment area for germination due to oligotrophication would increase from the current 41 to 45-61%. Thus, up to 261 x 10(12) more dormant akinetes could become part of the active akinete pool and consequently influence the future species composition and support the persistence of species.