Spatial variation in dinoflagellate recruitment along a reservoir ecosystem continuum

Physical and chemical gradients across ecosystems, such as stream-to-lake continua within human-made reservoirs, provide valuable opportunities to examine how organisms respond to changing environments. We quantified the rate of dinoflagellate recruitment across a small reservoir to test the hypothesis that organisms are controlled by different factors along a reservoir continuum. We predicted that recruitment would be tightly coupled with reservoir physics in the riverine zone and closely related to water chemistry in the lacustrine zone. For the dominant dinoflagellate genus in the reservoir, Peridinium, recruitment from the sediments accounted for a median of 16% of increases in pelagic cell abundance throughout the summer. As predicted, Peridinium recruitment rates at the riverine site were correlated with physical variables, while at the lacustrine site, recruitment rates were highly correlated with water chemistry (e.g. nutrient ratios and dissolved oxygen). Recruitment patterns of the second most common genus, Gymnodinium, were not correlated with environmental variables, though Gymnodinium's much lower densities suggest that its dynamics were controlled by other factors. Our results reveal that the physical-biological coupling controlling algal recruitment, which can play a large role in pelagic population growth and bloom formation, can vary substantially on a spatial gradient within even a small reservoir.