Abstract
1. Harmful algal blooms are increasing in both severity and frequency
across the globe. Many bloom-forming species are capable of vertical
motility and colony formation. The cyanobacterium Microcystis
aeruginosa is a common example of such a species, yet current models
poorly predict vertical distributions of M. aeruginosa. 2. To
couple the hydrodynamics, buoyancy, and the colony dynamics of
Microcystis, we present a system of one-dimensional
advection-diffusion-aggregation equations with Smoluchowski aggregation
terms. 3. Results indicate Smoluchowski aggregation accurately describes
the colony dynamics of M. aeruginosa. Further, transport dynamics
are strongly dependent on colony size, and aggregation processes are
highly sensitive to algal concentration and wind-induced mixing. Both of
these findings have direct consequences to harmful algal bloom
formation. 4. While the theoretical framework outlined in this
manuscript was derived for M. aeruginosa, both motility and
colony formation are common among bloom-forming algae. As such, this
coupling of vertical transport and colony dynamics is a useful step for
improving forecasts of surface harmful algal blooms.