Climate-induced interannual variability and projected change of two harmful algal bloom taxa in Chesapeake Bay, USA.

Retrospective analysis of water quality monitoring data reveals strong interannual shifts in the spatial distribution of two harmful algal species (Prorocentrum minimum and Karlodinium veneficum) in eutrophic Chesapeake Bay. A habitat model, based on the temperature and salinity tolerance of the two species as well as their nutrient preferences, provides a good interpretation for the observed seasonal progression and spatial distribution of these taxa. It also points to climate-induced variability in the hydrological forcing as a mechanism driving the interannual shifts in the algal distributions: both P. minimum and K. veneficum shift downstream during wetter years but upstream during dry years. Climate downscaling simulations using the habitat model show upstream shifts of the two species in the estuary and longer blooming seasons by the mid-21st century. Salt intrusion due to sea level rise will raise salinity in the estuary and cause these HAB species to migrate upstream, but increasing winter-spring flows may also drive favorable salinity habitat downstream. Warming leads to longer growing seasons of P. minimum and K. veneficum but may suppress bloom habitat during their respective peak bloom periods.