<em>Karenia brevis</em>, a toxic dinoflagellate, forms harmful agal blooms (HABs) along the West Florida Shelf (WFS) nearly annually, making it one of the most predictable HABs globally. These blooms create significant ecological and economic impacts for affected areas, which make understanding the underlying mechanisms that drive bloom initiation and severity important for modeling efforts. We examined various global and regional climatic stressors for specific regime shifts or trends which might play a role in forcing in long-term trends in <em>K. brevis</em> bloom severity along the southwest Florida coast. Regime shifts in the North Atlantic Oscillation (NAO) to a positive phase between 1989 and 1995 and then to a negative phase between 1995 and 2008 were identified in the <em>K. brevis</em> bloom severity index, a measure derived from historical cell count data from 1953 to 2019. Changing patterns in the accumulated cyclone energy index were also reflected in the bloom severity index.  We hypothesize that the warmer temperatures and higher precipitation seen in the southeastern United States during the positive NAO phases played a role in changes to observed bloom severity.

Primary Presenter: Tristyn Bercel, Mote Marine Laboratory (tbercel@mote.org)

Authors:

Tristyn Bercel, Mote Marine Laboratory  (tbercel@mote.org)

Cynthia Heil, Mote Marine Laboratory  (cheil@mote.org)

Bruna Sobrinho, University of Maryland  (bsobrinho@umces.edu)

Patricia Glibert, University of Maryland  (glibert@umces.edu)