Pseudo-nitzschia in the Gulf of Maine: investigating bloom dynamics, species introduction, and climate change implications with observations and models

Abstract

The apparent global increase in harmful algal blooms (HABs) includes Pseudo-nitzschia blooms in the Gulf of Maine, where shellfishery closures can cost millions of dollars. Temperatures in the gulf are warming, which can affect the severity of some HABs. Yet Pseudo-nitzschia in the region are understudied. Pseudo-nitzschia bloom dynamics, P. australis introduction, and potential future changes thereof were investigated in the Gulf of Maine. Data from ship surveys and moorings were used, as well as hydrodynamic, climate, and Lagrangian particle tracking models. Pseudonitzschia bloom toxicity was driven primarily by species composition, not environmental factors. P. australis was introduced to the region in 2016 via a coastal current from the Scotian Shelf. Climate change might intensify Pseudo-nitzschia blooms, shift bloom timing 1–2 weeks earlier in the spring or 4–6 weeks later in the fall, or lengthen the growing season by 3 weeks. It might also affect species composition and connectivity within the gulf. This work has implications for the monitoring of current and future blooms in the Gulf of Maine and for our understanding of HAB introduction to the region. It can also be used to develop predictive models for Pseudo-nitzschia, which could be applied to other HABs.