Evaluating the influence of press and pulse disturbances on community dynamics of the Northeast US Large Marine Ecosystem

ABSTRACT: As climate change intensifies, there is a pressing concern regarding how ecological communities respond to disturbances occurring at different intensities and time scales. We explored how the type of disturbance influences the dynamics of a marine community. A pulse disturbance is an abrupt, high-magnitude shift in conditions that can cause immediate and significant impacts to an ecological community. Alternatively, press disturbances are long-term, multi-generational pressures acting on communities over time. The Northeast US Continental Shelf Large Marine Ecosystem (NES LME) is one of the fastest-warming regions in the world and has experienced historic overfishing. Assemblage shifts in the NES LME have previously been characterized; however, these were prior to an unprecedented pulse disturbance marine heatwave (MHW) event in 2012 followed by punctuated MHWs over the last decade. We quantified community change across the NES LME using a community trajectory analysis, a multivariate tool that utilizes geometric analyses and comparisons of community trajectories, to quantify shifts in dynamic beta diversity. We hypothesized that the pulse MHWs would strongly influence ecosystem structure; however, no significant impact was detected. Our analysis indicates that the NES LME continues to tropicalize. However, it was not the pulse MHW events that seemed to drive change but rather ecosystem overfishing and rising temperatures. We quantified beta diversity over time in marine communities undergoing abrupt environmental changes and press disturbances. When expanded globally, this analysis can compare how variable disturbance pressures may result in different manifestations of beta diversity change within marine assemblages.