Hurricane Impacts and the Resilience of the Invasive Sea Vine, Halophila stipulacea: a Case Study from Puerto Rico

Abstract

Category five hurricanes Irma and Maria (September 2017) caused significant damage to shallow seagrass communities across Puerto Rico. The magnitude and spatial extent of hurricane impacts on representative seagrass habitats of Culebra Island were addressed using a combination of random photo-quadrats and before–after hurricanes GIS-based imagery analyses. There was a significant loss of shallow seagrasses across all nine surveyed locations. Most of the documented impacts were associated with sediment bedload (horizontal transport), which resulted in burial and suffocation. There was also localized physical disruption of the seagrass habitat matrix across locations exposed to stronger wave action, creating major scars and exposing below-ground structure to further disintegration by future storm events. Displaced coral rubble also caused seagrass burial. Aerial imagery analyses (2007, 2010, 2017) showed a significant decline in seagrass percent cover. Seagrass decline was positively correlated with wave exposure (p < 0.05). Seagrass cover, density, and changes in benthic community structure were documented across five of the surveyed locations during 2018, and these data were further compared to data collected in 2004 at these same sites. There was a decline in percent seagrass cover and density and a change in benthic community structure favoring habitat homogenization. A remarkable finding was the rapid recovery, expansion, and increased localized dominance of the invasive seagrass, Halophila stipulacea. This was particularly evident in areas impacted by recurrent land-based runoff pulses, anchoring, sediment resuspension due to navigation, trampling or by the accumulation of decaying Sargassum mats. Hurricanes triggered a localized shift in marine vegetation, favoring the invasion of H. stipulacea, with potentially significant consequences on ecosystem resilience and on the ability of native in seagrasses to persist and adapt to projected climate change impacts.