Evidence for Ecosystem Changes Within a Temperate Lagoon Following a Hurricane-Induced Barrier Island Breach

The Great South Bay (GSB) is a shallow temperate lagoon in New York, USA, that has experienced a long-term decline in ecosystem maturity, defined as possessing increased complexity, stability, and resilience, dating back to the nineteenth century that is attributed to the loss of filter-feeding and upper trophic-level diversity and biomass. The observed decline is hypothesized to result from reduced connectivity to the Atlantic Ocean following installation of permanent inlets along the barrier island that reduce the probability of rapid state change through breaching. In October 2012, Hurricane Sandy created a breach in Fire Island that increased connectivity between GSB and the ocean, resulting in higher bay-wide salinity. We hypothesized that increased connectivity would result in a state change reminiscent of a mature system, characterized by higher nekton and mobile invertebrate species richness and diversity, and occurrence of migratory biomass. Otter trawl surveys were conducted throughout GSB from 2013 through 2015 and compared to a pre-breach survey conducted in 2007. An increase in species richness, diversity, and biomass in the 3 years following the breach and a difference in the dominant species collected between sampling periods was observed. Transition in the nekton and mobile invertebrate assemblage was also observed, whereby the assemblages in 2007 and 2015 differed from 2013 and 2014, with the greatest differentiation between the 2007 and 2015 assemblages, highlighting the influence of the breach rather than seasonal and/or inter-annual variation in driving these assemblages. This temporal trajectory of assemblage change clearly aligned with observed changes in salinity; however, this conclusion should be interpreted with caution given the lack of pre-breach survey replication. Nonetheless, our findings suggest that even a modest breach can cause detectible change in the community assembly in GSB. The expanded community diversity observed in GSB is suggestive of initial recovery of ecosystem maturity and underscores the importance of breaching as fundamental in maintaining lagoon ecosystems.