Beta diversity changes in estuarine fish communities due to environmental change

Estuarine ecosystems are intrinsically resilient to the dynamic fluctuations of environmental conditions. Yet, it is unknown how the changes in environmental variability associated with climate change will affect fish communities. We assessed how species turnover over space and time in estuaries is influenced by changes in environmental conditions over years. We used fish abundances and water quality sampled at 42 stations among 7 estuaries in New Brunswick (Canada) from 2005 to 2012 to estimate (1) spatial turnover between stations based on the local contribution to beta diversity (LCBD) index, and (2) temporal turnover from year to year based on the 13-Sorensen index. We found that beta diversity was potentially structured (i) over space due to inherent within-year differences in each estuary and (ii) over time related to the environmental condition of the previous year which led to changes in salinity, dissolved oxygen, and water temperature at sampling stations. Species contribution to spatial beta diversity (SCBD) was attributed across all years to 4 key species which were sensitive to dissolved oxygen. The current environmental condition of dissolved oxygen, temperature, salinity, and eelgrass Zostera marina affected temporal year-to-year turnover. When each year is analyzed separately, the estuaries with the greatest annual summer temperature fluctuations within a station contribute the most to spatial beta diversity between estuaries. Understanding how fish community structure responds to changes in environmental conditions can help inform the management of estuarine resources in the face of a rapidly changing environment.