Spatial-temporal distribution of Aureoumbra lagunensis (“brown tide”) in Baffin Bay, Texas

•A. lagunensis blooms are strongly affected by interannual variability in rainfall.•Highest abundances were found in a tributary, which may act as a reservoir of cells.•Extreme hypersalinity is not a requirement for A. lagunensis bloom formation.•Results highlight potential for bottom-up and top-down controls on A. lagunensis. Once limited to the Laguna Madre of Texas, blooms of the brown tide organism, Aureoumbra lagunensis, have recently been reported elsewhere. Previous studies have focused on the role of extreme hypersalinity and lack of grazing pressure as facilitators of brown tide blooms. However, development of blooms in systems that are not experiencing extreme hypersalinity, and also that are undergoing eutrophication, suggests that our understanding of A. lagunensis bloom dynamics requires additional refinement. The goal of this study was to quantify the spatial-temporal distribution of, and potential controls upon, A. lagunensis in Baffin Bay, Texas. Five sites were sampled monthly over a three-year period, encompassing nearly two years of drought and hypersaline conditions, followed by a high rainfall, lower salinity period. A. lagunensis abundances were higher during drought in May 2013 – March 2015 compared to the higher rainfall period of April 2015 – April 2016. Abundances typically peaked in summer months, though the seasonal pattern was disrupted in 2015 during the shift from high to low salinity conditions. Persistently high abundances of A. lagunensis were observed in the Laguna Salada tributary of Baffin Bay, which typically has higher dissolved organic nitrogen concentrations and may be less well flushed than other parts of Baffin Bay. Thus this location may serve as a reservoir for A. lagunensis in the system. Overall, A. lagunensis abundance was positively correlated with DOC and salinity, and negatively correlated with ammonium, orthophosphate, and ciliate biovolume. These results suggest a variety of physical, chemical and biological factors affect A. lagunensis population dynamics and stress the need for more research on nutrient-A. lagunensis relationships.