Blooms In Systems Research Articles

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

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.

Allelopathic effects of Chara species (C. aspera, C. baltica, and C. canescens) on the bloom-forming picocyanobacterium Synechococcus sp.

The role of macroalgal allelopathy in aquatic systems has received increasing attention as a potential means of controlling cyanobacterial blooms. However, the allelopathic activity of Chara sp. on coexisting and bloom-forming picocyanobacteria is still largely unknown. Therefore, the laboratory experiments were conducted to investigate the allelopathic activity of extracts of Chara aspera, C. baltica, and C. canescens on the growth, the fluorescence parameters: maximum and effective quantum yield of photosystem II (PSII) photochemistry (Fv/Fm and ΦPSII, respectively) and photosynthesis parameters such as the initial slope of photosynthesis-irradiance (P-E) curves (alpha) and photosynthetic capacity (Pm) of the picocyanobacterium Synechococcus sp. Batch cultures of picocyanobacterium were exposed to three concentrations of extracts originating from three charophyte cultures and the effect was followed at three sampling times. Dried specimens of C. aspera, C. baltica, and C. canescens were extracted in the water-based matrix and the initial Synechococcus sp. inoculum, derived from unialgal culture media, was used. We found both negative and positive allelopathic effects of all tested Chara extracts on Synechococcus sp. The strongest adverse impact of picocyanobacterium growth was caused by C. baltica. This study clearly demonstrated that the allelopathic effect depends on the Chara species identity. Our results also suggested that some allelopathic Chara sp. have the potential to mitigate harmful cyanobacterial blooms in systems dominated by Synechococcus sp.

Allelopathic inhibition of microalgae by the freshwater stonewort, Chara australis, and a submerged angiosperm, Potamogeton crispus

Eutrophication is a major management issue in shallow lakes worldwide. The role of allelopathy in aquatic systems has received increasing attention as a potential means of controlling algal blooms. Macrophytes with allelopathic potential may play an important role in the restoration of eutrophic lakes. Our objective was to investigate the allelopathic effect of the freshwater stonewort, Chara australis, and the submerged angiosperm, Potamogeton crispus, on microalgae. To detect possible allelopathic effects, we compared the growth of a cyanobacterial species, Anabaena variabilis and a green alga, Scenedesmus quadricauda, in the presence and absence of macrophyte extracts, exudates and live material. We found a significant negative effect of all treatments on A. variabilis, with the strongest effect produced by C. australis. In contrast, no effect of macrophyte extracts was evident on the growth of S. quadricauda. This absence of effect confirmed earlier findings that macrophyte allelochemicals are specific to particular target organisms. Our results suggest that allelopathic macrophytes have the potential to mitigate phytoplankton blooms in systems dominated by A. variabilis and perhaps other cyanobacteria.