Response of planktonic microbial assemblages to disturbance in an urban sub-tropical estuary

Responses of coastal phytoplankton communities to seasonal herbicide inputs: Tolerance or degeneration?

Herbicide-induced phytoplankton inhibition threatens coastal biodiversity and ecosystem function. Although studies employing single-frequence exposure aid in understanding the phytoplankton community's responses to herbicides, it's difficult to objectively assess their response to cyclic herbicide inputs (long-term low-dose and short-term high-dose) in marine ecosystems. Here, we analyzed the concentration and distribution of herbicides in global coastal waters and simulated this cyclic process through a two-phase atrazine exposure mesocosm experiment and laboratory tests. The results indicated that, the herbicide concentrations (0.82 nmol L-1, 95 % CI 0.55, 1.74) from May to August were significantly higher than that (0.14 nmol L-1, 95 % CI 0.02, 0.38) in the remainder months, and highest concentrations typically emerged in summer; the changes in phytoplankton community composition under environmental concentrations of triazine herbicides could recover in the short term, but sustained inhibition of biomass was produced; the dominant populations were more likely to develop tolerance through preexposure and recover from subsequent impulse of atrazine, but this process was accompanied by the loss of rare groups and a decrease in biodiversity, meanwhile, affected the bacterial community in phycosphere. Consequently, we considered that the cyclic herbicide inputs may cause more detrimental effects than single-frequence exposure, potentially leading to a large-scale decline in coastal primary productivity.

Microbial, holobiont, and Tree of Life eDNA/eRNA for enhanced ecological assessment

Microbial environmental DNA and RNA (collectively 'eNA') originate from a diverse and abundant array of microbes present in environmental samples. These eNA signals, largely representing whole organisms, serve as a powerful complement to signals derived from fragments or remnants of larger organisms. Integrating microbial data into the toolbox of ecosystem assessments and biotic indices therefore has the potential to transform how we use eNA data to understand biodiversity dynamics and ecosystem functions, and to inform the next generation of environmental monitoring. Incorporating holobiont and Tree of Life approaches into eNA analyses offers further holistic insight into the range of ecological interactions between microbes and other organisms, paving the way for advancing our understanding of, and ultimately manipulating ecosystem properties pertinent to environmental management, conservation, wildlife health, and food production.

The impact of extreme weather events exceeds those due to global-change drivers on coastal phytoplankton assemblages

Extreme wind and rainfall events have become more frequent phenomena, impacting coastal ecosystems by inducing increased mixing regimes in the upper mixed layers (UML) and reduced transparency (i.e. browning), hence affecting phytoplankton photosynthesis. In this study, five plankton assemblages from the South Atlantic Ocean, from a gradient of environmental variability and anthropogenic exposure, were subjected to simulated extreme weather events under a global change scenario (GCS) of increased temperature and nutrients and decreased pH, and compared to ambient conditions (Control). Using multiple linear regression (MLR) analysis we determined that evenness and the ratio of diatoms/ (flagellates + dinoflagellates) significantly explained the variations (81-91 %) of the photosynthesis efficiency (i.e. Pchla/ETRchla ratio) for each site under static conditions. Mixing speed and the optical depth (i.e. attenuation coefficient * depth, kdz), as single drivers, explained 40-76 % of the variability in the Pchla/ETRchla ratio, while GCS drivers <9 %. Overall, assemblages with high diversity and evenness were less vulnerable to extreme weather events under a GCS. Extreme weather events should be considered in global change studies and conservation/management plans as even at local/regional scales, they can exceed the predicted impacts of mean global climate change on coastal primary productivity.