Abstract
Coastal systems such as estuaries are threatened by multiple anthropogenic stressors worldwide. However, how these stressors and estuarine hydrology shape benthic bacterial communities and their functions remains poorly known. Here, we surveyed sediment bacterial communities in poorly flushed embayments and well flushed channels in Sydney Harbour, Australia, using 16S rRNA gene sequencing. Sediment samples were collected monthly during the Austral summer-autumn 2014 at increasing distance from a large storm drain in each channel and embayment. Bacterial communities differed significantly between sites that varied in proximity to storm drains, with a gradient of change apparent for sites within embayments. We explored this pattern for embayment sites with analysis of RNA-Seq gene expression patterns and found higher expression of multiple genes involved in bacterial stress response far from storm drains, suggesting that bacterial communities close to storm drains may be more tolerant of localised anthropogenic stressors. Several bacterial groups also differed close to and far from storm drains, suggesting their potential utility as bioindicators to monitor contaminants in estuarine sediments. Overall, our study provides useful insights into changes in the composition and functioning of benthic bacterial communities as a result of multiple anthropogenic stressors in differing hydrological conditions.
Highlights
Estuaries are diverse and productive ecosystems that support many human activities
To investigate the effect of multiple anthropogenic stressors and estuarine hydrology on benthic bacterial communities, a total of 96 sediment samples were collected in embayments and channels once a month in the Austral summer-autumn between February 2014 and June 2014 (Figure 1 and Supplementary Table 1)
We analysed the effect of retention type and proximity to storm drain as well as their interaction on water and sediment properties with linear mixed-effect models (Table 1) and visualised these differences with Principal Components Analysis (PCA) ordination (Supplementary Figure 1 and Supplementary Table 1)
Summary
Estuaries are diverse and productive ecosystems that support many human activities. the diversity and functioning of these ecosystems are increasingly threatened by multiple anthropogenic stressors including contamination and habitat modification (Johnston et al, 2015a; Mayer-Pinto et al, 2017; Vadillo Gonzalez et al, 2019). The distribution and concentrations of contaminants in estuaries is largely dependent on hydrological conditions (Birch and Rochford, 2010; Mayer-Pinto et al, 2015; Machado et al, 2016; Nystrand et al, 2016). Hotspots of contamination have been documented where low flow estuarine environments exist naturally, such as at the ends of embayments (Birch and Rochford, 2010; Sutherland et al, 2017), or those created by built structures such as breakwalls surrounding marinas (Floerl and Inglis, 2003; Johnston, 2011; Sim et al, 2015). Understanding the consequences of these hydrological differences for the distribution and potential impacts of contaminants is important to manage the health and stability of estuarine ecosystems
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