The importance of environmental parameters and mixing zone in shaping estuarine microbial communities along a freshwater-marine gradient

Abstract

Microbial communities are important elements in the marine environment, contributing to nutrient cycling and biogeochemical processes. Estuaries comprise environments exhibiting characteristics from freshwater to marine, leading to distinct microbial communities across this environmental gradient. Here, we examine the spatial dynamics of microbial communities in Macquarie Harbour, an estuarine system on the West coast of Tasmania, Australia. Water was sampled along the estuary to explore the structure and composition of the microbial communities using 16S/18S rRNA gene amplicon sequencing. Multivariate analyses showed environmental variables and community compositions varying along a longitudinal (river to adjacent ocean) gradient at the surface. In the harbour, differences in the microbial community were observed between surface (0-1 m) and intermediate depths (4.5-11 m depth). The results of differential abundance, network and Partial Least Square analyses suggest that Macquarie Harbour is a mixing zone, where the distributions of archaeal, bacterial and eukaryotic communities are influenced by oceanic and riverine inputs. Coupled with the natural characteristics of the Harbour, the heterotrophic component of this microbial communities inhabiting the surface and intermediate waters may play important roles in the nutrient cycle in the studied area. These results provide critical insights into the Macquarie Harbour environment and the importance of understanding the role of microbial communities for similar systems elsewhere.

Effects of finfish farms on pelagic protist communities in a semi-closed stratified embayment

“…The distribution of Chytriodinium and Syndiniales rely on host and nutrient availability (Anderson & Harvey 2020; Fulton 1984; Gómez & Skovgaard 2015; Strassert et al 2019). Copepods, a known host of Chytriodinium are more abundant in the surface waters of the Harbour (da Silva et al 2022). Syndiniales on the other hand is a more flexible parasite infecting other dinoflagellates, radiolarians, and copepods in coastal environments (Bråte et al 2012; Chambouvet et al 2008; Guillou et al 2008; Skovgaard 2014).…”