Periodic change in coastal microbial community structure associated with submarine groundwater discharge and tidal fluctuation

Abstract

Coastal areas where submarine groundwater discharge (SGD) occurs are active mixing zones with characteristic biogeochemical and ecological functions. In this study, we investigated the microbial community associated with the changes in groundwater discharge flux at a coastal beach site on Jeju Island, South Korea. We performed water chemistry analyses, 16S rRNA gene-based pyrosequencing, and microbial community statistical analyses on coastal water samples systematically collected as functions of tidal stage and distance from the groundwater discharge point. We also carried out groundwater level monitoring and numerical simulation of the coastal aquifer to reproduce tidally induced variations in the SGD rates of the study site. Pyrosequencing and statistical analyses revealed a periodic shift in the microbial communities in the coastal waters as functions of tidal stage and SGD rates. Interestingly, the community structures in the samples collected at flood and ebb tide were markedly different, despite the similarities in their water chemistry. Groundwater simulation and canonical correspondence analyses suggest that groundwater discharging at higher velocities at ebb tide can detach and transport subsurface bacteria from the aquifer to the coastal water body, resulting in an increase in facultative anaerobes in the ebb tide samples. In addition, release of the sand-attached bacteria as a result of particle resuspension and flushing of shallow subsurface bacteria in the intertidal zone could contribute to shaping the relative abundance of the coastal microbial community. We conclude that SGD rate is an important factor influencing the dynamics of the bacterial community structure at the coastal zone of the study site.

Enhanced Growth Rates of the Mediterranean Mussel in a Coastal Lagoon Driven by Groundwater Inflow

“…In the Mediterranean Sea, which is an oligotrophic basin characterized by limited surface water inputs, groundwater discharge is a major source of nutrients to coastal systems and may thus affect the primary production in the ecosystems (Herrera-Silveira, 1998;Basterretxea et al, 2010;Tovar-Sánchez et al, 2014;Rodellas et al, 2015). However, the impacts of groundwater discharge are not limited to nutrient loading: a wide range of organisms also respond to changes in water salinity, light penetration into water column, pH and turbulence (Short and Burdick, 1996;Troccoli-Ghinaglia et al, 2010;Lee et al, 2017). For example, groundwater input has been demonstrated to increase meiofauna diversity (Encarnação et al, 2015) and the abundance and body size of Mediterranean mussels (Piló et al, 2018) in Olhos de Agua beach in Portugal, and enhance species richness, abundance and biomass of fishes and invertebrates in Japanese coastal waters, where high groundwater-borne nutrient concentrations have been reported (Hata et al, 2016;Utsunomiya et al, 2017).…”

Investigating the Land-Sea Transition Zone

“…On the one hand, the way of alteration depends on the community composition of the STE. On the other hand, the microbial communities and thus their metabolic potential are influenced by the physicochemical properties (e.g., salinity, temperature) within the STE (Santoro et al 2008;Lee et al 2016). Understanding which microbes are driving specific biogeochemical cycles in the STE and the respective conditions that are necessary for them to thrive in this habitat will help to predict the effects of SGD on different coastal environments.…”

“…However, microbial community compositions are not only shaped by the availability of electron acceptors but also by the physicochemical properties of the investigated systems (Santoro et al 2008;Lee et al 2016). Santoro et al (2008) investigated a sandy STE at Huntington Beach, California, USA, with a focus on the abundances of ammonium-oxidizing proteobacteria and ammoniumoxidizing archaea.…”

“…They also observed that the shift between those two groups migrated with the brackish mixing zone during the year. Another study that found a correlation between microbial community structure and hydrology was performed at Jeju Island, Korea, by Lee et al (2016), who discovered that the microbial community composition can be altered by the SGD rate within the different stages of a tidal cycle.…”

Synthesizing the Effects of Submarine Groundwater Discharge on Marine Biota

“…However, the effect of SGD on organisms is not limited to nutrient loading. In regions with substantial SGD flux, organisms may respond to changes in salinity, light penetration into the water column, turbulence, and/or pH [30,[39][40][41][42]. Fresh SGD has even been proposed to aid in the removal of parasites from fish, a common aquaculture practice [43].…”