Standing at water edges: Ecohydrological interactions between coastal groundwater discharge and intertidal community dynamics

The intertidal zone on rocky shores is of key ecological importance because it supports high biodiversity, provides critical ecosystem services such as nurseries and refuges, and facilitates complex species interactions in the transition to offshore areas. Important local shaping factors such as groundwater discharge complexify the ecological dynamics of rocky shore communities. The role of submarine groundwater discharge (SGD) in coastal ecosystems is well established. Here, I introduce the Intertidal Groundwater Discharge (IGD) concept to provide a standardised format for distinguishing it from other discharge types. Despite receiving recent increased attention, the importance of direct inland groundwater discharge into intertidal rocky habitats is still scattered. Rocky shores are hallmark habitats long hailed as biodiversity hotspots and key ecological players in adjacent environments; however, consolidated scientific assessments of GW-ecology linkage features and vulnerabilities are lacking. This review is the first to merge fragmented research and identify gaps in knowledge and methodological needs in assessing groundwater-mediated ecological intertidal processes. By filling these gaps, we can gain insights into the vulnerabilities of coastal ecosystems to climate-driven changes related to groundwater availability and design strategies that promote ecological resilience. Rising sea levels, altered precipitation and temperature patterns, and resource exploitation and pollution are increasing threats to the sustainability of rocky shore communities. Here, I integrate hydrogeochemical insights into the broader ecological context of these biodiversity hotspots to develop informed conservation strategies that safeguard the stability and functionality of dynamic and vulnerable habitats.