Temporal and depth-associated changes in the structure, morphometry and production of near-pristine Zostera marina meadows in western Ireland

•First baseline data of temporal changes in shoot and population dynamics, including biomass production, from western Ireland.•Discernible temporal and site-specific differences in morphometry and population structure.•Depth- acclimatization induced significant changes in the vegetative development.•Latitudinal comparison of leaf production places Irish populations within global trend for temperate regions.