Seasonal plant development and meadow structure of Irish and southern Spanish seagrass populations

Abstract

Zostera marina and Z. noltii are two dominant meadow-forming seagrass species in temperate regions in the northern hemisphere. Seagrass meadows provide several goods and ecological services and rank amongst the most valuable ecosystems worldwide. Phenological shifts in Zostera species occur along latitudinal or temperature gradients, leading to an expectation for distinct seasonal dynamics and annual production in Spain and Ireland. Despite their global ecological importance, seasonal seagrass traits of populations exposed to contrasting climate settings from Ireland and southern Spain are poorly described. To address this gap, we evaluated the seasonal vegetative development (morphology, population structure, and productivity) of Z. marina and Z. noltii populations exposed to cold (western Ireland) and warm (southern Spain) temperatures over a year-long period. Our results highlight contrasting dynamics of Z. marina populations across their temperature range. The Irish population exhibited maximal growth during warmer months while the Spanish population revealed signs of growth reduction under maximum annual temperatures. Our results suggest that plants of Z. marina in Ireland were temperature-limited at most times, but in southern Spain exceeded their optima temperature for growth during summer. In addition, Irish and Spanish Z. noltii populations displayed differential vegetative dynamics and population structures, likely related to the contrasting local temperature regimes. These differences were particularly evident in summer when shoot size and growth rates were reduced in warm-temperate locations. This study represents an essential comparative baseline for future assessments of ecological status, and anticipated growth stress induced by climate change across the distributional gradient, of these important Zostera species.