Environmental drivers of flowering in the genus Zostera and spatio‐temporal variability of Zostera muelleri flowering in Australasia

Abstract

Seed‐based seagrass restoration strategies demand precise understanding of the environmental drivers influencing flowering. Flowering varies across diverse spatial and temporal scales, yet environmental drivers' effects on these dynamics have received less attention. Lack of knowledge regarding this life‐history stage limits the advancement of seed‐based restoration efforts, especially the establishment of shore‐based seagrass nurseries to enhance seed production. A systematic literature review on the flowering of the genus Zostera was conducted to develop a conceptual model that links influential environmental drivers with flowering. Additionally, a case study using existing survey data supplemented by additional field surveys was designed to explore the spatio‐temporal variability of flowering along the latitudinal gradient in Australasia for the species Zostera muelleri. Predictive models for flowering times were developed using regional climatic variables, following hypotheses generated from long‐term mesocosm observations. The review identified the direct and/or indirect effects of temperature, light, tidal variation, nutrients, salinity and grazing pressure on flowering dynamics. Four categories of flowering variables were identified based on their implications on restoration, namely, timing, abundance, the ratio between reproductive and vegetative growth and morphological characteristics. The spathe densities varied significantly among sites along the latitudinal gradient. While first (r2 = 0.71) and peak (r2 = 0.68) flowering times showed significant correlation with latitude, first flowering was equally predicted by mean winter air temperature and mean winter solar radiation (r2 = 0.73), whereas peak flowering time was best predicted by mean winter air temperature (r2 = 0.60). Accurate predictions of flowering times can improve conservation outcomes by enabling restoration practitioners to forecast flowering times and subsequent wild seed harvesting. The strong correlation between flowering times and climatic variables suggests future shifts in flowering times under climate change are likely, which is crucial knowledge for maintaining the contribution of restoration projects to seagrass conservation.