Phenology and growth cycle of annual subtidal eelgrass in a subtropical locality

Abstract

This study describes the phenology, life cycle and reproductive potential of Zostera marina L. (eelgrass) in Bahı́a Concepción, the southernmost population on the west coast of the Gulf of California. Z. marina populations in the Gulf of California are the unique annual subtidal meadows existing only in the coldest season of the year, from December to May, and surviving the adversely warm summer season as seeds. The maximum shoot density was 2334 shoots per square meter in January, the minimum recorded during the growth season was 664 shoots per square meter in May. Before December and after May no living plants were found. Until March, the percentage cover of the meadow was up to 90%, in April some patches of dead shoots were found (16%) and in May the meadow disappeared. Several growth variables, such as above-ground biomass, rhizome branching, leaf-blade morphology, and leaf area index, showed that the main vegetative growth was in the period December–January. The appearance of the first flowering shoots was in late January and the first fruit appearance was observed in March. The presence of flowers was observed from February to May. Fruit production was maximum in late March (21 fruits per shoot), decreasing later to eight fruits per shoot due to the release of seeds. Seed production was estimated to be 30,000 seeds per square meter.