Seasonal variation in a deep subtidal Zostera marina L. bed in southern Spain (western Mediterranean Sea)

Abstract

Abstract The seasonal variation in biometric and biomass features of a deep subtidal Zostera marina bed (depth 12–14 m) in Cañuelo Bay (southern Spain) was studied through an annual cycle. Shoot density was greatest in September 2004 (402.4±22.01 shoots m-2) and lowest in March 2005 (220.8±51.2 shoots m-2). Shoots with inflorescences were only observed in June 2004, with up to 9.6 fertile shoots m-2. Mean shoot height, leaf width and leaf area index also varied seasonally, with maximum values in June–September and minimum values in December– March. The above-ground (leaf) biomass also varied seasonally, with maximum values in June–September (90–100 g dw m-2) and minimum values in March 2005 (8.4±2.7 g dw m-2). The below-ground (rhizome) biomass remained very stable (90–100 g dw m-2) throughout the year. The deep Z. marina bed in Cañuelo Bay had a similar, but less pronounced, seasonal pattern compared to that observed in shallower beds in temperate areas of the Northern Hemisphere. The rather low attenuation coefficient and stable temperature (14–21°C) of the water column throughout the year may favour the development of eelgrass beds at this depth and in this part of the distribution range.