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

The seasonal variation in biometric and biomass features of a deep subtidal Zostera marina bed (depth 12-14 m) in Canuelo 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 Canuelo 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 degrees 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.