Effects of sediment sulfides on seagrass Posidonia oceanica meristematic activity

Seagrass meadows rank amongst the most productive ecosystems on Earth, growing along tropical and temperate coasts, where they have important structural and biogeochemical functions (Hemminga & Duarte 2000). Seagrasses are clonal plants, which expand into new areas vegetatively by adding modules produced by the meristems located at the rhizome apices, rendering seagrass demographics and productivity closely dependent on rhizome meristematic activity (Tomlinson 1974). Currently, seagrass meadows are undergoing a worldwide decline, as reflected by losses in cover and density during the 20th century (e.g. Orth et al. 2006). Excess inputs of nutrients and organic matter have been identified as the main drivers of this decline (e.g. Orth et al. 2006). Organic carbon and nutrient inputs to the sediment stimulate bacterial activity, increasing sediment oxygen demand and the production of bacterial metabolites such as sulfides, which are toxic for seagrasses (Terrados et al. 1999). Several die-off events in subtropical Thalassia testudinum (Borum et al. 2005) and temperate Zostera marina (Goodman et al. 1995) seagrass meadows have been linked to episodes of high sediment sulfide concentrations. It has been suggested that Caulerpa spp. invasions accelerate the decline in Posidonia oceanica meadows, since these macroalgae species cause the MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 372: 1–6, 2008 doi: 10.3354/meps07714 Published December 9