Evidence for vertical growth in Zostera noltii Hornem.

We report first evidence for rhizome vertical growth (driven by sediment burial) in the temperate seagrass Zostera noltii . The study was carried out in a population of Z. noltii occurring on the intertidal sandflats of Cádiz Bay Natural Park (Spain), an area subjected to episodic events of a high sediment transport driven by wind. In surveyed plants of Z. noltii, rhizomatic vertical growth was observed (9 cm maximum, 6.1±0.31 cm average) with shorter internodes and longer leaf-sheaths (0.74±0.05 cm and 10.1±0.5 cm, respectively) than those recorded for horizontal rhizomes (2.2±0.05 cm and 3.3±0.18 cm, respectively). Mean vertical rhizome growth rate, calculated from reconstructive techniques (0.083±0.003 cm d -1 ), is half than that estimated for horizontal rhizome growth (0.15±0.008 cm d -1 ) using the punching method. Vertical nodes lacked shoots, and resumed horizontal growth and shoot recruitment once the meristem reached the sediment surface. Plasticity in this trait allowed Z. noltii populations to withstand moderate burial in this highly dynamic environment.