Poster presentation: Interactive effects of hydrodynamics and light stresses on seagrass Zostera noltii

Seagrasses encounter multiples stresses due to environmental heterogeneity, which may be partly overcome through the ability of being phenotypically plastic. As hydrodynamic energy often enhances turbidity, seagrasses may be expected to frequently experience a combination of light and mechanical stress. We hypothesise that these stresses to induce opposite responses on dynamic and morphometric seagrass features. In the present study we investigated the phenotypic response of Zostera noltii when exposed to combinations of light and mechanical stresses. A bi-factorial mesocosms experiment was conducted on Z. noltii plants at two different light levels (39 and 240 µmol photons m2 s-1) and three current velocities (35, 10 and 1 cm s-1). No interactive effects of both variables were observed and, generally, light effects prevailed to hydrodynamic effects. Light-limited plants showed lower survival rate (which improved at high velocity), higher aboveground/belowground biomass ratio (AG/BG) and a poor developed root system. Under non-limiting light and high velocity, plants presented lower AG/BG and plastochone index for internodes, smaller and less abundant leaves, and longer internodes. We conclude that, under concurrently stresses due to light and hydrodynamics, the seagrass Z. noltii responds firstly to constraining light, and only in non-limited light conditions, plants showed plasticity to hydrodynamics.