Testing the predictive power of seagrass depth limit models

The power of equations predicting seagrass depth limit (Z_c) from light extinction (K_z) was tested on data on seagrass depth limits collected from the literature. The test data set comprised 424 reports of seagrass colonization depth and water transparency, including data for 10 seagrass species. This data set confirmed the strong negative relationship between Z_c and K_z. The regression equation in Duarte (1991) overestimated the realized seagrass colonization depths at colonization depths < 5 m, while there was no prediction bias above this threshold. These results indicated that seagrass colonizing turbid waters (K_z > 0.27 m^-1) have higher apparent light requirements than those growing in clearer waters. The relationship between seagrass colonization depth and light attenuation shifts at a threshold of light attenuation of 0.27 m ^-1, requiring separate equations to predict Z_c for seagrass growing in more turbid waters and clearer waters, and to set targets for seagrass restoration and conservation efforts.