Seagrass dominance over seaweeds in oligotrophic coastal ecosystems

Simon von Sachsen-Coburg und Gotha

Seagrasses and marine macroalgae co-exist in shallow coastal environments where they compete for space and resources such as nutrients. The paradigm that seagrasses have a higher nutrient affinity than macroalgae at low nutrient concentrations may explain the seagrass dominance in shallow oligotrophic environments. To test this hypothesis, we conducted a systematic review, extracting 1,507 uptake kinetic values of 158 species in 92 genera from 104 peer-reviewed publications. We tested differences in the nutrient kinetic parameters maximum uptake rate (Vmax) and uptake affinity (alpha) between seagrasses and macroalgae, considering two uptake phases (surge and internally controlled uptake), different nutrient sources (ammonium, nitrate and phosphate), and major taxonomic groups. Macroalgae displayed higher Vmax and alpha rates than seagrasses during the surge uptake phase for ammonium and nitrate in all phyla. Additionally, green macroalgae demonstrated significantly higher Vmax and alpha rates than brown and red macroalgae and seagrasses during both uptake phases. Our results showed that the dominance of seagrasses over macroalgae in oligotrophic environments cannot be simply explained by their nutrient uptake kinetic parameters. Other factors, such as light availability or interspecific interactions during nutrient uptake may play an important role.