Long-term coexistence between the macroalga Caulerpa prolifera and the seagrass Cymodocea nodosa in a Mediterranean lagoon

The potential negative influence of the seaweed Caulerpa prolifera on seagrass Cymodocea nodosa was explored in a Mediterranean coastal lagoon (Mar Menor, Spain) where alga suddenly and rapidly spread four decades ago. An extensive field sampling carried out across to characterise distribution abundance both macrophytes at different spatial scales, as well sediment characteristics. Generalised linear additive models were performed whole-lagoon scale, for deep shallow bottoms, independently, explore factors influencing C. abundance. A high-spatial-resolution macrophyte map also generated by integrating underwater imaging, direct visualisations orthophotographs. This showed that largely dominated ecosystem but with opposing depth patterns mainly reflected their specific light requirements. dominant depths grew intermingled dense bed over large areas seafloor highly anoxic muddy sediments. Models did not reveal overall relationships between macrophytes, indicating main driver this lagoon. Findings highlighted absence or indirect nodosa, supported fact distributions similar those reported 1980s, just few years after had We conclude, therefore, is progressively replacing ecosystem, species have coexisted decades.