Macrophytes and Phytoplankton, Two Primary Antithetical Producers in Degraded Water Systems

One year of monthly sampling in some lagoons of the Po Delta and a pond in the Comacchio Valleys helped fill a gap in the knowledge of the primary producers of these degraded environments, focusing on the competition between macrophytes and phytoplankton. Key water column and surface sediment parameters showed a strong association with the different primary producers, explaining the main factors influencing the dominance of one group over the other. Phytoplankton, recorded as Chlorophyll-a and Phaeophytin-a, and Chlorophyceae among the macrophytes, dominated in conditions of high water turbidity and elevated nutrient concentrations. In contrast, macrophytes, particularly Rhodophyceae, their abundance, total biomass, and number of taxa. prevailed in clear, oxygenated waters. Under optimal conditions, sensitive macroalgae and aquatic angiosperms were also present. Additionally, the current list of macroalgal taxa has been updated, highlighting the dominance of some nonindigenous species (NIS) that had not been recorded before the 2000s. Specifically, Gracilaria vermiculophylla and Ulva australis, native to the North West Pacific (Japan, Korea, China, and Vietnam) and to South Australia, as well as the Indo-West Pacific (India, South Africa, Japan, and Korea), respectively, are now the most frequent and abundant taxa in these lagoons.