Nitrogen enrichment ameliorates the negative effects of reduced salinity on the green macroalga Enteromorpha intestinalis

In southern California estuaries, the green macroalga Enteromorpha intestinalis experiences wide fluctuations in both nitrogen (N) supply and salinity. We investigated the effects of simultaneous variation in N and salinity on the growth, biomass accumulation and tissue nutrient dynamics of E. intestinalis. We conducted a fully crossed 2-factor experiment in which we varied N enrichment (low, medium and high) and salinity (15, 25 and 35 psu). Overall, addition of N enhanced algal growth while salinity reduction decreased growth. High N enrichment mitigated the negative effects that reduced salinity had on dry biomass, wet:dry biomass ratios, tissue nutrients and ability to remove phosphorus from the water column. Largely, E. intestinalis abundance was governed by N availability rather than salinity, indicating that blooms of macroalgae will likely continue to proliferate in estuaries unless nutrient loading is reduced.