Brackish water macroalgae diversity: population vs community stability

"Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting temporal stability of natural communities. Macroalgae community in temperate brackish waters may be detectable only in few days during blooms throughout the year. Thus diversity-abundance and diversity-stability of macroalgae can only be investigated during blooms. The most contributing macroalgae to blooms are benthic ephemeral green algae, growing on the bottom and often producing biomass drifting on the water surface. We collected two-year (from Sept 2008 to Aug 2010) data to estimate biomass for each macroalga species in a North-West Sardinian lagoon. The aim was to investigate how stability-enhancing mechanisms varies with time (bloom 2009 and bloom 2010, in spring) and habitat (bottom vs surface). ANOVAs tested the differences. Shift in species occurrence were detected between times, as species composition in bloom 2009 was different than in bloom 2010. Macroalgae community biomass was significantly different between times both in mean and variation (μ and σ). Because higher μ corresponded higher σ, stability (μ\/σ) did not vary through time. Community stability did not vary with habitat either, mostly as a consequence of negative covariance of species fluctuations. Overyielding promoted stability, but the strength did not vary with time nor habitat. Our study suggests low variation in stability of macroalgae biomass in this environment. Our findings provide valuable information for predicting biomass production in macroalgal blooms despite species composition changes between blooms."