The causes and consequences of algal blooms: The Cladophora glomerata bloom and the Neva estuary (eastern Baltic Sea)

The biomass dynamics of the green alga Cladophora glomerata was studied in the shallow-water littoral zone of the Neva estuary during May–October of 2003–2005. Additionally, the average production rate of C. glomerata, the biomass of drifting algae and oxygen depletion were examined during period of algae decomposition. Two peaks in C. glomerata biomass, in July and in September, were observed during all years studied, reaching a maximum 300 ± 100 g DW m−2. The primary production of C. glomerata varied from 3.6 to 7.9 g C m−2 contributing to around 90% of the total primary production in this habitat. From the middle of July to late August the biomass of drifting C. glomerata exceeded the biomass of the attached algae, accounting for 62% of the total algal biomass in shallow areas (0–1 m). The hypoxia (a minimum oxygen level of 5% or 0.62 mg dm−3) in the water was recorded near shore (to 20-m distance from the shore), negatively influencing the quality of shallow-water habitats.