Community development and modes of phosphorus utilization in a late summer ecosystem in the central Gulf of Finland, the Baltic Sea

Abstract

The development of a filamentous, nitrogen-fixing cyanobacterial bloom was followed during July-ugust 1990 in a stratified basin in the central Gulf of Finland, altic Sea . Hydrography, dissolved inorganic, particulate and total nutrients, chlorophyll a, alkaline phosphatase activity, 32 P04-uptake and phytoplankton species were measured . The study period was characterized by wind-induced mixing events, followed by marked nutrient pulses and plankton community responses . Phosphate uptake was highest throughout the study period in the size fraction dominated by bacteria and picocyanobacteria ( 2 am) and the proportion of uptake in the size fraction 2-10 pm remained low (2-6%) . Higher phosphate turnover times were observed in a community showing signs of enhanced heterotrophic activity. The bloom of filamentous, nitrogen-fixing cyanobacteria phanizomenon flos-aquae was promoted by a nutrient pulse with an inorganic nutrient ratio (DIN :DIP) of 15 . The results show that the quality, frequency and magnitude of the physically forced nutrient pulses have an important role in determining the relative share of the different modes of phosphorus utilization and hence in determining the cyanobacterial bloom intensity and species composition in the altic Sea .

Use of different phosphorus sources by the bloom-forming cyanobacteria Aphanizomenon flos-aquae and Nodularia spumigena

“…Thus, in summer, during periods when other phytoplankton are nitrogen-limited and bacteria are limited by the resource ratios, available phosphorus from inorganic and organic pools might be channelled to the diazotrophic cyanobacteria despite excess leakage of alkaline phosphatase. However, filamentous cyanobacteria have been usually reported to be responsible for only a minor fraction of phosphorus uptake during blooms (Grönlund et al 1996. Their phosphorus demand in any case seems to be small, and the N:P ratios display remarkable plasticity, as growth rates can withstand increases in cellular N:P ratios of at least up to 80:1 (Fig.…”

“…N. spumigena seems to have developed an adaptation to efficient growth in conditions of phosphate deficiency in systems that nevertheless have abundant phosphorus available in other forms. The fraction of the DOP pool during summer in the surface layer of the Baltic Sea may represent 70 to 100% of the total phosphorus (Kononen & Nômmann 1992); Grönlund et al (1996) observed that during short (40 min) incubations, more than half of the added phosphate ended up in the DOP pool. estimated that 4 to 43% of DOP would be bioavailable.…”

“…through phosphate uptake during early summer with subsequent growth on intracellular stores (Larsson et al 2001) and through recycling of organic compounds in the planktonic food web (Tamminen 1989, Grönlund et al 1996, Kangro et al 2006. Deep-water excess phosphorus is channelled to the cyanobacteria by frontal hydrodynamic processes , upwelling (Vahtera et al 2005) and turbulent mixing (Kononen & Nômmann 1992) during the growth period.…”

Interaction effects of N:P ratios and frequency of nutrient supply on the plankton community in the northern Baltic Sea

“…Large filamentous cyanobacteria are superior in the storage of P (Larsson et al 2001, Walve 2002 and have therefore been thought to benefit from a pulsed nutrient supply (Sommer 1985). Accordingly, mass occurrences of N 2 -fixing cyanobacteria in the Baltic Sea have sometimes been recorded after previous nutrient pulses originating from the upwelling of nutrient-rich bottom water (Grönlund et al 1996.…”

“…Large filamentous cyanobacteria are superior in the storage of P (Larsson et al 2001, Walve 2002 and have therefore been thought to benefit from a pulsed nutrient supply (Sommer 1985). Accordingly, mass occurrences of N 2 -fixing cyanobacteria in the Baltic Sea have sometimes been recorded after previous nutrient pulses originating from the upwelling of nutrient-rich bottom water (Grönlund et al 1996.The increase in cyanobacterial blooms in the Baltic Sea is of particular concern as they are often toxic. The toxicity of the blooms is mainly due to 1 species, Nodularia spumigena Mertens, which produces a hepatotoxin called nodularin (Stal et al 2003).…”