Tight Coupling ofGlaciecolaspp. and Diatoms during Cold-Water Phytoplankton Spring Blooms.
Early spring phytoplankton blooms can occur at very low water temperatures but they are often decoupled from bacterial growth, which is assumed to be often temperature controlled. In a previous mesocosm study with Baltic Sea plankton communities, an early diatom bloom was associated with a high relative abundance ofGlaciecolasequences (Gammaproteobacteria), at both low (2°C) and elevated (8°C) temperatures, suggesting an important role for this genus in phytoplankton-bacteria coupling. In this study, the temperature-dependent dynamics of free-livingGlaciecolaspp. during the bloom were analyzed by catalyzed reporter deposition fluorescencein situhybridization using a newly developed probe. The analysis revealed the appearance ofGlaciecolaspp. in this and in previous spring mesocosm experiments as the dominating bacterial clade during diatom blooms, with a close coupling between the population dynamics ofGlaciecolaand phytoplankton development. Although elevated temperature resulted in a higher abundance and a higher net growth rate ofGlaciecolaspp. (Q10∼ 2.2), their growth was, in contrast to that of the bulk bacterial assemblages, not suppressed at 2°C and showed a similar pattern at 8°C. Independent of temperature, the highest abundance ofGlaciecolaspp. (24.0 ± 10.0% of total cell number) occurred during the peak of the phytoplankton bloom. Together with the slightly larger cell size ofGlaciecola, this resulted in a ∼30% contribution ofGlaciecolato total bacterial biomass. Overall, the results of this and previous studies suggest thatGlaciecolahas an ecological niche during early diatom blooms at low temperatures, when it becomes a dominant consumer of phytoplankton-derived dissolved organic matter.
Leibniz Institute for Baltic Sea Research Warnemünde Rostock, Germany.
Markus
M
von Scheibner
Helmholtz Centre for Ocean Research Kiel, Germany.
Ulrich
U
Sommer
Leibniz Institute for Baltic Sea Research Warnemünde Rostock, Germany.
Klaus
K
Jürgens
Baltic Sea; CARD-FISH; Glaciecola; marine bacteria; phytoplankton; spring bloom; temperature