A new method of describing phytoplankton blooms: Examples from Helgoland Roads

a r t i c l e i n f o Phytoplankton blooms, in their pivotal position in pelagic seasonal succession require precise classification criteria in order to evaluate such parameters as bloom start, bloom timing, bloom maximum and growth rates. Such bloom parameters are linked directly to species and bloom specific features. Currently the phytoplankton bloom concept, though intuitively clear, lacks operational criteria allowing the precise definition of bloom parameters. We present a semi-quantitative method of classification of marine phytoplankton blooms based on an algorithmic estimation of several bloom descriptors computed from densely recorded phytoplankton data, like the Helgoland Roads long-term time series. Combining these descriptors we propose a novel classification scheme which may serve useful in the discussion of species fitness, competition and succession of marine algae. Special emphasis is put on the detection of the bloom start, because of its crucial importance for many current research topics, including trigger mechanisms and climate-induced temporal shifts in the context of the match/mismatch hypothesis. Visual examination of scatter plots of these parameters leads us to propose three types of blooming algae. Phytoplankton are commonly distinguished by their morphology to a species level or, with less specificity combined into taxonomic groups (diatoms, dinoflagellates, cyanobacteria, flagellates etc.). Commonly over a seasonal cycle algal species or groups develop blooms, sometimes also called 'phytoplankton events' (Beliaeff et al., 2001). Abundance and timing of these phytoplankton blooms are pivotal to a proper functioning of the marine food web and climate induced shifts are currently discussed in the context of the match/ mismatch hypothesis (Beaugrand et al.e. the temporal and/or spatial decoupling of hitherto synchronised processes. When discussing phytoplankton blooms, scientists base their assessments on classical batch culture studies whereby cell count records/biomass concentrations are segmented into different phases. Phytoplankton blooms, spring blooms as well as red tides, are considered to have a lag phase with a few initial cells (Spencer, 1954), an exponential growth phase where cells produced also produce more viable cells, a declining growth rate phase where cessation of the exponential growth occurs, a stationary phase where cell death and growth are balanced and, finally, a death phase where the population declines (Fogg and Thake, 1987; Spencer, 1954) caused by several factors e.g. sinking, grazing, nutrient depletion, viral infection etc.. Indeed, in situ algae can actually bloom in roughly such a manner as has been shown in the works of Lund (1950) and …