Changes in the phytoplankton community at Helgoland, North Sea: lessons from single spot time series analyses

Abstract

In recent regime shift analyses, the phytoplankton compartment of the marine food web was essentially represented by phytoplankton color or chlorophyll concentration. A detection of changes directly at the species level is highly desirable. The Helgoland Roads data series, a collection of high frequency long-term time series comprising biological and physico-chemical components of the southern North Sea, allow such an investigation at the level of single species. Aiming at a detection and characterization of habitat and community changes in the observation period (1962 until the end of 2008), we selected six species as representatives of certain classes, for example, benthic or neritic species, and applied a combination of novel analysis methods-a fitness-based analysis of the realized niche, a bloom-triggered averaging and a Markovian analysis of co-occurrence and succession patterns-to related abundance time series and concurrent environmental parameter time series. We found a general trend toward enlargement of niche size and shifts of the niche position, interesting salinity patterns around bloom events of two species, and statistically highly significant changes of a phytoplankton community segment after 1965 and after 1998. Interpreting our observations in ecological terms leads to the formulation of testable hypotheses.

The acclimative biogeochemical model of the southern North Sea

“…The comparison of the present model with earlier attempts is neither in the scope of this study nor possible without a dedicated benchmarking effort, using standardized forcing data and skill performance assessment datasets and methodology (e.g., as in Friedrichs et al, 2007). Even a qualitative comparison is difficult, given that spatial and temporal binning of the data, frequently employed in model validation (such as in our Fig.…”

“…This is noteworthy, given that phytoplankton is represented by a single species in our model, whereas in other modeling approaches several species or groups are resolved. The inclusion of multiple functional types is motivated by the spatial and seasonal variability in the phytoplankton composition observed in the field: coastal areas of the SNS are dominated by diatoms throughout the year in some sites (e.g., Alvarez-Fernandez and Riegman, 2014) and during spring in some others, later replaced by Phaeocystis during summer (e.g., , whereas the offshore areas are often dominated by dinoflagellates especially during summer (Freund et al, 2012;Wollschläger et al, 2015). These phytoplankton groups differ from each other in a number of traits, including the physiological traits that determine their ability to access the (mineral and light) resources and build biomass.…”

Ocean Net Heat Flux Influences Seasonal to Interannual Patterns of Plankton Abundance

“…As phytoplankton form the base of the marine food web, an understanding of their population dynamics, including species succession [4], is important for determining whole ecosystem trajectories. The spring bloom is manifested as a dramatic increase in the phytoplankton standing stock over a relatively short period of time [5].…”

Projecting effects of climate change on marine systems: is the mean all that matters?

“…Our Helgoland data suggest the lack of selective pressures leading to the need for optimal temperatures at temperatures with very low frequency of occurrence, and hence the relative paucity of species with an optimum at the in-between temperatures [27]. It remains to be seen whether the changes in phytoplankton community composition at Helgoland [28] can be linked to the changes in the relative frequency of certain temperatures (figure 5), or whether other factors such as for example the changes in nutrients are more important [17].…”