Abstract
The Helgoland Roads time series is one of the longest and most detailed time series in the world. It comprises daily phytoplankton counts accompanied by physico-chemical measurements. As such, it provides valuable long-term record of changes and their underlying causes in the phytoplankton community around Helgoland. This work provides an updated check-list of the phytoplankton species encountered at the Helgoland Roads LTER station with additional taxonomic assessments from live net samples and scanning electron microscope surveys. Since the last check-list was published 11 additional taxa have been recorded for the first time comprising 9 diatom and 2 dinoflagellate species. Of the 9 diatom species 3 were Chaetoceros species: Chaetoceros anastomosans, C. pseudocurvisetus and C. lorenzianus (the latter identified by their resting cysts) which were all first recognised in September 2009. The toxic dinoflagellate Dinophysis tripos, and the bipolar centric diatom Odontella longicruris both were first observed in September 2015. The latest new record is the potentially toxic dinoflagellate Alexandrium ostenfeldii, first recorded in August 2017. All of the first records (with the exception of Dinophysis tripos) were first observed in semi-quantitative surveys based on live samples and SEM demonstrating that adding less frequent but very detailed assessments can complement high frequency counts of fixed samples as long as these data of different origin are linked efficiently to the individual sampling event and all metadata including representative pictorial metadata are recorded in a consistent manner. In this manner the enhanced checklist serves as a baseline against which long-term changes in phytoplankton potentially related to ecosystem state can be addressed.
Highlights
The Helgoland Roads long-term data series is one of the longest and richest biodiversity datasets in Europe [1]
Prior to the present work the LTER list that forms the basis for the Helgoland phytoplankton counts, contained 261 entries with 84 distinct diatom and 41 dinoflagellate species recognized
These new records fall into two categories: (1) those identified from routine counts of Lugol-fixed samples or semi-quantitative assessments of live and preserved net samples, and (2) those resulting from occasional intensive surveys using additional microscopy techniques (SEM, transmission electron microscopy (TEM) and epifluorescence microscopy)
Summary
The Helgoland Roads long-term data series is one of the longest and richest biodiversity datasets in Europe [1]. Helgoland Roads LTER time series, three transects from Helgoland towards the Elbe and Eider estuaries and one transect into the open North Sea are sampled from the RV Uthörn, on a monthly basis. Helgoland is located in a very dynamic hydrographic environment under the influence of varying regimes ranging from open North Sea conditions to more coastal conditions with reduced salinity [4, 5], which is pronounced during periods of high river discharges from the river Elbe. This contributes to a rich microalgal community but with considerable interannual variability. Additional studies based on live and fixed net samples (20 μm mesh size), collected regularly at Helgoland Roads (see below) were investigated and this data included in the check-list
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