The Helgoland Roads time-series on meso- and macrozooplankton was started in 1974 as a spin-off data collection stemming from the daily life-food catches of the small cutters of the BAH (Biologische Anstalt Helgoland) marine station. These zooplankton samples were provided to the laboratory for cultivation experiments and for eventual observation. Phytoplankton and nutrients had been measured every work-day since 1962; the expected availability of this information, the then dominant bottom-up theory and the measurement of meso- and macrozooplankton led to the expectation that even in a hydrographically complex locality the trophic controls of zooplankton population abundance and distribution might become evident. The aim was the production of time-series which would permit the testing of simulation models on the trophodynamics of the pelagic ecosystem then believed to be the decisive mechanism of population control. The basis of modelling in those days was a conceptual model of the IBP type.

The plankton nets commonly used for the sampling of zooplankton on the small cutter "Ellenbogen" until 1974 were neither equipped with a counter for the measurement of the volume filtered nor with a design that avoided escape responses of zooplankton approaching the net. These nets were replaced by the HYDROBIOS quantitative collection device 438040 (150 µ hand-net, aperture 17 cm, net length 100 cm, FlowMeter, ballast weight) and the HYDROBIOS ring trawl net 438 700 (Calcofi Net) (mesh size 500 µ, 100 cm aperture, length 400 cm, depressor and FlowMeter). Both nets were used for oblique hauls under the current conditions of Helgoland Roads, generally not permitting vertical hauls. Since 1975 the crew of the cutter "Aade" took over the daily sampling, occasionally replaced by the cutter "Uthörn" or the cutter "Diker".
Sampling was generally carried out during morning hours shifting the sampling by 45 minutes daily through the tidal cycle. The crew washed and sieved the contents of the sampling buckets with a slip of paper indicating ship, net, date, timing and flow meter readings. Samples were life-counted until 1981 on a work-daily basis. Since 1982 sampling was reduced to Monday, Wednesday and Friday. Samples are preserved in 4 % formaldehyde aboard and sent to Hamburg for further identification and analysis. As some species (e.g. Bolinopsis infundibulum) cannot be preserved, occasional life counts were continued for limited time- periods on the basis of plane transports from Helgoland to Hamburg as long as the main station of the BAH was positioned there.
The taxonomic and numeric biodiversity was investigated and documented to the earliest possible date handling meso- and macrozooplankton separately. While mesozooplankton was determined by Reiners and Greve only, macrozooplankton was determined by Greve, Nast, Hoffmann and various other assistants and students. The list of species and stages counted varied with taxonomic changes and learning. Fish larvae which were intentionally excluded from taxonomic analysis have been determined and counted since 1990 for 7 years, so far.

Metazoa continuously change their characteristics with growth. Fixation does not preserve the pigments of fish larvae; they continue to get bleached out. Therefore the taxonomic treatment of the complete size class especially of macrozooplankton requires expertise that can only be obtained after a long training period. Though this training could be supported by the experiences gained, individual inconsistencies cannot be excluded.
The training was supported by selected literature (e.g. (Kermack, Pesta, 1928, Pierrot-Bults & Chidgey, 1988, Grimpe and Wagler, 1911-1942, Ingle, 1992, Jones, 1976, Russell, 1953, Russell, 1970, Russell, 1976, Sars, 1903, Williamson, 1957, Zimmer, 1909) ) photographs and drawings, sampled during the sorting exercises and a collection of reference samples.
The plankton was sub-sampled according to the number of organisms present. An aliquot of 60 individuals of each key species was regarded as an acceptable threshold level. Determination and counting were carried out in counting chambers with microscopes.

computer programs

The sorting and counting protocols are transferred into electronic storage via computer programs written in Visual Basic under Excel. Data are entered via separate queries for meso-, macrozooplankton and ichthyoplankton on the computer screen. From the numbers counted, the size of the sub-sample, the volume filtered - calculated from the current meter readings - the individuals * m-3 are calculated as the standard value.
Storage occurs in ASCII. Besides files for each day of sampling ASCII files are calculated for each variable representing a species, a developmental stage of a species, or a group of species, which can be based on counting in groups or on the calculation of sums of counted species.
Control programs warrant plausibility of data with respect to value limits, parameter names and double entrance.
Additional external information on weather, physical parameters, nutrients and phytoplankton is available as ASCII files in comparable format.
For the analysis of data programs are extracted according to analytic queries which then permits the graphic representation, the statistical calculation of number of values, mean and standard deviation is enabled through specific macro programs.
Further macros enable the comparison of current parameter values in with a 20years standard mean in visualisation and in ranking according to the variation of parameters, including the start of season, end of season, length of season on the basis of calculated annual cumulative sums.
The ASCII files are accessible for the application of further analytic programs.