Helgoland Roads Phytoplankton time series

The Helgoland Roads time series is one of the richest temporal marine data sets available. It includes daily surface water sampling from 1962 until present, resulting in a pelagic data set comprised of phytoplankton, salinity, Secchi and nutrient analyses. The pelagic time series are augmented by the biological parameters such as zooplankton, rocky shore macroalgae, macro-zoobenthos and bacteria. Until recently it was quite difficult to interpret the Helgoland long term data. This was due to a lack of meta-information and quality control which has now been rectified. These data sets are presented and examples of the major changes from bacteria, phytoplankton through to macro-benthos at Helgoland are given. The hydrographic environment around Helgoland is analysed and shown to have changed considerably. With changes in currents, in the late 1970's, water inflows from the southwest to the German Bight increased and corresponding flushing rates increased by nearly 30%. These conditions prevailed for 15 years. The salinity at Helgoland Roads shows an increase from 1962 to the present. The annual mean temperature in the surface water at Helgoland Roads has risen significantly by a mean value of 1,67oC since 1962. We show that temperature has influenced the seasonal growth of phytoplankton, i.e. the number of "growth" days for phytoplankton have extended significantly. There was a significant shift in diatom densities and in the numbers of large diatoms (eg. Guinardia delicatula and Coscinodiscus wailesii) which are difficult for copepods to graze. Large shifts in zooplankton diversity were observed with the input of Mnemiopsis leidyi being the most obvious new species. Losses and additions to the macroalgal flora were identified for the last 100 years, but macroalgal species richness has not changed. The number of green algal species has increased and the number of brown algal species has decreased after 1959.More than 30 macrofaunal species have been newly recorded at Helgoland Roads over the last 20 years. There has been a distinct shift in benthic animals towards southern species and an increase in local species diversity. From the data on the seasonality of bacteria through to investigations into changes in macrofauna, we provide the basis for long term analyses of changes on many trophic levels at Helgoland Roads.