Helgoland Roads summary
The Helgoland Roads time-series, located at the island of Helgoland in the German Bight, approximately 60 km off the German mainland (54°11'N 7°54'E), is one of the richest temporal marine datasets available. The time-series was initiated in 1962 at the Helgoland Roads site, which is located between the main island of Helgoland and a small sandy outcrop, the so-called 'dune'. The location near Helgoland is of particular interest because the site is essentially in a transitional zone between coastal and oceanic conditions, which is seen most clearly in the salinity patterns at Helgoland Roads. Initially, the sampling frequency was thrice weekly, but this was increased to daily in the early 1970s. Since then, the high sampling frequency has provided a unique opportunity to study long-term trends in abiotic and biotic parameters, but also ecological phenomena, such as seasonal interactions between different foodweb components, niche properties, and the dynamics and timing of the spring bloom (Grüner et al. 2011; Mieruch et al. 2010; Tian et al. 2008; Wiltshire et al. 2015; Wiltshire et al. 2010). The measured parameters comprise phytoplankton, temperature, salinity, and nutrient analyses. Inorganic nutrients. The taxon list now contains over 350 entities (with 230 distinct species). Both the phytoplankton and chemical dataseries are fully quality-controlled, based on original data sheets and metadata (Wiltshire and Dürselen, 2004; Raabe and Wiltshire, 2009). The phytoplankton time-series is augmented by the biological parameters zooplankton, rocky shore macroalgae, macro-zoobenthos, and bacteria, providing a unique opportunity to investigate longterm changes at an ecosystem scale. Some historic data sets are also available and have been archived in the online repository Pangaea, alongside all core phytoplankton and environmental data sets for Helgoland Roads (Kraberg et al. 2015).
Analyses by Wiltshire et al. (2010) have demonstrated the statistical significance of these changes, with temperature since 1962 amounting to 1.7°C (Wiltshire et al., 2010). In tandem with the increases in temperature and salinity, nutrient dynamics at Helgoland Roads have also changed considerably, with phosphate concentrations having declined significantly since 1962.
Long-term trends are also seen in the biota, with Diatoms in particular having exhibited an increase in abundance, with a concomitant increase in positive trend for total Dinoflagellates (see also (Wiltshire et al. 2008)). This was not a gradual change, but a rapid shift from negative to positive anomalies around 1998. The exact causes for this are still under investigation. Breaking this down to monthly trends, the swing seems to be largely driven by shifts in autumn and winter. There was also a significant shift in seasonal densities of individual Diatom species (Guinardia delicatula, Paralia sulcata) and in the numbers of large Diatoms (e.g. Cocinodiscus wailesii), which are difficult for copepods to graze. The large Diatom Mediopyxis helysia has recently been observed for the first time and now occurs almost throughout the year, with an intensive bloom in spring 2010 (Kraberg et al. 2012). Generally speaking, the spring Diatom bloom now appears to start later, if the preceding autumn was very warm (Wiltshire and Manly, 2004). It is worth noting that species introductions are also occurring in the zooplankton, with the ctenophore Mnemiopsis leidyi being the most obvious new species (Boersma et al. 2007).
References
Boersma M, Malzahn AM, Greve W, Javidpour J (2007) The first occurrence of the ctenophore Mnemiopsis leidyi in the North Sea Helgoland Marine Research
Grüner N, Gebühr C, Boersma M, Feudel U, Wiltshire KH, Freund JA (2011) Reconstructin g the realized niche of phytopankton species from environmental data: fitness versus abundance approach Limnology and Oceanography methods 9:432-442
Kraberg A, Carstens K, Tilly K, Wiltshire KH (2012) The diatom Mediopyxis helysia at Helgoland Roads: a success story? Helgoland Marine Research 66:463-468
Kraberg AC, Rodriguez N, Salewski CR (2015) Historical phytoplankton data from Helgoland Roads: Can they be linked to modern time series data? Journal of Sea Research 101:51-58
Mieruch S, Freund JA, Feudel U, Boersma M, Janisch S, Wiltshire KH (2010) A new method for describing phytoplankton blooms: Examples from Helgoland Journal of Marine Systems 79:36-43
Tian Y, Kidokoro H, Watanabe T, Iguchi N (2008) The late 1980s regime shift in the ecosystem of Tsushima warm current in the Japan/ East Sea: Evidence from historical data and possible mechanisms Progress in Oceanography 77:127-145
Wiltshire KH, Boersma M, Carstens K, Kraberg AC, Peters S, Scharfe M (2015) Control of phytoplankton in a shelf sea: Determination of the main drivers based on the Helgoland Roads Time Series Journal of Sea Research 105:42-52
Wiltshire KH et al. (2010) Helgoland Roads: 45 years of change in the North Sea Estuaries and Coasts DOI 10.1007/s12237-009-9228-y
Wiltshire KH et al. (2008) Resilience of North Sea phytoplankton spring bloom dynamics: An analysis of long-term data at Helgoland Roads Limnology and Oceanography 53:1294-1302
