MURSYS - North Sea





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MURSYS - North Sea

   
 
 

Biological Conditions in the German Exclusive Economical Zone of the North Sea in 2008 (Summary)

  Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
commissioned by
Bundesamtes für Seeschifffahrt und Hydrographie, Hamburg, Rostock
(Federal Maritime and Hydrographic Agency of Germany, Hamburg, Rostock)

(http://www.io-warnemuende.de/)

The original report is published in German with an English summary :
Wasmund, N., L. Postel, und M. Zettler (2009): Biologische Bedingungen in der deutschen ausschließlichen Wirtschaftszone der Nordsee im Jahre 2008. Meereswiss. Ber.,Warnemünde,79, 1-68. (link see below):

In 2008, a complex biological monitoring was conducted in the German exclusive economical zone of the North Sea for the first time, conducted by the Leibniz Institute of Baltic Sea Research Warnemünde (IOW) and commissioned and supported by the Federal Maritime and Hydrographic Agency (BSH). Phytoplankton (inclusive chlorophyll a), mesozooplankton and macrozoobenthos were investigated at 12 stations (Figure 1). The plankton was sampled at 5 cruises and the zoobenthos at 2 cruises.

The phytoplankton comprised 128 taxa, most of them belonging to the diatoms. The lowest diversity was found in February (20 taxa) and the highest in October (81 taxa). The 5 samples per year and station showed clear seasonal patterns, but did not allow discussions on phytoplankton succession. The highest phytoplankton biomass occurred in spring and summer. The maximum of chlorophyll a was 12.33 mg/m³ on 30.5.2008 at station BRIFF. A Phaeocystis-bloom with 17.3 Million cells/L was found in the same region, i.e. in front if the Isle of Borkum, on 2.4.2008. Sound information on the duration and magnitude of phytoplankton blooms is however not possible because of the low temporal coverage. The most important species in terms of biomass were Noctiluca scintillans, Rhizosolenia styliformis and Guinardia flaccida (Table 1).

The mesozooplankton was sampled by vertical WP-2 net tows (200 µm) over the entire water column. The successive sequence and the magnitude of the maximum abundance for different feeding types of calanoid copepods on the station closest to Helgoland Island corresponded to the local long-term average, which is a positive sign for data quality.

A total of 113 taxa of twelve phyla and a subphylum were noted. Those were about three times more than have been identified in the open Baltic Sea between the Belt Sea and the central Gotland Sea in 2008. The greatest variety was observed in the group of Crustaceans which covered 58 taxa. The twelve phyla and the subphylum Crustacea were present throughout the year except for the Nemertea and Platyhelminthes which were restricted to early spring or summer respectively, due to their temporal reproduction patterns.

Spatial patterns of species were closely related to estuarine properties. With increasing distance from river mouths (Elbe, Weser), initially the number of species decreased to a minimum. In the direction to the open North Sea, the number of species increased again, in August. Thereby the proportion of euryhaline taxa decreased, e.g. the genus Acartia. Conversely, the proportion of marine representatives increased, as of Para-/Pseudocalanus and Oithona.

The Elbe River plume was characterized by low salinity and high chlorophyll a-concentrations. It was northward oriented, while the zooplankton abundance maximum was found west of Helgoland. This suggests that there was no successive relationship between both. Zooplankton seemed to originate from more westerly regions. This was underlined by the appearance of the Mediterranean species Penilia arivirostris in this zone. Finally, adult calanoid copepods Acartia species were numerically the most ubiquitous, as in the Baltic Sea. The total maximum of adult calanoids of approximately 20,000  ind./m³ remained below the 25 - 30 thousand ind./m³ in the Baltic Sea. Consequently, the trophic stage of the Baltic Sea was slightly higher than that of the North Sea.

The macrozoobenthos was sampled during spring and autumn 2008. In both sampling campaigns altogether 218 species were recorded. Between the stations the species number varied from 23 (off Amrum) to 65 (northwestern German Bight). With 82 species (both campaigns added) the station at the Dogger Bank was most diverse. Whereas the shallower and exposed areas off Amrum and Sylt were settled with low individual numbers (in maximum 200 ind./m²), in the deeper parts higher abundances were observed. Maximum values of 3000 to 4000 ind./m² could be found at stations southwest of the White Bank and in the central German Bight. Partially the dominant species at stations varied significantly. Species with major percentage of the total abundance at the distinct stations were the bivalves Corbula gibba and Nucula nitidosa, the polychaetes Lanice conchilega, Owenia fusiformis, Nephtys caeca and Magelona mirabilis, the amphipod Bathyporeia elegans, the phoronid Phoronis sp. and the ophiurid Amphiura filiformis.

The ash free dry weight at stations ranged from 1.82 g/m² west of the White Bank in spring and 20.77 g/m² north of Borkum. Biomass dominated groups and species at the sampled stations were very different. Bivalves (Ensis directus), sea urchins (Echinocardium cordatum) and polychaetes (Lanice conchilega, Nephtys caeca and Nephtys hombergii) showed the highest biomasses at the distinct stations. The monitoring stations represent five of the eight known benthic communities of the German part of the North Sea.

34 species from the Red List (RACHOR 1998) could be observed during this study. The decapod Upogepia stellata belongs to the category 1 (critical endangered) and 4 species to the category 3 (vulnerable).

Figure 1: The stations of biological monitoring in the German Exclusive Economical Zone of the North Sea, GIF-Graphik: 14 KB

Figure 1: The stations of biological monitoring in the German Exclusive Economical Zone of the North Sea

Tabelle 1, PDF-Datei, 117  kB

Table 1: The 10 most abundant phytoplankton taxa (percentage of total phytoplankton biomass) in the upper 10 m during the cruises from March/April, May, August and November 2008.
The mean phytoplankton biomass (in µg/L) is given on the top of each block. Unspecific taxa ("Unidentified", "Dinophyceae", "Gymnodiniales", "Peridiniales", "Centrales", "Pennales") were disregarded in the list if they accounted for less than 10 %.

The complete report with an English summary can be found on the Internet:
(http://www.io-warnemuende.de/tl_files/forschung/meereswissenschaftliche-berichte/mebe79_2010-zustand-bio-nordsee.pdf)

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