Dagmar Lackschewitz

Macrofauna on flood delta shoals in the Wadden Sea with an underground association between the lugworm Arenicola marina and the amphipod Urothoe poseidonis

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of Römö and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetesSpio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceansCumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m−2 of ind >1 mm) and biomass (12.9 g AFDW m−2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugwormArenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers ofUrothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately montly intervals revealed no apparent seasonality ofU. poseidonis abundance. Together with smallCapitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerousSpio martinensis andUrothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.

Das marine Ökosystem um Sylt unter veränderten Klimabedingungen

Bei einer Klimaerwarmung um 1,5 bis 2,5 °C wird der direkte Einfluss hoherer Wassertemperatur das biologische Artenspektrum im Sylter Gezeitenbereich nicht wesentlich verandern. Dies ergibt ein Vergleich mit Watten der franzosischen Atlantikkuste. Bedeutender sind voraussichtlich Auswirkungen hoherer Wasserstande und einer zunehmenden Hydrodynamik. Seegraswiesen und Muschelbanke werden dadurch im Wattbereich abnehmen. In Ufernahe werden schlickige von sandigen Watten verdrangt. Einer verstarkten Erosion an ungeschutzten Wattufern wird voraussichtlich mit weiteren Befestigungen begegnet. Dadurch werden naturliche Uferbiotope mit ihren charakteristischen Lebensgemeinschaften auf der Sylter Wattseite selten. Bei solchen Veranderungen nimmt der Erlebniswert der Watten ab und es leidet die Landschaftsasthetik. Dem konnte durch kunstliche Sedimentversorgung auf der Wattseite von Sylt entgegengewirkt werden. Der fur die Erholung attraktive Sylter Brandungsstrand ist durch eine auserst vielfaltige Fauna des Sandluckengefuges gekennzeichnet. Sie kann als Indikator fur eine hohe Qualitat des Badestrandes gelten. Nach Sandvorspulungen zum Ausgleich von Erosionsverlusten stellt sich diese Fauna schon nach drei Monaten weitgehend unverandert wieder ein. Die partielle Umwandlung von Erosionsstranden in Depositionsstrande durch eventuelle Baumasnahmen des Kustenschutzes wurde die Biodiversitat der Sandluckenfauna verringern.

Heading northward to Scandinavia: Undaria pinnatifida in the northern Wadden Sea

Abstract The kelp Undaria pinnatifida, native to East Asian shores, was unintentionally introduced with Pacific oysters into the Mediterranean in 1971. Intentional introduction from there to the French Atlantic coast 12 years later led to a gradual spread to the British Isles and the North Sea. Here, we report on the northernmost established population in continental Europe, and suggest a further spread into Scandinavian waters to be almost inevitable. In 2016, several thalli were found washed ashore at the eastern side of the island of Sylt in the northern Wadden Sea (German Bight, Eastern North Sea). Most specimens bore fertile sporophylls and thallus lengths of >1 m were common. In June 2017, 91 sporophytes were found attached to a mixed bed of Pacific oysters and native blue mussels, located just below low tide level in a moderately sheltered position. Mean thallus length was 0.2 m and the longest 0.7 m. Most had distinctive sporophylls and released spores in the laboratory. From sporophylls collected in the previous year, we successfully reared a new generation, demonstrating the kelp’s potential for further spread by natural means or human vectors.