Sewage, green algal mats anchored by lugworms, and the effects on Turbellaria and small Polychaeta

Abstract

On sandy tidal fiats at the Island of Sylt (North Sea) ephemeral mats of green algae covered wide areas in the vicinity of sewage outflows. Algae became anchored in the feeding funnels of lugworms (Arenicola marina] and thus were able to resist dispIacement by tidal currents.Below the algal mats anoxic conditions extend to the sediment surface. After about one month a rough sea removed all algae. Polychaetes endured this short-term environmental deterioration, while the more sensitive Turbeilaria decreased in abundance and species richness. Diatom-feeders were affected most, predators to a medium extent, and bacteria-feeders the least affected. Rare and very abundant species were more affected than moderately abundant ones. None of the turbellarian species increased in abundance and none colonized the algal mats above the sediment. In a semicontrolled experiment with daily hand-removal of drift algae from a 100-m 2 plot within an extensive field of algal mats, this deaned "'island" served as a refuge to Turbellaria escaping from their algal covered habitat. Here abundance doubled relative to initial conditions and was 5-times higher than below algal mats.

Macroalgal mass development in the Wadden Sea: First experiences with a monitoring system

“…In the Niedersachsen Wadden Sea, like in many other places investigated (Perkins & Abbott, 1972;Nicholls et al, 1981;Reise, 1983), the bottom fauna under thick algal carpets undergoes a fast succession, coincident to the detailed description given by Pearson & Rosenberg (1978) for macrobenthic response to organic pollution. Mass mortality of bivalves is the most obvious effect, but polychaetes and meiofauna besides suffer from oxygen deficiency and toxic hydrogensulfide in the sediment.…”

“…However, they already indicated early symptoms of a possible increase caused by the rising nutrient load. Also Michaelis (1978) related gigantic growth which he found in thalli of Ulva, Enteromorpha and Porphyra spp., to eutrophication; and Reise (1983), in 1979 observed an increasing abundance of green algae in Schleswig-Holstein. During benthic surveys in the 1980s, this increase also became obvious in Niedersachsen (Michaelis et al, unpubl.…”

Historical changes in the benthos of the Wadden Sea around the island of Sylt in the North Sea

“…In August, these algae were no longer apparent. With respect to green algae, the situation has changed dramatically since 1979 (Reise, 1983). Explosive growth of Enteromorpha slop.…”

“…Another muddy area was completely covered by a green algal mat in 1988. This was detrimental to the fauna underneath (see Reise, 1983). …”

“…Extensive green algal mats in the vicinity of sewage outlets have been reported from several shores since the 1970s (i.e. Perkins & Abbott, 1972;Wharfe, 1977;Nicholls et al, 1981), and it was described for K6nigshafen by Reise (1983).…”