Influence of the Thin Drift Algal Mats on the Distribution of Macrozoobenthos in Kõiguste Bay, NE Baltic Sea

Abstract

Macrozoobenthic communities within and outside of the drift algal mats were compared in Ko˜iguste Bay, NE Baltic Sea. The patches of the drift algae were on average 0.5-1 km wide in diameter covering about 25% of the total bottom area of the bay. Thickness of the mat did not exceed 6 cm. The biomass of the mat varied between 35 and 1391 g dw m )2 . The drift algal mats had no clear negative effect on macrozoobenthos except for a few infaunal species. The drift algae favoured several detrivorous, herbivorous and carnivorous species. Among the studied variables, the thickness of algal mat and oxygen concentration at near-bottom layer explained the best the structure of macrozoobenthos. Total number of invertebrate species increased curvilinearly with the thickness of algal mat having the peak value at 3-5 cm thick algal mat. To conclude, moderate drift algal mats increased habitat complexity and, thus, the diversity of benthic faunal assemblages in otherwise poorly vegetated coastal areas.

Seasonal variability in the grazing potential of the invasive amphipod Gammarus tigrinus and the native amphipod Gammarus salinus (Amphipoda: Crustacea) in the northern Baltic Sea

“…Consequently, the recent blooms of P. littoralis are expected to induce a shift from G. salinus dominated communities to G. tigrinus dominated communities in the coastal range of the northern Baltic Sea. This is also consistent with the field data of increasing biomass shares of P. littoralis and G. tigrinus in recent years (Lauringson and Kotta 2006;Herkül and Kotta 2007).…”

“…However, this figure actually reflects a strong negative effect of G. tigrinus on G. salinus within P. littoralis. Following the increasing eutrophication the biomass of ephemeral algae especially P. littoralis have increased tremendously in the last decades and currently P. littoralis prevails in the northern Baltic Sea (Rönnberg et al 1992;Karez et al 2000;Kotta et al 2000;Lauringson and Kotta 2006). In concurrent with filamentous algal blooms the diversity of macroalgal species has significantly declined (Rönn-berg et al 1992;Kotta et al 2006).…”

“…The prevailing depths are between 1 and 4 m. The area is influenced by a diffuse nutrient load from the moderately eutrophicated Gulf of Riga (Astok et al 1999). The benthic vegetation is well developed and extensive proliferation of ephemeral macroalgae and the appearance of drift algal mats have been reported from the area in the recent years (Paalme et al 2004;Lauringson and Kotta 2006).…”

Temperature-dependent adverse effects of drifting macroalgae on the survival of Manila clams in a eutrophic coastal lagoon

“…Macroalgal mats have been acknowledged as a factor inducing widespread mortality in organisms of limited mobility, such as infaunal bivalve species (Petersen et al 1994, Norkko et al 2000, Marsden & Bressington 2009. The most destructive factor connected to algal mats is hypoxia or anoxia, often accompanied by the release of sulfide from sediments (Lavery & McComb 1991, Krause-Jensen et al 1999, Lauringson & Kotta 2006. In the experiments, the macroalgal presence at the summer temperatures (mean±SE: 29.0±0.73°C, n=168) also caused highly reducing conditions and lowered pH in bottom waters, suggesting an accumulation of reduced substances beneath the algal mats.…”

“…We emphasize the importance of drifting macroalgae on inducing bottom water hypoxia and resultant Manila clam mortality in this study. Although the process is important in certain shallow and stagnant water bodies (Hauxwell & Valiela 2004, Lauringson & Kotta 2006, it may be less important in deeper or higher energy shallow systems. In deeper waters, stratification-induced hypoxia is important because the macroalgae most frequently occur above the halocline on euphotic shallow bottoms (Norkko & Bondsdorf 1996a).…”