Baltic Sea Portal

Sonja Salovius-Laurén / ÅA

Academic dissertation by Sonja Salovius-Laurén in Marine Biology was presented in Åbo Akademi University on May 15th 2004.

Salovius-Laurén, Sonja (2004). Drifting and attached macroalgae:distribution, degradation and utility for macroinvertebrates. PhD-thesis, Dept. of Biology/ Environmental and Marine Biology, Åbo Akademi University, p. 36.

Enhanced nutrient loads to coastal ecosystems have, among other things, resulted in increased growth of opportunistic fast growing algal species. In the northern Baltic Sea, filamentous algae partly outcompete perennial canopy forming algae, and dominate on the rocky shores. As the filamentous algae detach, they either get washed up on the shores, or accumulate at the sea bottom where underlying sediments become anoxic during algal decay. Changes in the dominant algal communities due to eutrophication likely affect associated macroinvertebrates and littoral food webs, and this work aims to predict some consequences of coastal eutrophication.

I have studied ecological impacts of filamentous algae over time and in space in the Archipelago Sea, SW Finland. Results show that growing attached and drifting filamentous Cladophora glomerata, form important habitats for macrofauna and that C. glomerata in summer along the littoral zone, host more macroinvertebrate species with a higher abundance than the canopy alga Fucus vesiculosus per m² of algal cover. As the filamentous algae drift to adjacent areas they are useful habitats for macroinvertebrates occurring in the water column. These animals rapidly enter the drifting algae to escape predators, to find food, shelter or a suitable habitat. Drifting algal material, which accumulate at the sea bottom is also rapidly inhabited by littoral and benthic macroinvertebrates and algal patches small enough not to cause severe hypoxia during degradation serve as important habitats and food sources.

In late autumn, large biomasses of algal material accumulate at deep bottoms causing anoxia over vast areas. During algal degradation at the deeper bottom areas, high water temperatures and the presence of sediments enhance the degradation rates, which seem to be controlled mainly by microbial activity.

Nutrient enrichment in the Archipelago Sea has changed the algal composition, but convincing evidence that macroinvertebrate communities associated with the littoral rocky shore macroalgae are negatively affected has not been found. The macrofauna is tolerant and adaptive, and considerable changes in the littoral ecosystem may occur before the fauna becomes threatened. If this happens a dramatic decline in biodiversity and ecosystem function is to be expected.

Further information
Sonja Salovius-Laurén
Dept. of Biology/ Environmental and Marine Biology
Åbo Akademi University
Akademigatan 1
FIN-20500 Åbo
Finland
e-mail: sonja.salovius@abo.fi