Macrophyte meadows and beds

Compiled by: Dieter Boedeker, Germany

1. Description of the habitat

Macrophyte meadows and beds occur only in the photic zone. Because of the salinity gradient in the Baltic Sea area this biotope is highly variable with respect to its plant communities and ecological characteristics. It may be composed of vascular plants and/or macroalgae, respectively, and a depth zonation of the vegetation is always typical. Further marine and limnic macrophytes can be associated at the same spot, but the number of marine macroscopic algae decrease from more than 356 species in the Kattegat to less than 100 species in low saline (5-6 ppt) waters in the North (Bäck et al. 2002). The biotope provides a substrate for epiphytic species, micro-invertebrates, and a habitat for many other species, e.g. a sheltered nursery area for young fish. Characteristic macrophyte species include Fucus sp. and several charophytes. Seagrass beds dominated by Zostera sp. are not included in this biotope, they form a biotope on their own.

2. Distribution (past and present)

Macrophyte meadows and beds occur on soft and hard bottoms in the whole Baltic Sea area. Significant changes have been observed in distribution along depth gradient for characteristic species. For example, Fucus vesiculosus was recorded at 8-10 metres depth in the Tvärminne archipelago in the 1930s and the 1970s, but only at 5 metres in 1994. Some species also disappeared from areas where they had been observed before, like Chorda filum which probably disappeared from the inner Puck Bay and the Klif Red owski area in the mid 1970s (Bäck et al. 2002).

3. Importance (sub-regional, Baltic-wide, global)

Baltic macrophyte meadows and beds are considered to be of Baltic-wide importance in the HELCOM area.

4. Status of threat/decline

From a Baltic-wide perspective the exact status of threat and/or decline is not known, however the biotope is considered to be threatened and declining, because characteristic species have not been found as deep on the shore as before. Moreover, in some areas, like in the inner Puck Bay, Poland, it may be provisionally stated that the current number of taxa has decreased by about 50% in comparison with data from the 1885 -1905 period (Bäck et al. 2002).

5. Threat/decline factors

Mainly eutrophication, causing reduced light penetration, and growing filamentous algae mats which cover the macrophyte meadows and lead to their die off. Other threats include pollution and physical habitat destruc­tion like sand and gravel extraction.

6. Options for improvement

A Baltic wide biotope inventory and a threat assessment is needed, macrophyte meadows and beds should be considered as highly sensitive and therefore in high need of strongest protection. Eutrophication must be reduced significantly through further programmes and measures.

7. References

Bäck S, Kautsky H, Kruk-Dowgiallo L, Jurgilaite D 2002: Phytobenthos. In HELCOM 2002: Environment of the Baltic Sea 1994-1998. Baltic Sea Environ­ment Proceedings 82b, Helsinki Commission: 164-165:215.