Monitoring of macro algae and blue mussels stocks in the Eastern Baltic

Abstract

The Latvian coastal zone in the South-Eastern Baltic is a very important part of the Baltic Sea. The environmental conflict is observed in this area. On the one hand this area is under high level of contamination and sedimentation, on the other hand biocenoses which occur most frequently and basic herring spawning grounds are situated there. Blue mussels (Mytilus edulis) and marine red algae (Furcellaria lumbricalis) are the basic species-indicators for the coastal area of Latvia and Lithuania. Blue mussels are a filtrator, Furcellaria is the oxygen producer, an organic and mineral substance user, therefore these biocenoses exhibit high biofiltration and biosedimentation ability and thereby cooperate in the water self purification processes. Furcellaria is the best natural substratum for herring spawn. Furthermore, the algae are valuable raw material for agar-agar production. Different researchers investigated the distribution and abundance of Furcellaria at the Lithuanian and Latvian coast from 1955 to the present day. Investigations of herring spawning grounds, distribution and abundance of Furcellaria and Mytilus edulis were the main part of benthic biocenoses monitoring which was annually carried out by the Latvian Fisheries Research Institute in 1980-1990 from Klaipeda to Ventspils and episodically in 1998-2003 in the Latvian coastal zone. The values on Furcellaria biomass for 1928-1938 were reconstructed basing on the data of the algae discharges on a shore in that period and the total biomass of Furcellaria was estimated at the level of about 200 thousand tones. The high level of Furcellaria stock in the Latvian coastal zone in 1928-1938 indicates good environmental quality of coastal waters. The extreme decreasing of algae biomass was observed after two large oil accidents near the coast (tankers “Antonio Gramshi” near Ventspils in1979 and “Globe Asime” near Klaipeda in 1981). In the result of the accidents environmental conditions changed for the worse and the habitat of Furcellaria strongly diminished. Our observations in 1998, 1999 and 2003 showed some relative restoration of Furcellaria stock as compared with 1990. Blue mussel distribution and biomass changed inconsiderably during 1980-1998. However, after dumping of dragging sand near the Liepaja port (2001) total biomass of blue mussels decreased about 2 times as compared with previous estimations. The observations and sampling of macrobenthos were carried out using underwater photography, a TV system and SCUBA diving. Surfer Mapping System was used to mapping of Furcellaria and Blue mussels.