01A1
Black mussels and/or barnacle communities on mediolittoral rocks
Relationships with habitat classifications. EUNIS: A1.11 Mytilus edulis and/or barnacle communities; Pal. class.: 11.29 Rocky shore littoral Mytilus edulis communities, 11.291 Mediolittoral fringe rocks; HD 92/43: 1170 Reefs.
Conservation status. BDA, HD.
Category. Vulnerable [VU – A1, 2 D2 E2 G1 H1].
General characteristics. The habitat occurs in the mediolittoral (surf zone) of the Black Sea coast on monolithic rocky sea beds, rock blocks or stones. Its upper border is marked by the so called lichen zone of the rocks – rocks covered by the black lichen Verrucaria maura – and it can be considered that its lower border occurs at 0,5–1 m depth. The strength of the waves is among the most important physical factors of the environment that have impact on the communities living on the mediolittoral rocks. The shores subjected to strong waves are inhabited by communities dominated by the black mussel Mytilus galloprovincialis and the barnacles Balanus improvisus, Balanus eburneus and Chthamalus stellatus. They grow on both mussel shells and the clear rock surfaces. The three barnacle species are alien to the Black Sea. The Balanus species were introduced in Bulgaria at the end of the 19th century by ships, probably from the Atlantic coast of North America whose hulls were covered by them. At the same time, it is accepted that Chthamalus stellatus expanded its area of distribution from the Sea of Marmora to the Black Sea. Of all three barnacle species only B. improvisus is invasive and covers the bottom of underwater installations and ships. The other two species are rare; the latter is typical for the southern part of the Black Sea coast. Chthamalus stellatus can endure relatively long drought as a result of which it accumulates above the Mytilus layer in the direction to the supralittoral. The green algae Enteromorpha intestinalis and Ulva rigida occur on the rocky beaches subjected to weaker waves. They attach to the shells of the black mussels or the rocks themselves. These species are abundant in places with organic pollution. Strong winter storms can cause the removal of the community of Mytilus and Balanus. Periodically, the strong winter storms can cause the removal of the parts of the community of black mussels and barnackles.
Characteristic taxa.
- Plants: Algae – Rodophyta: Bangia atropurpurea, Corallina officinalis, Dermatolithon litorale, Porphyra leucisticta; Phaeophyta: Padina pavonica (only in clean waters), Scytosiphon simplicissimus; Chlorophyta: Bryopsis plumosa, Cladophora spp.
- Animals: Anthozoa: Actinia equina;Polyplacophora: Lepidochitona cinerea;Gastropoda: Patella ulyssiponensis, Melarhaphe neritoides;Crustacea: Idotea baltica basteri, Eriphia verrucosa, Pachygrapsus marmoratus.
Distribution in Bulgaria. Along the whole Bulgarian Black Sea coast, in the surf area, at 0–1m alt.
Conservation importance. Species included in the Red Data Book of the Black Sea (1999) are: Eriphia verrucosa, Pachygrapsus marmoratus, Patella ulyssiponensis. The critically endangered species Monachus monachus that is included in the IUCN Red List (2004) was recorded in the past.
Threats. The habitat is on the border between land and sea and hence is very vulnerable to anthropogenic activities on the land, especially in the coastal area. Among the major threats are the pollution from agriculture, household, industry and tourism which cause eutrophication of the coastal waters and rapid development of green algae that replace the black mussels. The insufficient capacity of the existing purification stations cannot provide for adequate cleaning of the increased quantity of the waste waters during the intensive tourism season. Fuel pollution and fuel spills are typical for the port areas. Potential threat is the invasion of alien species but also exploitation of certain species (e.g. Eriphia verrucosa).
Conservation measures taken. The habitat is included in Annex 1 of the Bulgarian Biodiversity Act. Some of its localities are within sites of the European Ecological Network NATURA 2000 in Bulgaria.
Conservation measures needed. Establishment of a network of marine sites that ensures connectivity among the separate parts of the habitat; elaboration and implementation of management plans for the already existing protected marine sites; investigation of the changes of the area of distribution and fragmentation of the habitat; observations on the state, composition and structure of the living communities; periodical assessment of the conservation status of the characteristic taxa according to the contemporary IUCN criteria and categories.
References. Dimitrova-Konaklieva 2000; Marinov 1990; Palazov & Stanchev 2006.
Author: Valentina Todorova
