10A4

A. Marine habitats

Sublittoral sands

Relationships with habitat classifications. EUNIS: A5.2 Sublittoral sands; Pal. Class.: 11.22 Sublittoral soft sea beds; HD 92/43: 1110 Sandbanks which are slightly covered by sea water all the time, 1160 Large shallow inlets and bays.

Conservation status. BDA, BC, HD.

Category. Nearly Threatened [NT – A1, 2 D1 F1 I L2].

General characteristics. The sand sediments are distributed in the infra-littoral zone (0,5–15 m) along the accumulative coast or in specific shapes – sand banks at deeper levels (15–25 m) in the circumlittoral. Due to the fact that the habitat is with small depth it is often subjected to the wave impact; as a result the quantity of the mud can be as much as 15%. The hydrodynamic regime, the sediment composition and depth determine the characteristics of the community that inhabits the sandy sublittoral. In places not subjected to waves (down to 4–5 m depth) sea grasses can be found on the fine sand: Zostera spp., Potamogeton spp. and Zannichellia spp. They are overgrown by epiphytic green and red algae. Often there are no macrophytes on the sandy bottom and the community consists only of the representatives of the substrate fauna – polychaetes, mussels, snails, crustaceans, etc. The infralittoral, large-grained sand is inhabited by the mussel Donax trunculus. At a deeper level the large-grained sand is inhabited by the community of Modiolus adriaticus, Aonides paucibranchiata and Gouldia minima. The circumlittoral sands mixed with shells are inhabited by the polychaetes Branchiostoma lanceolatum, Protodorvillea kefersteini and Ophelia limacina. The assemblage of Chamelea gallina, Lentidium mediterraneum and Divaricella divaricata is typical for the fine sands in shallow waters. The interstitial fauna is represented by psammophytic polychaetes such as Microphthalmus fragilis, M. similis, Protodrilus flavocapitatus, Polygordius neapolitanus, Magelona papillicornis,and M. rosea. Another polychaete worm typical for the infralittoral fine and muddy sands is Arenicola marina, which creates J- or U-shaped burrows in the sediment. The permanent establishment of the alien mussels Mya arenaria and Anadara inaequivalvis and the snail Rapana venosahave caused permanent changes in the habitat of the fine and muddy sands. Mya arenaria, registered for the first time on the Bulgarian coast in 1972, is a species of great ecological plasticity and high tolerance to pollution and hypoxia. All this, combined with its high reproductive capacity and quick growth, makes it an aggressive invasive competitor of the autochthonous mussel species for the existing resources of the environment. Its populations have high numerical strength. The maximum value registered reaches 4862 individuals/m2. Anadara iaequivalvis was established in Varna bay in 1982 for the first time. Most probably it is the oldest population in the Black Sea. The species is moderately invasive and is a competitor of the local malacofauna. Rapana venosa, registered for the first time in Bulgaria in 1956, occupies a free ecological niche as an active carnivore on all bivalve species. It is ecologically plastic, has no competitors and is a strongly invasive species in the Black Sea coast thus having negative impact on the mussel populations.

Characteristic taxa.

Distribution in Bulgaria. Black Sea coast, the sandy bed, at 0,5–25 m depth.

Conservation importance. Many species of national and international conservation importance occur in this habitat: Acipenser stellatus, Branchiostoma lanceolatum,Callionymus risso, Carcinus aestuarii, Chelidonichthys lucernus, Diplodus annularis, Mesogobius batrachocephalus, Mullus barbatus, Nerophis ophidion, Pegusa lascaris, Raja clavata,Sciaena umbra, Squalus acanthia, Trachinus draco,Upogebia pusilla, Uranoscopus scaber, Zostera marina, Z. noltii.

Threats. Existing threats are industrial and chemical pollution and deposition of solid waste on the sea bottom. Potential threat are the anthropogenic activities related to sand extraction from sand banks and the change in the hydrological conditions as a result of building embankments, breakwaters that influence the direction of the sediment transport, etc. A serious threat to the biodiversity is the intensive fishing and especially the illegal bottom trawling for turbot. The latter destroys the structure of the bottom communities. The sub-littoral sands are inhabited by the invasive bivalve Mya arenaria which competes with and replaces the local molluscs. Rapana venosa, feeds on various bivalve species from this habitat and has impact on the structure of the community.

Conservation measures taken. The habitat is included in Annex №1 of the national Biodiversity Act. Trawling is prohibited by the Law on fishing and aquaculture. Parts of the habitat are included in Pyasachna Banka Koketrais Protected Site and Kaliakra Strict Nature Reserve. The habitat is included in a site of the European Ecological Betwork 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, including this habitat; definition of quotas for the turbot fishing, control on the fishing intensity, and strict control on the use of forbidden fishing devices (bottom trawls); investigation on the changes of the state, composition and structure of the living communities; periodic assessment of the conservation status of the characteristic taxa according to the contemporary IUCN criteria and categories.

References. Georgiev 1964; Kaneva-Abadzhieva & Marinov 1984; Kaneva-Abadzhieva 1958, 1974; Konsulova & Tokmakov 1995; Marinov et al. 1982, 1983; Panayotova et al. 2006; Tsvetkov & Marinov 1986; Zolotarev et al. 1996.

Authors: Valentina Todorova, Marina Panayotova


Sublittoral sands (distribution map)