Shell Gravel Bottoms

Compiled by: Dieter Boedeker, Germany

1. Description of the habitat

Sea bottoms consisting largely of mollusc shells or small shell fragments, often building small patches inside other sediments. Due to the large variety of interstitial space, inhabited by many species of often very specialised fauna ,e.g., of the lancelet Amphioxus. In offshore areas shell gravel bottoms are often exposed to currents and they are mainly found permanently at the same location, whereas in inner waters they can also shift dynamically from one location to another.   

(EUNIS classification A 5.113; A 5.144).

2. Distribution (past and present)

Shell gravel bottoms occur mainly in the southern and western parts of the Baltic Sea area, but are very rare. Nothing is known about their historical distribution.

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

The Baltic Sea area population is considered to be of Baltic-wide importance in the HELCOM area.

4. Status of threat/decline

From a Baltic-wide perspective the status of threat and/or decline is not exactly known, however the biotope is considered to be rare and only small in area, and therefore “potentially endangered”.  

5. Threat/decline factors

Eutrophication and pollution, bottom trawling, oil and gas exploration and exploitation, sand and gravel extraction, offshore installations.

6. Options for improvement

A Baltic-wide biotope inventory and a threat assessment is needed, for the time being shell gravel bottoms should be considered as highly sensitive and worthy of protection.

7. References

HELCOM (1998). Red List of Marine and Coastal Biotopes and Biotope Complexes of the Baltic Sea, Belt Sea and Kattegat - Including a comprehensive description and classification system for all Baltic Marine and Coastal Biotopes. HELCOM-Baltic Sea Environ­ment Proceedings 75, Helsinki Commission. 115 pp.