Reefs

Compiled by Dieter Boedeker, Germany

 

1. European Union's Natural Marine Habitat types definitions: 1170 Reefs

PAL.CLASS.: 11.24, 11.25

 

1.1. Description of the habitat

Reefs can be either biogenic concretions or of geogenic origin. They are hard compact substrata on solid and soft bottoms, which arise from the sea floor in the sublittoral and littoral zone. Reefs may support a zonation of benthic communities of algae and animal species as well as concretions and corallogenic concretions.

Clarifications:

• "Hard compact substrata” are: rocks (including soft rock, e.g. chalk), boulders and cobbles (generally >64 mm in diameter).
• “Biogenic concretions” are defined as: concretions, encrustations, corallogenic concretions and bivalve mussel beds originating from dead or living animals, i.e. biogenic hard bottoms which supply habitats for epibiotic species.
• “Geogenic origin” means: reefs formed by non biogenic substrata.
• “Arise from the sea floor" means: the reef is topographically distinct from the surrounding seafloor.
• "Sublittoral and littoral zone” means: the reefs may extend from the sublittoral uninterrupted into the intertidal (littoral) zone or may only occur in the sublittoral zone, including deep water areas such as the bathyal.
• Such hard substrata that are covered by a thin and mobile veneer of sediment are classed as reefs if the associated biota are dependent on the hard substratum rather than the overlying sediment.
• Where an uninterrupted zonation of sublittoral and littoral communities exist, the integrity of the ecological unit should be respected in the selection of sites.
• A variety of subtidal topographic features are included in this habitat complex such as: Hydrothermal vent habitats, sea mounts, vertical rock walls, horizontal ledges, overhangs, pinnacles, gullies, ridges, sloping or flat bed rock, broken rock and boulder and cobble fields.

1.2. Examples for typical reef species

Reef vegetation: A large variety of red, brown and green algae (some living on the leaves of other algae).

Examples for typical reef animals: animals forming biogenic reefs: Bivalves (e.g. Modiolus modiolus, Mytilus sp., Dreissena polymorpha); other animals: Distribution and abundance of invertebrate species settling on hard substrates are limited by the salinity gradient from west to east. Typical groups are: hydroids, ascidians, cirripedia (barnacles), bryozoans and molluscs as well as diverse mobile species of crustaceans and fish.

1.3. Corresponding categories:

German classification: “Benthal der Ostsee mit Hartsubstrat (020204)“, “Riffe der Ostsee (020204a)“, „Benthal der Flachwasserzone der Ostsee mit Hartsubstrat, makrophytenarm (040204)“, „Benthal der Flachwasserzone der Ostsee mit Kies- und Hartsubstrat, makrophytenreich (040206)“, „Miesmuschelbank des Sublitorals der Ostsee (040207)“, „Vegetationsreiches Windwatt mit Hartsubstrat (060203) (Ostsee)“.

EUNIS classification: Relevant types within “A1.1, A1.1/B-ELR.MB, A1.2, A1.2/B-MLR.MF, A1.3, A1.3/B-SLR, A1.4, A1.5, A1.6, A2.8, A3.1, A3.2, A3.2/M-III.6.1.(p), A3.2/H-02.01.01.02.03, A3.2/H-02.01.02.02.03, A3.3, A3.4, A3.5, A3.6, A3.6/B-MCR.M, A3.7, A3.8, A3.9, A3.A, A3.B, A3.C, A4.6, A5.1, A5.6”, A6.2, A6.3.

HELCOM classification: “Sublittoral soft rock reefs of the photic zone with little or no macrophyte vegetation (2.1.1.2.3)”, “Hydrolittoral soft rock reefs with or without macrophyte vegetation (2.1.1.3.3)”, “Sublittoral solid rock reefs of the photic zone with or without macrophyte vegetation (2.1.2.2.3)”, “Hydrolittoral solid rock reefs with or without macrophyte vegetation (2.1.2.3.3)”, “Sublittoral stony reefs of the photic zone with or without macrophyte vegetation (2.2.2.3)”, “Stony reefs of the hydrolittoral zone with or without macrophyte vegetation (2.2.3.3)”.

Nordic classification (Kustbiotoper i Norden, Nordiska Ministerrådet 2001): ”Klippbottnar (7.7.1.3; 7.7.2.3; 7.7.3.3; 7.7.4.3; 7.7.5.3; 7.8.1.3; 7.8.2.3; 7.8.3.4; 7.8.4.3; 7.8.5.3; 7.8.6.13; 7.8.7.16)”, ”Sublittorale samfund på sten- och klippebund (7.9.1.2)”, ”Sublittorale samfund på stenbund (7.9.2.2; 7.9.3.2)”.

1.4. Associated habitats:

Reefs can be found in association with “vegetated sea cliffs” (habitats 1230, 1240 and 1250) ”sandbanks which are covered by sea water all the time” (1110) and “sea caves” (habitat 8830). Reefs may also be a component part of habitat 1130 “estuaries” and habitat 1160 “large shallow inlets and bays”.

1.5. References

Borja, A., Aguirrezabalaga, F., Martinez, J., Sola, J.C., Garciaarberas, L., & Gorostiaga (2003). Benthic communities, biogeography and resources management. In: Borja, A. & Collins, M. (Ed.). Ocenaography and Marine Environment of the Basque Country, Elsevier Oceanography Series n. 70: 27-50.

European Environment Agency (2002). EUNIS habitat classification. Version 2.3. Copenhagen, EEA (Internet publication: http://mrw.wallonie.be/dgrne/sibw/EUNIS/home.html). HELCOM (1998). Red List of Biotopes and Biotope Complexes of the Baltic Sea, the Belt Sea and theKattegat. Baltic Sea Environment Proceedings No. 75.: 126pp.

Holt, T.J., Rees, E.I., Hawkins, S.J. & Seed, R. (1998). Biogenic Reefs (volume IX). An overview of dynamic and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Science (UK Marine SACs Project), 170 pp. (www.ukmarinesac.org.uk/biogenicreefs.htm).

Kautsky, N. (1974). Quantitative investigations of the red algae belt in the Askö area, Northern Baltic proper. Contrib. Askö Lab. Univ. Stockholm 3: 1-29.

Nordiska Ministerrådet (2001). Kustbiotoper i Norden. Hotade och representativa biotoper. TemaNord 2001: 536. 345 pp.

Ravanko, O. (1968). Macroscopic green, brown and red algae in the south-western archipelago of Finland. Acta Bot. Fennica 79: 1-50.

Riecken, U., Ries, U. & Ssymank, A. (1994). Rote Liste der gefährdeten Biotoptypen der Bundesrepublik Deutschland - Schriftenreihe für Landschaftspflege und Naturschutz. 41: 184 pp.

 

2. Additional HELCOM information

2.1 Description of the habitat

Reefs are ridges of solid rock or accumulations of coarse mineral substrata protruding above the level bottoms and found entirely below or extending partly above the surface of the water (HELCOM, 1998). Further, compact sessile mussel beds of the hydrolittoral and sublittoral are considered as reefs. Although the common mussel (Mytilus edulis) occurs throughout most of the Baltic Sea area, the horse mussel (Modiolus modiolus) is common in the Kattegat and the zebra mussel (Dreissena polymorpha) in coastal lagoons and estuaries. All of them form dense colonies and often create multi-layered beds on hard or soft substrata. They act as substratum themselves for other animals and macrophytes. The animal and plant communities of reefs vary with the salinity, light penetration and exposition to water motion.

2.2 Distribution

Reefs occur in all HELCOM sub-regions of the Baltic Sea area.

2.3 Importance (sub-regional, Baltic-wide, global)

Reefs are of Baltic-wide importance and are in many cases hot spots for the biodiversity. They provide shelter for many aquatic animals (fish, invertebrates), and they are important feeding grounds for birds. The benthic flora is often rich and may include threatened and/or declining plant species.  

2.4 Status of threat/decline

Human activities have caused various pressures on reefs which in some cases resulted in severe damages. The habitat type is under threat or decline mainly in the southern Baltic Sea area. According to the HELCOM Red List of Biotopes and Biotope Complexes (HELCOM, 1998) the Baltic-wide threat category for all reef sub-types is "Endangered".

2.5 Threat/decline factors

Human activities have caused various pressures. According to the HELCOM Red List of Biotopes and Biotope Complexes (HELCOM, 1998) they are caused by constructions, dumping of dredged material, eutrophication, pollution, fishing, mineral extraction (e.g. stonefishing) and military activities.

2.6 Options for improvement

The restoration of natural conditions where the habitat type was degraded due to e.g. bottom excavation would help to improve the conservation status of this natural habitat type. It is also essential to introduce ecologically sound fishing methods which do not harm the habitat. As for all natural habitat types, an inventory and a monitoring and assessment programme (also for human activities) is obligatory for EU Member States. They are further obliged to take all appropriate steps to avoid further deterioration. This includes the obligation to protect this natural habitat type within the Natura 2000 network, and thus to designate as many SACs as necessary to guarantee its favourable conservation status. Member States have to follow Article 6 (3) of the Habitats Directive: Plans and projects which are not directly connected with or necessary to the management of a Natura 2000 site but likely to have a significant effect thereon, either individually or in combination with other plans or projects, shall be subject to appropriate assessment of its implications.

2.7 References

European Commission (2007). Guidelines for the establishment of the Natura 2000 network in the marine environment. Application of the Habitats and Birds Directives. Appendix I: Marine Habitat types definitions. Update of “Interpretation Manual of European Union Habitats” (EU interpretation manual).

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.