Sea pens and burrowing megafauna communities

Compiled by: Mats Lindegarth, Sweden

 

1. Extract from OSPAR Case Reports:

Initial List of Threatened and/or Declining Species & Habitats in the OSPAR Maritime Area (OSPAR 2006)

OSPAR definition for habitat mapping

Plains of fine mud, at water depths ranging from 15-200 m or more, which are heavily bioturbated by burrowing megafauna with burrows and mounds typically forming a prominent feature of the sediment surface. The habitat may include conspicuous populations of seapens, typically Virgularia mirabilis and Pennatula phosphorea. The burrowing crustaceans present may include Nephrops norvegicus, Calocaris macandreae or Callianassa subterranea. In the deeper fiordic lochs which are protected by an entrance sill, the tall seapen Funiculina quadrangularis may also be present. The burrowing activity of megafauna creates a complex habitat, providing deep oxygen penetration.

 

2. Additional HELCOM information

2.1. Description of the habitat (EUNIS classification A 5.35; A 5.36)

The ‘Sea pens and burrowing megafauna’ communities are found in subtidal (>15 m) sedimentary habitats. In these areas water velocities are generally benign and the sediments are therefore ranging from muddy sands to clayey muds. These communities are defined by the presence of one or either of two groups of animals, sea pens (e.g. Pennatula phosphorea or Virgularia mirabilis) and/or burrowing decapod crustaceans (e.g. Nephrops norvegicus, Calocaris macandreae, Upogebia spp. and Callianassa spp.).

2.2. Distribution (past and present)

The species of sea pens and burrowing megafauna, which define these habitats, occur only in full marine conditions (e.g. salinity >30 psu). Therefore, within the HELCOM area, they are found only in the deeper parts of the Kattegat. Because sea pens are very vulnerable to fishing with mobile fishing gear, it is likely that the past distribution in this area has been more extensive than at present, in terms of area and quality. Similarly, the distribution of burrowing megafauna is likely to have been affected by fishing and occasional hypoxic conditions in the deeper parts of the Kattegat.

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

This habitat does not correspond to any category defined in the Habitats Directive Annex I classification. Areas associated with the offshore banks could be included within the category of “1110 (Sandbanks which are slightly covered by sea water all the time)” although this is more typically associated with sandier habitats. The Kattegat localities are considered to be of Baltic-wide importance in the HELCOM area.

2.4. Status of threat/decline

The defining species are long-lived, sensitive to disturbances and, in the case of Nephrops norvegicus, subject to commercial fishery. Although current assessments suggest that the Kattegat population of Nephrops norvegicus is exploited at sustainable levels, it is likely that the physical structure of the habitat is more affected. Therefore, the threats to these habitats from fishing and anoxic conditions are persisting. From a Baltic perspective the biotope is rare and must therefore be considered “potentially endangered”.

2.5. Threat/decline factors

In some cases sea pens are totally destroyed by bottom trawling. Anoxic conditions (probably due to eutrophication by organic enrichment) are also impacts to the habitat.

2.6. Options for improvement

Protection and possibly even recovery from mechanical impacts on the physical structure and species composition of these habitats can be achieved by protection of certain areas from bottom trawling. In a long-term perspective, impacts due to anoxia can be alleviated by reduced input of nutrients to the sea.

2.7. References

Fiskeriverket (2007). Fiskbestånd och miljö i hav och sötvatten: resurs- och miljööversikt 2007. ISSN 1652-5841.  166 pp.

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 Environ–ment Proceedings 75, Helsinki Commission. 115 pp.

Hughes, D.J. (1998).  Sea pens & burrowing megafauna (volume III).  An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Science (UK Marine SACs Project).   105 Pages (in Swedish).

Naturvårdsverket (2006).  Inventeringar av marina naturtyper på utsjöbankar. Rapport 5567. ISBN 91-620-5576-3. 69 pp.  Available at www.naturvardsverket.se (in Swedish).

Nordiska Ministerrådet (2001).  Kustbiotoper i Norden: hotade och representativa biotoper.  TemaNord 2001:536.  ISBN 92-893-0626-2.  pp.  345. (in Swedish).

OSPAR (2006). OSPAR Case Reports for the Initial List of Threatened and/or Declining Species and Habitats in the OSPAR Maritime Area. Publication no. 276, pp 144-147. (http://www.ospar.org/eng/html/welcome.html).