Draft online platform (Fact sheet)
1. Habitat type
code & name
AB.E1F Baltic aphotic shell gravel characterized by epibenthic chordates
Photo of habitat type
 Please upload 1 or 2 photos of the habitat type
 Photo description (describe habitat and location of the photo):
Photo is attached in the Habitat Definition.
Habitat definition
A description of the habitat’s distribution, characteristic native biota, abiotic features, key ecological
processes and interactions.
Subheaders are:
 Description
 Characteristic species
 European Vegetation Checklist alliances (only for terrestrial types)
 Indicators of quality
Habitat description
Baltic photic bottoms with at least 90% coverage of shell gravel. Epibenthic chordates cover at
least 10% of the seabed and more than other perennial attached erect groups. Substrate is
shell gravel and depth is below approximately 20 m. Most often encountered in high energy
exposure areas.
One sub-biotope can be identified; ‘Baltic photic shell gravel dominated by vase tunicate (Ciona
intestinalis) (AA.E1F1).The biotope occurs in areas where the bottom consists largely of mollusc
shells or small shell fragments, often constituting small patches inside other sediments. Due to
the combination of the extended interstitial space and the presence of biotic hard substrates, it
is inhabited by a unique combination of endobenthic and epibenthic species, such as the vase
tunicate (Ciona intestinalis). 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 (HELCOM Website).
In these habitats coverage of epibenthic chordates is at least 10% of the sea floor, of which
vase tunicate (Ciona intestinalis) often constitutes at least 50% of the biomass. The tunicates
might be overgrown by Ectocarpus spp. or Desmarestia spp. during summer in the photic zone.
1
C. intestinalis is an epibenthic filter feeder. It has no specific substrate preferences, but it has
been reported to occur abundantly especially on rocky substrates. The filter feeding of C.
intentinalis populations can greatly impact on phytoplankton abundance, making it as a key
species in habitats where it occurs abundantly (Petersen & Riisgård 1992). In Scandinavia, the
most of C. intestinalis populations are locally distributed in fjords and inlets (Petersen & Svane
2002). As an euryhaline marine species, the distribution of C. intentinalis is limited by salinity in
the Baltic Sea, where the outermost distribution limit lies at the Danish Straits and the Darss
Sill. The minimum salinity is 11 psu (Dybern, 1967). Depth is usually 2–25 m.
Ciona intestinalis can grow to nearly 30 cm in height, but grows seldom higher than 15 cm. In
the Baltic Sea the species is largely annual. After the larvae have settled on a suitable substrate,
the vase tunicate grows to a height of 4–5 cm during two summer months (Moen & Svensen
2008).
The biotope is known from German waters in the Baltic Sea, but may also occur in other areas
in the southwestern Baltic Sea where the vase tunicate (Ciona intestinalis) occurs. The biotope
may potentially occur in other areas with high salinity on shell gravel covered bottoms, but is
currently not known from other locations in the Baltic Sea.
Eutrophication causing oxygen depletion and increased siltation is the main threat of the
biotope. Bottom trawling also threaten the physical integrity of the biotope.
The predicted increase in atmospheric CO2 causing ocean acidification can be seen as a
potential future threat of the biotope, as the precise effect of the acidification is currently not
known. Ocean acidification may affect the shell gravel substrate severely. The natural
degradation process of the calcium-carbonate shells may accelerate if the water becomes more
acidic. Therefore the occurrence of the biotope may become more restricted in the future.
Pollution from various sources introducing hazardous substances to the Baltic Sea, as well as
construction activities such as offshore installations and sand or gravel extraction, pose
additional threats to the biotope. However these effects are assumed to be smaller than that
posed by eutrophication.
Characteristic species
Ciona intestinalis
Indicators of quality
-
Classification
Please indicate equivalent classification types as relevant, including:
 EUNIS type
2








Annex 1 type of the Habitats Directive
IUCN Habitats Classification Scheme
Emerald type
Marine Strategy Framework Directive type
EUSeaMap type
European Forest Type
MAES type (level 2)
Other types...
Annex 1 relationships
The relationship between HUB biotopes and Annex 1 habitats has not yet been mapped by
HELCOM.
MAES relationships
Marine - Marine inlets and transitional waters
Marine - Coastal
MSFD relationships
Shallow sublittoral coarse sediment
Shelf sublittoral coarse sediment
EUSeaMap relationships
Shallow coarse or mixed sediments
Shelf coarse or mixed sediments
IUCN ecosystem relationships
9.3 Subtidal Loose Rock/Pebble/Gravel
Other relationships
EUNIS (2004) A5.115: Baltic shell gravel bottoms of the aphotic zone.
Level 5 of the HELCOM HUB classification (2013). This habitat has one sub-habitat on HUB level
6; Baltic photic shell gravel dominated by vase tunicate (Ciona intestinalis) (AA.E1F1).

Does the habitat type present an outstanding example of typical characteristics of one or more
biogeographic regions?
Please tick () one box only:
(A habitat represents an outstanding example of typical characteristics of one or more
biogeographical regions, if it is especially characteristic of one or more biogeographic regions, in
terms of area, species composition, structure or functioning).
YES :
NO:
UNKNOWN:

 If Yes – please indicate the regions
3
For terrestrial types:
Alpine
Atlantic
Black Sea
Boreal
Continental
Macaronesia
Mediterranean
Pannonian
Steppic
For marine types:
Marine Atlantic
Marine Baltic
Marine Black Sea
Marine Macaronesia
Marine Mediterranean
Justification:
-
4
2. Geographic occurrence and trends
Distribution map (in 10x10 km grids) of the habitat type in Europe (provided by Alterra/ NatureBureau)

For both terrestrial and marine types, please tick () the countries in which the habitat type is
present based on the territorial data sheets (please select “Present” or “Presence Uncertain” as
relevant)
EU 28
Austria
Belgium
Bulgaria
Croatia
Czech Republic
Cyprus
Denmark
Estonia
Finland
Finland mainland
Åland Islands
France
France mainland
Corsica
Germany
Greece
Greece (mainland and other islands)
Crete
East Aegean islands
Hungary
Ireland
Italy
Italy mainland
Sardinia
Sicily
Latvia
Lithuania
Luxembourg
Malta
Netherlands
Poland
Portugal
Portugal (mainland)
Azores
Madeira
Savage Islands
Romania
Slovakia
Slovenia
Spain (mainland)
Spain
Balearic Islands
Canary Islands
Sweden
United
Great Britain
5
Kingdom
Northern Ireland
Gibraltar
EU 28+
Albania
Andorra
Bosnia and Herzegovina
Faroe Islands
Guernsey
Iceland
Isle of Man
Jersey
Kaliningrad
Kosovo
Liechtenstein
Former Yugoslavian Republic of Macedonia (FYROM)
Monaco
Montenegro
Norway (mainland)
Norway
Svalbard
Jan Mayen
San Marino
Serbia
Switzerland
Vatican City

For marine habitats, please tick () the MSFD region and subregion in which the habitat type
occurs (please select “Present” or “Presence Uncertain” as relevant):
Mediterranean Sea
Black Sea
North-East Atlantic
Baltic Sea
Adriatic Sea
Aegian-Levantine Sea
Ionian Sea and the Central Mediterranean Sea
Western Mediterranean Sea
Black Sea
Sea of Marmara
Bay of Biscay and the Iberian Coast
Celtic Seas
Kattegat
Greater North Sea
Macaronesia
Baltic Proper
Belt Sea 
Gulf of Bothnia
Gulf of Finland
Gulf of Riga
The Sound
6

Is the list of countries/seas selected above in correspondence with the provided map?
Please tick () the box confirming that a consistency check has been done:

For EU 28 and EU 28+:
1. Using the distribution map, the Project Management Team will provide the value for Extent
of Occurrence (extent of a minimum convex polygon enclosing all occurrences) and for Area
of Occupancy (number of 10*10 km cells occupied by the habitat type).
2. Using the territorial data sheets (along with additional information if relevant), please
provide the estimated total area (actual area in km2 of the habitat), calculated by adding up
the area of the habitat type in each country/sea.
Extent of
Occurrence
(EOO)
EU 28
EU 28+

Area of
Occupancy
(AOO)
Current
estimated Total
Area (km2)
Comments
≤ 50,000 km2
How much of the current distribution of the habitat type lies within the EU 28?
Please estimate in percentage the proportion of the habitat type that the EU28 hosts in relation to
the habitat type’s total worldwide distribution. For the marine types this is (by definition)
compared to the total area within EU28+.
In the Baltic Sea 100% of this habitat lies within EU 28.
Trends in quantity
Using the territorial data and any other relevant information, please describe the historical, recent and
estimated future trends in quantity (extent, distribution).
Current: The biotope occurs only in the south-western Baltic Sea, in the southern parts of the
Belt Sea. Information on the biotope is scarce, but it is assumed to be rather rare and restricted
to small patches which meet the environmental demands of the biotope. It is assumed to have
been reduced in distribution mainly due to increased siltation and bottom trawling.
Past: No data available.
Historic: No data available.
Future: No estimates available.
7

Average current trend in quantity (extent):
EU 28
EU 28+

Stable
Increasing
Decreasing 
Unknown
Stable
Increasing
Decreasing 
Unknown
Does the habitat type have a small natural range following regression?
Please tick () one box only:
(The habitat has a small natural range following regression if the EOO ≤ 50,000 km² and the habitat
has undergone an important decline during the last 50 years)
YES :
NO:
UNKNOWN:

Justification (please indicate whether the decline is ongoing or has stopped, and provide any additional
supporting information):
The biotope is assumed to be rather rare and restricted to small patches which meet the
environmental demands of the biotope. It is assumed to have been reduced in distribution
mainly due to increased siltation and bottom trawling. The EOO of the habitat is estimated to be
≤ 50,000 km².

Does the habitat have a small natural range by reason of its intrinsically restricted area?
Please tick () one box only:
(A habitat has a small natural range by reason of its intrinsically restricted area if the underlying
factors for the occurrence of the habitat occupy a very limited area and range)
YES :
NO:
UNKNOWN:

Justification:
Please see previous text box.
8
3. Habitat condition and trends
Please describe the current quality of the habitat type, historical trends in quality and estimated future
trends. Use and build on the information from the territorial data sheets and the quality indicators from
the description.
No information exists on the quality of the habitat.

Average current trend in quality:
EU 28
EU 28+
Stable
Increasing
Decreasing
Unknown 
Stable
Increasing
Decreasing
Unknown 
4. Country/regional sea trends
Using the territorial data sheets please indicate at the country or regional sea levels if the trends in
quantity and quality are increasing, decreasing, stable or unknown.
Current area of Recent trend in
habitat (km2) quantity (last 50 yrs)
Baltic
Sea

No data.
Decreasing.
Recent trends in
quality (last 50 yrs)
No data.
Please upload all the territorial data sheets for this habitat type
9
5. Pressures and threats
Indicate in the look-up table below (provided by Doug Evans and based on Article 17/MSFD) the five
most significant threats affecting the habitat and whether these are of past, current or future
importance.
In the accompanying text field below, indicate the main causes of the threats affecting the habitat and
their scale of significance within the EU 28 and EU 28+. Use and build on the information from the
territorial data sheets and other available information.
Past and Current Threats (Habitat directive article 17):
Climate change (ocean acidification M01.04), Eutrophication (H01.05), Contaminant pollution
(H03), Fishing (bottom trawling F02.02.01), Construction (D03, oil and gas exploration and
exploitation C02), Mining and quarrying (sand and gravel extraction C01.01, oil and gas
exploration and exploitation C02)
Future Threats (Habitat directive article 17):
Climate change (ocean acidification M01.04), Eutrophication (H01.05), Contaminant pollution
(H03), Fishing (bottom trawling F02.02.01), Construction (D03, oil and gas exploration and
exploitation C02), Mining and quarrying (sand and gravel extraction C01.01, oil and gas
exploration and exploitation C02), Random threat factors (–)
Oxygen depletion and increased siltation caused by eutrophication is the main threat for the
biotope. In addition, bottom trawling threatens the physical integrity of the biotope. The
predicted ocean acidification caused by the increasing atmospheric CO2 can be seen as a
potential future threat for the biotope. Ocean acidification may affect the shell gravel substrate
severely, as the natural degradation process of the calcium-carbonate shells may accelerate if
the water becomes more acidic. This can lead to a more restricted distribution of the biotope in
the future.
Additional threats to the biotope are hazardous substances introduced to the Baltic Sea via
pollution, offshore installations and sand or gravel extraction. The effects of these are however
assumed to be smaller than that posed by eutrophication.
10
6. Conservation and management
Please describe the main (e.g. no more than 5) current approaches to conservation and management of
this habitat type, and outline what additional actions are needed.
In order to conserve the biotope its distribution should be mapped to gain better understanding
of its environmental requirements. The area where the biotope occurs should be protected and
bottom trawling should not be allowed within this area. Further eutrophication should be stopped
in order to improve the oxygen conditions of the biotope and also reduce the overgrowth of
annual brown algae on the vase tunicates.
 Conservation and management needs
Please tick the main essential and realistic conservation and management actions needed for the habitat
type (following the description provided above). The actions should be selected only if they are relevant
to the conservation of the particular habitat being assessed (the classification below is derived from the
Habitats Directive Article 17 reporting)
Code
1
1.1
1.2
1.3
Measure
No measures
No measures needed for the conservation of the
habitat/species
Measures needed, but not implemented
No measure known/ impossible to carry out
specific measures
2
Measures related to agriculture and
open habitats
2.0
2.1
Other agriculture‐related measures
Maintaining grasslands and other open habitats
2.2
Adapting crop production
3
Measures related to forests and
wooded habitats
3.0
3.1
Other forestry‐related measures
Restoring/improving forest habitats
3.2
Adapt forest management
4
Examples
species migrations, habitat changes due to climate change,
glacier retreat, monitoring changes without intervention
mowing, burning, grazing, removal/control of shrubs and
other woody plants
adapting input of nutrients and pesticides/herbicides;
adapting crop timing (advance/delay harvest dates)
replanting with autochthonous species, enable/
promote natural re‐growth, removing non‐natives
species, change single species and even‐aged stands
into multi‐species and uneven‐aged stands, burning/
maintaining a fire regime
adapting harvesting cycles, adapting techniques and
equipment
Measures related to wetland,
11
freshwater and coastal habitats
4.0
4.1
4.2
Other wetland‐related measures
Restoring/improving water quality
Restoring/improving the hydrological regime
4.3
Managing water abstraction
4.4
Restoring coastal areas
5
Measures related to marine habitats
5.0
5.1
6
Other marine‐related measures
Restoring marine habitats
Other spatial measures
Establish protected areas/sites
Establishing wilderness areas/ allowing
succession
6.3
Legal protection of habitats and species
6.4
Manage landscape features
6.5
Adaptation/ abolition of military land use
Other species management measures
Regulation/ Management of hunting and
taking
7.2
Regulation/ Management of fishery in limnic
systems
7.3
Regulation/ Management of fishery in marine
and brackish systems
Specific single species or species group
management measures
8
8.0
8.1
no intervention after calamities, natural catastrophic
events, succession where no management is
necessary
legal habitat type protection (regardless where they
occur, also outside protected areas), strictly legally
protected species including their habitats
maintenance or creation of hedges, tree lines,
corridors
nature management on military training grounds,
abolition of military use
Measures related to hunting, taking and
fishing and species management
7.0
7.1
7.4
controlling invasive species, favouring
re‐establishment of natural communities
Measures related to spatial planning
6.0
6.1
6.2
7
restoring alluvial situations,
reducing eutrophication
restoring river dynamics, removal of barriers and artificial
margins, managing water levels (e.g. in bogs and mires)
managing periods and/or quantity of water abstracted for
irrigation, energy production
stabilisation of dunes, re‐establishing dune dynamics,
removing coastal infrastructures
regulation of hunting (periods, species), collection
permits for plants, berries etc., regulation of game
density
regulation of amount, fish species & catching
methods allowed, removal of certain fish species,
control of measures for enhancing fish production,
maintenance of traditional fish pond systems
Restrict bottom trawling.
Measures related to urban areas,
industry, energy and transport
Other measures
Urban and industrial waste management
12
8.2
Specific management of traffic and energy
transport systems
8.3
Managing marine traffic
9
Measures related to special resource use
9.0
9.1
Other resource use measures
Regulating/Management exploitation of natural
resources on land
Regulating/Managing exploitation of natural
resources on sea
9.2

measures to reduce collision, maintenance of semi
natural roadsides, protection of birds on high voltage
systems, regulations to manage traffic density
managing routes, boat speed,
management of quarries with amphibians,
wind exploitation
Restrict construction works and exploitation of
marine soil resources like sand or gravel.
Conservation status
Please indicate the overall conservation status in the relevant biogeographical regions of all related
Annex 1-types according to the Habitats Directive. For marine types, please also indicate the OSPAR
or Helcom status if relevant.
The habitat has one sub-biotope “Baltic photic shell gravel dominated by vase tunicate (Ciona
intestinalis)” (AA.E1F1) which according to HELCOM Red List Assessment 2013 has been given the threat
category Vu according to criterion B1a (ii).

When severely damaged, does the habitat retain the capacity to recover its typical character and
functionality? Estimate the time taken for such recovery (1) naturally and (2) through intervention.
Please fill in the matrix below.
Justification (please also describe the specific resources and actions required to recover the habitat,
if possible):
Time
(years)
None
Low
Effort required
Medium
High
10 yrs
20 yrs
50+ yrs
200+ years
13
7. Synopsis
Please synthesize the relevant information obtained from the territorial data sheets and other sources in
order to facilitate the assessment process.
Input data:
-
HELCOM Red List of Biotopes Questionnaire raw data
-
Expert judgement
-
Subsequent expert discussions in the HELCOM Red List of Biotopes assessment
-
HELCOM Biotope Information Sheet for the habitat AB.E1F Baltic aphotic shell gravel
characterized by epibenthic chordates
8. Red List assessment
Criterion A: Reduction in quantity
Please indicate in the table below the percentage of decline obtained after applying Criterion A, as far as
data are available. Explain the percentage and provide any supporting evidence, including the map base
or other source(s) used to estimate change in distribution. If A2b was applied, please also give the
beginning and end (in years) of the 50-year period over which the decline was measured. Please cite
data sets and other sources of information used; if the primary data has not been published, please
provide a copy for archive to support future re-assessments.
Criterion A
EU 28
EU 28+
A1
No data
available
No data
available
A2a
No data
available
No data
available
A2b
No data
available
No data
available
A3
No data
available
No data
available
Criterion B: Restricted geographic distribution
Please indicate in the table below the values obtained after applying Criterion B, as far as data are
available. Explain the values and provide any supporting evidence. If B1a or B2a is used, please indicate
which subcriteria (i, ii and/or iii) this is based on. If B1b or B2b is used, please explain the threatening
processes and their effects. If B3 is used, please give the most serious plausible threat and justify how it
will cause the habitat to become Critically Endangered or Collapsed, including the time frame in which
this could occur. Please cite data sets and other sources of information used; if the primary data has not
been published, please provide a copy for archive to support future re-assessments.
Criterion B
EU 28
B1
EOO
a
≤ 50,000 km2
ii
B2
b
c
AOO
No data
a
b
c
B3
No data
14
EU 28+
available
No data
available
No data
available
available
No data
available
The biotope is assumed to be rather rare and restricted to small patches which meet the
environmental demands of the biotope. It is assumed to have been reduced in distribution
mainly due to increased siltation and bottom trawling.
Criteria C and D: Reduction in abiotic and/or biotic quality
Please indicate in the table below the percentage of change in abiotic and/or biotic quality. Please
report them together (criterion C/D), but if possible, also report abiotic (criterion C) and biotic (criterion
D) percentages separately.
Please explain the resulting values obtained, and provide any supporting evidence. Whenever possible,
please identify the abiotic environmental and/or biotic ecological factor(s) and data sources used to
assess reduction in quality. If criteria C/D2, C2 or D2 are used, please define the 50-year time period
over which the reduction was measured. Please cite data sets and other sources of information used; if
the primary data has not been published, please provide a copy for archive to support future reassessments.
C/D1
Criteria C/D
EU 28
EU 28+
Criterion C
EU 28
EU 28+
Criterion D
EU 28
EU 28+
Extent
affected (%)
No data
available
No data
available
Relative
severity
No data
available
No data
available
C1
Relative
Extent
severity
affected (%)
(%)
No data
No data
available
available
No data
No data
available
available
D1
Relative
Extent
severity
affected (%)
(%)
No data
No data
available
available
No data
No data
available
available
C/D2
Extent
Relative
affected
severity
(%)
No data
No data
available
available
No data
No data
available
available
C2
Extent
Relative
affected
severity
(%)
(%)
No data
No data
available
available
No data
No data
available
available
D2
Extent
Relative
affected
severity
(%)
(%)
No data
No data
available
available
No data
No data
available
available
C/D3
Extent
affected
(%)
No data
available
No data
available
Extent
affected
(%)
No data
available
No data
available
Extent
affected
(%)
No data
available
No data
available
Relative
severity
No data
available
No data
available
C3
Relative
severity
(%)
No data
available
No data
available
D3
Relative
severity
(%)
No data
available
No data
available
15
Criterion E: Quantitative analysis to evaluate risk of habitat collapse
Describe the method/model used to estimate risks of habitat collapse. Please explain the resulting
values obtained, specify the basis and provide any supporting evidence. Please cite data sets and other
sources of information used; if the primary data has not been published, please provide a copy for
archive to support future re-assessments.
Criterion E
EU 28
EU 28+
E
No data
available
No data
available
No quantitative analysis has been carried out for this habitat.
Overall assessment “Balance sheet” for EU 28 and EU 28+ 1
Please complete the table below, indicating the Red List Category that the habitat type qualifies for,
after assessing the habitat types against all criteria for which data is available. If any criteria were not
applied, the habitat type should be considered Data Deficient (DD) under those criteria.
Category
EU
28
EU
28+
A1
DD
DD
A2a
DD
DD
A2b
DD
DD
A3
DD
DD

Category
EU
28
EU
28+
B1
VU
VU
B2
DD
B3
DD
Category
EU
28
EU
28+
C/D1
DD
DD
DD
C/D2
DD
DD
C/D3
DD
Category
EU
28
EU
28+
C1
DD
DD
DD
C2
DD
DD
C3
DD
Category
EU
28
EU
28+
D1
DD
DD
DD
D2
DD
DD
DD
D3
DD
DD
Category
E
EU
28
EU
28+
DD
DD
Overall Category &
Criteria
EU 28
VU
B1a
(ii)
Synthesis
Provide a summary of the reasons why the habitat type qualifies for the Category and Criteria
recorded above, justifying assessment decisions, limits of data quality, reliability of assessment,
etc.), using the information from above.
The biotope is assumed to be rather rare and restricted to small patches which meet the
environmental demands of the biotope. It is assumed to have been reduced in distribution
mainly due to increased siltation and bottom trawling.
1
This table possibly will be filled automatically in the online platform
16
EU 28+
VU
B1a
(ii)

Please indicate the confidence in the assessment; please tick () one box only:
Low
(mainly based on uncertain or indirect information, inferred and
suspected data values, and/or limited expert knowledge)
Medium
(evenly split between quantitative data/literature and uncertain
data sources and assured expert knowledge)
High
(mainly based on quantitative data sources and/or scientific
literature)


Sub-habitat types that may require further examination
Indicate and specify if any sub-types of the assessed habitat type which may require further
examination due to their particular character or potentially threatened status. These may be
subtypes in a specific region, or thematic subtypes, having a certain specific species composition or
structure.
The biotope has been further categorized into a sub biotope on HELCOM HUB level 6: ‘Baltic
photic shell gravel dominated by vase tunicate (Ciona intestinalis)’ (AA.E1F1).

Assessors
Please indicate the names of the individuals that have assessed the status of the habitat type (the
working group members, first name is the member tasked to write up the draft assessment).
HELCOM RED LIST Biotope Expert Team 2013 and Baltic Sea Working Group for the European
Red List of Habitats 2014.

Contributors
Please indicate the names of the individuals that have contribute to the assessments (including
providers of territorial data, and providers of descriptions of types, and any other contributors).
HELCOM RED LIST Biotope Expert Team, November 2013.

Reviewers
Please indicate the names of the individuals that have reviewed the assessment.

Dates of the assessment
Please indicate the date when the habitat type was assessed (WG assessment workshop and/or
synthesis workshop if changes are made in a later stage).
November 2013.

Date of review
Please indicate the date when the habitat type assessment was peer-reviewed.
17
9. References
Provide a list of all published and unpublished reference sources used for the information recorded
above, including data sets and other sources of information. If the primary data has not been published,
please provide a copy for archive to support future re-assessments. Please provide full references, and
try to avoid abbreviations (e.g. write Conservation Biology rather than Cons. Biol.).
HELCOM 2013. Red List of Baltic Sea underwater biotopes, habitats and biotope complexes.
Baltic Sea Environmental Proceedings No. 138.
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