Red List of European Habitats
Habitat code & name
AB.A1H–Baltic aphotic rock and boulders characterized by epibenthic moss animals
(Bryozoa)
Author and Date
HELCOM RED LIST Biotope Expert Team, November 2013.
Relationship to EUNIS
The biotope does not correspond directly to any EUNIS (2012) level 4 habitats due to
structural differences the classification systems. The best correspondence is found in
subhabitats of ‘Baltic exposed infralittoral rock’ (A3.4), ‘Baltic moderately exposed
infralittoral rock’ (A3.5) and ‘Baltic sheltered infralittoral rock’ (A3.6).
Habitat description
Baltic bottoms in the aphotic zone with at least 90% coverage of rock, boulders or stones
of more than 63 mm in diameter. Sessile/semi-sessile epibenthic moss animals cover at
least 10% of the seabed and more than other perennial attached erect groups. Salinity
range: All; Exposure range: all, more common in exposed areas; Depth range: photic
zone. There is a corresponding photic biotope AA.A1H.
Moss animals can commonly be found between vegetation in the photic zone, but are
more commonly dominant in the aphotic zone. The biotope does not exhibit a distinct
lower depth limit in the Baltic Sea, in the aphotic zone the availability of suitable hard
substrates limits the occurrence.
Two sub-biotopes with different dominant (>50% of the biovolume) macrofaunal taxa
can be identified. The sub-biotopes differ in their geographical distribution depending on
salinity. The sub-biotope ‘Baltic aphotic rock and boulders dominated by crustose moss
animals (Electra crustulenta)’ (AB.A1H1) is found in the whole Baltic Sea, while the subbiotope ‘Baltic aphotic rock and boulders dominated by erect moss animals (Flustra
foliaceae)’ (AB.A1H2) ) is found only in western and southwestern Baltic Sea due to
salinity constraints (15 psu).
The latter subbiotope is formed by erect growing moss animals (Bryozoa) of which brownleaved hornwrack (Flustra foliacea) constitutes at least 50% in volume or biomass. Flustra
foliacea occurs on stony sublittoral bottoms and favours areas with bottom currents
(Ryland & Hayward 1977) as the bryozoans feed on plankton, detritus and dissolved
organic material (Tyler-Walters & Ballerstedt 2007). Accompanying epibenthic species
are other erect growing moss animals like Eucratea loricata or crust-shaped bryozoans
but also sponges, sea squirts or hydrozoans. Erect and laminar bryozoans form calcified
substrata that is attractive to many other marine organisms, e.g. barnacles, hydroids and
other bryozoans. Erect bryozoans increase the complexity and diversity of their habitat
(Bitschofsky et al. 2011), giving shelter to small invertebrates and fish. Beside other
attached species the bushy colonies also provide shelter for small mobile amphipods or
scale worms. Nudibranchs, pynogonids and sea urchins (e.g. Psammechinus miliaris) are
known to feed on Flustra foliaceae (Ryland & Hayward 1977).
The Flustra foliacea colonies are bushy and up to 20 cm high. The fronds are flat, several
centimetres broad, branched and have rounded lobes (Ryland & Hayward 1977).
Because of its branched flat fronds, the species is often mistaken for a seaweed (Picton &
Morrow 2010), especially in videos records without adequate illumination the growth form
resembles that of perennial foliose red algae such as Phyllophora spp. potentially leading
to a biotope misidentification. Flustra foliacea is a cold-water species (Ryland & Hayward
1977). Compared to the fan-shaped and broad growing specimens of the North Sea, the
species tend to reduce branching, width of their fronds and height in brackish waters. In
the aphotic zone the bryozoan can form denser ‘meadows’ and also live on mixed
gravel like substrates.
Characteristic species
Electra crustulenta, Flustra foliacea, other Bryozoa (Eucratea loricata), also sponges, sea
squirts or hydrozoans.
Indicators of quality
Diversity, abundance and biomass of fauna.
Relationships with other schemes
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 rock & biogenic reef
Shelf sublittoral rock & biogenic reef
EUSeaMap relationships
Shallow aphotic rock or biogenic reef
Shelf rock or biogenic reefs
IUCN ecosystem relationships
9.2 Subtidal Rock and Rocky Reefs
Other relationships
Level 5 of the HELCOM HUB classification (2013). This habitat has two sub-habitats on HUB
level 6;
‘Baltic aphotic rock and boulders dominated by crustose moss animals (Electra
crustulenta)’ (AB.A1H1)
‘Baltic aphotic rock and boulders dominated by erect moss animals (Flustra foliaceae)’
(AB.A1H2)
Photograph
See the end of the document.
Countries list
To be inserted when data sheets completed.
Regional Sea
Baltic Sea
Baltic Proper
Belt Sea
Gulf of Bothnia
Gulf of Finland
Gulf of Riga
The Sound
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Map
This will be inserted by NatureBureau based on the Regional Sea information above.
References
HELCOM Website
http://helcom.fi/Red%20List%20of%20biotopes%20habitats%20and%20biotope%20compl
exe/HELCOM%20Red%20List%20AA.A1H2,%20AB.A1H2,%20AA.M1H2,%20AB.M1H2.pdf
Bitschofsky F., Forster S., Scholz J. 2011. Introduction in: ‘Regional and temporal changes in
epizoobiontic bryozoan-communities of Flustra foliacea (Linnaeus, 1758) and implications for North
Sea ecology’. Estuarine, Coastal and Shelf Science 91(3): 423–433.
HELCOM (1998). Red List of marine and coastal biotopes and biotopes complexes of the Baltic
Sea, Belt Sea and Kattegat. Baltic Sea Environmental Proceedings No. 75. Helsinki Commission,
Helsinki. 115pp. Available at: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep75.pdf
HELCOM Website
Picton, B.E., Morrow, C.C., (2010).Encyclopedia of Marine Life of Britain and Ireland Available at:
http://www.habitas.org.uk/marinelife/species.asp?item=Y6940 (viewed 3 June 2013).
Ryland J.S., Hayward P.J. (1977). British anascan bryozoans. Synopses of the British Fauna (New
Series), No. 10. Academic Press, London.
Stresemann E., Hannemann H.-J., Klausnitzer B. Senglaub K. 1992. Exkursionsfauna von
Deutschland. Band 1, Wirbellose (ohne Insekten). Volk und Wissen Verlag gmbH Berlin.
Tyler-Walters H., Ballerstedt S. 2007. Flustra foliacea. Hornwrack. Marine Life Information Network:
Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological
Association of the United Kingdom. [cited 08/07/2013]. Available at:
http://www.marlin.ac.uk/generalbiology.php?speciesID=3342
Aphotic boulder covered by various erect growing moss animals with Flustra foliacea as the dominant species
(Photo: Karin Fürhaupter) (left), Flustra foliacea on sieve (Photo Alexander Darr) (right)