2024 Red List II of Benthic and Pelagic Habitats
Benthic habitat assessment
The version of HELCOM HUB classification system used in this assessment identifies 207 benthic biotopes in the photic zone and 115 in the aphotic zone, totaling 322 HUB classes (BSEP139 HUB). From the total list of 322 habitats 7 habitats were considered threatened (CR-VU) in the HELCOM Red List II assessment compared to the 15 threatened habitats in 2013. The total list of the benthic habitats and the categories assigned to them are available in Annex 1 of the Red List II habitats report.
One habitat, Baltic aphotic muddy sediment dominated by Haploops spp., was evaluated as Critically Endangered (CR) in 2024, previously as Endangered (EN). Baltic aphotic muddy sediments dominated by seapens remained as Endangered (EN) as in 2013. 5 habitats were categorized as Vulnerable in Red List II.
Red List categories within the assessed benthic habitats
The proportion of category Not Evaluated (NE) was very high: 223 habitats (69.25%) in 2024 due to the lack of available data, compared to the 119 habitats in 2013 (36.96%). Previous assessment assigned 146 habitats category Least Concern (LC), current assessment has 53 habitats as Least Concern, this is because many habitats have in 2024 assessed from 2013 Least Concern into Data Deficient and Not Evaluated category due to the data limitations.
Altogether, 99 species were red-listed (CR-LC) in 2024, compared to 203 species in 2013. Not Evaluated (NE) for the Red List II refers to HELCOM HUB classes that were not possible to assess due to data limitations. The 2013 assessment was expert judgement driven.
Of these, 173 are benthic habitat types at Level 6. Data provided by Contracting Parties covered 90 of these 173 Level 6 classifications, thereby 52% of all HUB defined biotopes were covered in the current assessment at least to at some level. Supplementing this with extrapolated data from HELCOM Biodiversity and the ICES databases increased the coverage to 128 Level 6 HUB classifications, or to 74% coverage.
These HUB classes have been documented in the data may not have had sufficient coverage and albeit their acknowledgement in the data, it was not possible to carry out an assessment on these.
It is important to note that, for most habitats/biotopes, the threat assessment relies not on comprehensive, long-term monitoring data, but rather on the best available data to provide insights into the occurrence of various habitats within the Baltic Sea.
The Zostera marina and Zostera noltii (eelgrass) monitoring program is presented as an example of a relatively data-rich case, contrasting with the more typical situation of limited data availability. These Zostera marina-dominated biotopes (AA.H1B7, AA.I1B7, AA.M1B7, and AA.J1B7) with their greater data availability, coupled with expert consensus that these habitat types are under considerable pressure throughout the Baltic Sea, which leads to applying the SPIA methodology to identify the threat category based on IUCN criterion C1.
The Red List II 2024 assessment, incorporating valuable expert input, reveals a complex picture of the conservation status of Baltic Sea habitats and biotopes, as habitats are varying in rarity across the Baltic, being common in one place and rare in another. The varied nature of the Baltic Sea, of its salinity gradient lowering the further into the Baltic the sea water travels and the change of landscape from sandy to rocky shores. This elaboration on results helps to better understand the threats faced by these habitats and to guide the conservation efforts.
Pelagic habitat assessment
Pelagic habitats have been excluded from direct assessment in the Red List II project. The primary reason for this exclusion is that the pelagic habitats definition is based on oxic and anoxic properties, which was now considered to be more suited to describe the quality of a habitat rather than defining it. An update of the HELCOM HUB classification of habitats was considered appropriate, but outside the scope of the Red List II project, to complete before a threat assessment would be carried out. The total list of pelagic habitats is also available in Annex 2 of the Red List II habitats report.
The Red List II assessment was carried out only for the Baltic Sea seasonal ice evaluating it as Endangered (EN) compared to the previous categorization Vulnerable (VU) made in 2013 Red List assessment.
The concerns for Baltic Sea seasonal ice are based on the most important factor being air temperature, but also wind, snow cover and ocean currents. Over the past 100 years, the winters have become milder, the ice season shorter and the maximum ice extent decreased (HELCOM climate change factsheet 2021). This is why the Baltic Sea seasonal ice threat category is EN.
Red List categories and Biotope Information Sheets
The Biotope Information sheets (BIS) were updated for those habitats that were categorized as threatened during the Red List II project, meaning those assessed as Critically Endangered, Endangered and Vulnerable.
Benthic habitats
| Red List II / BIS 2024 | Criteria 2024 | HUB code | HUB name | Red List / BIS 2013 | Criteria 2013 |
|---|---|---|---|---|---|
 | A2b | AB.H1I2 | Baltic aphotic muddy sediment dominated by Haploops spp. |  | A1 |
| A2b | AB.H2T1 | Baltic aphotic muddy sediment characterised by sea-pens | | A1 |
 | B2 | AA.J3L3 | Baltic photic sand dominated by ocean quahog (Arctica islandica) |  | A1 |
| B2, C1 | AA.I1B7 | Baltic photic coarse sediment dominated by common eelgrass (Zostera marina) | | A1 |
| B2, C1 | AA.M1B7 | Baltic photic mixed substrate dominated by common eelgrass (Zostera marina) | | A1 |
| B2, C1 | AA.J1B7 | Baltic photic sand dominated by common eelgrass (Zostera marina) | | A1 |
| B2 | AA.J1Q1 | Baltic photic sand dominated by stable aggregations of unattached Fucus spp. (typical form) |  | A1 |
| AA.H1A2 | Baltic photic muddy sediment dominated by sedges (Cyperaceae) | | A1 | |
| AA.H1B4 | Baltic photic muddy sediment dominated by Charales | | A1 | |
 | B2, C1 | AA.H1B7 | Baltic photic muddy sediment dominated by common eelgrass (Zostera marina) | | A1 |
 | AB.H3L3 | Baltic aphotic muddy sediment dominated by ocean quahog (Arctica islandica) | | A2 | |
| AB.H3L5 | Baltic aphotic muddy sediment dominated by Astarte spp. | | A1 | |
| AB.J3L3 | Baltic aphotic sand dominated by ocean quahog (Arctica islandica) | | A1 | |
| AA.H1B5 | Baltic photic muddy sediment dominated by spiny naiad (Najas marina) | | A1 | |
| AA.J1B5 | Baltic photic sand dominated by spiny naiad (Najas marina) | | A1 | |
| AB.J3L7 | Baltic aphotic sand dominated by striped venus (Chamelea gallina) | | A1 | |
| AA.H3L6 | Baltic photic muddy sediment dominated by Unionidae | | A1 | |
| AA.H3L3 | Baltic photic muddy sediment dominated by ocean quahog (Arctica islandica) | | A1 | |
| AA.I1B4 | Baltic photic coarse sediment dominated by Charales | | A1 | |
| AA.J1B4 | Baltic photic sand dominated by Charales | | A1 | |
 | AB.B1E4 | Baltic aphotic hard clay dominated by Astarte spp. | | B2c(ii) | |
| AA.D | Baltic photic maërl beds | | B1+2a(ii) | |
| AB.D | Baltic aphotic maërl beds | | B1+2a(ii) | |
| AA.M1Q2 | Baltic photic mixed substrate dominated by stable aggregations of unattached Fucus spp. (dwarf form) | | A1 | |
| AA.J1Q2 | Baltic photic sand dominated by stable aggregations of unattached Fucus spp. (dwarf form) | | A1 | |
| AA.I1Q2 | Baltic photic coarse sediment dominated by stable aggregations of unattached Fucus spp. (dwarf form) | | A1 | |
| AA.H1Q2 | Baltic photic muddy sediment dominated by stable aggregations of unattached Fucus spp. (dwarf form) | | A1 | |
| AA.G | Baltic photic peat bottoms | | B2b | |
| AB.E1F1 | Baltic aphotic shell gravel dominated by vase tunicate (Ciona intestinalis) | | B1a(ii) | |
| AA.E1F1 | Baltic photic shell gravel dominated by vase tunicate (Ciona intestinalis) | | B1a(ii) | |
| AA.A1H2 | Baltic photic rock and boulders dominated by erect moss animals (Flustra foliacea) | | A1 | |
| AB.A1H2 | Baltic aphotic rock and boulders dominated by erect moss animals (Flustra foliacea) | | A1 | |
| AA.M1H2 | Baltic photic mixed substrate dominated by erect moss animals (Flustra foliacea) | | A1 | |
| AB.M1H2 | Baltic aphotic mixed substrate dominated by erect moss animals (Flustra foliacea) | | A1 | |
| AA.E1C4 | Baltic photic shell gravel dominated by kelp | | B1a(ii) | |
| AB.E3Y | Baltic aphotic shell gravel characterized by mixed infaunal macrocommunity in fine sand-like shell fragments | | B1a(ii) | |
| AA.E3Y | Baltic photic shell gravel characterized by mixed infaunal macrocommunity in fine sand-like shell fragments | | B1a(ii) | |
| AB.A1J | Baltic aphotic rock and boulders characterized by epibenthic sponges (Porifera) | | A1 | |
| AB.M1J | Baltic aphotic mixed substrate characterized by epibenthic sponges (Porifera) | | A1 | |
| AB.M1G2 | Baltic aphotic mixed substrate dominated by sea anemones (Actiniarida) | | A1 | |
| AB.A1G2 | Baltic aphotic rock and boulders dominated by sea anemones (Actiniarida) | | A1 | |
| AB.M1G3 | Baltic aphotic mixed substrate dominated stone corals (Scleractinida) | | A1 | |
| AB.A1G3 | Baltic aphotic rock and boulders dominated stone corals (Scleractinida) | | A1 | |
| AB.M1G4 | Baltic aphotic mixed substrate dominated by soft corals (Alcyonacea) | | A1 | |
| AB.A1G4 | Baltic aphotic rock and boulders dominated by soft corals (Alcyonacea) | | A1 | |
| AB.A1F1 | Baltic aphotic rock and boulders dominated by sea squirts (Ascidiacea) | | A1 | |
| AB.M1F1 | Baltic aphotic mixed substrate dominated by sea squirts (Ascidiacea) | | A1 | |
| AB.J3L10 | Baltic aphotic sand dominated by multiple infaunal bivalve species: Macoma calcarea, Mya truncata, Astarte spp., Spisula spp. | | A1 | |
| AB.I3L10 | Baltic aphotic coarse sediment dominated by multiple infaunal bivalve species: Macoma calcarea, Mya truncata, Astarte spp., Spisula spp. | | A1 | |
| AA.J3L10 | Baltic photic sand dominated by multiple infaunal bivalve species: Macoma calcarea, Mya truncata, Astarte spp., Spisula spp. | | A1 | |
| AA.I3L10 | Baltic photic coarse sediment dominated by multiple infaunal bivalve species: Macoma calcarea, Mya truncata, Astarte spp., Spisula spp. | | ||
| AB.I3L11 | Baltic aphotic coarse sediment dominated by multiple infaunal polychaet-species including Ophelia spp. | | A1 | |
| AA.J3L11 | Baltic photic sand dominated by multiple infaunal polychaete species including Ophelia spp. and Travisia forbesii | | A1 | |
| AA.I3L11 | Baltic photic coarse sediment dominated by multiple infaunal polychaete species including Ophelia spp. | | A1 | |
| AB.J3L11 | Baltic aphotic sand dominated by multiple infaunal polychaete species including Ophelia spp. and Travisia forbesii | | A1 | |
| AB.H4U1 | Baltic aphotic muddy sediment dominated by meiofauna | | A1 | |
| AB.H3N1 | Baltic aphotic muddy sediment dominated by Monoporeia affi nis and/or Pontoporeia femorata | | A1 | |
| AA.M1B4 | Baltic photic mixed substrate dominated by Charales | | A1 |
Pelagic habitats
| Red List II / BIS 2024 | Criteria 2024 | HUB code | HUB name | Red List / BIS 2013 | Criteria 2013 |
|---|---|---|---|---|---|
| A1, A2a | AC | Baltic Sea seasonal Ice | | A1, A2a |
| AE.O5 | Baltic Sea aphotic pelagic below halocline oxic | | A3 |