2024 Red List II of Benthic Invertebrates
Benthic invertebrates are small aquatic animals that live on or in the bottom substrate of water bodies, including rivers, lakes, and oceans. They include various animals such as clams, worms, crustaceans, and mollusks, and play a crucial role in aquatic ecosystems by contributing to sediment turnover and nutrient recycling. These organisms serve as an important food source for many fish and other aquatic animals. In the Baltic Sea, benthic invertebrates of both marine and freshwater origin co-occur, creating a unique ecosystem. The number of species from marine and freshwater origins changes along with the salinity gradient of the Baltic Sea.
Overview of the assessment results for benthic invertebrates
There were 42 benthic invertebrate species assessed as threatened (CR-VU) of the total 871 species that were evaluated in the HELCOM Red List II assessment. Two species, Haploops tenuis and Haploops tubicola, were categorised as Critically Endangered (CR), nine species as Endangered (EN) and 31 as Vulnerable (VU). Altogether, 198 species were red-listed (RE-DD) in 2024, compared to the 51 species in 2013. The total list of the assessed benthic invertebrate species and the categories assigned to them are available in Annex 3 of the Red List II species report.
231 species are restricted to the Kattegat region of the Baltic Sea, giving them a very limited habitable area (species marked with an asterisk in Annex 3 of this report).
Evaluated, Not Evaluated (NE) or Not Applicable (NA) species
Out of the total list of 2 043 benthic invertebrate species of the HELCOM Checklist 2.0 (HELCOM 2020), a total of 1 401 species entered the Red List II assessment process, out of which 871 species were evaluated, eight (0.9%) were left unevaluated (Not Evaluated) and the category Not Applicable (NA) was given to 522 species. In 2013 Red List 1211 species were evaluated, 627 (33.1%) were left unevaluated (NE) and 60 species were categorized as NA.
Red List categories within the assessed benthic invertebrate species
The proportion of the category Least Concern was by far the highest among the assessed species: 673 (48%) in 2024 and even higher in 2013, being 1 160 (61.3%) species. The proportion of the assignment of the category Not Applicable (522 species, 37.3%) and Data Deficient (124 species, 8.9%) were also the highest among the benthic invertebrate species group in the Red List II assessment. In 2013 the NA category was assigned only to 60 species (those considered vagrants and introduced in the HELCOM area after 1800) and only 23 species were considered as DD. In 2024, 522 species were categorized as NA due to being a freshwater species or considered not to be a Baltic Sea species. In 2013 627 species were categorized as Not Evaluated (NE) due to being very poorly known or where taxonomic difficulties existed, compared to 8 NE species in 2024.
Red List categories and Species Information Sheets (SIS)
The Species Information Sheets (SIS) were updated for those species that were categorized as threatened during the Red List II project, meaning those assessed as Critically Endangered, Endangered, Vulnerable and those categorised as Regionally Extinct. For those species that were categorized as threatened for the first time, a SIS was produced with only a summary table and distribution map.
| Red List II / SIS 2024 | Criteria 2024 | Scientific name | Common name | Red List / SIS 2013 | Criteria 2013 |
|---|---|---|---|---|---|
 | A2b | Haploops tenuis |  | B1ab(i,iii) +2ab(ii,iii) | |
| A2b | Haploops tubicola |  | B1ab(i,iii) +2ab(ii,iii) | |
| B2ab(iii,v) | Stomphia coccinea* | Spotted sea anemone; spotted swimming anemone; swimming anemone | | B1ab(iii) |
| B2ab(v) | Hippasteria phrygiana* | | B1ab(i,iii) | |
| B1ab(v) +2ab(v) | Cliona celata* | Boring sponge; red boring sponge; sulfur sponge; yellow boring horny sponge; yellow boring sponge | | D2 |
| B2ab(v) | Corophium multisetosum |  | B2b | |
| B2ab (i,ii,iii) | Boreotrophon truncatus | | B2ab(ii,iii) | |
| B2ab (i,ii,iii,v) | Epitonium turtonis | Finely ribbed wentletrap; Turton’s wentletrap |  | |
| B2ab(v) | Upogebia stellata | | ||
| B2ab | Talitrus saltator | Sand hopper | | |
| B1ab(iii) +2ab(iii) | Hanleya hanleyi | Eastern hanleya; Hanley’s chiton |  | |
| A2c | Modiolus modiolus | Horse mussel; horse-mussel; northern horsemussel | | A2c |
| D2 | Pelonaia corrugata* | | D2 | |
| B1ab(iii,v) +2ab(iii,v) | Clelandella miliaris* | | B1ab(i,iii) | |
| B1ab(iii,v) +2ab(iii,v) | Hippolyte varians | Chamaeleon prawn; chameleon prawn | | B1ab(iii) |
| D2 | Parvicardium hauniense | Copenhagen cockle | | B2ab(ii,iii) |
| D2 | Atelecyclus rotundatus* | Circular crab; old mans face crab; old-man’s face crab | | D2 |
| B1ab(iii,v) +2ab(iii,v) | Euspira pallida* | Pale moonsnail | | B1ab(iii) |
| B2 | Deshayesorchestia deshayesii | | B2ab(iii) | |
| A2 | Macoma calcarea | Chalky macoma | | A2c |
| A2 | Nucula nucleus | Common nut clam; nuclear nut clam | | A2c |
| A2 | Scrobicularia plana | Peppery furrow clam; peppery furrow shell | | A2c |
| B1 | Solaster endeca | Purple sun star | | B1ab(iii) |
| A2ac | Mya truncata | Blunt gaper; blunt gaper clam; clam; truncate softshell; truncate softshell clam | | A2c |
| B2ab(iii) | Amauropsis islandica | Iceland moonsnail | | B2ab(ii,iii,iv) |
| B1ab(v) +2ab(v) | Corystes cassivelaunus* | Helmet crab; masked crab | | D2 |
| B1ab(v) +2ab(v) | Amphipholis squamata* | Brooding snake star; dwarf brittle star | | |
| B1ab(iii,v) +2ab(iii,v) | Roxania utriculus* | | ||
| B1ab(iii) +2ab(iii) | Leptochiton alveolus* | | ||
| A2b | Nuculana pernula | Müller’s nut clam; Müller’s nutclam; northern nut clam; northern nutclam | | |
| D2 | Crenella decussata | Cross-sculpture crenella; decussate crenella | | |
| B1ab(i,iii) | Alvania testae* | | ||
| A2ac | Calocaris macandreae* | | ||
| B1ab(iii) +2ab(iii) | Eurynome aspera* | Strawberry crab | | |
| B1ab(ii,iii) +2ab(ii,iii) | Campylaspis costata | | ||
| D2 | Diastylis cornuta* | | ||
| D2 | Eurynome spinosa* | | ||
| B2ab(ii,iii) | Ophiura robusta | | ||
| B1ab(i,ii,iii) +2ab(i,ii,iii) | Eupolymnia nesidensis* | | ||
| B1ab(i) +2ab(i) | Palliolum incomparabile* | | ||
| A1 | Musculus niger | Black musculus; black mussel; little black mussel | | |
| A2c | Pinnotheres pisum* | | ||
 | B1ab(v) +2ab(v) | Abra prismatica | | B1ab(iii) +2ab(iii) | |
| B1ab(v) +2ab(v) | Epitonium clathrus | Common European wentletrap; common wentletrap; European wentletrap; false wentletrap | | B1ab(iii) |
| B2b(v) | Sabella pavonina* | Peacock feather-duster worm; peacock worm | | B1ab(iii) |
| B2 | Alderia modesta | | B2a | |
| D2 | Skeneopsis planorbis | Flat skenea; planorb skenea | | |
| B1a+2a | Agrypnetes crassicornis | | ||
| B1ab(iii,v) +2ab(iii,v) | Geryon trispinosus* | | ||
| B1b(v) +2b(v) | Inachus phalangium* | Leach’s spider crab; Mediterranean spider crab | | |
| D2 | Gammarellus angulosus | | ||
| D2 | Palaemon varians | | ||
 | Ekmania barthii | Barth’s sea cucumber | | ||
| Lekanesphaera rugicauda | | |||
| Limnoria lignorum | Gribble; wood gribble | | ||
| Myosotella myosotis | Mouse-eared snail | | ||
| Orchestia gammarellus | Beach-flea; common scud; common shore-skipper; shore-hopper | | ||
| Thia scutellata | Polished crab; thumbnail crab | | ||
| Eurydice pulchra | Speckled sea louse; speckled selouse | | ||
| Cryptonatica affinis* | Arctic moonsnail; Artic moonsnail | | ||
| Epitonium clathratulum* | Small wentletrap; white wentletrap | | ||
| Inachus dorsettensis | Scorpion spider crab | | B1ab(iii) | |
| Gammarus inaequicauda | | |||
| Macroplea pubipennis | | |||
| Pleurogonium rubicundum | | |||
| Monoporeia affinis |  | |||
| Vitreolina philippi | | |||
| Pontoporeia femorata | | |||
| Saduria entomon | | |||
| Macroplea mutica | |