Idotea balthica

Idotea balthica is a species of marine isopod[1] which lives on seaweed and seagrass[2] in the subtidal zone of rocky shores and sandy lagoons.

Idotea balthica
Idotea baltica.jpg
Scientific classification edit
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Superorder: Peracarida
Order: Isopoda
Family: Idoteidae
Genus: Idotea
I. balthica
Binomial name
Idotea balthica
(Pallas, 1772)
  • Idotea pusilla Eichwald, 1842
  • Idotea balthica stagnea Tinturier-Hamelin, 1960
  • Idotea baltica Pallas, 1772 [orth. error]
  • Idotea basteri Audouin, 1826
  • Idotea sarsi Collinge, 1917
  • Idotea tricuspidata Desmarest, 1825
  • Idotea tridentata Latreille, 1806
  • Idotea variegata Roux, 1830
  • Oniscus balthica Pallas, 1772
  • Oniscus tridens Scopoli, 1763
  • Stenosoma irrorata Say, 1818


Idotea balthica has a broad geographical distribution, having been recorded from the Belgian Exclusive Economic Zone, The British Isles, Cobscook Bay, Dutch Exclusive Economic Zone, European waters, Greek Exclusive Economic Zone, Gulf of Maine, Knokke, North West Atlantic, Red Sea, Voordelta, West Coast of Norway, Wimereux and the Black Sea.[1]


The male is larger than female, and can reach 4 centimetres (1.6 in) long.[3] The color of the body is extremely variable, ranging from muted greens to striking black-and-silver patternings; the female is usually darker.[3] The species can be distinguished from other idoteids by the shape of the telson, which is dorsally keeled with straight sides in I. balthica, and has a distinct protrusion at the end.[3]


Adults are potentially omnivorous,[4] but mainly feed on different types of vegetation. In the Baltic, these include brown algae (Fucus spp., Elachista fucicola, Pylaiella littoralis), green algae (Cladophora glomerata, Ulva spp.), and Phanerogams (Stuckenia pectinata, Ruppia spp., Zostera marina).[5]

In the Baltic, I. balthica prefers Fucus vesiculosus, an algal seaweed, as host plant over other algae and vascular plants.[6] The apical and basal parts of F. vesiculosus differ as food and as shelter, and males grow faster when fed with the apical parts, but females grow equally well with both.[7]

As a pollinatorEdit

In 2022, I. balthica was discovered to help Gracilaria gracilis reproduce – the first known case of an animal helping algae reproduce.[8][9]


  1. ^ a b Gary Poore & Marilyn Schotte (2011). Schotte M, Boyko CB, Bruce NL, Poore GC, Taiti S, Wilson GD (eds.). "Idotea balthica (Pallas, 1772)". World Marine, Freshwater and Terrestrial Isopod Crustaceans database. World Register of Marine Species. Retrieved January 1, 2012.
  2. ^ "Baltic Isopod - Idotea balthica - Details - Encyclopedia of Life". Encyclopedia of Life. Retrieved 2016-03-25.
  3. ^ a b c Kåre Telsnes. "Baltic Isopod – Idotea balthica". The Marine Flora & Fauna of Norway. Retrieved January 1, 2012.
  4. ^ Salemaa, Heikki (1978). "Geographical variability in the colour polymorphism of Idotea baltica (Isopoda) in the northern Baltic". Hereditas. 88 (2): 165–182. doi:10.1111/j.1601-5223.1978.tb01619.x.
  5. ^ Leidenberger, Sonja; Harding, Karin; Jonsson, Per R. (2012-05-01). "Ecology and distribution of the isopod genus Idotea in the Baltic Sea: key species in a changing environment". Journal of Crustacean Biology. 32 (3): 359–389. doi:10.1163/193724012X626485.
  6. ^ Salemaa, Heikki (1978). "Herbivory and microhabitat preferences of Idotea spp. (Isopoda) in the northern Baltic Sea". Ophelia. 27 (1): 1–15. doi:10.1080/00785236.1987.10422007. Retrieved April 21, 2020.
  7. ^ Vesakoski, Outi; Merilaita, Sami; Jormalainen, Veijo (2008). "Reckless males, rational females: Dynamic trade-off between food and shelter in the marine isopod Idotea balthica". Behavioural Processes. 79 (3): 175–181. doi:10.1016/j.beproc.2008.07.005. PMID 18692551. Retrieved April 21, 2020.
  8. ^ Roth, Annie (28 July 2022). "Like Bees of the Seas, These Crustaceans Pollinate Seaweed". The New York Times. Retrieved 21 August 2022.
  9. ^ Lavaut, E.; Guillemin, M.-L.; Colin, S.; Faure, A.; Coudret, J.; Destombe, C.; Valero, M. (29 July 2022). "Pollinators of the sea: A discovery of animal-mediated fertilization in seaweed". Science. 377 (6605): 528–530. doi:10.1126/science.abo6661.

External linksEdit