BIOTIC Species Information for Obelia longissima
Researched byDr Harvey Tyler-Walters Data supplied byMarLIN
Refereed byThis information is not refereed.
Distribution and Habitat
Distribution in Britain & IrelandProbably occurs throughout the British Isles but may be confused with Obelia dichotoma so that its recorded distribution may be inaccurate.
Global distributionNearly cosmopolitan. Recorded north to the New Siberian Island and south to the South Orkney Isles in the Atlantic, penetrates the Baltic Sea and the Black Sea, with numerous records in the Indo-Pacific (Cornelius, 1995b; Stepanjants, 1998).
Biogeographic rangeNot researched Depth rangeSee additional information
MigratoryNon-migratory / Resident   
Distribution Additional InformationStepanjants (1998) reported that Obelia longissima was a cold water species, present in northern and southern hemispheres and the Black Sea but absent from tropical areas. Stepanjants (1998) therefore, regarded it as a bipolar species. However, Cornelius (1995b) suggested that numerous records from the Indo-Pacific probably referred to this species.

Obelia longissima occurs primarily in the subtidal but occurs occasionally in the littoral if washed up or in rockpools (Cornelius, 1995b). Zamponi et al. (1998) reported Obelia longissima in the sublittoral of Argentina between 36 and 70 m depth. Stepanjants (1998) noted that Obelia species were found in all oceans, preferentially no deeper than 200 m but cited a record of Obelia longissima between 300 and 510 m deep in Patagonian waters.

Substratum preferencesLarge to very large boulders
Other species (see additional information)
Small boulders
Coarse clean sand
Biogenic reef
Artificial (e.g. metal/wood/concrete)
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Enclosed coast / Embayment
Biological zoneLower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral
Wave exposureExtremely Exposed
Very Exposed
Moderately Exposed
Very Sheltered
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
SalinityReduced (18-30 psu)
Full (30-40 psu)
Variable (18-40 psu)
Habitat Preferences Additional InformationSubstrata
Most hydroids do not show a high specificity of substrata (Gili & Hughes, 1995). Obelia longissima has been recorded from a wide variety of hard substrata including rocks, shells and artificial substrata (pilings, harbour installations, buoys, bridge supports), bivalve cultures (e.g. mussels and oysters), or floating debris, as epiphytes on kelp stipes or Halidrys siliquosa, and may occur in sandy areas where shells or other hard substrata provide attachment (Cornelius, 1992; Gili & Hughes, 1995; JNCC, 1999).

Habitat preferences
Water movement is important for hydroids to supply adequate food, gas exchange, remove waste products, prevent excessive siltation and provide suitable substratum. Hydroids tends to be abundant where water movement is sufficient to but not high enough to cause damage. Hydroids with long stems tend to occur in calmer waters (Riedl, 1971; Hiscock, 1983; Gili & Hughes, 1995). Hydroids tend to occur in low light conditions, possibly due reduced competition from algae and/or settlement preferences of their planulae larvae (Gili & Hughes, 1995). The majority of hydroid species are stenohaline, i.e. do not tolerate reduced salinities. However, Obelia longissima was reported from sites subject to reduced salinity such as the Taw and Fal estuaries (JNCC, 1999). Temperature is an important factor controlling growth and reproduction in hydroids, and many species have optimal temperature ranges for reproduction (Gili & Hughes, 1995). For example, Berrill (1949a) reported that growth in Obelia longissima ceased at 27 °C and that newly formed hydranths rapidly regressed at 25 °C.

Distribution References Cornelius, 1995b, NBN, 2002, JNCC, 1999, Picton & Costello, 1998, Stepanjants, 1998, Boero & Bouillon, 1993, Judge & Craig, 1997, Boero & Fresi, 1986, Hunter, 1989, Zamponi et al., 1998, Bourget et al., (in press), Boero, 1984, Cornelius, 1992, Riedl, 1971, Hiscock, 1983, Sommer, 1992, Berrill, 1948,
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