BIOTIC Species Information for Obelia longissima
|Researched by||Dr Harvey Tyler-Walters||Data supplied by||MarLIN|
|Refereed by||This information is not refereed.|
|Growth form||Arborescent / Arbuscular
|Feeding method||Passive suspension feeder
|Typical food types||Small zooplankton, small crustaceans, oligochaetes, insect larvae and probably detritus.||Habit||Attached|
|Bioturbator||Not relevant||Flexibility||High (>45 degrees)|
|Height||Up to 35 cm.||Growth Rate||Rapid, see additional information|
|Adult dispersal potential||10-100m||Dependency||Independent|
|General Biology Additional Information||Obelia longissima exhibits a typical leptolid life cycle consisting of a sessile colonial, vegetative hydroid stage, a free-living sexual medusoid stage, and a planula larval stage. For the sake of this review, the relatively long-lived and easily visible hydroid stage is regarded as the adult stage, while the medusa stage is considered to be a dispersive larval stage and the planula another larval stage specialized for settlement. The size range for males and females above relates to the medusa (see general biology larval). However, the definition of adult and larval stages in leptolids is a matter of debate (see Gili & Hughes, 1985).
In Obelia longissima branching begins earliest behind the newest internodes of stolons at the periphery of the colony, in closest contact with the environment, and only if there is adequate food does branching continue in the central older parts of the colony (Marfenin, 1997). If food supply decreases then parts of the colony can be reabsorbed (Marfenin, 1997).Growth rates
Many hydroids exhibit rapid growth, partially because the number of feeding hydranths, and hence the food catching potential, increases with size (Gili & Hughes, 1995). Growth rate is therefore, dependant on food supply (Marfenin, 1997). However, growth is also dependant on temperature. Berrill (1949) reported that stolons grew, under optimal nutritive conditions, at less than 1 mm in 24 hrs at 10-12 °C, 10 mm in 24 hrs at 16-17 °C, and as much as 15-20 mm in 24 hrs at 20 °C. Overall, growth is expected to be rapid, for example in experiments, Standing (1976) clipped the stems of Obelia back to the surface of his settlement plates every eight days since they grew back rapidly. Similarly, Cornelius (1992) stated that Obelia longissima and Obelia dichotoma could form large colonies within a matter of weeks. The hydranths of the colony demonstrate a regular cycle of development and regression with, in general, older hydranths regressing before younger ones (Crowell, 1953). Each hydranth takes about 24 hrs to develop at 20 °C and lives for a few days before it regresses (less in unfavourable conditions) (Berrill, 1949; Crowell, 1953; Kosevich & Marfenin, 1986).
Seasonal changes in the composition of Obelia colonies (no species stated) was examined by Hammett & Hammett (1945) and Hammett (1951a,b,c,d,e) in the Massachusetts area . They reported that budding peaked in April, complete hydranths in August and free-living medusae in July. Hammett & Hammett (1945) suggested that seasonal decline was common, colonies declining in June in North Carolina and after July in Woods Hole. Berrill (1949) noted that rapid growth continued at temperatures as high as 25 °C but ceased at 27 °C. Brault & Bourget (1985) noted that Obelia longissima exhibited a annual cycle of biomass, measured as colony length, on settlement plates in the St Lawrence estuary. Colony length increased from settlement in June, reaching a maximum in November to March and then decreasing again until June, although the decline late in the year was attributed to predation, and data was only collected over a two year period.
|Biology References||Cornelius, 1995b, Stepanjants, 1998, Berrill, 1949, Marfenin, 1997, Judge & Craig, 1997, Calder, 1990, Salvini-Plawen, 1972, Kosevich & Marfenin, 1986, Boero, 1984, Standing, 1976, Brault & Bourget, 1985, Crowell, 1953, Hammett, 1943, Hammett & Hammett, 1945, Hammett, 1951a, Hammett, 1951b, Hammett, 1951c, Hammett, 1951d, Hammett, 1951e, Cornelius, 1992, Cornelius, 1995a, Lauckner, 1980, King, 1974, Salvini-Plawen, 1972,|