Morpho‐functional adaptation to suspension feeding inEudendrium(Cnidaria, Hydrozoa)

Abstract

Hydropolyps are generally assumed to be carnivorous, capturing their prey by means of nematocysts, but there is evidence that some species may use particulate matter suspended in the water column. Laboratory experiments were employed to investigate the existence of a filter-feeding strategy related to particle concentration and water movement intensity in Eudendrium racemosum. The experiments showed that in this species a morpho-functional modification is induced by increase of water turbulence and particle concentration, whereby the hydroid acquires the ability to efficiently collect suspended matter. The suspension feeding strategy leads to a marked rearrangement of polyp morphology: the tentacles are closely contracted and covered by the everted mouth. Under these conditions, the mucous gastroderm plays a major role in capturing food, while the tentacles, normally used for predation, are nor used at all. Comparison between the behaviour of Eudendrium in turbulent conditions and under the administration of amino acids showed a profound difference between the normal feeding response stimulated by the chemical compounds released by prey and the one induced by water movement.

Population dynamics of Eudendrium racemosum (Cnidaria, Hydrozoa) from the North Adriatic Sea

“…The annual trend of E. racemosum is similar to those observed in other Mediterranean areas such as Portofino (Boero and Fresi 1986;Azzini et al 2002), Livorno harbour (Rossi 1964) and Medes Islands (Barangé and Gili 1988), with an increase in abundance during the warm season and a regression in winter. In the present study, quantitative data on seasonal fluctuations of the hydroid biomass are given for the first time.…”

“…Smaller items, such as diatoms, sediment or pine pollen, are normally recorded in the coelenteron. Puce et al (2002) demonstrated that E. racemosum is able to collect the suspended particulate matter when the water turbulence intensity is high. Larvae of mussels are the favourite preys of the studied species up to sizes not exceeding 500 lm.…”

Effects of turbulence on the feeding rate of a pelagic predator: The planktonic hydroid Clytia gracilis

“…In 249 general, small hydroid species are found in water with intense water movement, while large 250 species are found in calm areas (Riedl 1971, Boero 1984, Gili & Hughes 1995. In addition, a 251 recent study on a Mediterranean hydroid Eudendrium racemosum shows that water movement 252 can induce changes in the hydroid morphology, which leads to a change in its feeding strategy 253 (Puce et al 2002). Our data suggest that with increasing colony size the overall number of 254 captured prey per hydranth will decrease.…”

Description and ecology of Cytaeis capitata n. sp. (Hydrozoa, Cytaeididae) from Bunaken Marine Park (North Sulawesi, Indonesia)

“…Christensen (1967) reported on a predator strategy in Hydractinia echinata that feeds on animals belonging to the bottom fauna while the hydroid is buried in the sand. Moreover, a sediment-eating strategy was demonstrated by Cerrano et al (1998) in Podocoryna exigua, a Mediterranean hydroid living on shells occupied by the hermit crab Diogenes pugilator and by Puce et al (2002) in Eudendrium racemosum.…”