Experimental Feeding of Some Medusae and Chaetognatha

Abstract

The feeding behaviour of eight species of medusae was studied; total food consumed, rates of digestion, and growth rate were noted, especially in Cyanea and Aurelia.Aurelia up to 5 cm diam can accept a wide range of size of food organisms obtained by filtering sea water through the curtain of tentacles during pulsation, whereas most other species find their food by random contact with the tentacles. In Bougainvillia it is the dichotomously branched oral tentacles that capture the food. The apparent selectivity of Sarsia in feeding on copepods is shown to be a physical effect produced by its method of swimming. Leuckartiara can catch and eat active organisms larger than itself. None of the medusae examined showed any reaction to artificial stimulation by a vibrating probe.The method of transfer of food from the tentacles to the mouth is closely associated with the structure of the medusa. Long trailing tentacles contract and lift food towards the mouth and if the manubrium is long it can be manipulated to pick off the food from the tentacles. If the tentacles are short the umbrella edge folds inwards towards the mouth. If there is no manubrium, as in Staurophora, the cruciform stomach can accept food at any point.Larval fish are important in the diet of most medusae and rough estimates are given of a probable consumption of 50–250 larval fish per hydromedusa, about 450–500 by each Aurelia, and in the order of 15,000 by Cyanea. A conversion factor is given for food eaten by medusae of 37%, though this is based on only few data.Following the work of Horridge and Boulton (Proc. Roy. Soc. (Ser. B) 168: 413–419, 1967), who found that Spadella could be artificially stimulated to bite vibrating probes, similar experiments were made with Sagitta elegans. Although the chaetognaths were successfully kept alive the probes produced no feeding reaction. The methods are outlined for the benefit of others wishing to continue such investigations.

Abundance and composition of zooplankton at Sitakunda coast of Chittagong, Bangladesh

“…Similar results have also been reported in the coastal waters of Bangladesh by Bhuiyan et al (1982), Ali et al (1985) and Zafar (2000). Fraser (1969) and Suwanrunpha (1983) reported that big carnivorous zooplankters namely Ctenophora, Chaetognatha, Medusae and Siphonophora are planktonic predators of fish larvae. In this study, a high correlation between fish larvae and their predator, especially chaetognatha was observed.…”

Predation by planktonic and benthic invertebrates on larvae of estuarine crabs

“…Although they primarily eat M. leidyi and fish larvae (Cargo & Schultz, 1967;Phillips et al, 1969;Turner, 1982), C. capitella sometimes feeds on crab larvae and C. quinquecirrha preys on crustacean zooplankton when ctenophores are absent (Kelly, 1983). The moon jellyfish, Aurelia aurita, is common during the summer in lower estuaries and coastal waters, where it primm~ly feeds on copepods and fish larvae, but it also occasionally eats decapod larvae (Fraser, 1969;Feigenbaum & Kelly, 1984;Moiler, 19~4;Van der Veer & Oorthuysen, 1985). Lebour (1922)observed that A. aurita would eat crab larvae only in the absence of its preferred prey, which are gelatinous zooplankters, chaetognaths and fish larvae.…”

The recovery of the Barents Sea capelin (Mallotus villosus) from a larval point of view

“…Invertebrates select mostly for small prey due to their small size and modest capturing abilities, while vertebrates often select for a wider range of prey, using vision to detect them. Important invertebrate predators on fish eggs and larvae are: gelatinous zooplankton (Fraser 1969;M0ller 1980;Bailey and Batty 1984;Purcell 1985), euphausiids (Theilacker and Lasker 1974;Bailey 1984;Theilacker 1988), amphipods (Sheader and Evans 1975), copepods (Greene 1986) and chaetognaths (Lebour 1923;Brewer et al 1984). The most important vertebrate predators on fish eggs and larvae are fish themselves.…”