First report on the throphic ecology of the machrophagous ascidian Cibacapsa gulosa Monniot & Monniot, 1983.

FUENTES, V L.; LESCANO, MN.; SAHADE, R.; TATIÁN, M.

Ushuaia

Simposio; IBMANT/ANDEEP International Symposium & Workshop: Interactions between the Magellan Region and the Antarctic. Antarctic Benthic Deep-Sea Biodiversity; 2003

the aim was to know the trophic ecology of the macrophagous ascidian Cibacapsa gulosa Monniot & Monniot 1983 (Ascidiacea, Octacnemidae), microscopical analyses were performed both, on stomach contents and the inner wall of the postpharyngeal digestive tract. Octacnemids represent different pathway in the evolution of the typical suspension-feeding strategy in ascidians. A total of three specimens were collected during the LAMPOS cruise in the area of the South Sandwich Islands at the depth of 580 m. Specimens were immediately fixed in buffered formaldehyde 2.5% in sea water. The different prey items found in the gut contents were identified and counted under stereo-microscope using a Bogorov 10 ml counting chamber. Additional microscopical observations were performed on slides containing cuts corresponding to different sections of the gut (esophagus, stomach and intestine). A high diversity of prey items was found: from harpacticoid and calanoid copepods, lumbrineriform polychaetes, halacarids, and gamaroid amphipods, isopods and ophiurids to diverse crustacean fragments. The wall of the postpharyngeal digestive tract is lined by cylindrical monoestratified epithelium which reposes on a wide mesenchyme with blood sinus and extravascular blood cells. The external epithelium along the whole postpharyngeal digestive tract is mainly formed by cubic cells. At the level of the esophagus, the inner epithelium is ciliated and shows an intense basophilia in the apical region, while abundant vacuoles appeared in the anterior third. The stomach is characterized by an epithelium with microvillii; cells with apical basophilic granules, 2 nucleolus and supranuclear vacuoles. There are also many concretion cells. The final portion belonging to the intestine showed microvillii, cells with oval (intense basophilia) or rounded nucleus (less basophilia) and supranuclear vacuoles. Capture of this wide variety of preys (some of these having a great mobility), suppose a special behaviour of this sessile animals. Although prey items have a benthic and pelagic origin, the presence of components from the zooplankton could explain the high quantities of oil drops found in the contents: lipid storage as been stressed in amphipods and copepods living in polar ambients, reaching the lipids an important percentage of its dry weight during the year-round. Moreover, findings of crustacean fragments indicate that enzyme secretion must be intense in the esophagus and stomach. Regarding the scarcity of plant material that could reach this benthic ambient, this special feeding ecology (based in the capture of a very energetic, but occasional prey items) must ensure enough energy to maintain metabolic functions.