Ctenophore ingestion rates are linearly related to food density up to concentrations much higher than those usually assumed to be representative of the natural environment. Daily rations in excess of l,OOO% of their body weights at high prey densities are matched by growth rates characteristic of phytoplankton (daily doublings). Digestive efficiencies >70% were recorded at moderate prey densities. Growth efficiencies rarely exceed 10% bccausc the bulk of assimilated food (up to 80% of that ingested) is required for the energy metabolism of these organically dilute (carbon 2% of dry wt) creatures.
The benthic Spadella schixoptera and the planktonic Sagitta hkpidu both attacked a fine vibrating glass probe over a broad range of frequencies after being starved for l-3 days. The response curve for S. schimptem had a peak at 30 Hz and was similar in shape but far broader than that found by prior workers for Spade&z cephalopteru.Sagitta hispida responded differently, with a peak response at 150 Hz and no apparent preference among lower frequencies.It also had a strong (37% ) response to nonvibrating, lateral sweeps. Neither species would attack the probe at a distance >3 mm. This extremely short attack distance was confirmed, for S. hispida, in a 50-liter aquarium by a series of feeding experiments, the results from which were applied to a simple model. Sagitta hispidu starved for 1 day searched 2,667 mms min-' and had an attack distance of 0.88 mm. These experimental data were used to determine the ability of S. hispida to sustain itself nutritionally in its natural environment, Chaetognaths are important predators, feeding on a wide variety of zooplankters including crustaceans, appendicularians, fish larvae, and other chaetognaths (see Nagasawa and Marumo 11976). Yet, because the planktonic species are difficult to keep in the laboratory, few observations have been made of their feeding behavior (e.g. Parry 1944; Reeve 1970b; Cosper and Reeve 1975; Kuhlmann 1976). ming copepods and hence can select their food. Fraser (1969) tried to get a planktonic species to attack a similar probe, but without success. We have made tests with a vibrating probe with both the benthic Spaci!eZZa schfxoptera and the planktonic Sagitta hispida and have also observed the feeding behavior of S. hispida in large aquaria to determine its dependence on prey density. John ( 1933) directed a small jet of water at the body surface of the benthic SpacZeZZa to try to analyze its ability to detect prey; Bieri (1966) touched different parts of Pterosagitta with a needle and also observed that Sagitta reacted to a glass rod when the rod was moved in the water, but not when it was above the water. Horridge and Boulton (1967) found that Spadella cephaloptera would attack a fine glass probe when it was vibrated from 9 to 20 cycles per second (Hz), with a distinct peak response at 12 Hz. This led Newbury ( 1972) to speculate that chaetognaths recognize the specific vibration rates produced by swimWe are grateful to many people at the Rosenstiel School for helpful ideas and assistance, particularly C. Gordon and R. Tusting who supplied parts of the probe apparatus and L. Farmer and M. A. Walter who aided in obtaining and handling some of the chaetognaths, E. Houde suggested the use of the model which led to the attack distance and has made valuable suggestions on the manuscript. We also thank J. Sprogis for drawing the figures. In these tests a thin glass probe was mounted on a magnetic pen motor driven by a signal generator (oscillator).The probe was vibrated at various frequencies at low amplitudes and also made to perform slow lateral s...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.