Journal of Plankton Research Vol.25 no.7 pp.759-769, 2003
© Oxford University Press 2003
Predation by Buenoa macrotibialis (Insecta, Hemiptera) on zooplankton: effect of light on selection and consumption of prey
1 Laboratorio De Fotobiología, Universidad Nacional Del Comahue-Crub, Unidad Postal Universidad, 8400 San Carlos De Bariloche, Río Negro, Argentina and 2 Department of Biological Sciences, Dartmouth College, HB 6044, Hanover, NH 03755, USA
* Corresponding Author: dieguezmc{at}infovia.com.ar
In this study we test the hypothesis that the notonectid Buenoa macrotibialis shows a strong periodicity in foraging on small zooplankton because it relies on sight to detect the smaller items of its diet. In contrast, B. macrotibialis may be able to detect larger prey organisms by mechanoreceptors and therefore consume them independently of light availability. We conducted laboratory and field experiments with light and dark treatments to analyze the effect of light on the efficacy of B. macrotibialis(1.2–7 mm) in preying on the rotifer Brachionus calyciflorus (~0.25 mm body length), the cyclopoid copepod Tropocyclops extensus (~0.5 mm) and the cladoceran Daphnia pulex (~1.8 mm). We studied the feeding of B. macrotibialis on Tropocyclops extensus during the daytime and night-time in light and dark treatments in the laboratory, and in natural daylight and full moonlight in the field. Our results show that B. macrotibialis depends on sight to capture small (<0.5 mm) prey, probably because these prey produce little disturbance in the water, but that it appears to rely almost exclusively on mechanoreception to capture larger prey (>1 mm). Buenoa macrotibialis consumed Daphnia pulex, the largest prey offered, independently of light availability, while the consumption of T. extensus and Brachionus calyciflorus was recorded only in lit treatments. Furthermore, Buenoa macrotibialis presented a strong periodicity in feeding on small prey, controlled exclusively by light. The inability of B. macrotibialis to feed on small organisms during the night was found to be due to inadequate light for prey detection, rather than to an endogenously controlled decrease in feeding activity during the night. Under natural light conditions, B. macrotibialis preyed voraciously on T. extensus in daylight but not in the full-moon treatment or in the dark treatments, regardless of the time of day, suggesting that there is a threshold of light intensity below which small prey cannot be detected by the backswimmer.