Influences of nutritional state and temperature on suspension-feeding rates and mechanics in the spionid polychaete Polydora cornuta

Abstract

Benthic suspension feeders can respond to variations in food resources by behavioral and physiological means, but little is known about their ability to adjust the mechanics of particle capture. We examined influences of nutritional state (i.e. growth rate as influenced by food level) and temperature on suspension-feeding mechanics of the spionid polychaete Polydora cornuta (previously P. ligni). Worms were conditioned for 5 to 10 d in 4 treatments including 2 levels of suspended algae (50 or 0.1 μg chl a l-1, representing bloom and non-bloom conditions, respectively) and 2 temperatures (15 or 5oC , representing temperate spring/summer and winter, respectively). Both of these factors had significant, direct influences on growth rate. Worms of equal body size were then video taped while suspension feeding in a flume at their respective temperatures but with identical concentrations of food, including polystyrene beads for observing feeding mechanics. Worms with the lower growth rate captured beads at a rate 2.1x that of worms with the higher growth rate, and worms at 15oC captured beads at a rate 1.9x that of worms at 5oC, with no interactions between these factors. Particle contact rates did not differ among treatments; rather, the results were due solely to altered retention efficiencies (the proportion of contacted particles that were captured). Further experiments indicated that worms with the lower growth rate had enhanced adhesive strength of the mucous coating that retains particles on the palps and that low temperature inhibited the effectiveness of cilia in aiding retention. This is the first evidence that a benthic suspension feeder modifies the retention efficiency on its appendages, which it does in response to changes in its nutritional state. The enhancement of retention by mucus when under nutritional stress should act as a compensatory response at times or places of sparse food.