Feeding rates of the nemertean Prosorhochmus americanus (Hoplonemertea) on two species of gammaridean amphipods

Abstract

. The intertidal hoplonemertean Prosorhochmus americanus is a common inhabitant of the fouling community of rock jetties of the southeast coast of the United States. We undertook a laboratory investigation of the feeding rate of this nemertean, which is a suctorial predator of amphipod crustaceans that co-occur in abundance in the fouling community. While submerged in water (simulating high tide), worms fed on the tube-building amphipods Jassa falcata and Corophium cf. insidiosum at rates of 0.19 amphipods nemertean−1 d−1 (n=10) and 0.26 amphipods nemertean−1 d−1 (n=14), respectively. These predation rates were not significantly different (two-tailed t-test, p>0.05), and are similar to those estimated in laboratory studies of other suctorial nemerteans. Many nemerteans are typically more active at night, and indeed, adults of P. americanus consumed more individuals of J. falcata during dark periods than during light periods (χ2 analysis, p<0.05). However, no difference in consumption of individuals of C. cf. insidiosum was observed in dark versus light. We attribute these contrasting results to differences in tube-building behavior exhibited by these two species of amphipod under laboratory conditions. Our results and those of other laboratory investigations suggest that nemerteans that prey on amphipods feed at a rate of ∼0.2 prey items nemertean−1 d−1, but under natural conditions this rate may not be obtained because of limited feeding time, longer foraging distances, and emigration of prey from regions of high nemertean activity.