CONCOMITANT DIEL VERTICAL MIGRATION OF A PREDATORY LEECH AND ITS AMPHIPOD PREY

SUMMARY.  The concomitant diet vertical migrations of the predaceous leech Erpobdella montezuma and its pelagic amphipod prey Hyalella montezuma were monitored for 1 year in Montezuma Well, Arizona, U.S.A.  High densities of H. montezuma occurred in the subsurface strata of the water column during the day, but a substantial portion of the population migrated into the surface 1 m at sunset. E. montezuma remained in the lower water strata during the day, but migrated vertically after sunset to exploit the high densities of H. montezuma near the surface. Densities of E. montezuma progressively increased in the upper strata of the water column after sunset as light energy fell below 1 μEin m−2 s−1.  It is suggested that the synchronized nocturnal migrations of the predator E. montezuma in relation to its prey H. montezuma, increases the foraging efficiency of the leech in the highly predictable environment of Montezuma Well. Copyright © 1990, Wiley Blackwell. All rights reserved