Spineless… but not wimpy: invertebrate predator (Chaoborus) prompts diel horizontal migration of large-bodied Daphnia

BURKS R.L., H. MICHELS, M. A. GONZALEZ SAGRARIO AND E. JEPPESEN

Utah, USA.

Congreso; ASLO, Aquatic Science Meeting,; 2005

American Society of Limnology and Oceanography

Predation pressure from plentiful planktivorous fishes prompts vertical, and sometimes horizontal, migration of herbivorous zooplankton.   However, the potential for pelagic invertebrate predators to initiate horizontal migration by large zooplankters remains unclear.  Through multiple sampling efforts, we investigated the horizontal distribution of Daphnia in a small, eutrophic, Danish lake dominated by a pelagic invertebrate predator (Chaoborus).  Point sampling found between 3 and 9x as many D. magna in reed beds versus open water during day versus night.  Funnel traps captured many Daphnia magna moving both in and out of the reed beds, although results lacked clear directionality within time periods.  Taxa less vulnerable to predation failed to show any horizontal distribution.  Transect samples indicated large densities of D. magna during day in reed beds, indicating an asymmetric horizontal migration.  Highest densities occurred at night in open water.  However, relatively high densities still occurred in reed beds, perhaps indicating that only a fraction of daphnids migrate.  Overall, multiple lines of evidence from our study support the occurrence of horizontal migration of D. magna in a lake dominated by an invertebrate predator.