Document: DIN-3-74-8

Daphnia migrations in the presence and absence of UV radiation: Which way do they go?

LEECH, D.M.* and C.E.WILLIAMSON

Lehigh University, Bethlehem, PA 18015, USA ¹

Abstract:
Migrations are exhibited in a wide variety of organisms from invertebrates to fish, birds, and mammals. Factors that induce these migrations across diverse taxa are surprisingly similar and are often associated with movements across habitat gradients both in time and space. In zooplankton, migrations are primarily thought to be induced by factors such as temperature, food, and especially predation. Damaging solar radiation may also play a role in inducing these migratory behaviors in zooplankton. Recent experiments have shown that ambient levels of solar UV radiation (UVR) are potentially lethal to zooplankton, and negative phototactic behavior has been demonstrated in the laboratory. However, to date, no studies have demonstrated a direct relationship between UVR and zooplankton migration in nature. Here we present the first evidence from in situ experiments demonstrating that UVR induces diel vertical migrations under full spectrum solar radiation. Cylindrical acrylic columns that transmitted or blocked UVR were used to examine the vertical migration patterns of Daphnia . Experiments were conducted in the surface waters of a high UV system at midday and in late afternoon. In both experiments, a large proportion of individuals migrated downward in the presence of UVR while those in the UVR-shielded treatments tended to remain closer to the surface.

Keywords: Migration, UV Radiation

This abstract is being presented at: 9:45 AM in session:
Oral Session #54: Lake Ecology.