 |
SEPG 2205 Date Awarded 2003
Effect of Eichhornia crassipes on the horizontal migration pattern of large-bodied Cladocera
Mariana Meerhoff
Abstract
The predation risk by fish on pelagic zooplankton is very significant in shallow lakes. This is thought to be one of the reasons why zooplankton displays diel horizontal migration in temperate lakes: to decrease the risk of being predated in the pelagic during daytime, vulnerable zooplankton swim to the littoral zone for shelter in the submerged plants. However, the plants-fish-zooplankton interactions in tropical and subtropical systems are anticipated to be more complex than in temperate systems due to major biological differences.
In this work, I determined experimentally the effects of the (sub)tropical, large, free-floating plant Eichhornia crassipes (water hyacinth) on the horizontal migration behaviour of Daphnia pulex in the presence and absence of chemical stimuli from a small subtropical omnivorous-planktivorous fish, Cnesterodon decemmaculatus.
In the absence of other stimuli, C. decemmaculatus and E. crassipes significantly changed the spatial distribution of Daphnia, promoting repellence. The repellence appeared to be chemically mediated in both cases. However, contrary to expectations, when exposed also to predator cues, daphnids did not move to the water hyacinths in search for refuge.
These results suggest that the costs of exposure to E. crassipes are not outweighed by the benefits of swimming away from predators and, therefore, that the “refuge effect” hypothesis developed for submerged plants in temperate lakes cannot be extended to subtropical free-floating plants.
Full report: SEPG2205
|
Home
