Document: CAR-3-52-42

Blowing in the wind: The passive overland dispersal of freshwater zooplankton.

CÁCERES, C.E.* ^1,2 and D.A.SOLUK ^1,2

Center for Aquatic Ecology-Illinois Natural History Survey, Champaign IL 61820, USA ¹
University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA ²

Abstract:
Experimental studies of dispersal and colonization by zooplankton are rare, making it difficult to assess the relative importance of local vs. regional processes in the structuring of aquatic systems. To test for colonization rates and identify potential dispersal vectors, we performed a field experiment in which we manipulated access to 150 L mesocosms. Treatments were: 1) Closed (covered with plastic), 2) 500 um netting, 3) 2.5 cm netting, 4) 10 cm netting, and 5) open (no netting). The 25 enclosures were placed in a Latin Square design within our experimental pond facility that has numerous ponds and cattle tanks as potential sources of zooplankton. Each tank was sterilized and then filled with filtered city water (1 um). Sampling was weekly for May-August 1998 and biweekly or monthly thereafter. After 79 weeks, there was no significant effect of mesh size on the number of taxa per treatment (p=0.49). Of the 26 non-insect taxa found to invade the array, on average only 13.9 0.6 (SE) taxa were recorded from each enclosure. The fact that the 500 um-mesh treatment received this many colonists indicates that at least some taxa are transported easily by wind and rain. Bdelloid and monogonant rotifers were the first non-insect colonists, beginning in week 3. The cyclopoid copepod Eucyclops agilis, which eventually colonized all of the enclosures, was first found at week 5. The first cladoceran, Chydorus sphaericus, appeared at week 8, but several cladoceran species were not found until the following spring. Diaptomid copepods, although present at the pond site, were never found in the mesocosms. Our results suggest dispersal limitation of some taxa, but also highlights the importance of local processes in structuring zooplankton assemblages.

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This abstract is being presented at: 3:45 PM in session:
Oral Session #47: Zooplankton Ecology.