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Crayfish alter succession of pond communities.
Dorn, Nathan *,1, Wojdak, Jeremy1, 1 W. K. Kellogg Biological Station, Hickory Corners, MI
ABSTRACT- Succession studies in freshwater ecosystems have commonly focused on the seasonal-succession of plankton in pelagic zones of lakes and relatively less is known about succession of littoral habitats. In this study, we documented the establishment and abundance of plants and animals in replicated ponds (2 m deep, 29 m diam.) with and without crayfish from June 2001 to June 2002. The ponds were constructed in November 2000, and in May 2001 bluegill sunfish (Lepomis macrochirus) were added to all 6 of the ponds and crayfish (Orconectes virilis) were added to 3 (density within natural range). Zooplankton biomass was higher in crayfish ponds in both years (due to crayfish effects on fish recruitment in 2001), however phytoplankton biomass was also higher in crayfish ponds during 2001. High phytoplankton biomass in crayfish ponds was probably the result of bioturbation and resuspended nutrients (crayfish ponds had higher levels of suspended inorganic matter in 2001). In control ponds, Chara and other macrophytes covered 34% of the bottom by June 2002, while crayfish ponds completely lacked Chara and other macrophytes. In 2001, mats of metaphytic green algae (Cladophora and Zygnema) were abundant in the control ponds but were absent from the crayfish ponds. Selective grazing by crayfish incited a bloom of filamentous blue-green algae (Gleotrichia), which dominated the metaphyton community in crayfish ponds late into the summer, but was never found in the control ponds. Bullfrog tadpoles were absent from crayfish ponds due to indirect effects (breeding site destruction). Snails were also less abundant, and the negative effects on these grazers cascaded to periphyton which was more abundant in the crayfish ponds at the end of 2001. Total benthic invertebrate biomass did not differ between treatments, but chironomids and mayflies had altered size-distributions. These results indicate that omnivorous crayfish can have strong impacts on successional pathways of shallow freshwater ecosystems.
Key words: crayfish, amphibians, succession, littoral zone