The diets and parasites of larval and 0+ juvenile twaite shad in the lower reaches and estuaries of the rivers Wye,Usk and Towy,UK |
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Authors: | A D Nunn R A A Noble J P Harvey I G Cowx |
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Institution: | (1) Department of Biological Sciences, Florida Atlantic University, Davie, FL 33314, USA |
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Abstract: | Aquatic predators and habitat permanence can jointly affect benthic invertebrate biomass and community composition. In 2006
I sampled fish and invertebrates in ten ponds embedded in a seasonal wetland before and after a natural drought. Drought reduced
fish biomass and density leaving some ponds in a fishless condition when rains returned in July. In July, large aquatic insects
and crayfish colonized and reproduced in the ponds, but did not colonize all of the ponds equally. Using measurements of fish
abundance and other environmental parameters of the ponds, I conducted linear regression analyses to explore potential drivers
of variable invertebrate biomass in July. Fish biomass had a negative effect on invertebrate biomass and it explained more
of the variation in total invertebrate biomass and total non-shrimp biomass than fish abundance (number of fish caught). Dissolved
oxygen and pond depth were both correlated with fish biomass, but were poorer predictors of invertebrate biomass. Ponds with
few or no fish had 20× greater total biomass and 200× more non-shrimp biomass than ponds with high fish biomass. Shrimp dominated
the invertebrate composition, and were only found in the two deepest ponds with the highest fish biomass; predatory insects
and crayfish dominated the other eight ponds. When taxa were analyzed separately, fish biomass explained a large portion of
the variation for predatory insects (Coleoptera, Hemiptera, and Odonata) and crayfish (Procambarus alleni), but dissolved oxygen was the best predictor of larval stratiomyid (order Diptera) biomass. These results are generally
consistent with studies demonstrating negative effects of fish on large predatory invertebrates, but also suggest that more
severe local droughts can seasonally enhance insect and crayfish populations by generating fishless or nearly fishless conditions.
Handling editor: J. Trexler |
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Keywords: | Disturbance Dragonfly Drought Fish Pond Procambarus alleni |
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