Loss and recovery of aquatic biodiversity across spatial scales following application of rotenone

Background/Question/Methods

The introduction of non-native species can have detrimental effects on ecological systems. For example, many aquatic habitats are stocked with non-native fish for recreation where they compete with native fish causing adverse affects on the rest of the ecosystem. Land managers often use rotenone, a common piscicide, to remove these fish to restore aquatic biodiversity and ecological functions.  Numerous studies have shown rotenone’s effects on non-target aquatic species and the recovery thereof.  However, most of this research has focused solely on local (within-pond) diversity and ignores the loss and recovery of diversity among sites (beta-diversity) and regional diversity.  We set out to test the effect of rotenone on pond invertebrates with a specific goal of investigating the effects of rotenone on and recovery of aquatic biodiversity across spatial scales.  Our study took place in twelve fishless ponds at Tyson Research Center near St. Louis, Mo.  Six ponds were treated with rotenone to obtain a concentration of 3mg/L, a level similar to fish removal management regimes, and six ponds were left as controls.  Macroinvertebrates and zooplankton were collected for species richness data one day before treatment, one week post treatment, and one month post treatment to assess recovery.

Results/Conclusions

In rotenone treated ponds, we found a significant decrease in local macroinvertebrate (p=0.015) and zooplankton (p=0.023) species richness one week after treatment.  We also found differences in regional and beta diversity between treatment groups.  Regional diversity of macroinvertebrates was reduced by 53% after rotenone treatment (from 34 to 18 species per 6 treatment ponds); however, one month post-treatment, macroinvertebrate species richness was similar to control levels both locally (9.5 species) and regionally (30 species), indicating a quick recovery of macroinvertebrates after rotenone-associated extirpations.  Rotenone significantly reduced zooplankton diversity across all spatial scales, but most severely at the local scale.  Local zooplankton richness was still significantly lower at both post treatment samplings (one week: p=0.023 and one month: p=0.033) but interestingly, the regional species richness was comparable to that found in the control ponds. The quick recovery of macroinvertebrates is not surprising given the mobile nature of many pond species, on the other hand, zooplankton species are more dispersal limited and therefore, more susceptible to a disturbance in their habitat and ultimately, a slower recovery.