LB 10-112 - Investigating the consequences of flooding for zooplankton diversity in a wetland metacommunity

Background/Question/Methods:

Ponds within a metacommunity often house unique species at the local scale (alpha), often resulting in high species diversity at broad landscape levels (gamma) due to high compositional turnover among ponds (beta diversity). However, abiotic and biotic homogenization due to flooding might cause local communities among ponds to become compositionally similar, thus potentially reducing alpha, gamma, or beta diversity. The reduction in local or regional diversity might be temporary or long-term, depending on the resiliency of each pond community. To investigate the resiliency of zooplankton communities to flooding, we collected bi-weekly or monthly zooplankton samples prior to and following flooding events at a freshwater wetland complex in Wayne, NJ, USA. The site consists of one main wetland body and twenty small satellite ponds along the Pompton River. Pond zooplankton diversity was quantified prior to flooding in August, 2021 and bi-weekly or monthly after flooding. We also collected soil samples from each pond to understand how sedimentation altered the egg banks of each pond. We placed soil and RO water in 500ml jars under growth lights in the lab with a 16:8 light cycle and quantified the emerging zooplankton communities every 14d.

Results/Conclusions:

Using NMDS and PCA, we found that post-flood zooplankton communities were homogenized and compositionally diverged when compared to the communities prior to flooding. Zooplankton species composition shifted from communities dominated by Moina sp., Daphnia sp. and rotifers to communities dominated by Bosmina sp. and Calanoid copepods. Over a three-month period, the community composition shifted back to primarily rotifer-dominated communities. The egg bank in the soil remained compositionally diverse and compositionally diverged from the species observed at any single time during the study period. Therefore, sedimentation likely did not result in long-term shifts in the egg bank communities, probably because the species present after flooding are not pond specialists and had very little time to produce resting eggs. Initial results suggest that the driver of compositional differences among pond communities are nitrate and total phosphorus, where ponds with higher total phosphorus are dominated by Daphnia sp. and ponds with high nitrate concentrations are dominated by Moina sp. We did not find evidence of an abiotic driver for ponds dominated by rotifer communities. Given the increased intensity and frequency of flooding events in urban wetlands, long-term studies of community dynamics will be imperative to understand the resiliency of urban wetland communities.