Submersion tolerance in floodplain arthropod communities

Abstract

Summary River floodplains in Europe have been altered radically by river regulation resulting in a destruction of floodplain habitats. Today, it is the aim of restoration projects to counteract these negative ecological impacts. Arthropods living in floodplains have to cope with a regular cycle of wet and dry conditions. In the floodplain of the Lower Oder we investigated whether the typical wetland fauna recolonises the floodplain after each flooding event or survives winter submersion in the habitat. Furthermore, we analysed whether flooding regimes affect the distribution and migration patterns of arthropod species. With receding water levels in May 2002, gauze-covered exclosure tents were placed at sites subject to different flooding regimes to prevent arthropod colonisation. In July samples were taken from underneath the tents and from adjacent uncovered control plots. Additionally, nearby plots were sampled at biweekly intervals during the whole vegetation period. Planthoppers, leafhoppers (Auchenorrhyncha), spiders (Araneida) and ground beetles (Carabidae) were studied in detail. Most species of plant- and leafhoppers [70%] tolerated submersion and overwintered in the floodplain, whereas most spiders [63%] and carabids [73%] immigrated with receding water level. A high proportion of submersion tolerant species overwintered in the egg stage, whereas only few species hibernating as juveniles or adults were submersion tolerant. Submersion tolerant plant- and leafhoppers as well as spiders occurred in high densities in sites affected by long-lasting winter floods. Many of these species were specialists. Immigrating species of all three groups had highest densities in sites subject to high flooding impact. We conclude that restoration measures in river floodplains should also provide suitable non-inundated overwintering sites for immigrating species. Restoring a natural flooding regime is essential for creating and maintaining a high diversity of habitats and specialists among the fauna.