Verifying the safe level of visitors’ pressure in aquatic protected areas: surrogate signal species, dummy individuals and bioindication

Abstract

Aquatic areas within nature reserves can suffer from certain anthropogenic pressures of its visitors. The littoral zone within small rivers and lentic freshwater systems is particularly threatened by water sports, such as swimming and canoeing. The core zone of the Central European National Park is an example of a popular location for visitors and tourists to canoe (Křenová and Kindlmann 2015). Evaluating the direct impact of disturbances on endangered species is often very difficult due to the low number of individuals or the long-lasting impacts; therefore, three methods on how to evaluate anthropogenic disturbance rates are presented. The degree of damage on submerged macrophytes, caused by human trampling, canoe movements or paddling, is measured by capturing truncated plant fragments within the stream via nets while recording the number of visitors and measuring the water level. Concrete replicas of shells were utilized to assess the risk of removing mollusc specimens. The reactions of visitors were then recorded in terms of observing, manipulating or destroying the species In-situ bioindication was performed in the river based on caging and exposure experiments of juvenile Freshwater Pearl Mussels. After exposure, both juvenile growth rate and survival rate were evaluated within localities where disturbances, erosion or pollution had occured in connection to camps, hotels or settlements (Černá et al. 2018). These described methods have enabled a safe limit for the control of visitors. The national park administration office allows a regulated entrance into the park's core zone and eliminate vistor impacts on macrophytes (priorite habitat V4A Macrophyte vegetation of water streams, with currently present water macrophytes) and critically endangered molluscs (Margaritifera margaritifera L. - Simon et al. 2015). By using precise data, it was possible to carry out these regulations against the strong pressures of boat rental companies and lobbyist. The described methods could be applied in diverse contexts within marine or freshwater ecosystems.

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Fig.1 Concrete replicas of pearl mussels were utilized in national park core area to assess the risk of removing or destroying the dummy mollusc colony.