The impact of an invasive mud crab on brood success of nest-building fish in the Northern Baltic Sea
Native fauna in species poor communities, such as those of the Baltic Sea, may be particularly vulnerable to the effects of species invasions. However, the interspecific interactions that result in the negative impacts on native species tend to be poorly understood. One contributing factor to this knowledge gap may be that the vulnerability of native species can vary between different life-history stages. For example, the parental care phase is often risky both for the developing offspring and care-giving parents. Accordingly, we investigated the interactions between invasive mud crabs, Rhithropanopeus harrissii, and native nest-building littoral fish, with a special focus on the sand goby, Pomatoschistus minutus. Firstly, our field survey demonstrated that while the recently established mud crab and native nest-building fish have different habitat and depth optima, their distributions also have a considerable overlap, with a high potential for interactions between them. Secondly, our laboratory experiments indicate that the crabs are likely to impact the fish negatively, especially by taking over occupied nests, as well as pre-occupying nesting resources that are of very limited supply in the studied population. We did not find evidence for successful predation on eggs guarded by male sand gobies naive to the mud crabs. Collectively, the results suggest that the invasive crabs have high potential to negatively impact native fish. Furthermore, the results support the scenario that the parental phase can be a particularly vulnerable life-history stage in face of novel selection pressures, such as species invasions.
KeywordsBaltic Sea Benthic fish Competition Mud crab Nest Reproductive behaviour
We thank the Finnish Foundation for Nature Conservation and the University of Turku for funding (to T.K.L.), and the Tvärminne Zoological Station staff for logistic support. We are also grateful to Maiju Lehtiniemi and the VIPU-project for additional funding towards the field survey (to J.Y.-R.) and for providing mud crab occurrence data (Fig. 1), which were based on the marine invasive species observations of the general public, reported at www.vieraslajit.fi. In addition, we thank Timo Rantanen for constructing Fig. 1, Vojtěch “Voltage” Lanta for statistical advice, Mikael von Numers and Linda Siltala (trainee at the Archipelago Research Institute) for assistance in the field, Natarsha Babic for improving the flow of the text, Cédric Tentelier for constructive assessment of an earlier version of the manuscript in Peerage of Science, and two anonymous reviewers for their helpful input.
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