Seed dispersal is a fundamental process for plant communities, especially now that our changing world demands rapid colonization of new habitats. Long-distance dispersal is especially important for plant population persistence and range expansions.

The contribution of fishes to plant seed dispersal in aquatic ecosystems (ichthyochory) has long been overlooked. Although we know fish disperse seeds, it is largely unknown where, when and how far – especially in temperate regions. Here we studied the potential of fish to disperse seeds locally and over long distances, specifically hypothesizing that i) dispersal by fish depends on the season, ii) individual fish contribute differently to seed dispersal, and iii) water regulating structures (barriers) inhibit seed dispersal.

We tested our hypotheses by acoustically tracking 71 common carp (Cyprinus carpio) with 21 hydrophones in a 38km-long study system for >2 years in the Netherlands. We calculated potential seed dispersal throughout this system by combining nearly 1.5 million location registrations with experimentally assessed retention times of seeds after ingestion (i.e. time between ingestion and egestion).

Seed dispersal on local scales was quantitatively most important during summer and autumn, with high dispersal potential in a range of four kilometres from the location of seed ingestion. Long-distance dispersal up to 16 km was possible at low probabilities in spring. In winter, most seeds were egested within two km. Maximum and median dispersal distances varied widely among individuals, emphasizing variation in effectiveness among individual fish for seed dispersal. Less than two percent of all fish movements reached beyond sluices and weirs, indicating that anthropogenic barriers in freshwater systems strongly reduced the potential of common carp to disperse seeds to these areas.

This study shows that common carp can locally disperse plant seeds with high probabilities, and over distances up to 16 km with low probabilities throughout temperate ecosystems. This can contribute to restoration and maintenance of plant community diversity. However, this ecosystem function of fish to plants requires intact fish populations – because not all individual fish contribute equally to dispersal – and unrestricted connectivity throughout aquatic ecosystems.

Temperate fish (common carp) were tracked using a Vemco positioning system in a temperate freshwater system in the Netherlands. Based on fish movements, their potential to disperse seeds of wetland plants was assessed.

We provide two data files in .csv format and one file with all background information in .xlsx format. In case of questions please contact Casper H.A. van Leeuwen (c.vanleeuwen@nioo.knaw.nl)