Dispersal of aquatic organisms in karst landscapes

The project Dispersal of aquatic organisms in karst landscapes aims to investigate colonization patterns of aquatic organisms in the Balkan Peninsula. Most of the Balkan Peninsula is covered by karst: usually a limestone or dolomite landscape defined by specific features such as flutes, sinkholes, vertical shafts, intermittent/sinking streams and/or caves, produced by water that dissolves the soluble rocks. A special characteristic of karst is the complex aquatic network characterized by variable water conditions throughout the year and many underground water connections. Therefore, karst represents a special environment for the resident organisms, which are highly influenced by the unstable aquatic conditions. Previous studies on dispersal routes of aquatic organisms in the Balkan Peninsula came to opposing findings. While some concluded that karst landscapes act as isolating factors, others found evidence of subterranean migration through underground water links. However, all the findings were a kind of by-product of studies, actually investigating population genetics or biogeographical questions not one aimed especially at resolving the hypothesis of underground migration. In this project, the migration in karst landscapes will be exclusively assessed using classical methods combined with the most modern techniques, such as next generation sequencing-based population analysis and state-of-the-art environmental DNA tracking. The project aims to resolve the population structure of three very different groups of aquatic organisms (fishes, cave olm and isopod crustacean) and to compare it with findings in the hydrological literature to answer the question if any of them migrate underground. This international and interdisciplinary project will contribute valuable knowledge for biological disciplines such as biogeography and biodiversity in karst landscapes. Moreover, it will also crucially influence research areas such as karstology, hydrology and water management. Finally, the project will increase the understanding of the high degree of endemism and potential for natural recolonization of areas, where populations disappeared and therefore represent a very important basis for conservation genetic and conservation management studies in karst landscapes.

The project Dispersal of aquatic organisms in karst landscapes aimed to investigate colonization patterns of aquatic organisms, especially fish, in the Dinaric Karst. The Dinaric Karst extends from Italy to Albania along the Adriatic coast of the Western Balkan Peninsula and is one of the best studied karst areas. It is characterized by typical karst phenomena such as karst poljes above the ground and sinkholes, caves and underground rivers below the ground. These features are formed by the ongoing process of karstification - water dissolving soluble rock, resulting in a complex water network connecting surface and underground water bodies. As a result, karst provides a unique environment for resident organisms that are strongly influenced by the unstable water conditions. Previous studies of the dispersal pathways of aquatic organisms in karst have been contradictory. Some identified karst landscapes as isolating factors that prevent dispersal between isolated populations, thereby inducing speciation - the emergence of new species. Others found evidence of subterranean migration through groundwater connections. In this project, we observed different fish species in karst areas to infer their dispersal potential in karst and whether they use underground water connections for dispersal. We included species that are adapted to fluctuating water levels in karst and can spend up to several months underground. These are not true cave species, they do not have the typical reduction in coloration and eyes. We also included "normal" surface-dwelling fish species. Our research showed that there is some dispersal through the underground water connections, but the population structure is mostly a consequence of the development of the water systems through history, and karst landscapes seem to be a limiting factor for fish dispersal. Thus, many fishes are locally endemic, occupying only one or two small rivers in limited karst areas, making them highly vulnerable as a single pollution event could wipe out the entire species. Furthermore, our study found that the fishes that have adapted to partial cave dwelling show some adaptation, such as a reduced number of scales. Their population density has decreased significantly in the last 20 years due to human intervention: introduction of non-native species, excessive water use and poaching. Therefore, their conservation should be a priority. This study also tested the use of the population structure of organisms to infer complex water conditions and possible water linkages in karst landscapes, and showed that this type of study can identify past linkages between water systems that are no longer visible in the present. Thus, the project has added important knowledge to the fields of biology of organisms in karst areas, but has also influenced research fields such as karstology, hydrology and water management.