Biodiversity drivers

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Work Package 2: Biodiversity drivers

A complex array of natural physical, chemical and biological factors are important in influencing the distribution and abundance of fish populations and other aquatic biota. The principal factors driving fish community structure in rivers appear to be related to catchment topography, flow regime and water temperature. Impacted on these factors are the effects of human manipulation of the river environment, plus the potential role of climate change. Climate change is predicted to lead to considerable changes in faunal composition of aquatic systems through alteration of environmental characteristics, especially hydrological regimes and loss of habitat, and proliferation of lower latitude and invasive species. However, the impacts on freshwater fish and fisheries have received limited attention, largely because there has been limited transferable linkage between fish communities, habitat characteristics and especially and river flow regimes.

Recent and on-going research has tended to focus on specific issues in localized situations, and hence failed to assess fully the factors influencing the dynamics of riverine fish populations from a catchment-scale perspective. There is, thus, a need to research the factors, both biological and environmental, that affect the abundance and distribution of fish populations and the mechanisms by which these factors operate. The objective of this work package is to identify the key descriptors of river form and function that affect aquatic communities and how modifications and manipulations of rivers alter available habitat for biota.

Task 2.1: Characterisation of fish species habitat and environmental requirements

Previous research has suggested that there are a number of distinct fish community types in rivers, and that these are regulated by, and behave differently to, environmental variables, especially flow. Meanwhile, a number of similarities have been observed in species responses to the physical habitat in different river types of different countries. This task will build on recent research and fish assemblage typologies developed under the EU FAME and EFI+ projects (, to determine the key environmental, physical and biological characteristics that influence fisheries population and community structure and habitat for species.

Task 2.2: Linkages between geomorphological and hydrological conditions and community dynamics

Current understanding of the drivers between dynamically varying hydro-morphological characteristics and fish community changes is weak. Information exists to improve this understanding substantially, such as the identification of synchronous dynamics over large scales, but this requires considerable investigation and compilation to determine the critical factors affecting the various life stages, and identify the causes and rates of recruitment success and how these relate to hydro-morphological parameters. Consequently efforts will focus on improving this understanding. Full use will be made of outputs of ecological modelling using tools such as MESOHABSIM and RIVPACS. Key habitat drivers will then be determined for specific life stages and the fish communities as a whole.

Task 2.3: Role of human intervention in defining species and community dynamics.

Human pressures are known to alter the distribution and abundance of biota through change in habitat quality and quantity, alteration of the habitat characteristics and perhaps most importantly in river modification of flow dynamics. This is compounded by global environmental changes and biological pollution. A fundamental component of this project is to gain a better understanding of how biota, in particular fish, respond to human pressures and which environmental characteristics/variables contribute to the changes observed. This is of particular relevance to this project because it will help support the design of rehabilitation actions that address the detrimental components of different human pressures. For example, to assess the wider environmental impacts associated with maintaining longitudinal and lateral connectivity (e.g. passage of fish past obstructions, and into backwater and refuge habitats), the following activities will be carried out: Examining fish community structure along longitudinal and lateral gradients in relation to different environmental, geomorphological and hydrological regimes. Determining optimal habitat and flow regimes to ensure fish species are able to successfully complete their life cycles. A simple method of assigning an impact / sensitivity index, such as one of the habitat simulation or RHABSIM methods will be used as the template for this work. Task 2.4: Generalizing biodiversity drivers

Biodiversity drivers are generally known at the local level, which makes it difficult to define management plans from a catchment-scale perspective. It is therefore essential to identify limits in the generalisation of physical drivers over catchment networks or larger scales, and to review recent efforts towards this goal. This task will build on developments of GIS-based models and aerial photographs for extrapolating hydrologic, hydraulic, substrate patterns over catchments, as well as indicators of physical habitat quality. Particular attention will be given to the uncertainty associated with spatial generalisation, a neglected but important issue.