How do river ecosystems provide the most efficient energy transfer function for the ecosystem service of fish production?

Ecosystem services are functions of rivers that are beneficial and/or valued by humans. Freshwater rivers and streams provide many ecosystem services, including fish production. Fish production is maintained by underlying functions of the river such as macroinvertebrates providing food. Figure 1 shows how fish production is provided in an ecosystem; the area highlighted is the part of system I will concentrate on.

Aspects of fish production as an ecosystem service

Macroinvertebrates provide many functions in rivers including sediment mixing, nutrient cycling and energy transfer through food chains. The function of energy transfer is particularly important because for macroinvertebrates to perform other functions they have to be supported by an energy base. The energy that is assimilated by the macroinvertebrates either comes from Autochthonus inputs or allochthonus inputs. That is from grazing on the in stream primary production or decomposing inputs from the riparian vegetation. Establishing the relative importance of the two forms is important for management in order to know which form is most important and to manage for this.
The primary production is mainly from algae, that has different traits and palatability for different macroinvertebrates. Different species of macroinvertebrates may prefer algae with different traits resulting in different energy transfer efficiencies depending on the traits of the organisms that are present. These issues are important to address so that systems can be managed to provide the best food sources for fish production by providing conditions most suitable for the organisms that best transfer energy in that environment.

Figure 2 show the pyramid of resources that results in fish at the top of the food chain, it demonstrates that for most systems the relative importance of primary production and decomposition is variable in providing energy for secondary production.

Figure 2: Trophic pyramid for the ecosystem service of fish production.

This study should help to answer the questions of whether there is an ideal periphyton community for fish production and how this can be maintained and also whether there is an ideal balance between primary production and allochthonous inputs. It will also help us understand if the community structure can be related to how the system is functioning or whether that is not enough to assess if the system is functioning well.