Development of an Index of Trophic Completeness for benthic macroinvertebrate communities in flowing waters

The analysis of the trophic structure of benthic macroinvertebrate communit ies can be used in biological assessments of the condition of river ecosyst ems. Using the trophic, or functional approach, the Index of Trophic Comple teness (ITC) was developed. The goal was to overcome the problems and drawb acks of using conventional diversity or biotic indices in biological assess ments of rivers, such as limitation to distinct geographical regions or foc us on species richness without regard for ecosystem functioning. Following an extensive review of the literature on the trophic characteristics of ben thic macroinvertebrates, a large number of species (+/- 300) were character ized according to a number of trophic criteria: plant:animal ratio in the d iet: feeding mechanism, food size, food acquisition behaviour, and energy a nd substance transfers. On the basis of their trophic characteristics, the species could be divided into 12 trophic groups. After examination of data from geographically diverse rivers, it was concluded that any undisturbed r iverine benthic macroinvertebrate community should be represented by member s of each of these 12 trophic groups, with each group fulfilling a function in the benthic community. Being a community which plays a central role in the functioning of the aquatic ecosystem, the benthic invertebrates are exp ected to respond to disturbances to the hydrobiocoenose. The outcome of an ITC assessment is clearly presentable in the form of a pie graph with 12 we dges, each representing one of the 12 defined trophic groups. Functionally complete communities are represented by 12 wedges; a blank wedge indicates that a trophic group is not represented. This paper describes the prelimina ry developments in the ITC method, its potential as a biological assessment method in rivers in different geographical zones, and presents examples of trial mappings of Russian and European rivers. The application of the ITC to these rivers demonstrated the absence of ITC trophic groups at sites und er the influence of anthropogenic activity.