INTRODUCTION

Aquatic invertebrates can be found in just about every imaginable freshwater habitat. They bridge the divide from glacial outwash to estuaries, torrential waterfalls to stagnant ponds and from water trapped in the tiny bracts of plants to the largest of our lakes and rivers. Across all of these habitats, invertebrates constitute the bulk of species diversity and account for most of the secondary productivity, as well as performing a multitude of ecological roles. They also create the vital link from primary producers and detrital materials to higher trophic levels. Not surprisingly then, the contribution of restoration activities to the structure and function of aquatic systems will be mediated largely through responses of invertebrates.

Aquatic invertebrates are represented by at least nine phyla in freshwater ecosystems, including the arthropods, molluscs, worms, rotifers and nematodes and many of the family groups are key players in food web structure and function. Various invertebrates may graze on algae, vascular plants and detritus or they may prey upon bacteria, protozoa, other invertebrates, and sometimes even fish or larval amphibians. Others also are parasitic.

Invertebrates influence nutrient cycling and rates of primary production in most aquatic environments. They play an important role in decomposition processes and in altering the transportation rates of organic and inorganic particles in streams (e.g. Wallace & Webster, 1996).