Invertebrates and stream health

Benthic invertebrates have long been recognised and widely accepted in water quality monitoring as indicators of stream health, as many species are known to be sensitive to pollution or habitat modification.

Insect larvae are the most commonly collected life stage in aquatic habitats, and primarily comprise the majority of aquatic invertebrates in terms of biomass and species. Most aquatic insects emerge as winged, terrestrial adults in the warmer months, where they may disperse to another stream, mate and lay eggs. Adult aquatic insects and can form an important food resource for fish, spiders, birds and even bats.

Mayfly larva Rallidens.

Streamside vegetation, instream habitat complexity and stability are important components of stream restoration projects, but what if our target organisms and/or invertebrate community structure are absent, or have failed to re-established to predicted expectations?

Natural recolonisation of a restored habitat can become more difficult or non-existent, particularly if there is lost connectivity with a perceived sources of colonists or the organism has low dispersal ability (e.g. due to a short life history, a non-winged life history stage or they are poor fliers). Subsequently, population recovery may shadow physical recovery of the habitat. As a consequence, community structure and function may be also delayed because the rates of arrival and the sequence of species arrival can strongly influence the resulting community.

Artificial introduction of aquatic invertebrates may be an option to ameliorate stream restoration. This may include ‘the re-introduction of native, aquatic invertebrate species with the purpose of restoring viable populations, that have become locally extinct, and are unable to repopulate suitable, restored habitat by natural means. For aquatic invertebrates, and in particular insects, this may need to encompass many life history stages such as eggs, larvae, pupae and adults. Past and present distribution of target invertebrates may dictate what species should be expected within a restored habitat. 

Life histories of common invertebrates

larva (singular), larvae (plural) – young or juvenile form of an invertebrate. If something relates to larvae, it is said to be larval.