Ministry of Agriculture entomologist Mike Bowie with insect boxes. TIS/24020901
Last week in our Te Ipukarea Society article, we touched on some of the water quality monitoring that can be done in our streams to help determine if they are healthy or not.
For today’s article, we ask Ministry of Agriculture entomologist (that is a fancy word for insect scientist) Mike Bowie, a few questions about what we might find in our freshwater streams, and why they are important.
are stream macro and micro invertebrates?
Macroinvertebrates are insects and other
invertebrates you can see with naked eye. e.g. dragonfly larvae, prawns,
snails, mosquito larvae, worms.
Micro invertebrates require a microscope to
see as they are smaller. e.g. Protozoa and other single-celled organisms, small
or immature invertebrates.
is their role in the stream?
They are an integral part of our food webs.
They eat microbes, live and dead vegetation, algae, worms, dead animals/organic
matter, etc. They help clean up the streams. Birds, fish, eels, insects and
larger crustaceans rely on them for food.
can their presence tell us about water stream quality?
Because macroinvertebrates live in the
stream for most, or all of their time, they have to put up with all that we
‘throw at them’. This may be nitrates, phosphates, pesticides, bacteria (E. coli) and other pollutants that run
off our land or chemicals we don’t dispose of properly. Working up the land
near streams also exposes our precious waterways to siltation which fills the
gaps between the rocks in the stream bed where macroinvertebrates live and
Some aquatic invertebrates are more
susceptible to low oxygen levels, high nutrients, animal effluent and chemicals
than others, so we can use known tolerances by species as indicators of water
quality. Just like the canary in the coal mine – if the sensitive species are
alive and present in the waterway, then the water is in good health; if the
sensitive species are absent then the water quality is too poor for them to
are the methods involved in catching, and identifying them?
The main tool for catching
macroinvertebrates is an aquatic net. It is triangular in shape to allow the
horizontal end of the net to sit on the streambed. By disturbing the stones
just upstream from the net, invertebrates get dislodged and float into the net.
The net contents are tipped into a white tray and invertebrates are sorted and
kept in sample containers – that’s the easy part! Identifying can take time and
a microscope to differentiate between the different cryptic species. Shrimp
species for example may differ in appearance by some small shape or hairs which
is very difficult to determine in the field.
can we do to improve our streams’ health?
Planting natives around streams have many
benefits or us and the species living within:
Plants stabilise banks from
Plants shade the water to help
keep it cool which reduces algal growth
Plants reduce silt running into
Some plants are phytoremedial
(suck up and use nitrates/phosphates)
Plants provide habitat for
birds and invertebrates
Plants can slow water movement
down in floods
is it important for us to care and want to know more?
happens in our stream also impacts the ecology within the reef – the food webs
are linked. Many of us are naïve of the species living around us, providing
ecosystem services (e.g. pollination, predation, phytoremediation,
decomposition of organic matter). When we appreciate species and their ecology,
we are more likely to care for them.