Macroinvertebrates - Focus on 'bugs'

Welcome to this part of Council's site. We hope that you will enjoy exploring it and that you will take the time to view the video files that show the live 'bugs' under microscopes. If you get to know the macroinvertebrates that live in different parts of streams, you will be able to check water quality very easily.

Click here to find out what macroinvertebrates are.

This map shows the sites that we sampled in the autumn of 2002. We have chosen this way of getting into the site because the 'bugs' that are found in any stream are affected by things like shade, pollution, and the amount of oxygen and sediment in the water. To view a stream, click on a red star on the map or follow the links below Lincoln stream Opanuku stream (lower) Opanuku stream (upper) Oratia stream Glen Esk stream

We have included two streams with muddy beds, as muddy beds are typical of many Auckland streams. These are the Oratia and Lincoln Streams.

There are also two sites on the Opanuku River. While we were sampling and filming to build the website, we made a short video for schools, to show the differences between different parts of the river. Click here for more information about the video.

Generally, the streams in the upper parts of the catchment have better water quality than those which run through urban areas. In Waitakere, we have lots of streams, many of which are small and run through private gardens. Most native fish need to migrate to lower parts of streams to breed, so these sections of streams are really important.
 

What are Macroinvertebrates?
 

Streams are homes to lots of tiny animals that live on and under the rocks, on the water plants or on bits of wood lying in the stream. These animals include insects, crustaceans, molluscs, worms, leeches and anemones. They are all tiny - 3mm to 20mm long - and they are difficult to see at first glance. Collectively they are called macroinvertebrates - insects without backbones, which can be seen without the help of a magnifying glass or microscope.

Click on the images to find out the names of some of the bugs which belong to these groups.

Insects	Molluscs	Leeches
Crustaceans		Worms

In good quality streams there may be 30 or more different types of macroinvertebrates in one small area, and there may be many thousands of individuals per square metre of streambed.

What can stream invertebrates tell us about streams?

When people start looking at streams to see how healthy they are, they get a reasonable idea of the water quality from testing for things like temperature, dissolved oxygen, artificial nutrients and acidity, and from checking to see if there are trees and other plants beside the stream. To get a more precise answer about the health of different sections of the stream, it is a good idea to collect some macroinvertebrates and then sort them to see what range of animals is there and which kinds of animals occur most frequently.

This is useful because lots of stream invertebrates have specific habitat requirements. We know which species require cool water and high dissolved oxygen levels, and which species can tolerate the typical contamination from city road runoff. 

Generally, the more different types that are present the better, and the presence of mayfly and stonefly larvae is a good sign. This is because they can only survive in streams that stay cool and have a reasonable amount of oxygen dissolved in them. If there are only a few different kinds of animals and a high proportion of snails and worms, the stream is not in good health. Some invertebrate groups are associated with algae-covered habitats, some thrive in waters polluted by excessive organic waste, some are specialised to live in near-stagnant conditions, and some are tolerant of quite high levels of heavy metal pollution. A total lack of stream invertebrates is the result of a serious habitat or water quality problem. 

Why are invertebrates important?

Many stream invertebrates feed on the green and brown slimy algae growing on streambeds, and without these invertebrates our streams would probably be much more slimy than they are. Some invertebrates feed on leafy material that drops into streams from surrounding trees, breaking down plant matter and "cleaning" our streams. Others feed on fine particles drifting in the current, and some feed on other invertebrates. 

Our native and introduced freshwater fish feed on all of these invertebrates. There are very few fish in those streams with only a few aquatic invertebrates, or in those streams where snails are the dominant species, as they are not are not a good food source.

Surveying stream invertebrates

Stream invertebrates are often visible as soon as you look closely at a stone lifted from a streambed. It is a good idea to place a small net or even a kitchen sieve downstream of stream stones as you turn them over, because this will collect the invertebrates washed off the stones by the current. If this sample material is placed in shallow water in a white tray, the movement of stream invertebrates will be easier to see. A white tray is also useful for looking at invertebrates amongst a handful of water plants from a weedy stream. 

Small invertebrates can be picked out of the tray with a leaf, stick or eye dropper and placed into a small container for closer inspection. A magnifying glass or binocular microscope will allow you to see these amazing creatures in greater detail. Stream invertebrates found in flowing water may not survive for long in containers, so keeping them cool and in very shallow water will allow these invertebrates to live for longer out of the stream.

Remember, many stream invertebrates including some three-tailed mayflies, two-tailed stoneflies and cased caddisfly larvae are mostly restricted to cool waters and are therefore absent from most unshaded, slow-flowing streams. Moderate to fast flow is also important to many invertebrates because flowing water assists their breathing underwater. They also need firm surfaces to hold on to in fast-flowing water. The best places to find a wide range of invertebrates is stony-bedded, fast-flowing sites (or "riffles") especially in bush-covered streams. So, you may not find all the all the invertebrate groups shown on this website, as the stream you are surveying may be degraded.

What can affect the existence of invertebrates at some sites?

Removal of trees from beside farm or city streams:

• Causes overheating from sunlight so that the water becomes too warm for some of these sensitive invertebrates.
• Means that fewer branches fall into streams for invertebrates to live amongst, and there is less leafy material for some species to feed on. 
• Reduces shade and encourages long filamentous green algae, which are not suitable as food for most invertebrates to grow and may sometimes smother the streambed. 
• Means that there are fewer resting places in trees on the banks for the flying adults of some of the stream insects.

Sediment getting into streams is a problem 

Partial shade over a streambed is the best option because enough light needs to reach the stream banks to allow the growth of low-lying plants to help stabilise the banks. Sometimes there is too little low-lying stream bank vegetation under dense forest canopies and, as a result, the stream banks erode more easily. Earthworks in the catchment can also add lots of sediment when it rains. Sediment that gets into the stream from erosion covers the water plants and clogs the gills of animals.

Piping streams underground makes them unsuitable

When streams are piped underground to allow for urban development, they provide very poor, unnatural habitats for invertebrates. Piped streams lack the light necessary for water plants or the edible forms of algae to grow and they provide no shelter for fish and invertebrates in times of flood. 

Straightening streams causes problems

Surface streams that have been straightened or lined with concrete also lack shelter from floodwaters and cover from predators, so they seldom provide a habitat suitable for invertebrates. 

Flow reduction

Reducing the amount of water in a stream system happens in different ways:

• Water is sometimes pumped out of streams for city supplies or for irrigating farmland. If too much water is taken, the stream may stop flowing altogether. 
• Wetlands are drained reducing the reservoir of water that once kept many streams flowing, making it more difficult for sensitive animals to survive.
• Trees such as pines, which draw large amounts of water from the ground, are planted reducing the amount of groundwater that would otherwise reach the streams. This reduction in flow allows fine sediment and algae to settle out of the water onto the bed smothering invertebrate habitats. 

Water pollution

• Many substances poison invertebrates and fish when carelessly tipped into streams or into drains that lead to streams. It is important to be aware that drains along roads, drives and footpaths are usually designed to carry rainwater to a nearby stream. They do not direct water to a treatment plant. People tip wastes down stormwater drains killing fish and invertebrates every year. 
• Drainage from city roads always contains some contaminants including a range of petrochemicals and heavy metals. These chemicals can be harmful to stream invertebrates especially if the runoff enters small streams that provide little dilution.

Streambed instability

Most of the larger mayflies, stoneflies and caddis flies require cool, fast-flowing water and hard streambed material for attachment.

Flooding, which increases as a result of the high levels of impervious surfaces like roofs, roads and car parks in urban environments or when trees are removed, significantly reduces streambed stability.