Invertebrates
Invertebrates are small animals without backbones. Despite their small size they represent the most diverse group of animals on the planet. Of the 1.5 million known species, 97% are invertebrates (1.3 million total). Not surprisingly invertebrates have adapted to, and are found, living in every kind of environment, including waterways. Invertebrates that are associated with waterways are known as ‘aquatic invertebrates’.
In waterways and lakes there are many different types of invertebrates including: insects, molluscs, worms, flatworms, crustaceans, spiders, and hydra. Of these groups, insects contribute the largest number of different species. Often the larval, or immature stages are aquatic, living under the water; whereas most adult insects are terrestrial, that is, they live on land.
Although invertebrates are small and often overlooked, they play an important role in the ecosystem of a waterway.
Many small invertebrates feed on plants - for example leaf litter, twigs, and aquatic plants- taking in the energy the plants harnessed from the sun. When larger predatory invertebrates, or fish, eat these smaller invertebrates, they too are provided with energy. The same happens when larger fish or birds feed on the predatory invertebrates or smaller fish. This process is known as a food chain or food web.
Because the adult stage of aquatic insects is usually land based, they also contribute to terrestrial food webs, becoming a source of food for spiders, birds, lizards and other animals that live on land.
Consequently these aquatic invertebrates, which are frequently overlooked, are an essential part of both waterway and terrestrial ecosystems.
Additionally, aquatic invertebrates are useful in determining the health of a waterway. Because of their close links to the environment they respond quickly to any changes to that environment. Variation in substrate type, water flow patterns, water quality or water temperature occur, often as a result of changes in land use around the waterway or within the catchment, and this results in noticeable changes within aquatic invertebrate communities.
Aquatic insects also respond to changes in the types of vegetation growing along a waterway, because the adults rely on this vegetation for food and shelter. 'Clean water taxa' is the term used to describe aquatic invertebrates that are most sensitive to habitat degradation. Changes in the number and type of clean water taxa in a waterway will give a clear indication of whether the health of the waterway is becoming degraded, or is improving in health.
Objectives
There are a number of reasons for collecting information about the Styx River and its tributaries. These include:
To monitor habitat, aquatic plants and invertebrate communities over time.
To ascertain if there are any trends between changes in habitat and changes in invertebrate communities over a period of time.
To compare invertebrate communities in the Styx with invertebrate communities in other catchments within the Canterbury region.
To improve understanding of the current state of the in-stream habitat and invertebrate communities.
Method of Data Collection:
Firstly, assemble all necessary equipment including 1 long handled fine mesh net, 4 large pottles, preserving ethanol, waterproof labels and a pencil. Waterproof waders are often worn when collecting invertebrate samples.
First step
Enter the water at the zero metre point. Two samples are to be collected at this point.
Positioning your net to collect dislodged matter, disturb the substrate with your foot in a 30 cm band upstream of the kick net. If there are macrophytes in your sample area use your hand to brush them before collecting the sample, as this should dislodge any invertebrates into the water.
Move to the side of the channel you entered from and carefully swirl the kick net in the water being careful to keep the mouth of the kick net above the water. This is to wash out any fine sediment.
Splash water on the outside of the net to wash all of the sample material taken into the bottom of the kick net.
Up-end the kick net sample dropping all the contents into a large pottle.
Add some water from the stream and enough ethanol to make up an alcohol solution of approximately 70%. If the sample contains a lot of plant material or fine sediment more ethanol will be required.
Screw the lid on the pottle and attach a waterproof label to the pottle. Details on the label should include the site, date and transect number. Write on the waterproof label in pencil, as ink will dissolve if it comes into contact with alcohol.
Second Step
Repeat this whole process again, only this time the sample should be taken near the centre of the channel and for a distance of approximately 60cm across the channel in line with the zero transect marker.
After having collected 2 samples in line with the zero boundary of the monitoring site exit the stream.
Third Step
This process is again repeated at the upstream 10 metre transect mark where 2 further samples should be taken.
The resulting samples are now ready to be taken to a laboratory where each sample will be sorted using a microscope, and all invertebrates counted, identified and recorded. The numbers of each invertebrate type are then converted to a percentage abundance value.