Invertebrates are the most diverse of all life in the animal kingdom. Invertebrates are also the most important organisms in wetland habitats for he range of roles that are played by different invertebrates. Insects such as mayflies and caddis flies provide food for a whole range of like such as fish, birds and other invetebrates. Also insects such as mayflies show the water quality of rivers in biotic indexes. This is because insects such as mayfly nymphs are sensitive to oxygen levels in the water in which require fast flowing well oxygenated water, whilst insects such as midge larvae or bloodworm are able to live in areas that are polluted and low in oxygenated water this is because bloodworms have heamoglobin in the blood enable to transfer oxygen more efficiantly than mayfly nymphs so bloodworms can survive in areas where mayfliy nymphs can't. So this makes an effective way to record the water quality of a river of lake.
Where invertebrates are found they are important to the ecosystems whether its for food for other animals or has important functions with in each ecosystem. On coral reefs the corals, spunges and the crusteacans provide shelter, food and services as partnership to other lifeforms.