Aquatic Invertebrates
Aquatic Invertebrates of the Avalon Marshes
The Avalon Marshes have a RAMSAR designation as an important international wetland area. This is largely due to the aquatic invertebrate population that exists here and supports a growing list of other species.
Base of the food chain
Aquatic invertebrates play an important part in maintaining the biodiversity of the area, perhaps most importantly as the biomass at the bottom of the food chain. For example, frogs lay masses of eggs, “frogspawn” which hatches into many thousands of tadpoles. If all those tadpoles grew up into frogs, we soon would not be able to move without stepping on a frog. Most of them end up as food for a larger creature. Without the large numbers of frogs that inhabit the Avalon Marshes, we would not see the superb populations of herons, egrets and bitterns that inhabit this area and delight visitors. If the frogs did not have thousands of aquatic invertebrates such as mosquitoes and flies to feed on, they would not survive, therefore neither would the creatures that feed on the frogs. It is a similar situation with mosquito and fly larvae that spend their early stage underwater. They largely end up as food for fish, dragonfly, damselfly and predatory aquatic beetle juvenile stages.
Dragonfly and damselfly nymphs
The dragonfly and damselfly nymphs that emerge as adults in April/May in their hundreds of thousands, form an important source of food for the migratory falcon, the Hobby. These birds spend the winter in Africa, arriving back in the UK in early May. After such a long migration, they need a feed before starting to nest and so spend most of May feeding on dragonfly and damselfly adults. They then find a crow’s nest that is no longer in use, as the crows have fledged by that time, and they raise their family in that before starting the long migration back to Africa for the winter. Places such as the Avalon Marshes, with such a concentration of dragonflies and damselflies are an important stop off for large numbers of Hobby during May.
Aquatic molluscs
Aquatic molluscs are very numerous and probably form one of the most important sources of biomass within the pools and ditches. They are herbivores and keep the aquatic vegetation in check as well as being a food source for many other species. They range in size from the tiny Shining Ramshorn Snail to the huge Swan Mussel and have a vital role to play in keeping our aquatic environment healthy.
Healthy waterways
Some aquatic invertebrates perform a very important job in maintaining the health of our waterways by helping to clear the detritus that falls to the bottom of the pools and ditches. The Hog Louse (think submarine woodlouse) exists in large numbers at the bottom of pools and ditches and eats decaying vegetable matter. Many other worm species perform a similar function and keep our ditches cleaner than they would otherwise be.
Monitoring aquatic invertebrates
RoAM has an important role to play in monitoring the state of these important populations of invertebrates. They are an early warning system when things go wrong, their populations decrease dramatically, and a signal that all is going along nicely when they are in good numbers.