The purpose of ponds

Researching Tower Hamlets Cemetery Park’s aquatic insects with Europonds

Guest post written by Liam Nash (Queen Mary University of London), in collaboration with Laura Sivess (Natural History Museum, London) for the Europonds project as part of the Freshwater Biological Association.

From the Arctic circle to the Azores, there are thousands of ponds across Europe, everywhere from Alpine wildernesses to inner-city London. Great or small, these blue oases provide essential freshwater habitat for a massive diversity of amphibians, insects, plants and more. Many people’s first experience with nature is through ponds – enjoying an afternoon of pond-dipping for dragonfly larvae, or watching frogspawn develop into tadpoles. But ponds are not only important for these strange-looking, underwater creatures. They also hugely benefit their surrounding landscape. As with all things in nature, pond animals are tightly interconnected with their wider ecosystem, including that outside of their pond, on land.

Many pond insects, such as midges, mosquitoes and dragonflies, undergo metamorphosis, transforming from aquatic larvae to emerge as flying adults. Well-known is the mass mayfly emergence in spring, where millions of adults emerge just for a few hours to mate before dying. Anyone who spends time near water will be acutely aware of adult midges and mosquitoes, winged and able to bite us. But, as much of a nuisance as these animals are for us, they are a food source for many other species of bird, bat and spider. Ponds become “insect chimneys”, attracting predators for miles around to eat these newly adult aquatic insects.

 

However, we understand very little about the importance of this food source. What factors influence it, and how does this vary in different environments?

Europonds is an exciting pan-European research project targeting these questions. Scientists from all across the continent are examining the impact that pond insects, as a food source, have on surrounding land animals. We are two London-based PhD researchers heading up the UK team. The Cemetery Park is a key site to investigate the benefit of emerging insects on urban wildlife.

Catching the insects as they leave the water is made possible with emergence traps, essentially floating pyramids of netting. After counting and identifying the insects, they will be sent to Austria for ‘fatty acid analysis’ to assess their nutritional value for birds and other animals. We’ll also look out for the cast-off ‘skin’ (called an exuvia) dragonflies leave behind when they emerge, collect larvae using nets, and take some water samples to build a complete picture of everything going on, in and out of the pond.

Ultimately, all the teams will share and collate their data from fifteen European countries carried out in autumn, winter, spring and summer. This will be used to determine how ponds impact their surroundings, what pond characteristics are most important and how this varies over space and time. Everything we find will be shared with the Friends, to see how their ponds, specifically, are providing food for their own wildlife. Each year the Cemetery Park attracts around 60 bird species, 30 butterflies and nationally rare beetles and spiders into the heart of London. It may well just be that the ponds are part of the reason why.