Maddie Stannard explores the link between declining numbers of invertebrates, like dragonflies, and the damage being done to global wetlands.
Image credit: Pixabay
Any habitat seasonally or permanently covered with water can be regarded as a wetland – the definition even goes as far as to include coral reefs, alongside mudflats, marshes, fens, swamps, and, of course, peat bogs. Wetlands are vital havens for one in ten of the world’s known species, with Eurasian otters, marsh marigold, water voles and a wide variety of waders in the UK. Greater flamingos and West Indian manatees live slightly further afield, and these are just some of the organisms making wetlands their home. Acting also as massive carbon sinks, absorbing and sequestering atmospheric carbon dioxide, wetlands play a huge role in the fight against climate change and global warming.
So, how are we destroying them?
Thousands of hectares of wetland ecosystems are drained each year for housing and industrial development, as well as agriculture. Not only that, but as we pollute our waterways with sewage, phosphates and other run-off fertilisers, wetlands are suffering chemical changes making them unsuitable to support the life that has evolved to exist there. The Wildfowl and Wetlands trust reports that 80% of global wastewater that is left untreated, is released into wetlands around the world.
Every day, as the human race finds more and more ways to cause irreversible damage to the planet, it is often the keystone (but vastly under-appreciated ecosystems) that suffer the consequences. These water-saturated habitats are unable to escape the effects of climate change – with rising carbon dioxide concentrations in the atmosphere as a result of fossil fuel combustion, agriculture and other anthropogenic processes, causing global warming, wetlands are simply drying out. In a vicious cycle, the more we drain and build over wetland habitats, the more we burn peatlands, and the more of that stored and sequestered carbon we inadvertently release, we are only furthering our problem.
As well as those charismatic and popular species we know and love, wetlands around the world are home to creatures far smaller, but equally as fascinating, and just as important. Dragonflies, as fierce as their namesakes and voracious predators, exploit wetland habitats for most, if not all, of their hemimetabolous life cycle.
The Odonata (the name given to this particular grouping of carnivorous insects), the dragonflies and the damselflies (suborder Zygoptera), dominate the skies, using their aerial skill sets to hunt and chase other insect species, like mosquitoes which can carry malaria. The dragonflies existed in their current form even during the Jurassic period, and so their prehistoric origin makes them experts of longevity.
Their compound eyes (each made of 30,000 individual ommatidia: small photoreception units) allow them to hone in on prey while on the move, and their two sets of wings give them extreme control and precision while in the air.
Most of a dragonfly’s life is spent underwater, as larvae or nymphs. In fast-flowing or still freshwater wetlands, these drab nymphs spend usually one to two years on the riverbed, for example, undergoing a series of moults where their chitin exoskeletons are shed to allow the insect to grow, in a process called incomplete metamorphosis. Surviving larvae climb up emergent vegetation to undergo their final moult, transitioning into adult dragonflies ready to take on the world. Returning to wetlands to breed and lay their fertilised eggs on submerged vegetation (or directly into the water, depending on the species), dragonflies’ lives revolve around these aquatic habitats.
There are approximately 57 species of dragonfly recorded in the United Kingdom, with estimates of 7,000 species globally. And yet, the IUCN last year reported that 16% of 6,016 dragonfly species studied are at risk of extinction. While there was insufficient data to report on the conservation status of around 1,700 species, 95 of those studied are critically endangered.
More than one quarter of South and South-East Asian species are threatened, particularly due to the clearance of wetlands, and on top of this, more than a quarter of all insect species worldwide are threatened with extinction altogether. But is this really surprising, given that humans are actually destroying wetlands six times faster than we are rainforests?