As you wander around the Royal Parks you’re likely to pass by one of our many lakes or ponds. As you spend a moment watching the wonderful waterfowl, take a closer look below the water - there's a hive of activity that you might not be aware of.
As part of our Summer of Kindness we want to introduce you to some of the curious aquatic life that dwells beneath the surface.
An almost villainous looking creature is the dragonfly nymph, apex predators of the aquatic invertebrate world. Dragonflies go through complete metamorphosis, which means that they develop from egg to larvae to pupae and finally to the flying adult. The nymph stage is the longest of these with some nymphs living for two years or more before they dramatically emerge to complete their development. If there are adult dragonflies inhabiting a water body, it is a clear indication that there is a good aquatic invertebrate population as the dragonfly nymphs feed on smaller invertebrates and occasionally very small fish. We regularly see darters and hawkers in the central London Royal Parks.
The aptly named sow louse is one of the most commonly occurring macroscopic aquatic invertebrates, found in temperate zones across the globe. It is very distinctive looking and resembles a wood louse. They can be found in all the major waterbodies in the Royal Parks in large numbers despite being encountered infrequently by visitors. The sow louse is also quite an underappreciated invertebrate as it is an excellent contributor to water clarity. They feed on algae and decaying submerged vegetation whilst being prey for predatory invertebrates, waterfowl and fish. They are most often spotted on detritus and decaying material that has been removed from the water, either by nesting waterfowl or maintenance works.
Rudd are a brightly scaled fish with brilliant orange to red fins, found in lakes and ponds throughout Europe. They are omnivorous and in the summer they prefer to feed near the surface of the water, eating floating insects, algae and submerged vegetation. Sometimes you might see them surfacing for this reason in large numbers. They are the most common fish in St James’s Park lake, but also occur frequently in several of our other large waterbodies. They require clear water with lots of aquatic vegetation and consequently they are a good indicator of water quality. Young fish form enormous shoals in the late summer and can be seen from the Blue Bridge in St James’s Park on summer mornings and evenings.
Perch are a predatory species of fish found in most of the water bodies in the Royal Parks. They are probably the most identifiable fish in Britain, striped with bright green and black scales. They rarely exceed 30cm in length, but they are veracious pack hunters, working together to corral and prey on smaller fish and sometimes other smaller perch in the shallows. Keep an eye out for darting shoals of smaller fish on quiet mornings and evenings as this behaviour is indicative of prowling packs of perch.
Swan mussels are the largest freshwater aquatic bivalve in Britain. Bivalves are the class of hinge shelled molluscs characterised by marine species such as cockles and mussels. Swan mussels often measure over 10cm across and have very robust shells that clamp shut rapidly if the mussel is disturbed. Their shells range from cream coloured to light green depending on the water conditions. They seem quite out of place in freshwater as they resemble marine bivalves, often being mistaken for clams or oysters when their shells are left by predators. They are rarely seen by people, but sometimes their shells can be spotted on dry land when they have been consumed by predators such as gulls. They are frequent in Regents Park lake and The Serpentine, providing a natural water filtering service which helps to cycle and balance nutrients.