Adaptations: Rivers and streams

Rivers and streams are constantly flowing bodies of water. Their currents present challenges for the plants and animals that live in and around them. But many species are very well-suited to these ecosystems! To help them survive, these plants and animals have developed special features and behaviours – adaptations. The Chinook salmon is a prime example of a fish that is well-suited to river and stream ecosystems.

When Chinook salmon are born, they start their lives in freshwater rivers. As they grow, they swim downstream and eventually reach the ocean, where they spend most of their lives. But when it's time to lay their eggs, they must return to the same river where they were born. So, they have to go from living in saltwater to living in freshwater again. To do this, Chinook salmon have adapted.

Their gills and kidneys change to allow them to maintain the appropriate balance of salt and water in their bodies. Chinook salmon bodies are also streamlined, with robust muscles. This helps them swim smoothly against strong currents. They can even leap three metres in the air over obstacles like rocks and waterfalls to reach their spawning grounds! The freshwater mussel is also well-adapted to rivers and streams.

It extracts food particles from flowing water through a process called filter-feeding. Specialised structures pump water through their bodies, while tiny hair-like strands called cilia trap food particles. Insects, too, have adapted to life by rivers and streams. Dragonflies spend a significant portion of their life cycle as larvae in streams and rivers, equipped with gills to extract oxygen. Once the larvae mature, they develop long, slender bodies and four powerful wings.

These help them hover above the water and snatch prey with their legs. For plants living in rivers and streams, the biggest challenge is the constantly flowing water. However, aquatic plants have evolved to thrive in these environments. There are three main types of aquatic plants. Eelgrass, with its long, flexible stems and narrow, ribbon-like leaves, is an example of the first type.

It grows completely underwater and is a submerged aquatic plant. Its structure allows it to sway and bend with the current, reducing damage caused by the force of the constantly flowing water. The second type has leaves that float on the water's surface, while their roots dangle below in the water. These are floating aquatic plants. Floating aquatic plants, such as water lilies, have broad, flat leaves to maximise their exposure to sunlight for photosynthesis.

Their roots are long and feathery, with tiny root hairs. These increase the surface area of the roots so they can absorb more nutrients from the water. The third type is rooted in the riverbed, but has stems and leaves that extend above the water's surface. These are emergent aquatic plants. Their sturdy, upright stems provide stability against the current, while their waxy or hairy leaves repel water to prevent damage.

Cattails are one example of an emergent aquatic plant. Their seeds are fluffy and buoyant. This allows them to float on the water's surface and be dispersed by the wind or water to new areas. Through their many adaptations, plants and animals of rivers and streams are able to survive, and thrive, in these complex ecosystems.