Amazing Nature

Ready to Adapt - Animals of Seasonal Wetlands

Jun 2021
Author: Green Power
A Romer’s Tree Frog Liuixalus romeri
Tadpoles of  Romer’s Tree Frog (Liuixalus romeri) grow up quickly, and turn into  adult frogs to go on land before the water bodies disappear.
© Elaine Yuen

Imagine what it would be like if your home disappeared once every year! A seasonal wetland is a natural habitat that constantly changes between aquatic and terrestrial environments. To the animals that live there, it is like losing their home repeatedly year after year. The large water body appears only in seasons with abundant water, while at other times it is largely reduced or even vanishes. The living conditions seem tough, yet many little creatures find it ideal to settle as home, and have different ways to adapt to the ever-changing habitats.

Fast Growing

The water body of a seasonal wetland occurs only for a short period of time. Hence, for large aquatic predators it is not a desirable habitat. In the eyes of smaller creatures, however, this becomes a safer dwelling place. Many aquatic species have developed amphibious life cycles with short stages as eggs and larvae in water, allowing them to grow into ground-dwelling adults quickly as an adaptation to the fast-disappearing water bodies. For example, the tadpoles of the globally endangered and locally endemic Romer's Tree Frog (Liuixalus romeri) can grow into adults within four to six weeks. Some dragonflies and damselflies, such as members of genera Gynacantha and Lestes, also have fast growing larvae. These species live on land as adults, and go back to breed when the water bodies appear again.

A Hong Kong Paradise Fish Macropodus hongkongensis
The labyrinth  organ of the Hong Kong Paradise Fish (Macropodus hongkongensis) allows  it to absorb more oxygen from the air to resist the low-oxygen environment in  shrinking water bodies.

Highly Tolerant

As water sources and water bodies diminish, the density of aquatic animals increases. Insolation speeds up the rate the water body’s temperature rises, which greatly reduces the oxygen level in it. Toxic metabolic wastes accumulate and threaten the survival of the animals. Some species have evolved mechanisms to withstand the poor conditions. Macropodus spp., for instance, have specialised gill-rakers as supplementary respiratory organs, otherwise known as a labyrinth organ, which helps the fish to absorb more oxygen from the air in the low-oxygen environment. The Oriental Weatherfish (Misgurnus anguillicaudatus) is another example of a species well-known for its high tolerance. Besides using its intestine to assist breathing, it can adjust the pH level of its ambient water to reduce toxic ammonia waste entering the body.

The Oriental Weatherfish Misgurnus anguillicaudatus
The Oriental  Weatherfish (Misgurnus anguillicaudatus) is a hardy fish with a  variety of mechanism to go without food and water for a long time, as an  adaptation to worsening water quality as water bodies dwindle.
© Tommy Hui

Leaving Temporarily and Staying Dormant

When the water body is about to disappear, or when the conditions worsen, some fish species, such as Climbing Perch (Anabas testudineus), can leave water for a while. The species can breathe with its labyrinth organ and make use of its pectoral fins, tail and gill covers to support its body to move slowly on land. The Oriental Weatherfish again stands out with its ability to stay dormant in soft mud, and tolerate an arid environment without food for a long time until water comes again.