The Drainage Services Department (DSD) has implemented a pilot project on biodiversity improvement of drainage channels by rehabitating river habitats to bring back fluttering fireflies of rare species. Recently, the DSD together with the Firefly Conservation Foundation and a group of secondary school students visited one of the pilot sites, Kwan Tei River in Fanling, to release firefly larvae to the river channel where they would continue to grow and reproduce. This time, I have particularly invited a colleague of the DSD and the chairman of the foundation, to share with us the work of river rehabitation and its results, as well as the journey of how fireflies return to nature.

The number of fireflies as an indicator of water quality

In carrying out river training works, apart from considering the required drainage capacity to reduce flooding risk, the DSD tries its best to conserve the river’s natural habitat and introduce various water bodies revitalisation elements that can improve biodiversity and enhance ecological value. In so doing, the DSD tries to create an aquatic habitat suitable for the growth of insects and various species, with a view to striking a balance between flood prevention and conservation.

In 2013, the DSD invited the Firefly Conservation Foundation to co-work on the “Study and site trial on biodiversity improvement of drainage channels through rehabilitation of habitats for water-related organisms” to restore river ecology through such means as improving water quality and rehabilitating river habitats. The pilot sites include Kwan Tei River in Fanling, Kam Tin River in Yuen Long, and part of Ping Yuen River in Ta Kwu Ling. By monitoring the number of fireflies found, the project’s effectiveness in boosting biodiversity could be assessed. Engineer of the DSD, Mr. TAM Kit-fan, Keith, says that the existence of fireflies has all along been regarded as a biological indicator of unpolluted waters due to their extreme sensitivity to water quality. Their survival points to the very good water quality of rivers.

Creating natural habitats for fireflies

The whole rehabilitation project was completed in September 2016. Not only has it improved the ecological environment instream, but it has also achieved biodiversity enhancement. Taking Kwan Tei River as an example, Mr. Keith TAM says that a lack of water mobility in the river itself, coupled with its rather high water temperature due to direct exposure to sunlight, has made it hard for aquatic organisms or insects to settle there. The project team decided to re-arrange rocks on the riverbed to create waterways of various velocities, and grow suitable plants. After revitalisation, the river has become a suitable habitat for snails - food for fireflies. Besides, insects can rest in the rock crevices to avoid being washed away by floods or rainwater.

According to the Chairman of the Firefly Conservation Foundation, Mr. MAK Siu-fung, Mark, their study also shows that after completion of the rehabilitation works, the number of fireflies has increased from a few to about 50 along Kwan Tei River within 12 months, including a very rare aquatic species - the Aquatica ficta. This very rare Aquatica ficta has once disappeared from Hong Kong for more than a century before it was rediscovered in Tai Po in recent years. Currently, there are no more than 300 Aquatica ficta fireflies in Hong Kong, with more than 20 making Kwan Tei River their home.

Bringing fireflies back to nature

Recently, the DSD, Firefly Conservation Foundation and Stewards Pooi Tun Secondary School, forming a group of about 40 people, visited Kwan Tei River for an activity to release firefly larvae to nature. Since last year, 140 students of the secondary school have joined the “Sparkling Life” programme to spawn and rear firefly larvae in a laboratory. The firefly larvae released on this occasion had been reared by the students. During the release, the students had to carefully place the firefly larvae in suitable locations, such as a shaded area under the leaves, for them to slowly adapt to the new environment. Some students said that they had devoted a lot of time and energy outside school hours to rearing the fireflies. They felt very grateful and happy to witness their return to nature.

Learning to cherish Hong Kong’s natural environment

The fireflies released in this activity were mainly Luciola terminalis and Aquatica ficta (shown in the pictures). According to Mr. Mark MAK, the students have more opportunities to come into contact with the former because they live on land and are easier to observe, record and take care of. As for Aquatica ficta, a very rare species in the world, they live in water and are very sensitive to water temperature. It requires a certain amount of knowledge and time to take care of them. Through rearing and releasing fireflies to nature, he hopes young people will understand the importance of nature and cherish the natural environment in Hong Kong.

The DSD will continue to monitor the living organisms that have settled in the rehabilitated river channels. It will review the effectiveness of its ecological enhancement works, which may be implemented in other river channel projects in future. I am very pleased to see that the students have learnt about the DSD’s work in the restoration of river ecology through the release of fireflies to nature in this activity. It is hoped that we will see fireflies fluttering and flickering along our rivers in the near future.