Global urbanisation and climate change have threatened coastal marine ecosystems and the survival of marine organisms. The global academic community is hoping to save the day. A research team led by Professor Kenneth Leung Mei-Yee, Director of State Key Laboratory of Marine Pollution (City University of Hong Kong), has also contributed to a study that has successfully increased the number of coastal species from 19% to 51% and the number of organisms from 59% to 416% fostering the development of biodiversity along the Hong Kong coast. They have developed an ecologically engineered tile (i.e., eco-tile) to reduce the chance of organisms dying due to heat and desiccation stresses driven by strong sunlight. Their research results have been published in international journals, “Marine Pollution Bulletin” and “Global Ecology and Biogeography”, and recognised by the European Union to guide environmental policy.
The coast of Hong Kong is full of natural rocky shores but after continuous reclamation, about 16% of the coastline is now built with artificial seawalls. At present, there are two types of artificial seawalls along the coast of Hong Kong, namely vertical seawalls and sloping breakwaters. Do you know the difference between them?
We can see both natural rocky shores and artificial seawalls (e.g. vertical sea walls) in the same water area. The natural rocky shore allows all kinds of intertidal organisms to grow but the intertidal organisms on the seawall are fewer in number, mostly just some barnacles, rock oysters, limpets and woodlouse-like isopods.
One of the enormous differences between man-made seawalls and natural rocky shores is their surface and morphological characteristics. Simply put, natural rocks have eroded due to weathering over millions of years creating uneven surfaces, large and small pools and a variety of holes and crevices that provide habitats for different organisms to cool down, hide, inhabit and forage enriching the food chain and hence promoting biodiversity.
In contrast, the surface structure of a seawall is generally simpler with no shade or water storage area. The biofilm on the wall can be easily dried out and thus the primary food chain is broken, which is not conducive to foraging and living of marine organisms. Therefore, the number of organisms found on artificial seawalls is relatively small.
In the long run, artificial seawalls, which do not possess suitable habitats for marine species, will continue to depress coastal biodiversity. Let’s see how this study addresses this ecological crisis.
Although Hong Kong is a small city, we have a unique geographical environment. Hong Kong is surrounded by sea on three sides with a total coastline of 1180 km. Studies estimated that there are at least 6,000 species of marine life in Hong Kong waters. Even though Hong Kong’s marine area only accounts for 0.03% of China, its richness in marine species already accounts for 25% of the recorded marine life in the whole of China.
Due to global warming and frequent urban development, different coastal metropolises around the world are facing a similar ecological crisis. Professor Leung led his team to join the World Harbor Project initiated by the Sydney Institute of Marine Science alongside teams from 14 coastal cities around the world, including London, San Francisco and Sydney, each of whom conducted a similar research project in their own cities.
Fashion maverick Alexander McQueen once said, “There is no better designer than nature.” As mentioned earlier, natural rocky shores have remained stable for many years but artificial seawalls are not conducive to biodiversity. How can we create artificial conditions to increase biodiversity against all odds?
Professor Leung has a brilliant idea. It’s just like providing a more comfortable shelter for street sleepers; we can add an “ecological” element to the existing artificial seawalls to build a comfortable home for marine life and provide food. An “ecological seawall” is thus created.
The building block of an “ecological seawall” is an eco-tile that combines the principles of “ecology” and “engineering”. The surface of the eco-tile is rough and pitted creating gaps and grooves. The more complex the surface of the eco-tile, the more shades and water storage areas it can provide. This can also lower the temperature of the tile’s surface allowing more species to grow such as sea snails and limpets.
In addition, the research team used a bivalve shellfish planting method. Native rock oysters (also known as Saccostrea cucullata) were planted on behalf of the eco-tiles to increase habitat complexity in a more natural way.
Therefore, the “ecological seawall” made by artificial eco-tiles has become the key to save the ecology of Hong Kong’s coast.
The research team installed “eco-tiles” on the vertical seawalls of Sham Shui Kok on Lantau Island and Lok On Pai in Tuen Mun for 12 months. The results showed that the “eco-tiles” with gaps increased the number of species by up to 51% with a sharp increase of up to four times the number of organisms! The tiles with oysters attracted new oysters to grow on the tiles providing food for other organisms and forming a healthy ecosystem.
Professor Leung described the results as encouraging: “Even creatures not normally seen on the Hong Kong seawall have appeared!”
While the success of the “eco-block” in enhancing the marine ecosystem is encouraging, the research team found that the results of the test at Sham Shui Kok on Lantau Island were not as good as those of the Tuen Mun Lok On Pai. There are still marine organisms dying on the “eco-tile”.
Why?
It turns out that the test on Lantau Island was defeated by a natural obstacle: sunlight.
Although the “eco-tile” has deep pits, gaps and grooves, and shaded areas, it can still create a slightly cooler environment at low tide. In summer, it can solve the problem of overheating of the existing seawall. However, the location of Sham Shui Kok on Lantau Island is west-facing. In summer, when the tide is low in the afternoon, the sunlight shines directly on the eco-tiles causing the creatures to die from the sun. Therefore, the test also concluded that the orientation and sunlight conditions are the keys to the eco-tile’s cooling performance.
The challenges given by nature once distressed the research team.
Professor Leung recalled that the team often brainstormed and “came up with and made everything that was imaginable”. It then dawned on them that all they had to do was use empathy to figure it out. “If people are afraid of the sun, they will use umbrellas. Marine life needs them too. We finally decided to reverse the “eco-brick” by turning the concave and convex sides inward just like the concept of “living from the front to the back” so that creatures can hide in the shade, shared Professor Leung.
And so, the challenges caused by sunlight was overcome.
After the first set of research results, the team hopes to open up more possibilities. With funding and cooperation from the Civil Engineering and Development Department, the research team has conducted a second round of trials of ‘ecological seawalls’ through installation of various ecologically engineered fixtures on artificial seawalls in Ma Liu Shui, Sai Kung and Tuen Mun. Different shapes and complexities of eco-engineered fixtures, such as eco-tiles, eco-panels, tidal pools, armouring units and oyster baskets, were tested whether they could enhance marine biodiversity. The eco-tiles used in this test were designed and manufactured locally and made with waste materials including ashes from the T-Park incinerator in Tuen Mun and dredged marine sediment, which helped reduce waste and create an “eco-seawall” at the same time.
The sites selected for this study belong to different water bodies, including Sai Kung, which is more oceanic; Ma Liu Shui, which is located within a semi-enclosed water body; and Lung Kwu Tan of Tuen Mun, which is located within an estuary. It helped to evaluate the application of “ecological seawall” in different water bodies in Hong Kong.
The team were surprised by the preliminary results of the first nine months of testing. For example, 11 species were recorded on some of the eco-engineered fixtures on the “ecological seawall” at the Ma Liu Shui site which could not be found in the nearby artificial seawall, including seaweeds, coralline algae, crabs and different kinds of gastropods etc. This reflects that the diverse habitats of the “ecological seawall” can help increase biodiversity and promote ecological functions.
Professor Leung emphasised that the test results of the oyster shell baskets were unexpectedly successful and that marine organisms were particularly attracted to oyster shells in the oyster baskets. Such simple oyster baskets could harbour over 60 species of marine organisms. He believes that the habitat of the oyster baskets can protect the young creatures from being eaten by predators like big fish and they can then swim out of the baskets to survive after they grow up forming a healthy ecological chain.
Professor Leung’s research is recognised by both academic and applied science communities. Click below to learn more!
Hong Kong’s seawalls can be turned into life-creating breakwater
The “eco-engineering” technology can be applied to all existing seawalls in Hong Kong and can improve the marine ecosystem of Hong Kong’s man-made coast. The third runway system project at the airport, the Tung Chung New Town Extension Project as well as the development of the Integrated Waste Management Facilities in Shek Kwu Chau are the first projects to implement “eco-seawalls”. The research team will play a monitoring, collaborative and advisory role to improve the health of marine ecosystems on these “eco-seawalls”.
Hong Kong’s research is recognised worldwide and considered of significance
The research results of the “eco-tile” technology were published in the international scientific journal Marine Pollution Bulletin under the title “A global analysis of complexity–biodiversity relationships on marine artificial structures”. These research article was also selected as a feature in the European Union’s “Science for Environmental Policy”, which serves as a reference for EU environmental policy.
In addition, Professor Leung alongside 45 other international experts have presented a paper on the Global Harbor Research Initiative. The paper has been titled “A Global Analysis of the Relationship between Complexity and Biodiversity of Artificial Ecosystems Installed in the Ocean” and has been published in the scientific journal, “Global Ecology and Biogeography”.
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