Sea wall homes for marine life to get into the groove

Tile project aims to improve biodiversity on structures stressful to sea life
Carolyn Khew Straits Times 14 Oct 16;

Having tiles on the sea walls of Pulau Hantu where no one can see them may seem a strange idea, but a closer look will reveal that the concrete blocks are teeming with snails, oysters and mussels.

Ecological engineering - the design of sustainable ecosystems to integrate human society with the natural environment so that both can benefit - has taken root on the southern island. The aim is to enhance biodiversity on sea walls, which are generally a stressful habitat for sea denizens to take root on, as the structures are steep and do not provide much of a foothold.

Since 2009, Dr Lynette Loke, a 29-year-old postdoctoral research fellow from the Experimental Marine Ecology Laboratory at the National University of Singapore's (NUS) Department of Biological Sciences, has been studying sea walls and their biodiversity.

In her latest effort, she is working on how best to arrange the tiles, so that they can be habitats for more marine life. Previously, she found that tiles with complex designs, or grooves and pits, were best loved by creatures such as the pearl oyster and lightning dove snail (see sidebar, right).

So, more than 700 experimental concrete tiles - each measuring about 20cm by 20cm - were fixed onto the sea walls surrounding Pulau Hantu.

Using software she developed, Dr Loke was able to adjust the intricacy of each tile design, so that she could understand how habitat complexity affects the biodiversity of intertidal organisms.

Organisms found on experimental tiles

PURPLE CLIMBER CRAB

These crabs can grow up to 4cm in width, and algae serves as their main food source.

LIGHTNING DOVE SNAIL

These snails can be found in habitats such as Singapore's rocky shores. They can be distinguished by their black-and-white shells.

PEARL OYSTER

These oysters can be found in many parts of the world, but only a few species are sought after for their ability to produce good quality pearls.SOURCE: NATIONAL UNIVERSITY OF SINGAPORE, DR LYNETTE LOKE

Sea walls and other artificial forms of coastal defence are fast becoming the primary means of mitigating rising sea levels as well as more frequent and intense storms and flooding, explained Dr Loke.

"There is a growing realisation that because they cannot be removed, there is a need to look beyond their negative impact and to find ways they can be built to improve their value as a habitat," she said.

According to the National Climate Change Secretariat, much of Singapore lies only 15m above the mean sea level, with about 30 per cent of the island being less than 5m above the level.

To guard against coastal erosion and flooding, Singapore has been building sea walls and raising roads near coastal areas to prevent flooding. About 70 per cent to 80 per cent of Singapore's coastal areas have hard walls or stone embankments to help protect against coastal erosion, said the Building and Construction Authority (BCA).

Hard walls typically comprise vertical or sloping sea walls, while stone embankments are breakwaters built at short stretches, usually between 30m and 50m long. These can be found along East Coast Park, Pasir Ris Park and Sentosa beaches.

The BCA said it is conducting a study on Singapore's long-term coastal protection plans. It is expected to be completed next year.

A spokesman said ecological engineering methods will be considered where feasible, even though the authority's focus is on the safety and stability of coastal protection structures as well as building up Singapore's expertise in coastal protection.

Marine ecologist Peter Todd, an assistant professor at NUS' Department of Biological Sciences who supervised Dr Loke's project, said sea walls here are usually built to protect reclaimed land from erosion. "The effects of sea walls in Singapore are difficult to disentangle from the impacts of land reclamation," he said.

"Together, land reclamation and sea walls tend to result in the loss of entire habitats, as opposed to individual species."

So if engineers could find a way to retrofit tiles on sea walls, it would be the best of both worlds, he said.

In Blackwattle Bay in Sydney, Australia, for instance, scientists have built specially designed flower pots that attract more than 20 species of crabs, snails and starfish to live in them, according to a government website.

Dr Loke hopes that her work will encourage engineers and the authorities here to think of how they can design sea wall structures. Moving forward, she wants to understand the ecological processes that attract marine life to live on the tiles.

"At first glance, it seems kind of strange - natural habitats are lost by building sea walls and then we need to think of ways to make them better. But complaining won't fix the problem... We have to do something about it," she said.