Last Saturday morning, a group of excited friends travelled to Kallang Riverside Park to participate in Waterways Watch Society’s (WWS) first ever family carnival. We were invited by Li Jean who used to intern at the organisation. The river clean-up kayaking event had caught our attention and we signed up for it because we thought, “why not do something good for the environment while having fun?”
Reservoirs comprise a significant component of Singapore’s urban freshwater habitats. In fact, they have been found to have greater diversity of freshwater mollusc species as compared to forest streams, ponds and monsoon canals (Clements et al., 2006).
During the briefing session before we set off, participants were educated on the impacts of litter on aquatic organisms. We were told that litter, such as aluminium cans, form a surface for the eggs of the golden apple snail, Pomacea canaliculata, to be stuck in. The eggs hatch inside the cans, and when the snails get bigger they are unable to escape and eventually die inside. We were all urged to pick up any cans we find, give them a rattle to see if there are any trapped golden apple snails, and then cut up the cans to free the snails. This then sparked a discussion on whether we should actively save invasive species.
The golden apple snail was introduced into Singapore most likely because of the pet trade (Yeo & Chia, 2010) and has now exploded in numbers in many reservoirs, ponds and drains across Singapore (Tan et al., 2013). It is listed as one of the world’s 100 most invasive species (Lowe et al., 2000). If you have ever seen clumps of tiny pink round balls sticking to the sides of river banks, those are the eggs of the golden apple snail! Since the introduction of the golden apple snail, the abundance of the native snail, Pila scutata declined rapidly, which might be due to the presence of the invasive apple snail (Chan, 1996; Tan et al., 2012).
So back to the question. Are invasive species in general worthy of saving? Perhaps the creation of non-native habitats such as reservoirs made these alien animals ‘native’ to that kind of habitat? If so, then they might be considered native in that context. Or maybe it is more of a morality issue, i.e., we should help any animal in peril regardless of the damage it does to the ecosystem.
As we went on our kayaking adventure, we did not find any apple snail-containing cans, but we were shocked by how much rubbish we saw floating on the water surface and half-submerged. I had always thought that Singapore’s waterways are clean, especially the reservoirs where we also obtain our drinking water from. But this journey brought us closer to the litter that is hidden from the sight of most park users. We learnt that trash gets into our waterways via different paths, such as being blown in from land or carried in pipes that discharge water into the river.
As I was gliding across the river with my partner and trying to spot litter, I realised that riparian vegetation actually traps quite a lot of trash, making it difficult to remove. Thus, by accumulating trash, riparian vegetation could have made our waterways dirtier. Even so, we cannot deny the benefits that these plants bring, as they help to reduce erosion and provide breeding grounds and shelter for otters and birds (NParks, 2009). Another realisation I made was that most of the time, we only pick up visible litter, but upon closer inspection, I saw a lot of submerged trash – it would normally get missed. This litter, including plastic bags and straws, can pose a huge threat to wildlife. For example, WWS volunteers told us about the many times when they had to free fish stuck in plastic bags. I learnt that even though paid contractors and WWS volunteers regularly clean up the Kallang River, the volume of rubbish never seems to dwindle.
At the end of our 40-minute session of kayak clean-up, the total weight of rubbish we all collected totalled 16 kg. That might not seem like much, but we were told that contractors collect about 10 tonnes of trash from the Kallang River every day! It is undeniable that waterways in and near cities will tend to have greater pollution as compared to those in the forest. But modified habitats, such as our canals and reservoirs, are increasingly becoming important sites for native biota, such as the famous smooth coated otters, Lutrogale perspicillata, whose return signifies cleaner waterways in Singapore (BBC News, 2016). Therefore, I believe that one method to ensure the integrity of our urban freshwater ecosystem and possibly boost species richness is to maintain litter-free habitats.
So, for this World Water Day, apart from reinforcing our water-saving habits, let us remember not to litter and to pick up any trash we find near waterbodies, so they do not get washed or blown into our rivers and reservoirs!
You might recognise some of us in the photo to be from LSM4265!
Photo credit: Gwendolyn Chow
Literature cited
BBC News (2016) Singapore’s celebrity urban otter family. http://www.bbc.com/news/world-asia-36700728 (Accessed 21st March 2017).
Chan SY (1996) Some freshwater gastropods of Singapore. Of Sea and Shore, 18: 184–187.
Clements R, Koh LP, Lee M, Meier R & Li D (2006) Importance of reservoirs for the conservation of freshwater molluscs in a tropical urban landscape. Biological Conservation, 128(1): 136-146.
Crome F, Isaacs J & Moore L (1994) The utility to birds and mammals of remnant riparian vegetation and associated windbreaks in the tropical Queensland uplands. Pacific Conservation Biology, 1(4): 328-343.
Lowe S, Browne M, Boudjelas S & De Poorter M (2000) 100 of the World’s Worst Invasive Alien Species, a Selection from the Global Invasive Species Database. Invasive Species Specialist Group (ISSG), a specialist group of the Species Survival Commission (SSC) of the World Conservation Union (IUCN), Auckland, New Zealand, pp. 1–12.
National Parks Board (NParks) (2009) Singapore’s National Biodiversity Strategy and Action Plan. https://www.nparks.gov.sg/~/media/nparks-real-content/about-us/nparkbookletfinal4sep.ashx?la=en (Accessed 21st March 2017)
Tan SK, Chan SY & Clements GR (2012) A Guide to Snails and Other Non-marine Molluscs of Singapore. Singapore Science Centre, Singapore, 176 pp.
Tan SK., Lee YL & Ng TH (2013) The status of the apple snail, Pila scutata (Gastropoda: Ampullariidae) in Singapore. Nature in Singapore, 6: 135-141.
Yeo DCJ & Chia CSW (2010) Introduced species in Singapore: An overview. COSMOS, 6: 23–37.