Marine habitats in one of the world's busiest harbours

Abstract

Singapore's limited marine territory of approximately 600 km2 supports one of the world's busiest harbours. Over 133,000 vessels (above 75 gross tonnes) called at the port in 2004. Thirty-five percent comprised regional ferries linking Singapore with various ports of Indonesia's Riau province. Other vessels were mainly containers and tankers which facilitate movement of 1 billion gross tonnes of cargo through the port. To accommodate such intense shipping activity and provide safe navigation to the heavy vessel traffic, the port waters cover 82% of Singapore territorial waters. Most of the port provisions are located in the seas south of the main island, particularly the south-western sector (Figure 1). Wharf and berthing facilities dominate the southwestern coastline, which have been transformed by coastal reclamation. Fairways, anchorages and vessel manoeuvring areas intermesh between the fifty-odd smaller offshore islands scattered mostly in the southern waters. A spectrum of marine habitats typical of tropical regimes is found in this heavily utilized marine environment. Fringing and patch reefs are present among the southern islands together with seagrass meadows and mangrove stands, all varying in areal extent. A range of seashore types including rocky, sandy and muddy exists. The seafloor is now mostly dominated by mud bottoms as most of the sand deposits have been exhausted for reclamation while the continuous rain of suspended sediment adds more silt. Threats from shipping include vessel movement, grounding and accidental spillage of hazardous materials. Other activities such as land reclamation, seabed dredging and the dumping of dredged spoils contribute to increased suspended sediment, modification of hydrodynamic patterns and changed tidal speeds at different locations. High energy wash from increasing numbers and operating frequency of fast-going vessels such as high-speed passenger ferries scour exposed shores and reef flats. Large tracts of razed corals on reef flats provide evidence of grounding by flat-bottom barges, often connected with a nearby development activity. The spillage of 28,500 tonnes of heavy marine fuel oil into the sea (figure presented) resulting from the collision of two oil tankers, the "Evoikos" and the "Orapin Global" in October 1997, the largest in Singapore's history, firmly emphasised that this ever-present threat can happen at anytime even under fine weather conditions and with sufficient warning given to the approaching vessels. In August 2000 and July 2001, two separate incidents of phenol spills occurred in the Malaysian waters of the east Johor Straits, killing fish and mussels in Singapore waters as well. Both resulted from capsized cargo vessels transporting the toxic chemical from the Malaysian port of Pasir Gudang. Shipping also introduces the problem of invasive species. The exotic Mytilopsis sallei, which is of Caribbean origin, is now the most commonly-occurring bivalve in Singapore (Sachidhanandam and Chou, 1996), dominating walls of intertidal monsoon canals. Tolerant of large salinity fluctuations, they were possibly introduced by ships coming from across the Panama Canal (Tan and Chou, 2000). Imposex in females of muricid gastropods indicate organotin contamination, which is not surprising considering the shipping intensity (Tan, 1999). Exposed to the diversity of impacts, Singapore's marine habitats face three major problems: habitat loss, habitat degradation and habitat modification.