Abstract—Urbanization of coastal cities has resulted in extensive physical modification of the coast that is commonly accompanied by habitat destruction or degradation, marine biodiversity loss and ecosystem services decline. Conversion of the natural environment to a human-modified one is often permanent, and it is important that development considerations take into account biodiversity enhancement of the ‘new’ environment. Development of biological communities in the modified environment takes time and is unlikely to return to levels once supported by the original habitats, but efforts can be made to facilitate the establishment of biodiversity that is suited to the new environmental conditions. Active interventions such as water quality management and ecological restoration can help to transform the urbanized coastal environment into a suitable biodiversity support zone. Observations of marine biodiversity in marinas and restoration of corals on artificial structures in Singapore support this prospect. Assessment of the biodiversity in three marinas indicated that they can function as marine biodiversity refugia, especially with their relatively high artificial structural complexity and when designed with basic ecological considerations to enhance marine biodiversity. Separately, reef restoration projects give rise to the possibility of colonizing seawalls with corals and other reef-associated species, as well as improving degraded reefs and creating reef communities in areas originally devoid of corals due to the heavy sediment load of urbanized coastal waters. Maintaining marine biodiversity in challenging environmental conditions resulting from urbanization can help to ensure continued provision of some level of ecosystem services. Index Terms—Coastal, urbanization, biodiversity, Singapore. I. INTRODUCTION The island nation of Singapore has undergone decades of rapid urbanization especially since the 1960s. Its human population of 1.65 million in 1960 swelled to 5.64 million in 2018 [1]. During the same period, land area increased from 581.5 km 2 to 724.2 km 2 [2] through coastal reclamation. The restricted sea space of about 740 km 2 is intensively used for shipping making Singapore one of the world’s busiest ports. Manuscript received December 27, 2019; revised September 10, 2020. Most of the research covered in this review came from publications generated mainly from the following grants awarded to the author as Principal Investigator – Grant no. R-154-000-557-490 “Marinas as biodiversity refugia” funded by the National Parks Board, and Grant nos. R-347-000-190-592 and R-347-000-215-490 “Enhancing Singapore’s coral reef ecosystem in a green port” funded by the Singapore Maritime Institute, and Maritime and Port Authority of Singapore respectively. Other related research was supported by grants from various agencies such as Housing and Development Board, National Research Foundation (Marine Science Research and Development Programme), Wildlife Reserves Singapore Conservation Fund. Loke Ming Chou is with the Tropical Marine Science Institute, and the Department of Biological Sciences, National University of Singapore, Singapore (e-mail: tmsclm@nus.edu.sg). In 2018, the port managed over 140,000 vessel arrivals and handled over 630 million tonnes of cargo [3]. Coastal development has been extensive [4] and more than 60% of the country’s coastline are now lined by seawalls [5]. Urbanization of the coastal area replaced many of the natural coastal habitats with seawalls or new sandy shores [6]. Original shores are restricted to short stretches of the coastline and are to varying degrees impacted by changes to the immediate adjacent coastal landscape. Singapore’s coastal environment is defined by drastic physical change over the last five decades and this is likely to continue well into the future. What impacts have these changed conditions had on marine biodiversity, and should biodiversity enhancement and management measures be considered? This paper discusses Singapore’s coastal urbanization impacts on marine biodiversity and examines biodiversity in permanently changed habitats such as marinas, as well as reef restoration approaches to enhance degraded reefs and create reef communities in new urbanized habitats. II. THE CHANGING COASTAL ENVIRONMENT Urbanization has transformed much of Singapore’s coastal environment [7] and an obvious change is the reduction of sea space arising from land reclamation. Loss of sea space means compression of the already busy maritime activities into a smaller area and intensifying competition for its use by different agencies. Land reclamation has obliterated and diminished the extent of nearshore habitats such as mangrove forests [8], seagrass beds [9] and coral reefs [10]. Habitats located further away from land reclamation and coastal development sites remain affected by the increased sediment load in the sea that causes smothering and reduced sunlight penetration, thus compromising their primary production potential. Over 60% of natural coral reefs have been lost to land reclamation [10]. For the remaining reefs, a further reduction in the vertical zone that supports coral growth is seen with the lower depth limit raised from 10m in the past when waters were clearer to 6m now [4]. The reduced areal extent of coastal habitats resulted in a decline of abundance for many species but while species reduction has been recorded for some groups, e.g. mushroom corals [11] and pocilloporid corals [12], species richness diminution on the whole has been less apparent [13]. The full extent of Singapore’s marine biodiversity richness has not been realized but a relatively recent 5-year Comprehensive Marine Biodiversity Survey from 2010 to 2015 revealed over forty species new to science and over 120 species listed as new records [14], [15]. On-going studies Enhancing Marine Biodiversity in Singapore’s Urbanizing Coastal Environment Loke Ming Chou International Journal of Environmental Science and Development, Vol. 11, No. 11, November 2020t 519 doi: 10.18178/ijesd.2020.11.11.1301