Rehabilitation of Coral Reefs Exposed to Urbanization and Climate Change Impacts

Over 60% of Singapore’s coral reef habitat have been lost to decades of urban development pressure including land reclamation. Underwater visibility of less than 2m due to heavy sedimentation has restricted the healthy coral growth zone to the reef crest and upper 5m of the reef slope. Despite the impacts, coral species diversity has remained high together with predictable coral mass spawning events and vigorous growth of larval recruits. These features suggest that rehabilitation is viable and can improve reef resilience against urbanization as well as climate change impacts. Restoration techniques that are adopted must consider the high sediment environment, destabilized reef substrate, and biological community structure change. It is important to observe coral species dominance since this has shifted to favor those more tolerant of reduced light condition. Rehabilitation can be initiated with the dominant species to stabilize the rehabilitation site within the shortest time. Sloping hard substrates above the silt bottom disallow sediment accumulation and are more suitable for settling coral larvae or attached fragments. Coral nurseries comprising raised mesh-net platforms prevent sediment smothering and improves survival of coral fragments and juveniles. Corals have also naturally recruited and developed on seawalls constructed in areas which, did not support coral reef formation. Innovative design and engineering of structures can facilitate coral growth as sea level rises. Floating reefs and seawalls that incorporate terraced tidal pools can encourage continued growth and development of coral communities. Two approaches considered appropriate to rehabilitating coral communities exposed to impacts of urbanization and climate change are 1) increase live coral cover and diversity of degraded reefs, and 2) create reef communities in non-reef areas.