Building artificial islands can have significant impacts on the environment. One of the largest impacts is on coral reef and marine ecosystems. To construct these man-made islands, vast areas of the seabed need to be dredged and landfilled, which destroys sensitive coral reef and seabed habitats. Coral reefs are incredibly biodiverse ecosystems that are home to thousands of marine species. They also act as nurseries for many commercially and ecologically important fish. Destruction of reef systems displaces and kills coral polyps and reef fish. It releases sediments into the water column which can smother corals over large areas. The dredging activities also generate underwater noise that disturbs and disorientates marine life like whales, dolphins, and sea turtles. Reef systems often take decades or even centuries to recover from such damage.

The landfilling required for artificial islands uses enormous quantities of natural resources. Dredging extracts seabed sediments and rock, which is then deposited to expand existing land or build new islands. This process requires billions of cubic meters of materials. The extraction damages benthic habitats and increases turbidity in surrounding waters. It also releases nutrients, pollutants, and residues that were buried in these sediments. The new artificially placed substrates are often not suitable for colonization by corals or other marine organisms for long periods, affecting the reestablishment of natural communities.

Coastal and marine wildlife is at risk during island construction. Species like seabirds, turtles and marine mammals can become entangled in construction equipment or vessels. Noise and movement from dredging, landfilling and construction disturbs breeding and foraging behaviors of coastal dependent species. It also increases risks of vessel strikes. Migratory pathways may be blocked by new land formations altering how marine species access important habitats. Islands may also fragment seagrass beds and mangrove forests disrupting ecosystems. Light pollution from construction at night disorients sea turtles and hatchlings. Once operational, islands also introduce invasive species, debris, chemical and oil spills that degrade the environment.

Artificial islands impact water circulation and quality in surrounding areas. Land reclamation and dredging alters coastal hydrodynamics changing currents, waves and sediment flows. It reduces water depths that are vital for fish feeding and breeding. Deeper channels are required for ship traffic that increases erosion. The mixing of landfilled sediments releases nutrients, pollutants and other contaminants into the water column harming water quality. This can lead to algal blooms, dead zones, coral bleachings and disease outbreaks affecting ecosystems. Sand mining to obtain landfill materials erodes nearby beaches and coastlines increasing flooding and erosion risks.

The size of some mega islands is a major concern for climate change. Constructing structures on such a massive scale requires vast quantities of cement, steel and other materials which have significant embedded carbon emissions during manufacturing. Operational activities like transport, construction work, energy use and waste generation also contribute carbon emissions over the island’s lifetime. Coastal artificial islands may also interfere with ocean currents and affect regional weather patterns. If not properly designed, they can exacerbate the impacts of climate change like rising sea levels, stronger storms surges and more frequent extreme weather events on low-lying atoll nations.

Post construction, islands continue impacting the environment. Invasive species established on the new substrates spread rapidly with no natural controls. Toxic chemicals, plastics, sewage and trash pollute surrounding waters if not properly managed. Standing structures attract undesirable activities like overfishing. Islands may fragment ecologically important areas preventing wildlife movements. Lighting associated with development disrupts natural light cycles of turtles and seabirds. Building artificial islands is an immense anthropogenic intervention with multi-decadal environmental impacts that are often irreversible without active restoration efforts. Proper environmental planning, mitigation of impacts, and compensatory conservation are needed to offset their ecological footprint.

Artificially constructing islands causes substantive destruction to marine ecosystems through habitat removal and alterations, introduces invasive species, changes coastal processes, and increases pollution. It contributes carbon emissions on a massive scale. Some of these impacts like coral reef damage may persist for centuries. To minimize environmental harm, construction should avoid sensitive sites, adopt best practices, implement impact assessments, and include long-term monitoring and adaption. Offsets that protect natural marine habitats equivalent to those destroyed may also help mitigate long-term effects of island reclamations. Given the immense and potentially irreversible environmental costs involved, artificially building islands should only be an option of last resort after all alternatives are considered.