Wildlife of
Tonga

Primary Threats

• Warming seas drive coral bleaching and reef degradation, reducing habitat complexity and fish abundance that many communities rely on. Sea-level rise increases coastal erosion and saltwater intrusion, threatening mangroves, coastal wetlands, freshwater lenses, and low-lying settlements. More intense cyclones and storm surges (a major risk in Tonga) physically damage reefs, coastal vegetation, and nesting beaches for turtles and seabirds, and can increase sediment runoff into lagoons.
• High dependence on reef and lagoon fisheries for subsistence and local markets can lead to localized depletion of nearshore fish, invertebrates, and reef herbivores, especially near population centers and easily accessed reefs. Post-storm recovery periods can intensify fishing pressure as communities rebuild livelihoods, potentially slowing ecosystem recovery and reducing resilience to bleaching and cyclones.
• Coastal habitats (mangroves, wetlands, dunes, and reef flats) are lost or degraded through shoreline hardening, land reclamation, sand extraction, and expansion of villages and small harbors. On small islands, even modest changes can remove a large proportion of available habitat, affecting nursery areas for fish and coastal protection services that reefs/mangroves provide.
• Land-based runoff (sediment from cleared land, nutrients from agriculture, and wastewater from settlements) can smother corals and promote algal growth in lagoons, lowering water quality and reef health. Solid waste and plastics are persistent issues on small islands with limited waste management infrastructure, contributing to marine debris that can harm turtles, seabirds, and reef ecosystems.
• Invasive predators (notably rats and feral cats) and invasive plants can severely impact native seabirds, land birds, and island flora by predation on eggs/chicks and by altering habitat structure. On small, isolated islands, invasives can quickly dominate and cause disproportionate biodiversity losses; biosecurity is challenging across many ports and inter-island movements.
• Alterations to coastal and watershed systems-such as drainage or filling of wetlands, modification of mangrove edges, and changes to natural sediment flows from coastal engineering-can reduce nursery habitats and increase lagoon turbidity. Reef resilience can be further reduced when key functional habitats (mangroves/seagrass) are diminished or fragmented.
• Roads, wharves, seawalls, and cyclone-recovery reconstruction can increase coastal hardening and disturb sensitive shorelines and reef flats. Port and harbor works can cause localized dredging, turbidity, and habitat loss, and can elevate invasive-species introduction risk through increased vessel traffic.
• Expansion or intensification of agriculture on limited land can increase clearing and soil erosion, sending sediment into coastal waters after heavy rain. Nutrient runoff from fertilizers can contribute to eutrophication in sheltered bays and lagoons, affecting coral and seagrass health.
• Whale-watching and boating (when poorly managed) can disturb breeding and calving humpback whales through close approaches, repeated interactions, and vessel noise. Beach use and nearshore recreation can disturb turtle nesting sites and seabird roosting areas, especially on small islands where wildlife has limited alternative habitat.