UNDERSTANDING PRESSURES ON THE MANUKAU HARBOUR.
Manukau Harbour, Te Mānukanuka o Hoturoa, is one of Aotearoa’s largest and most ecologically significant harbours. However, like many estuarine environments, it faces a range of environmental, social, and economic pressures that threaten its health and sustainability. These pressures stem from urbanisation, industrial activities, climate change, and human interaction with the coastal and marine environment.
1. Sedimentation and Water Quality
The Manukau Harbour’s catchment is heavily modified due to land use changes, deforestation, and urban expansion. These activities have led to increased sediment runoff into the harbour, smothering seagrass beds, shellfish habitats, and other vital ecosystems.
Stormwater runoff from roads and developed areas carries heavy metals, hydrocarbons, and other pollutants into the harbour.
Erosion from land clearing in both urban and rural areas accelerates sediment deposition, reducing water clarity and degrading marine habitats.
Wastewater discharges, including historical issues with the Māngere Wastewater Treatment Plant, have affected the harbour’s water quality, although treatment processes have improved significantly in recent years.
2. Loss of Biodiversity and Habitat Degradation
The harbour supports taonga species such as kahawai, flounder, and snapper, as well as internationally significant migratory bird populations like the kuaka (bar-tailed godwit) and tōrea (oystercatcher). However, key habitats have been degraded or lost due to:
Destruction of coastal wetlands and mangroves, which play a crucial role in filtering pollutants and providing nursery areas for marine life.
Overharvesting of shellfish beds, leading to declining populations of tuangi (cockles), pipi, and kūtai (mussels).
Pest species, such as invasive fish and plants, outcompeting native species and altering the harbour’s natural balance.
3. Climate Change and Sea-Level Rise
Climate change poses an increasing threat to the harbour’s ecology and the communities that depend on it.
Sea-level rise is already affecting low-lying coastal areas, increasing the risk of coastal inundation and erosion.
Warmer ocean temperatures can lead to shifts in species distribution, affecting traditional kai moana stocks.
More frequent and intense storm events contribute to greater runoff and sedimentation, further degrading water quality and coastal habitats.
4. Urban Expansion and Infrastructure Pressures
The Auckland region is experiencing rapid population growth, putting additional strain on the harbour through:
Increased development around the harbour’s edges, reducing natural buffers like wetlands.
Port and transport infrastructure expansion, which can disrupt marine habitats and increase pollution.
Waste and litter, including plastic pollution, which accumulates in the harbour and poses risks to marine life.
5. Cultural and Social Impacts
The harbour is central to the identity and well-being of mana whenua, who have a long-standing relationship with its waters and surrounding landscapes. However, degradation of the harbour has impacted:
Access to traditional kai moana sources, affecting customary practices and food sovereignty.
Connection to significant wāhi tapu and historical sites, which are at risk from coastal erosion and development.
Loss of intergenerational knowledge, as environmental changes disrupt the ability to pass down traditional navigation, fishing, and conservation practices.