Our coastal waters, harbours, and estuaries are the marine habitats New Zealanders are most likely to visit for recreation, fishing, and shellfish harvesting. However, there are limited national data available with which to confidently quantify how the pressures discussed in this chapter are changing the state of this important part of our marine environment.
Increased sedimentation from changes in land use can have substantial impacts on nursery habitats and shellfish species but we have not been able to assess the extent to which this is changing our coastal environment on a national scale. We cannot yet quantify the impact of excess nutrients on marine ecosystems and species. Heavy metal concentrations in estuaries and harbours are mostly at levels unlikely to cause harm to seabed species in the 10 of 16 regions around the country for which we have data.
We know that a greater number of non-indigenous marine species are entering our waters, increasing the threat these species pose to natural ecosystems, aquaculture, and fisheries. The economic costs of marine pests are not well quantified, but are likely to amount to millions of dollars a year.
These pressures on coastal habitats can be cumulative and will not occur in isolation from ocean acidification and warming, or pressures from commercial and recreational fishing, which we discuss in the next chapter, Our fisheries and the impact of fishing on marine ecosystems.
For Māori, the degradation of coastal waters, harbours, and estuaries has been a significant source of grievance since early European settlement. Ngāti Whātua Ōrākei, Ōkahu Bay – aligning mātauranga and science to restore mauri aptly demonstrates the cumulative nature of human pressures on a coastal marine environment. It tells a compelling story of how the degradation of a bay in the Hauraki Gulf affected the local hapū’s health and undermined their customary values, including the traditional harvesting of pipi and other kaimoana.
In the 1980s, kuia and kaumatua (elders) of the Hauraki Gulf hapū, Ngāti Whātua Ōrākei, noticed a disturbing change in their ancestral Ōkahu Bay. The beach had become noticeably empty of whānau (family) collecting pipi and other kaimoana (seafood) from their ancestral pataka (food cupboard). Whānau noticed the bay ‘filling in’ and wondered where the sand had gone.
These changes were likely the result of a surge of housing development from the 1950s to the 1970s. Land clearing and the engineering of rock walls and marinas changed the flushing ability of the bay. This led to large quantities of sediment flowing into the bay but not out, altering the underwater landscape of the bay and smothering the habitat of shellfish such as pipi.
Human actions had been affecting the health of the Ōkahu Bay for some time. In 1914, against the wishes of Ngāti Whātua Ōrākei, a two-metre high sewer pipe was built along the beachfront to carry raw sewage from Auckland into the bay.
A sewer pipe under construction at Ōkahu Bay in 1910, in front of the ancestral village of Ngāti Whātua (buildings on left). Source: 7-A2929 Sir George Grey Special Collections, Auckland Libraries
Offensive from a cultural and spiritual perspective, the sewage also polluted shellfish beds, leading to a surge in illness and death from cholera and other water-borne diseases. In the mid-1930s, all streams in the catchment were piped underground, destroying stream and estuarine habitat, including inanga (whitebait) spawning grounds. In 1960, sewage was diverted to the Mangere Wastewater treatment plant, but a new road (Tamaki Drive) was constructed over the line of the old sewer pipe. The road created a permanent physical barrier between the sea and land and further dislocated Ngāti Whātua Ōrākei from the bay.
In 2005, Ngāti Whātua Ōrākei decided it wanted to better understand what was happening to the bay. The hapū commissioned the development of a model aligning mātauranga Māori (Māori knowledge) with empirical science. Central to this model is an annual kaimoana monitoring survey. Recent results from the survey found that the entire bay had only about 180 cockles, concentrated in isolated pockets. A healthy bay environment would expect to have abundant and widely dispersed populations.
Before urban development and intensification from the 1950s, the seabed of Ōkahu Bay was mainly sand, with sandbars throughout. However, a report commissioned by the hapū estimated that about 10,000 cubic metres of sediment enters the bay from the surrounding catchment every year (Kahui-McConnell, 2007). Stormwater also carries heavy metals and other contaminants that are harmful to the marine ecosystem. The report estimated that about 56 kilograms of zinc, 11 kilograms of copper, and 23 kilograms of petroleum hydrocarbons make their way into the bay through stormwater pipes every year (Kahui-McConnell, 2007).
Ngāti Whātua Ōrākei’s cultural health indicators for Ōkahu Bay reflect the hapū’s vision of restoring their cultural and spiritual relationship with the bay and strengthening mātauranga (indigenous knowledge). This would include: harvesting and eating kaimoana such as pipi, cockles, and crabs without fear of illness; swimming, diving, and boating in the bay; and maintaining access throughout the bay and into the wider Waitemata Harbour. Ngāti Whātua Ōrākei, in partnership with Auckland Council, will continue to monitor the bay and the wider catchment to track progress towards their goal of restoring the mauri (life force) of the moana (ocean).
This case study is based on interviews with Ngāti Whātua Ōrākei on 22 March 2016, and a report commissioned by the hapū (Kahui-McConnell, 2007). We thank Ngāti Whātua Ōrākei for sharing their stories and research with us.