Most New Zealanders flocking to the beach this summer will be unaware of the perilous state of the marine ecosystem
beneath the waves. Human land-based activities, sea level rise, disturbance to the seafloor and over-harvesting have
created one of the most rapidly changing natural systems in our environment.
I have witnessed this sharp decline in many locations – and I’m not alone. Many iwi and community groups around the
country are equally alarmed by the decline in shellfish and other species in their traditional shellfish gathering
Shellfish beds are our most impacted and endangered marine habitats and the story of their decline is being repeated
around the world. But these ecosystems are vital. They provide many tangible and deep benefits that support our life,
wellbeing and culture. They clean our waters, stabilise the seafloor, feed fish and birds, dampen the effects of storm
surge, enhance biodiversity, and remove nutrients that run off the land.
Globally, more than 85 percent of shellfish ecosystems have been impacted by human activity. Researchers have found many
oyster reefs, once common, are now rare or extinct as ecosystems. Most of the bays studied in North America, Australia,
and Europe were found to be at less than 10 percent of their prior abundance with oysters functionally extinct in others
(a measure of less than 1 percent of prior abundances).
We scientists have noted an alarming level of shellfish loss in New Zealand’s coastal harbours and bays – and you may
experience this yourself over summer as you revisit favourite shellfish gathering spots.
The photos below document seabed degradation in horse mussel beds in Mahurangi Harbour, north of Auckland. The photos
are taken in the same place 18 years apart. This destruction, which shows no sign of recovery, has been caused by the
cumulative effects of physical disturbance to the beds, elevated sediment runoff from the harbour’s catchment and a lack
The loss of shellfish habitats also has a knock-on effect for other species such as those that attach to shellfish, and
for juvenile fish (including snapper) who seek refuge from predators in these habitats. Shellfish also filter seawater
and remove suspended particles in the water thus directly removing the suspended sediments from the water column and
depositing this material onto the seafloor
So how do we generate a tipping point that changes the current trend of decline and loss into a trajectory of recovery
In recent years community groups and local and central government have, for example, mobilised to restore the integrity
of stream margins in farming areas and create predator-free environments for indigenous flora and fauna. I believe that,
as a matter of urgent priority, a similar programme is needed for the marine environment, supported by local and central
government. Currently, there is no coordinated partnership activity for coastline restoration. However, concerned at the
poor state of shellfish beds, several pioneering iwi and community groups have made a start in their local areas.
We need innovative research to inform targeted restoration actions and streamline policies. Research should include
gathering baseline data that will inform an in-depth understanding of the current state of our unique indigenous coastal
biodiversity, including shellfish ecology. This research could potentially have a similar impact to that around CFCs
several decades ago which led to ambitious, whole of system targets to eradicate the production of the chemicals eroding
the ozone layer.
Knowledge of the factors causing the rapid decline of our marine ecosystem will enable politicians, nationally and
internationally, to target policy and support the implementation of practical responses to greatest effect around our
Raising awareness and ensuring the public understands the risks and opportunities around our coastlines is integral to
ensuring that policy makers and politicians are also seized by the importance of this issue. Scientific knowledge alone
cannot ensure the success of restoring our coastal marine ecosystem, community participation and commitment are critical
to ensuring the long-term success and sustainability of restoration.
But for that commitment to pay off, we need to have clear and credible information on what, where and how to restore
shellfish beds to maximise their contribution to the health of our coastal ecosystems.