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With over harvesting a hot topic, Hibiscus Matters asked marine scientist Dr Emilee Benjamin of Auckland University to provide context.
The intertidal is a unique ocean zone that is revealed as the tide goes out. Twice a day, the tide pulls back to expose a living shoreline, a dynamic interface between land and sea. Important kaimoana species live here, such as mussels, oysters, and pāua, alongside a diversity of organisms that depend on these shellfish.
Shellfish beds and rock pools provide homes for many animals, such as crabs, sea stars, and algae, while also contributing to important food webs as they are feeding grounds for many coastal birds and fish. These ecosystems build up slowly over time, with each species playing a role in maintaining balance and biodiversity. For many people across Aotearoa/New Zealand, gathering kaimoana at low tide provides an important connection to the ocean.
A healthy ecosystem can recover from mild impacts, but more intense disturbances, such as removing too much of a species, or habitat, can cause overharvesting and limit its ability to recover. Overharvesting shellfish is especially harmful because they are ecosystem engineers, meaning they modify their environment and create habitat for other animals. When shellfish are depleted, biodiversity declines, food webs are disrupted, and the ability to harvest kaimoana in the future is put at risk.
Overharvesting has stripped Aotearoa’s coastlines of shellfish. In the Hauraki Gulf, over 500 square kilometres of mussel beds were removed, and in Kenepuru Sound, Marlborough Sounds, only about 3 per cent of the historical green-lipped mussel population remains. In both areas, mussels have been unable to recover naturally and are considered functionally extinct, meaning that some mussels remain, but the ecosystem services they once provided, such as water filtration and habitat creation, no longer occur at an effective level.
The key lesson is that harvesting from the ocean and intertidal zones must be done sustainably. Sustainable harvesting means taking only in moderation, ensuring ecosystems can recover and that future generations can enjoy kaimoana. Harvesting should be spread out, not concentrated in one area, and consideration should be given to methods. For example, scraping rocks and removing all sea life causes more damage than carefully taking a few adult mussels from a large clump.
When overharvesting does occur, ecosystems need time to rebuild. In some cases, shellfish beds can return, restoring biodiversity, food, and traditional harvesting. Allowing recovery prevents ecosystems from reaching a tipping point where they become functionally extinct, and are unable to recover naturally, requiring active restoration.
Protecting our coastal ecosystems requires action from everyone: providing education, following sustainable harvesting, and following fisheries regulations. Working together in this way will help to ensure these habitats, and the species that rely on them, remain for future generations.
