By Tegan Evans

PhD candidate at the University of Auckland

Using marine protected areas (MPAs) correctly can be an amazing tool for passive restoration—effectively taking away human impacts from fishing and letting the environment return, more or less, to its natural state. However, it’s important that we protect the right areas.

While experts have called for 30 percent of the Hauraki Gulf to be protected (currently no-take marine reserves make up just 0.3 percent), that doesn’t mean that we can just protect any 30% and our problems will be solved.

We need to identify the areas that are both impacted by fishing and have the potential to recover once protection is in place. By focusing on these, we are more likely to see the positive results from conservation efforts—and we need to understand the complexity of the environment around Hauturu in order to enhance it with MPAs.

University of Auckland researchers Jenny Hillman, Stefano Schenone, Ines Bartl and technician Errol Murray sampling the sediment core.

The government’s current Revitalising the Gulf proposal proposes protecting the seafloor on the south-eastern side of Hauturu, but the main scallop fishery is on the south- west of the island—and is one of the only areas in the Gulf where the government plans to allow continued commercial dredging, a fishing method that damages the sea floor and the structural animals that live there.

If no scallop dredging is occurring where we are proposing to ban it, then what restorative changes are we expecting to see?

This decision puts us at risk of having a residual reserve— where protection is in place, but it does not contribute to our restoration goals.

My research looks to support some of this important decision making. In 2021 I took sediment samples at 23 sites around Hauturu at depths ranging between 15-60m, in order to identify the types of animals living on and in the sediment, as well

as the environmental conditions. This will help us to identify specific areas around Hauturu that are performing important functions, and are therefore most in need of protection.

Sediment cores extracted near Hauturu

Soft-sediment marine environments are often thought about as simple and bare, but this could not be further from the truth, particularly around Hauturu, which is an area of high biodiversity in the Hauraki Gulf. Environments like this are complex, with hidden lifeforms on and below the sediment surface, all performing numerous ecosystem services, such as the provision of food, like scallops, and the storage of carbon, which determines how the earth responds to climate change.

Soft-sediment environments vary across space depending on the environmental conditions—like grain size, wave energy, currents—and by ecosystem. Patches of sediment that are right next to each other can be very different, with different abilities to support other animals living in or on them.

This results in a complex environment that delivers important functions that support overall biodiversity and the scallop fishery at Hauturu, such as productivity (food availability) and sediment stability (ensuring the seafloor is suitablefor juvenile animals to settle and grow)—functions we can measure to provide insights into environmental health.

If complexity is ignored when it comes to the implementation of MPAs, we risk missing out on the benefits we expect from the protection, such as increased biodiversity and enhanced ecosystem functioning. Scallops are not found everywhere around Hauturu. If they were, we wouldn’t see such concentrated fishing effort in the southwestern end of the island.

There are important ecosystem functions happening in this area, and it is worth protecting at least some of it.

A polychaete or bristly worm found in the sediment core.

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