Understanding Our Oceans: Seagrass & Rocky Reefs

Marine ecologist Anna Berthelsen develops techniques to restore coastal ecosystems

February 25, 2026

Anna's work includes restoring seagrass, a vital component of a healthy marine environment

Seaweek is a nationwide initiative set up to bring Kiwis together to celebrate the wonders of the ocean, and to explore the ways our lives are connected to it. As part of Seaweek 2026, Dive Pacific met up with Anna Berthelsen from the Cawthron Institute to talk about her work helping to restore seagrass and rocky reefs in New Zealand.

Marine ecologist and climate change team leader Anna Berthelsen is part of the Restoration Ecology Team at New Zealand's largest independent science organisation Cawthron Institute in Nelson. The Restoration Ecology team is part of the Institution's Healthy Oceans Group, which supports sustainable marine and coastal ecosystem management.

"Cawthron Institute has been around for over 100 years, and has done some amazing work researching and monitoring marine activity, but the Restoration Ecology Team was only set up in the past five years," explains Anna. "A lot of work was being done in monitoring the health of our marine environment, but we started to focus on restoration after we saw the obvious degradation that was taking place, both across New Zealand and the world. We wanted to be more active in dealing with the negative impacts we were seeing in the marine environment."

Anna's work involves monitoring and restoring seagrass, which is a marine biodiversity hotspot. Photo: Dave Hansford

Anna's work focuses on the restoration and management of seagrass and rocky reef systems. That includes keeping a close eye on what's affecting different parts of the country. "There is different emphasis on different areas, depending on what they are dealing with," she explains. "As part of our monitoring the health of the environment, we monitor inter-tidal and sub-tidal rocky reefs, but ultimately, each community has a responsibility to look after their own area.

"Being able to peer into rockpools and investigating what you can see is part of the magic of childhood - it was certainly a magical part of my childhood. We need to protect what we love."

Saving seagrass

While both seaweeds and seagrass have similar names, they have very different origins. "Both are important species for a healthy environment, but they have different taxonomy," explains Anna. "Seaweeds are algae, while seagrass is actually the world's only marine flowering plant. Every other flowering plant lives on land, but somehow this one has made its way into the ocean.

This seagrass flower was found at the Delaware Inlet at Wakpuaka, an inter-tidal estuary north of Nelson in the South Island. Photo: Dana Clark

"Seagrass is a biodiversity hotspot, as many species are reliant on it, from little animals like crustaceans and shellfish, to foraging birds on the seaflats. In the Kaipara area it's also home to nurseries for baby snapper."

Seagrass acts as a nursing ground for baby snapper

While seagrass is still healthy in some areas, there has been alarming rates of decline both here and overseas. This is due to a number of reasons:

Sedimentation. Runoff from land has had a huge impact on seagrass. It smothers seagrass habitats, causing impacts for filter-feeding animals who grab particles from the water, and causes problems for animals who rely on visually clear water to feed.

Fishing. The removal of certain species upsets the balance, impacting other species and causing kina barrens. Both commercial and recreational fishing can cause this imbalance, as can bottom trawling, bycatch and direct harvesting.

Climate change. Emerging threats like marine heatwaves, and ocean acidification (the worldwide reduction in the pH of seawater as a consequence of the absorption of large amounts of carbon dioxide by the oceans. Ocean acidification is largely the result of too much CO2 in the atmosphere, produced by vehicles and industrial and agricultural processes.

Excess nutrient runoff. Nutrients can run off land, causing problems such as low levels of oxygen in the water. This can block light needed for plants like seagrasses to grow.

Kina barrens are caused by an imbalance in the ocean's species, often caused by fishing

As part of their work, Anna and her team are teaming up with communities to restore our seagrass meadows. One of the first steps in restoring seagrass is knowing when and where it flowers, so they have launched the Aotearoa Seagrass Flower Survey Database, a national hub where anyone can record seagrass flowering.

"We don't know a lot about the behaviour of seagrass across the country - like the timing of when they each flower, for example," explains Anna. "By monitoring where seagrass is thriving and where it's struggling, we will be able to learn more about this vital plant, and develop techniques for coastal restoration that are usable and practical for everyone to use."

To take part in the survey:

Go to your local seagrass meadow at low tide

Crouch down and look closely for flowers

Record whether flowers are present or absent

Take photos of the flowers

Contact seagrass@cawthron.org.nz

Healthy seagrass is vital for a balanced marine ecosystem. Photo: Dana Clark

How you can help

Government sets New Zealand's environmental rules, and environment is set to be one of the key issues debated in the leadup to the 2026 election. "A key action people can take is to vote in their local and national elections for government representatives who have strong values around supporting environmental protection and marine conservation," says Anna. "We all have the ability and the right to communicate with the representatives who are in power to ensure they understand how important environmental protection is to New Zealanders."

Click here for more information on the Restore The Meadows research programme, and on this link to find out how you can add to the national effort to survey our native seagrass meadows in the Aotearoa Seagrass Flower Survey Database.