Category: Restoration

The Okiwi Estuary (Whangapoua, Aotea / Great Barrier Island) used to contain the last naturally occurring soft-sediment mussel reef in the Hauraki Gulf.

“Aggregations ranged from a few individuals to meters in diameter. Mussels were frequently attached to pipis, partially buried in the sandy substrate. There were an estimated 3.2 million adults. Compared to other sites Okiwi mussels had the poorest condition but highest densities of invertebrates” – Ian Mcleod’s 2009 thesis on soft-sediment mussel systems in northeastern New Zealand.

Unfortunately they were nearly completely wiped out by a major storm.

I went for a swim on the outgoing tide (excuse the murky tannin stained water) to investigate 2 years later (April 2017).

Only 50 meters or so upstream I found some small regenerating clumps.

I was really pleased to see juveniles. Note the abundant red (not green) algae. Short video below.

If we left the bed alone, I wonder how many years it might take for it to completely regenerate?

UPDATE January 2018

I was able to visit the site again and was so impressed with it’s growth. The bed is awesome:

• There are still areas with lots of shell including old mussel shell that have not been colonised by green-lipped mussels.
• Most mussels were 4-5cm long but there were much smaller juveniles too.
• The estuary has a lot of cushion stars and sea hares but no eleven armed starfish or octopus which predate mussels. It was quite strange to not see eleven armed starfish there.
• The network pattern was similar to that of both restored and reefs and the one at Marsden Point with a wide range of density. It is most compact in the center where the mussels will run out of space if they grow.
• I was told by a local that there were adults at the mouth of the estuary, they maybe crucial seed stock for the bed.
• Although I saw eagle rays in the estuary I did not see them in the bed. There was no evidence of rays or snapper feeding in the bed but it looked like rays had been digging elsewhere.

Update January 2019

The bed is doing well, there has been some harvesting at the eastern end but it may have been for pipi. I located the parent stock 1km away at the mouth of the estuary. The adults were only 6-7cm long so they are growing much slower than farmed mussels. Still no eleven-armed starfish. I hope the bed continues to grow. It would be interesting to survey the bed to see of recruitment was happening more at the edges (or not). The bed, size density and associated fauna and flora will help inform restoration efforts elsewhere in the gulf. Video here. Observations below:

Update January 2020

No major changes to density, heavy with algae, no juveniles seen. Locals driving vehicles on cockle beds to get to the pipi which surrounds the mussel bed and set a net right on its eastern side.

Update February 2021

Unfortunately the crab above was the invasive species and my find triggered a $10,000 biosecurity response.

A local has anecdotal evidence that the mussel bed may not be 100% natural. A mussel farmer from the other side of the island who has since passed (Dick Anderson) claimed to have seeded the bed with mussel spat around 1990. The same local who talked to the farmer reports having seen mussels in the channel at the time. The story questions the genetic makeup of the bed, however in 2015 (when the bed was nearly wiped out) most of the bed was replaced then by local spat (there are beds on nearby rocks). Locals recall mussels on these rocks from the late 1980’s to early 1990’s. I am now checking with Auckland University to see if surveys for a marine reserve in the 1970’s recorded the bed.

Update Feburary 2025

I was told by an ecologist monitoring the asian paddle crab problem that the kūtai bed was wiped out by moving sand in May 2022. Another local told me he thought there may be 200 kūtai in the estuary in December 2024. I spent 1.5hrs looking at low tide two months later and could not find any but did find a few juvenile blue mussels had recruited onto dead cockle shell.