Okiwi mussels

This is what Okiwi Estuary (Great Barrier Island) used to contain within the main channel close to the estuary entrance. It was the last naturally occurring soft-sediment mussel reef in the Hauraki Gulf.

Green-lipped mussels – Okiwi estuary. Photos by Dr Darren Parsons

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.

Okiwi June 2015. Photo by Richie Robinson

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

Some areas were thick with shell but most of the substrate was sand.

I found one spot that was thick with old mussel shell (and just the one live adult).

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 decades it would take for it to completely regenerate?

Weeds on Motukorea

After the fire on Browns Island, lots of noxious weeds took hold. Although it looked like the crater was going to be dominated by bracken the weeds are winning. Black nightshade is dominant and there are thousands of woolly nightshades coming up, some as large as 1 meter wide already. Inkweed, apple of sodom and boneseed are also sitting up above the kikuyu.

Click for high res 360° image of the crater

Wooly Nightshade

I casually pulled up about 100 mullien but did not make a noticeable impact. Most disturbing was this animal dropping I found on a large mullien leaf.

Pray mantis identification

New Zealand has two praying mantises, the invasive South African praying mantis and the native New Zealand praying mantis. The easiest way to tell the two species apart is the shape of the head. The thorax (bit that connects their heads to their abdomens) is much wider on a New Zealand mantis so by comparison the South Africans look like hammerheads.

Natural mussel recruitment

After more than half a century Green Lipped mussels have not returned to the soft seafloor of the Hauraki Gulf. However only 100km north at the mouth of the Whangarei Harbour something magic happened. Out of nowhere a huge bed of mussels appeared. I was slow to document it but here are some photos by Dr. Mary A. Sewell in April 2016.

The bed was quickly consumed. Locals could park their cars a few meters from the beds. There were reports of people turning up with wheel barrows and of cars and boats being confiscated for those who exceeded their limits. The beds have now been decimated, I turned up eight months later at low tide and followed some locals to the remaining beds. They looked like this:

Green lipped mussel bed with eleven armed starfish triple fins and fishing line. DEC 2016
Green lipped mussel bed with triple fins and red filamentous algae. DEC 2016
Green lipped mussel bed with alga and octopus. DEC 2016
Green lipped mussel bed showing algae diversity. DEC 2016
Destroyed green lipped mussel bed. DEC 2016

The remaining bed ran along the edge of the drop off about 4m at low tide and supported a wide range of marine life. On my way back to the beach I wondered what conditions bought about this beautiful natural phenomena? There may well have been sufficient spat from mussels growing on the refinery wharf, but did a closure of the cockle beds promote natural the recovery? Could the neighbouring marine reserve have played a part? Was this a once off or part of the recovery of the Whangarei harbour since the Firth cement works has cleaned up its act? Then I spotted these:

Juvenile green lipped mussels. DEC 2016
Juvenile green lipped mussel. DEC 2016
Juvenile green lipped mussels. DEC 2016

It seems the cockle and pipi shells have created a firm substrate for the juvenile mussels to attach to. Is this how the bed started of? No hydroids or red filamentous algae to attach to, just green algae and shell? If so this is a recipe worth exploring for aided restoration elsewhere in New Zealand.

algaes
I dived around the other side of the channel where there was tonnes of algae of every sort but no mussels. Not even on the rocks. It is possible that the mussels did their 1st settlement on this algae then drifted to the bank. It would be interesting to dive a similar distance in the opposite tidal direction to look for recruitment.

Note there was a large pipi & cockle die off on the shell bank where mussels appeared.

UPDATE: Nov 2017
The bed is back! The juveniles I photographed have grown and there are now house sized mussel beds growing on the shell banks. There are isolated individuals ranging for a hundred meters or so west of the main bed. Most mussels were around 6-8cm long. I could not find blue mussels in the bed, I did however see fish eggs, octopus, crabs, evidence of fish feeding on the mussels, triplefins and many shorebirds enjoying the exposed reef. The mussels were also growing in smaller patches off the edge of the sand bank into the channel where I found the remnants in Dec 16.

Isolated mussels. NOV 2017.
Isolated mussels. NOV 2017.
Isolated mussels. NOV 2017.
Isolated mussels. NOV 2017.
Soft sediment intertidal green-lipped mussel bed. NOV 2017.
Soft sediment intertidal green-lipped mussel bed. NOV 2017.
 I saw five octopus in half an hour. NOV 2017.
I saw five octopus in half an hour. NOV 2017.
Green-lipped mussels Marsden Point. NOV 2017.
Green-lipped mussels Marsden Point. NOV 2017.
Humans and variable oysetercatcher consuming mussels. NOV 2017.
Humans and variable oysetercatcher consuming mussels. NOV 2017.

Hopefully this bed continues to regenerate despite the massive human harvesting effort. Identifying and protecting the seed stock would go a long way towards this.

Evasive weeds

One of the hardest aspects of restoring and maintaining native habitat is weed control. Cliff faces are the most expensive often requiring carrying heavy loads to remote places and abseiling or a helicopter. Today I watched as DOC, Motuihe Trust and Yamaha trailed spraying pampas from an unmanned helicopter. The RMAX helicopters are piloted by remote control and used in a wide range of industrial and research applications overseas. The trial was a success and the team have plans to further improve the precision of the technology.

Fire on Browns Island

Just after the fire was put out on Browns Island I kayaked over to check on the shorebirds. I went for a short walk and was quite upset by the damage done to the reptiles.

I found so many burnt corpses. In places near the edge of the fire (where I think it was less hot) there was a native skink corpse (I checked the head scales) every meter or so. While sad it is nice to know so many lived on the island.
I found so many burnt corpses. In places near the edge of the fire (where I think it was less hot) there was a native skink (I checked the head scales) corpse every meter or so. While sad it is nice to know so many lived on the island.
This rare moko skink survived despite having her tail badly burnt. While other surviving skinks can live of the fat reserves in their tails while their habitat recovers this one will have to work harder.
This rare moko skink has survived despite having her tail badly burnt. While other surviving skinks can live of the fat reserves in their tails (while their habitat recovers) this one will have to work harder.
Although it was sad to see these golden bell frogs roasted alive, they are are not native. I was surprised to see them in multiple spots high up on the crater rim. Some seem to have survived under the rocks.
Although it was sad to see these golden bell frogs roasted alive, they are are not native. I was surprised to see them in multiple spots high up on the crater rim. At least one survived under a rock in the crater.

The rest of my photos here. Hopefully some good comes out of it.

UPDATE 30 DECEMBER 2016:
Six weeks later the grass has largely rejuvenated, however without the smothering grass, many seeds that lay dormant in the soil have germinated. Most of the new arrivals are invasive weeds, I saw wooly nightshade, apple of Sodom boneseed and moth plant. However the center of the crater is more interesting. From under the rocks bracken has emerged (how long could it have waited there?) and I think the reptiles will enjoy the extra cover.

Bracken now dominates the crater
Golden bell frog
Moko skink with re-generating tail