Marine restoration is a lazy business. All you have to do is stop fishing an area and marine ecosystems heal themselves. However this is not the case with green-lipped mussels in New Zealand.
100’s of square kilometres of sub-tidal mussel beds were fished to extinction in each harbour around New Zealand.
The industry collapsed and more than half a century later they have not returned. In the Hauraki Gulf there are a few places you can still find Green-lipped mussels. You would think that these places would be deep under the ocean (Green-lipped mussels have been found at 50m deep), but they are not.
Most are in the intertidal zone on rocky shores. Here there is usually a gradient with mussels thin higher up and getting thicker towards the low tide mark where the abruptly stop. I have asked several local experts and no one has a solid answer why they stop so abruptly.
As we spend 100’s of thousands of dollars restoring sub-tidal beds maybe the key to unlocking a lazier (and cheaper) solution is staring us in the face. Here are some thoughts on why the line exists:
Avian predation. Every exposed mussel bed has at least one pair of Variable oystercatcher eating the smaller mussels every low tide. So living in the subtidal zone would be of some advantage but we are more likely to see juveniles higher up. This suggests there is even more predation from below.
Starfish predation. Eleven-armed star fish were a big problem in the first beds put down by Revive our Gulf. However starfish do okay in the intertidal zone and are not particularly abundant in intertidal beds. We don’t see lots of them waiting below the low tide mark next to intertidal mussel reefs.
Fish predation. This seems like the most obvious cause but surely it can’t be Snapper as they have been fished down to 20% of their natural biomass. Rays are a possibility but I thought I would see more of them in the shallows if this was the case.
Octopus predation. They are nearly invisible and love eating mussels so at first this is a good fit. But octopus leave the shells, I will look for evidence on the next intertidal bed I explore. None of the predation theories show why the line is so strong.
Food. Mussels eat phytoplankton and algae. I am sure there will be more of this close to the surface. I am pretty sure this is why mussel farmers grow their mussels high in the water column. Wild mussels might also benefit from wave action on the rocks as it would increase the oxygen in the water. However I would have thought that these benefits would be offset by the fact they can’t feed while they are exposed to the air.
Sediment. If there is some other benefit to being exposed to the air maybe it’s that the water in the Gulf just has too much stuff in it. Mussels have to work hard sorting out the food from the dirt, maybe mussels are not good at taking a break and being forced to is good for them. Comparing the condition of intertidal and sub-tidal mussels would help dismiss this idea.
Or maybe like a lot of things in biology it’s a mixture of the above factors. As we are slowly losing our intertidal mussel beds it might be wise to set up a long-term monitoring project that might solve this mystery and inspire lazier restoration methods.
I have 1,612 verified observations on iNaturalist between Auckland and Whangarei documenting 552 species (mostly invertebrates) covering forest, freshwater, intertidal and marine habitats. I don’t take many photographs of plants. Of these observation 96 or 17% of species were introduced. Here is a break down showing areas where I have found more or less introduced species:
Rangitoto / Motutapu / Motuihe
I expected the restored and protected islands in the Hauraki Gulf to have a smaller percent of introduced species. I think the high number of introduced species (compared to the Waitakeres and the Hunua Ranges) reflects the islands farmed history with islands like Motukorea and Motutapu still dominated by kikuyu. The larger and older the forest the more indigenous biodiversity.
I teamed up with computer and environmental scientist Jordi Tablada to build a website for identifying New Zealand animal sign. I met Jordi through the New Zealand Dotterel Forum as he looks after dotterel at Piha. We had overlapping skills and were looking for a project to collaborate on. He came to me with the idea inspired by some materials produced by another dotterel minder Emily Roberts.
Now when I spot tracks in the sand and wonder what made them I load up the website and check them against the examples. It’s working really well and I hope to expand it to include other animal sign and more species. Others are using it too, mostly due to some great press. It was inspiring to see another citizen science identification guide go live this morning which will also help on beaches. This one is for shells.
With a lot more mowing at Point England this Winter the flocks of South Island pied oystercatcher are leaving a visible sign in the paddock. The probe holes are very dense right to the edges of the paddocks which means that I am also seeing holes from other species like White-faced heron and Pukeko. Casual counts put the number of little holes at around 100 per square meter.
Today I took photos of the shorebird roosts at Tahuna Torea when the tide had just covered the main spit roost. The tide height was predicted to be very high today (3 August 2019) at 3.4M Westhaven 8:53am. Conditions were relatively calm and the tide had not (yet) hit the high tide line on the Little spit.
I have seen tidal debris in the mangroves around Lockley Island that were above the height of the island (indicating that it sometimes gets swamped) but I think it would have made an ok roost today.
I was recently lucky enough to monitor kiwi on Hauturu with the Little Barrier Island Supporters Trust. I have done this many times before at Tāwharanui with TOSSI. The exercise involves a good hike to the destination at night then sitting quietly in the dark listening to the sounds of the forest for a couple of hours. I have met some great people doing this and this trip was no exception. They patiently waited for me as I inched along the tracks on the way back to the hut, inspecting every tree for hidden treasures and some even came out with me again on their free nights. I have posted all my invertebrate observations here on iNaturalist where the community is helping me identify them all. I have also posted some fungi which were a hot topic among the volunteers.
It’s an incredible island where one can get a sense for pre-human New Zealand. Here is a list of some observations I made over the 12 days I was there.
I saw less invertebrates, birds and geckos at elevation.
Piwakawaka following Tieke on two occasions.
By weight there was much more industrial plastic pollution (mussel floats) than domestic plastic pollution on the beaches.
Similar gecko numbers in winter compared to summer. One seen every 20 minutes on night walks.
Cave Weta were the dominant weta by a factor of 10 or more. Tree Weta, Ground weta and Wētāpunga active.
Winter invertebrate abundance similar to mainland sites with predator control (and less birds). At night, in two out of three tress invertebrates were easily found.
Invertebrates not much bigger than raindrops stay hidden during the rain.
NZ Giant Centipede found 3m above ground inside a Kanuka tree that fell in the middle of the day. The species is very arboreal.
Korimoko chasing Ruru during the day.
Flock of 18 Kereru feeding on Muehlenbeckia.
A high of 12 Shore Skinks seen from one observation point. No other skinks observed.
Invertebrate diversity high with many species I had not seen before. Some had not been previously photographed in the wild.
Strange absence of Katydid calls.
Very empty streams with only Shortfinned Eel and Banded Kokopu observed. Huge flushing events the likely cause of low freshwater diversity and abundance.
The MTLB have made changes to the OSNP as follows:
Page 10 (Coastlines and Waterways)
The Tāmaki Estuary is home to a varied number of shorebird species. The shorebirds roost in the reserves along the coastal edge throughout the year including Point England Reserve, Wellington War Memorial Reserve and Tahuna Torea Nature Reserve.
Several species are threatened and the populations are in decline.
Threats to the shorebirds include disturbance of their roosts preventing them from resting, particularly at high tide, from lighting of the reserves at night, dogs, humans, unsuitable vegetation and construction.
Page 20 (Environmental Quality)
+ Shorebird populations are in decline due to their roosts within the coastal reserves being disturbed
Page 36 (Improve biodiversity and water quality)
Protect and enhance shorebird roosting areas:
+ Investigate opportunities to restore roosting areas for shorebird populations
+ Provide opportunities to protect existing roosting areas.
The wording is well chosen and at a high level it addresses my core concerns. A good start to reversing the decline of the shorebirds in the Tāmaki Estuary.
We identified 19 tracking locations (S1-S19) in 2014. The first 10 (S1-S10) were used in this survey. The survey was repeated in March 2019. The first 10 locations were searched and three out of 10 tracking tunnels were found. Seven new tracking tunnels were installed on the 10th of March. On the 16th of March another 9 tunnels were installed and all the tunnels were filled with an inked tracking card with peanut butter in the middle. Some locations were adjusted to make access easier. I noticed when trying to find the tunnels again with the Garmin InReach and App that the positions were often off by up to 16M. Thats a lot in the bush!
I find these mashed up prints very hard to identify, but here is my best guess: