October 13, 2021

Coastal Dunes - Species that Matter - Sea Spurge

While not intending to focus on the dramatic, this month I once again divert from the focus on some of the amazing and wonderful native and endemic species that we have on this coast in our dune wilderness, to focus on a different kind of problem to last month's highlighted weed [1].

Two years ago I learned about sea spurge via


It took my iNaturalist colleagues some weeks to settle on the identification, since at the time, this species was only known in NZ from an initial invasion in the Waikato. A DoC lady woke us up to MPI's position on this species. The participants in this process celebrated finding this plant early, before the problem became serious. If only it remained so simple. MPI's management of this species stands in stark contrast to the sorry state of our coastal dunes ecology due to coastal wattle [1] which is a far more advanced problem, in terms of destroying the native coastal dunes ecosystems. So, what's the big deal?


a) Euphorbia paralias, as it is formally named, is a significant problem in Australia, where it is soaking up large sums of money to manage it.

b) Not only is the illustrated beach effectively overgrown, sea spurge can cause skin and eye irritation from the sap. This is a real deterrent for beach-oriented tourism. New South Wales is not the worst hit problem, but over 60% of beaches in NSW are affected already.

c) MPI regards this as an early-stage problem that needs to be beaten, before it starts to affect the New Zealand economy.


This reflected initially in the early finds with rapid, comprehensive reactions, an ecological parallel to the government's proactive stance on Covid-19.

From the single find on the lower North Island two years ago, a recent coastal dunes survey by Kelsi Hoggard of Horizons Regional Council, had over the past month, highlighted a further three instances in our region, which were mature enough to have spawned several generations of plants, at sites west of Moana Roa Scenic Reserve south of Scott's Ferry, half way between Waitarere Beach and Hokio Beach, and half way between Kuku Beach and Waikawa Beach.[2] There has recently also been a site highlighted south of Paraparaumu Beach, as well as one on the West Coast of the South Island.

To drive the situation home, recently I came across another patch, 4km north of the Foxton Beach Surf Club, ie. right in our back yard [3].

Once again, reporting this on a Sunday caused a furore, with multiple persons from MPI chasing details, as well as our local Council and DoC contacts. This is taken seriously.

Maybe you can use this material as a guide to recognising this problem when you happen to walk in the dunes. I certainly hope so! As a starting point, if you download and read the URL on the MPI website, it will give you the necessary details to report any find of this species. That's my bottom line message - how you can help. These are our New Zealand beaches that we're working to preserve.

Consider the larger context. This is broached nicely in my article from last month[1] for coastal wattle, or you can see another 'fine' example at the well managed estuary of the Waikanae River, which at the dune front, turns into a wall of tree lupin [4]. These problems are past an easy solution, so let's not let sea spurge get like that too.

Enough banging of the drum. Start with the URL from MPI, and let's work together on this.

[1] https://inaturalist.nz/journal/arnim/55596-coastal-dunes-species-that-matter-coastal-wattle

[2a] https://inaturalist.nz/observations/93765978

[2b] https://inaturalist.nz/observations/94880736

[2c] https://inaturalist.nz/observations/94880602

[3] https://inaturalist.nz/observations/96144946

[4] https://inaturalist.nz/observations/32318247

Posted on October 13, 2021 07:37 by arnim arnim | 0 comments | Leave a comment

August 24, 2021

Coastal Dunes - Species that Matter - Coastal Wattle

The intention is that the following is the first of a series of perspectives on species that live in our area, focusing on dunes, dune wetlands and estuaries along this west coast of the lower North Island. Often you’ll see upbeat material, covering threatened species that are doing well, or not so well, on this coast. Sometimes I’ll rant about problem species.

Because this time of year is the peak season for identifying it, I’ll start this series with a problem species. Coastal wattle, a.k.a. ''Acacia longifolia sophorae'' is the number one threat to our dunes and dune wetland environment on this coast. Here in Foxton Beach, to see this problem at scale, look at the south bank of the Manawatu River. There were formerly dunes along that shore well back in from the coast, but those dunes are all but gone, overgrown with a wide belt of coastal wattle from the plantation pine to the estuary. The native dune flora and fauna have disappeared under a coastal wattle forest:
We have other problem spots in the Foxton Beach area. A stalwart community team works with District Council to eliminate this from the dunes south of Foxton Beach township. On the north side of Foxton Beach at the end of Brown Terrace about one hectare of dune vegetation has gone lost to large, well established stands of coastal wattle.

To familiarise yourself with this species, as it has a characteristic flower in August/September:
The bright yellow flowers are identifiable from a distance this time of year.

The wattle problem is particularly obvious around Himatangi Beach:
The dunes are completely covered around the main beach entrance. To the north dozens of hectares of coast wattle forest have eliminated the original dune vegetation. To the south of Himatangi Beach settlement, some of the most scientifically interesting dune wetlands anywhere are under threat from encroaching coastal wattle.

This problem does not stop there, but is severe at Tangimoana, right past the Rangitikei estuary, and on to the mouth of the Whanganui River.

We have a particularly clean dune area around the north side of the Manawatu River mouth. Within the Manawatu Estuary Ramsar site[1] the dunes are free of coastal wattle, and are maintained that way by a dedicated team of volunteers. Further south than the Manawatu River, the coastal wattle problem is out of control too. The dunes are being overgrown to Waitarere Beach, and beyond. One of the finest examples of dune wetland on this coast is the 4km stretch between Kuku Beach and Waikawa Stream, but especially at the south end, the coastal wattle is running amok, over a host of native dune wetland species that deserve better.

This problem was originally created by the New Zealand Forest Service, and its predecessors, in their ambitious plans to plant New Zealand’s dunelands with pine forest[2]. With these plantations now commercialized it is difficult to push the current leaseholders of those forests to be responsible for the mess.

A retired scientist formerly associated with Landcare Research, Dr. Richard Hill, had been working for years to certify a species of invertebrate which preys on Acacia species, including coastal wattle. Whether this is a viable answer, I can’t say, but I’d like to find out more about the status of that work, as an option to consider. Our coastal dunes and their wetlands are unique, in New Zealand and wider. Dealing with this species would be a major step toward preserving them.

[1] Some pointers to the Manawatu Estuary Ramsar site:
https://en.wikipedia.org/wiki/Manawatu_Estuary https://en.wikipedia.org/wiki/Manawatu_Estuary

[2] http://dunes.letras.ulisboa.pt/wp-content/uploads/2021/07/Dunes20drifting20in20New20Zealand2c20Sampath2c20Beattie20and20Freitas_PREPRINT.pdf

Posted on August 24, 2021 09:29 by arnim arnim | 1 comment | Leave a comment

April 30, 2020

killing and conservation

Brought on by a conversation, one might say, visible at

My perspective, which isn't finished evolving, is that if you're not prepared to kill, then conservation work probably isn't for you. Weeding is killing, managing pest species is killing. I don't go out of my way to do either, and I don't even particularly enjoy it for its own sake, but it is part of ecosystem preservation, if we value biodiversity. If a species cannot live in the place where it evolved, where should it live?

Consequently, when I see a tree lupin or coastal wattle growing over Autetaranga or Tataraheke, it often stimulates me to action. Effects of weeds can be a great deal more subtle than that obvious example.

I have long identified four species of exotic spiders which prey on katipo. This is not published in any journal yet, but my scientific advisors have been aware of this state for more than five years. As a consequence, every time I see Sidymella trapezia, Steatoda capensis, Australomimetus hartleyensis or Nyssus coloripes, they get the squeeze. And I often reflect this information in my observations, to let others know that this is the case. If you look for it, there is hard evidence enough amongst my observations. At most I might some day update the Wikipedia article on katipo to reflect this, and address other shortcomings in that piece.

The situation is very different when native species impacts on native species. If mankind had not interceded to introduce all of these exotic species, then Mother Nature's plans would have had such native-vs-native conflicts resolved on her own terms. That's not my argument to get involved in.

Posted on April 30, 2020 19:05 by arnim arnim | 4 comments | Leave a comment