Stacey Balich

The ferns always had a major drawback when it came to occupying the dry land, and although their dominant sporophytes have well-developed internal tubes in their stems to carry water up to their fronds, they have a reproductive “Achilles heel” in that they possess mobile sperms with lashing tails which must swim in surface water films in order to reach female fern egg cells in order to fertilise them. 

The seed plants (Spermatophytes) overcame this limitation by producing male gametes (“sex cells”) in the form of dry pollen, often carried on the wind or transported stuck to insects bodies. Apart from other fundamental structural differences seeds are generally much larger than fern spores, and contain food reserves for the growth of the young embryo plant giving them a significant advantage. This subject would demand an entire episode to explore fully! These seed design breakthroughs would see the seed plants begin to replace the spore-bearing ferns as dominant players in the Gondwanan forests of the late Permian period 250 million years ago. 

The very first seed plants may have appeared as early as the Devonian 350 million years ago, starting with the so-called “seed ferns” but it wasn’t until the late Permian/ early Triassic periods 250 million years ago that the seed plants finally came into their own with forests dominated by the now extinct Glossopteris trees towards the end of the Permian.  

Todays seed plants are divided into 2 main groups:
Gymnosperms = “Naked seeded” Pinophyte Conifers with seeds exposed in cones, comprising the Pinophytes (Pines), Cycads, Ginkgos and Gnetophytes. These last three are not native to NZ but Cycads and Ginkgos are often grown in NZ gardens as introduced specimen plants. The second group of seed plants are the Angiosperms = Flowering plants with seeds hidden and enclosed within a fruit. This group includes the grasses. We will look at the Angiosperms in the next issue. 

We will look at the Gymnosperm pines or Pinophytes belonging to the Family Podocarpaceae (Podocarps) found on Tiritiri Matangi that originated from the ancient continent of Gondwana before New Zealand broke away some 80 million years ago. 

Those with Northern Hemisphere links will immediately associate the term “pine tree” with long thin needles and large fist sized pine cones – eg Pinus patula the Mexican weeping pine (see right), or Pinus radiata, the Monterrey Pine grown extensively in NZ for its timber and originating from California. 

However, in the Southern Hemisphere the dominant endemic pines are the Podocarps meaning “Foot-fruit” referring to the way the naked seed sits on top of a round fleshy “fruit” called an Aril. 

This is how the female cones of the two families of pines compare: 

Look out for the Kahikatea trees Dacrycarpus dacrydioides growing in the damp stream bed of the Nikau grove. The largest one produced fruit for the first time in 2022. 

Kahikatea can grow to a height of 55 meters with a trunk exceeding 1 meter in diameter, and is New Zealand’s tallest tree species, even beating the mighty Kauri. It prefers to grow in damp swampy conditions and often lines riverbanks and other wet areas. In immature trees, the leaves are about 8mm long and lie in a flat plane along the twigs (see picture left). When mature the leaves are scale-like and are 1-2 mm long. (below left) The cone scales swell to form a red fleshy aril with the seed on top about 5mm in diameter. Birds like pigeons find them irresistible and eat them dispersing the seeds as they do so. The largest tree in the Nīkau Grove (along the Wattle Track) produced about 100 arils in 2022 which were eaten very quickly as soon as they ripened. I was lucky to catch just one to photograph! Kahikatea are often referred to as “white pine” due to its clean white timber. It imparts no flavour to food and was used to make butter boxes for export to the UK up to the middle of the 20th century. There are still a few old-growth remnants of kahikatea left in the Waikato.

Māori used it for carving waka and for making bird spears. Its length meant it was used widely for shipbuilding, but it is not as resistant to rot as tōtara. Only 2% of the pre-European kahikatea forest remains.

The Tōtara Podocarpus totara is found in several places on Tiritiri Matangi, especially on the Tōtara, Kawerau and Ridge Tracks. Look out for the characteristic brown stringy bark and bunches of stiff and leathery leaves 20 mm long NOT on a flat plane on its twigs like the kahikatea, but protruding in all directions. 

Tōtara “cones” have two to four fused, fleshy, berry-like, juicy aril scales, bright red when mature. The cone contains one or two rounded seeds at the end of the aril scales. Tōtara can grow to 35m and its timber is favoured by Māori for large carvings, whare frames and waka building. The inner bark was used for roofing and for storage containers and the outer bark as splints to support fractured bones. 

Some of the larger canoes carved from a single tree could hold up to 100 warriors. Natural oils in the timber slow down rotting. When Europeans arrived in New Zealand, huge areas of tōtara were felled to supply general building timber, railway sleepers, bridge and wharf timbers and telephone poles. The red arils are an important food source for both humans and birds, especially tūī. Tōtara wood is very tough and can be used to produce fire by friction where a pointed stick is scraped on a slab of softer wood such as māhoe and a glowing ember created.

Which animals found on Tiritiri Matangi today would have appeared around this time 250 million years ago alongside these trees? 

The wētās belong to the Insect Order Orthoptera (meaning “straight wings”) alongside the locusts, grasshoppers and crickets. There are three species present on Tiritiri Matangi, the giant wētā (Deinacrida heteracantha), the ground wētā (Hemiandrus sp) and the Auckland tree wētā (Hemideina). 

The female giant wētā can achieve a weight of 70 grams making it one of the heaviest insects in the world. All insects rely on an air-filled tracheal tube system to deliver oxygen to their internal tissues and remove carbon dioxide. This is not a very efficient means of gas exchange, and it limits the maximum size an insect can grow to. Our giant wētā are right on that limit. Consequently, they spend much of their time sitting motionless – a good way to avoid being eaten by a passing tīeke. When they do have to move, they can do so quite rapidly but for a short time only before having to rest and recover. 

There are eleven species of deinacrida giant wētā in New Zealand, mostly restricted to mammal-free islands. On Tiritiri Matangi we have the Little Barrier giant wētā Deinacrida heteracantha translocated here in 2014. At one time this species was widespread from Northland to Auckland. It probably reached Tiritiri Matangi and Hauturu during the last Ice Age 11,00 years ago when sea levels dropped and Tiritiri Matangi was a hill surrounded by forest on flat coastal plains. 

One South Island species is an Alpine specialist and is capable of recovery after being frozen solid when temperatures drop below -5 C. These wētā are good examples of island gigantism. This is a biological phenomenon in which the size of an animal species isolated on an island increases dramatically in comparison to its mainland relatives. There are several possible reasons for this, a lack of predators on isolated islands allows larger less nimble individuals to survive that would otherwise have been eaten. Larger bodies are better able to store food and maintain a constant internal temperature giving a survival advantage. Other examples in New Zealand include takahē and moa. 

The Caddisflies (right) are another ancient group of insects that appeared around this time. Caddisflies belong to the order Trichoptera (meaning ”Hairy wings”). In New Zealand, we have many freshwater species and even five species of marine caddisfly, one of which, philanisus plebeius, is present on Hobbs beach living amongst the rockpools. Adult caddisflies are poor flyers with more than a passing resemblance to small moths. Adults lay their eggs within the bodies of cushion stars where the larvae develop for a time, eventually emerging by burrowing out through the mouth of the starfish, and then building a protective case of sand grains and silk to protect and camouflage themselves. In rockpools, they graze on red encrusting coralline algae and the diatoms that live on them. They pupate amongst the seaweed and emerge as a non-feeding adult to mate and repeat the cycle. Marine insects are incredibly rare and these caddisflies are found nowhere else on Earth. 

Visitors sometimes comment on the marked presence of small-leaved, twiggy shrubs in our forest. Our flora contains a high proportion of these small woody shrubs which have a tight interlocking branching pattern. They are called “divaricating shrubs”. They have small leaves and tough wiry stems with a dense meshwork of branches with multiple growing points inside the shrub. They often have a brownish colour, giving an almost dead-looking appearance.

Some of our trees also pass through a divaricating juvenile stage, changing to a less tangled normal growth above 3m height. These plants all lack sharp spines. Collectively they are a special New Zealand feature. Our flora contains over 50 species of these divaricates (about 10% of all our woody plants). How has this growth pattern come about?

Two theories have been postulated:

1. Browsing Moa:

This huge two-legged bird came to occupy the role of a four-legged grazing mammal in New Zealand. It would have spent many hours picking leaves and twigs off low trees and shrubs. Moa favoured fertile river flats, forest edges and wetlands rather than deep forests. Highly palatable and nutritious shrubs growing in this habitat would have suffered extensive damage from these birds. They, therefore, had to evolve a mechanism to survive – hence their divaricating nature. Small leaves and a brownish colour would have made them look less attractive and dense interlocking branches would have deterred browsing. The lack of thorns and spines can be explained by the fact that whereas they would be effective at repelling the sensitive lips and tongue of a browsing mammal this would not work when dealing with the strong horny beak of the moa. Its beak would have acted like secateurs nipping off thorns etc which would have been easily crushed by the stones stored in its gizzard. Those trees with a divaricating juvenile form would be able to change to the adult stage above 3m height which would be out of reach of the largest browsing moa.

2. Climate Change:

The last ice age (Pleistocene) circa 2 million years ago caused world climates to go through a series of fluctuations with long cold glacial spells interrupted by warmer interglacial. It was a highly significant time for the final moulding of New Zealand’s present flora. Our vegetation lost the last traces of its Australian look (known that eucalypts, proteas etc once grew here from the evidence of fossil pollen deposits). The small-leaved divaricating form would be well designed to adapt to the cold, windy arid climate prevailing. This theory suggests that the growth form would act as a defence against wind abrasion and frost damage as the whole plant may have acted as a heat trap keeping delicate growing points within a protective shield. Small leaf size would have led to less moisture loss through evaporation thus counteracting the arid conditions.

Botanists continue to argue these two theories. Perhaps they both contain merit and actually reinforce each other as the need to grow this way would have been even greater if it helped plants to survive both adverse climate change and excessive moa browsing.

Caulerpa brachypus and Caulerpa parvifolia are two almost identical species of invasive exotic seaweed that have been found growing intertidally on Aotea Great Barrier Island (2021) and now Kawau Island (2023). We need your help to detect it if it arrives on Tiritiri Matangi.

The Caulerpa species grow extremely rapidly and are said to smother everything living on the seabed. Native species either move away or die. The photos below are of C.brachypus on Aotea Great Barrier by kind permission of Jack Warden who discovered them there in 2021.

If it does establish itself on Tiritiri Matangi our Mana whenua may declare a rāhui over Tiritiri Matangi’s beaches and Biosecurity New Zealand and the Department of Conservation will impose legal controls on all boating and water activities to try and limit its spread. Whilst walking between the Wharf and Hobbs Beach please keep an eye open for this highly invasive seaweed which may be washed ashore amongst other flotsam on the tide line. You might not see it growing in situ unless it is an extremely low spring tide.

Caulerpa is a genus of marine algae with over 100 species spread widely over the Indo-Pacific region in warm tropical and subtropical seas. Most of these species are extremely variable in size and shape. In addition to the 100 or so known species, over 40 varieties are known. Many of these can also adapt and exist in more than 60 variable morphs (shapes or forms) depending on environmental conditions such as temperature and degree of exposure (wave impact). This can make precise identification difficult, to say the least.

The map above shows the current distribution of C. brachypus in the Indo-Pacific region (NZ in red). Controlling Caulerpa is very difficult due to its rapid growth rate and its ability to spread asexually using creeping runner called stolons, and by fragmentation when boat anchors or rough seas break it up.

Trials have been done using salt crystals spread onto the weed at a rate 25kg per m3 with hessian matting and tarpaulins on top to kill it by “osmotic shock” (salt essentially sucks water out by osmosis and it shrivels up). One Australian attempt involved strong chlorine bleach. Either way, as you can imagine the collateral damage to other native sea life is considerable and the week is soon back if just a small amount survives.

If you think you have discovered something suspicious washed up on the strandline, take a photo of it and report it to the rangers.

Several benign species of Caulerpa are native to New Zealand coastal waters and unlike the more recent invaders are not of concern. It would be useful to know what these native species look like to avoid any false alarms.

Most of the time Caulerpa species reproduce asexually by fragmentation, with sexual reproduction occurring infrequently. It seems to depend on local conditions. Some researchers found that the main plant is diploid (2 sets of chromosomes), and when sporangia are formed they release haploid gametes resulting a diploid embryo again after fertilisation. Other workers had conflicting results, finding the main plant to be haploid. However, given the extreme variation possible within each species, it is thought that perhaps they were looking at different species that appeared identical.

Some species are cultivated commercially in the Philippines as a valued seafood. Rich in iron, magnesium and antioxidants they are touted as possible treatments for heart problems and even some forms of cancer. Others are thought to be less palatable with a peppery taste. None are dangerously toxic to humans, however they are all capable of concentrating heavy metals if grown in polluted water. Some are grown as nitrate absorbers on fish farms, where periodically the weed is harvested and spread on the land as fertiliser.

Caulerpa is unusual in that they are syncytial, not multicellular organisms (left). The entire plant or colony could be looked upon as one enormous cell, with many nuclei scattered throughout. The cell membrane forms the outer “skin” of the thallus. Interestingly, if the thallus is cut, the cytoplasm does not leak out, but instantly forms a new cell membrane at the site of the cut. Enormous numbers of microtubules are present in the cytoplasm, and these are thought to give the thallus its shape. Indentations of the inner part of the cell membrane extend deep into the thallus and these could aid the diffusion of nutrients in, and wastes out of the thallus. Their explosive growth rates bear witness to the effectiveness of these various adaptations.

Their negative impact on the ecology of the seabed does seem to vary according to the species of Caulerpa involved, and the geographic location of the invasion. The Mediterranean has seen one of the worst invasions of what is thought to be the most pernicious of this genus  – Caulerpa taxifolia.  Strangely though, its presence has seemingly had little effect on Posidonia oceanica the resident seagrass there. Will our own native seagrass Zostera meulleri stand up to an invasion by C. brachypus?

Other published studies have shown that in French and Italian Mediterranean waters fish diversity and biomass are equal or greater in Caulerpa meadows than in seagrass beds and that Caulerpa had no effect on composition or richness of fish species. It all depends on whether the fish species present can use the Caulerpa species as food source or not. Shellfish beds have been particularly hard hit, with many long established sites smothered and destroyed in many parts of the world.

The two new species – Caulerpa brachypus and Caulerpa parvifolia we have here in New Zealand probably originated from the eastern coast of Australia, 2,200km away to the west. The main vector would have been ocean currents and tides. 

Boating and fishing activity are thought to play a significant role spreading fragments of weed between nearby locations within New Zealand. 

It takes only a small fragment to create an immense smothering bed in a few years. The South Pacific Gyre dominates the ocean circulation in the South Pacific. Driven by the trade winds and Earth’s rotation, warm equatorial surface water swings down from the northeast against the coast of Australia. Eddies detach forming the warm East Australian Current which can carry Caulerpa fragments from the east coast of Australia across the Tasman Sea to New Zealand. Here it forms the East Auckland Current which delivers subtropical water to the northeast coast of North Island and the Hauraki Gulf.

The reason why these exotic species have only recently become established here in Auckland is that until recent decades, the sea temperatures here have been too cold for them to become established. 

This July the seawater temperature off Tiritiri Matangi has been consistently between 3.5 to 4 ^oC warmer than it was compared to records made 50 years ago, possibly allowing these drifting exotic fragments to survive, settle and become established. Increasing nitrogen and phosphorus levels in the Hauraki Gulf from Auckland’s sewage will also stimulate the growth of algae living there.

Although all the Earth’s oceans are interconnected, it is temperature barriers that often set biogeographical limits for many marine species. For animal species that spend a few weeks drifting as planktonic larvae, time is also a barrier preventing them from travelling very far on ocean currents. The Mediterranean fan worm is a good example of an organism whose distribution is limited by both temperature and time. Their tiny larvae do not stay suspended in the water column for long enough to travel very far, before dropping to the bottom to attach as adult sessile fan worms. 

This wasn’t a problem until the advent of rapid ocean travel allowed them to get as far as New Zealand in ships ballast tanks or as adults fouling hulls. Travelling on ocean currents alone might have taken them years or decades. Oceanographers studying ocean currents became very excited when in 1992 a container ship heading to the USA from China shed 29,000 yellow plastic bath ducks into the sea during a storm. These eye catching objects were found on every shoreline around the Pacific within 4 months. Some were carried north where they were trapped in Arctic ice, and they eventually emerged in the North Atlantic where in 2007 some were washed up on the coast of Ireland and Spain.

Although Arctic temperatures and time would have killed any living organism undergoing this 15 year marathon, it shows how the world’s oceans are all part of one system and the hop from Australia to New Zealand is not such a big deal. 

All this does rather beg the question – how long will it be before MORE exotic species drift into our invitingly warm waters and set up home here? Caulerpa taxifolia is already established in the coastal waters off NSW in Australia.

We need to keep alert!