Tag Archives: New Zealand

Adrift amongst the mangroves

Back in 2001, on my first trip to New Zealand, I had a chance to go kayaking amongst the mangroves in the Bay of Islands. Recently, I found my notes on mangroves, particularly upon how they handle salt water – I’m always intrigued by life pushing the margins.

The New Zealand mangroves, according to my guidebook, are among the southernmost examples of these trees in the world.  Avicennia marina var resinifera – but the resinifera is a misnomer arising from the finding by Joseph Banks, Captain Cook’s scientific observer, of resin among the roots, resin that comes from kauri trees.  To the Maori they are manawa.  In NZ they’re near their southern limit, a single species out of 55 worldwide (54 in Hogarth, 1999). Around Auckland they’re stunted and impenetrable, but in the bay of Islands they grow up to 15 m.  According to Deanna (the guide), they filter seawater through their roots, but seawater is too salty for them, so they concentrate the salt in certain of their leaves.  The salt is either washed away by a heavy rainfall or the leaves die and drop off.  Mangroves shed constantly. They obtain oxygen through their leaves and through air-roots, which jut up from the mud and are submerged at high tide, so are sealed.  The roots are wide and shallow extending horizontally to up to five times the tree’s upper radius, since the aerobic layer in the mud is very thin.  Mangroves have no rings, and presumably do not have seasonally dictated cycles.  Mangrove seeds, which float, already contain a seedling consisting of two leaves, a stem and a root, so if they fall during low tide and strike solid ground, the seedling can root before the next tide.  If not, if the seed/pod falls into water, it can float for months until it comes to rest.  Among the roots are mangrove seedlings, planted, which can wait in a state of arrested growth for years until one of the trees around it dies.  Mangrove growth is self regulating. Nothing nests in the NZ mangroves, though they do in other mangrove species; however 36 species of fish use the mangroves as a nursery. As the tide receded we could hear the sharp little clicks of exposed shrimp.

Worldwide there are 55 species (54 in Hogarth) of mangroves, of which NZ has one (not exclusive to NZ). They are facultative halophytes, that is they can survive in freshwater but prefer diluted saltwater; in freshwater they are likely to be out-competed. They’re almost exclusively tropical, being frost-intolerant with vulnerable (vivaporous) seedlings, they rarely occur north of the winter position of the 20 C winter isotherm and the number of species decreases as the they approach their northern limit. They grow further south on the eastern margins of landmasses than the western, which reflects ocean circulation and the pattern of warm and cold currents. The highest-latitude species found is a species of Avicennia, in Australia.

Typical mangrove habitats are have periodic tidal inundation, waterlogged soil and fluctuating salinity. The diffusion rate of water is 10 000-fold less than through air, and oxygen movement into the mud is severely limited; mangrove soils are virtually anoxic. Ferric ion is converted to ferrous ion, with release of iron and inorganic phosphates, sulphate to sulphide, carbon dioxide to methane, and there is bacterial conversion of nitrate to nitrogen. Since they live in anaerobic mud, they take in oxygen through arial roots or pneumatrophores.  Black mangroves and white mangroves (including Avicennia), have pneumatophores, red mangroves have prop roots.

There are two principal adverse effects of salt in plants – osmotic stress and the toxicity of Na+ and or Cl-.  Glycophytes are salt-intolerant, whereas halophytes grow fine, and sometimes better, in
salt; there is a continuum from extreme glycophytes to extreme halophytes. Salt avoidance strategies minimize the salt concentration in cells.  Salt tolerance includes physiologic mechanisms and adaptations for maintaining viability with accumulation. Plants can protect themselves by salt exclusion or by ridding themselves of the salt. Exudatives have glandular cells capable of excreting excess salt. Succulants grow where there is no restriction on water – they use increase in water content within large vacuoles to minimize salt toxicity.  Obligatory halophytes require salt; facultative halophytes can live in fresh water.

Various mechanisms are involved in mangroves’ salt tolerance:

  • Salt exclusion – ultrafilters in the plant roots reduce uptake of salt.  This is less efficient than salt excretion: red mangroves, which rely on salt exclusion, require salinities < 60-65 ppt.  Black and white mangroves, which use salt excretion, can tolerate salinities up to 80-90 ppt.
  • Salt excretion – salt is excreted through specialized salt glands in leaves.  This is an active process, involving ATPase activity in plasmalemma
  • Water conservation under conditions of high stress.
  • Mangroves may also accumulate or synthesize other solutes to regulate and maintain osmotic balance – eg mannitol, proline, glycine betaine, aspartate, stachyose.  They also deliberately slow their water intake to prevent excluded salt from accumulating around their roots.
  • Low transportation and slow water uptakes is not characteristic of all mangroves.

There is a great deal of interest in salt resistant plants as a means of extending arable ground, water supplies and reclaiming land ruined by over-irrigation — this is well-represented on the web.

Report from Down Under

Days spent in NZ: 9
Days spent kayaking: 3
Kayak trips blown out: 2
Number of sandfly bites: 40+ (about 20 on my hands, since the bug lotion kept washing off)
Photographs taken: in the region of 100

I spent the first 3 days with family in Auckland. On the Thursday I signed up for an evening trip from Auckland to Rangitoto, which is a 600-year old island created by a volcanic eruption, but the wind came up and the trip was cancelled. Friday I flew to Queenstown, and took a bus to Te Anau. Saturday and Sunday I took an overnight trip into Doubtful Sound in Fiordland. This consisted of a 6 am start, van to Manapouri, launch across Manapouri Lake, a huge lake greatly expanded by the construction of a hydro dam in the sixties, then van up over the pass, and down into the sound.

This is fiord country, and rainforest – 8 m or so rain a year, and a daily record of 50 cm [corrected] – and stunning is hardly the word for it. Because it is so wet, because the rain streams constantly down the slopes, moss, lichen and ferns grow almost to the vertical, infiltrating the rock; the mat can be a meter thick, thick enough to root trees, so the trees grow up slopes so steep they almost appear to be growing parallel to the slopes – when not jutting out at wild angles. As a result, Fiordland is prone to tree avalanches – a high wind, an earthquake, or simply age and time can cause a tree or trees to lose their grip and fall, and because the roots are interlocked and embedded in the moss, the entire mat and forest comes away, stripping a wide triangular blaze down the rock and leaving it bare, to be gradually recolonized over decades by moss, ferns, and then the trees. The landscape is classic glaciated valley, steep, steep sides, the scale not appreciated until you see a group of kayaks at the base of one of those slopes looking like painted slivers of wood – the peaks around are in the 1500 m to 2000 m range. There are multiple long, long waterfalls, which look like white threads down the slopes.

We loaded all the gear (which we had loaded and off-loaded at each transfer) onto four double kayaks, with the guide in a single, and headed out from a spot called Deep Cove towards the sea. Weather was a little windy, misty, rainy, sun the occasional watery glimpse, though we were seeing the peaks around us. We paddled about 6 hours the first day, allowing for stops, and my winter of sheltered flat-water kayaking had not prepared me for it. My arms began to complain within 15 minutes, and after a couple of hours I managed to shift the complain to the muscles where it belonged and stop fighting the water every stroke. We campled overnight in a basic camp in the rainforest, consisting of a permanent mesh tent on a platform for a cooking/recreation area, a series of linked gravel areas linked by a winding and very narrow path which led to the composting toilet, enthroned a story above the forest. We were only supposed to use that for solid waste and the forest otherwise – I have bites in places not normally exposed to the air! I haven’t camped since tents were put together with a ridge-pole and supports, and I was short enough to stand upright in a tent. But I survived a largely sleepless night of wondering “what’s that???” at each rustle, and because I was blundering around in the early hours with a torch, I glimpsed a kiwi scuttling around the mesh tent.

The next day we struck camp early because there were strong south westerly winds forecast, and although Doubtful sound is very long and we were well inland, we did not know how that would funnel. We paddled out of the side arm where we had spent the night, and turned up towards the sea, intending to go around a long island in the middle of the fiord, but as we beached for a bio-break, we saw the first darkening of the water up the sound, and we paddled out into a squall, about 15 knots. Quite enough for yours truly, who couldn’t remember which side to apply a low brace on – fortunately it was needed. But as the seas got heavy, we rafted up, boats banging against each other, sorted out the steering – to stay with the wind and swell behind us, we needed to ply rudders, and raised sail, and cruised down the fiord towards the embarcation point on the wind and swell. After several hundred meters the sail expired and flopped across us, and we reeled it in, and kept paddling. Between the wind, the slow swell behind us, and the early start, we were in before 1 pm, although we were not caught by any more squalls, only drizzle that socked in the fiord between us. Then we off-loaded, re-stored the boats, loaded up the van and headed to the vantage over the outflow from the dam (two tunnels, draining into Doubtful Sound) and likely perturbing the ecosystem.

The ecosystem of the fiords is an interesting one, and it was the undersea aspect that originally got me interested in the area: the copious rainfall leaches substantial quanties of tannin and other products of vegetable decomposition into the fiords. The water is very deep and very dark, but even at the edges with pale rock underneath, it’s the colour of weak tea, a dark brown. So this shades the depths, and there are sponges and corals in the fiords that grow at 40 m or less below the surface that elsewhere grow at 200 m down, under the standard photic zone.

On the Monday I was supposed to go to Milford sound, but when I dragged myself out of bed at 6:30 am I felt so trashed I phoned and cancelled, went back to bed and slept until 11 am. As it turned out, it bucketed all day, there was a 25 knot wind in the fiord, and all kayaking trips were cancelled. I couldn’t rebook with the same group I went out with (all spots full), but there was another company, so I booked with them for Tuesday. Milford sound is the best known of the sounds because there’s a tarmac’d road from Te Anau into the Sound, 2 h spectacular driving along the shores of Lake Te Anau (glacier lake about 60 km long), then up through beech (not your northern beach) forest, through the Homer Tunnel (site of the Homer Nude Tunnel Race), and down – and I do mean down! – into the valley. Completely different weather – whatever front had come through had blown itself out – and we had brilliant sunshine all day. The morning had been cold, and I didn’t add much to my crop of sandfly bites, but I washed all the sunscreen off the backs of my fingers, so I’ve added scorched fingers to my plaints. Hardly any wind: the disturbance on the water was the wake of multiple tour launches, giving us the occasional half or so meter swell to ride. This time I was NOT the oldest person in the group, and my paddling was much better. Clear sight of the mountains, which are slightly drier and less moss-coated than Doubtful, but still steeply treed, and since it had been so wet the previous day, there were multiple waterfalls threading their way down from the heights.

And we saw dolphins. We’d were crossing at our midway point when we spotted the fins and soundings, and began paddling after them. They changed direction and charged past us, between us, on their way to meet up with a large launch behind us – we held no interest for them at all. Alas I was too busy watching the dolphins to press the shutter as two of them bore down on my kayak and surfaced almost within touching distance, and it was all over very fast. They intersected the lanch and were carried off with it, several of them literally riding its bow-wave. They’re bottlenose dolphins. We didn’t see the dolphins in Doubtful sound, which are supposed to be a distinct pod that only live within Doubtful sound – I have to look up the genetics.

We also saw juvenile fur seals, young batchelors kicked out of the herd to make their own way; a pair of moulting Fiordland crested penguins; a white gull of some kind which had obviously discovered kayakers as a source of food, hopped out of the water to perch on our kayaks; paradise ducks, with pure white head and red tail.

We pulled out at the start point after about 4 hours, and headed back to Te Anau at a very leisurely pace, stopping at multiple scenic points; got back to Te Anau just before 6 pm. I dithered, and then trotted along to go standby to see the Te Anau Gloworm Caves, which is a topic for another post, as I shudder to think how much I owe the Internet Cafe now (I started out to check my email, really … and if Blogger doesn’t save this, I will cry!)

Yesterday, in the pouring rain, I caught the 8 am bus from Te Anau to Dunedin, and here I am in Dunedin, with gale force winds forecast for later today. I didn’t move very fast this morning, and so I missed the calm, if there was calm – I looked into kayaking out around the Otago penninsula this afternoon, but no go – too windy. Now I have to work out what to do for the rest of the day! Tomorrow morning I have an even earlier start, for a flight up to Blenheim at the north end, where I hope, if the weather cooperates, I will get out on the Malborough Sounds and along the coast of Abel Tasman park.

And even at this length, this is still an abbreviated report.

(Originally published at Kayak Yak Yak)

Don't diss my trash, darn't!

Through obscure channels, doing research for TSP (like every other writer on the planet, I too have The Secret Project), I came upon Break of Day in the Trenches, the weblog of Esther MacCallum Stewart, who does research on, among other things, the First World War and popular culture. She also teaches SF. In her March 2005 archive page, she has a letter to Women’s Hour (BBC) in response to a program on women in SF which dealt with the subject superficially and by embracing all the stereotypes about both SF and female SF readers.

Which brought to mind my reaction to a recent BBC7 offering, the futuristic thriller Cold Blood. There was nothing original in the plot, but I could live with that. I followed along fine until we came to the “scientific” explosition. The homicidal villain of the piece was a scientist who found a cure for leukemia and pretty much everything else in the biology of the icefish (see left). In the best pulp tradition he self-administered his elixir and began turning into a human-icefish chimera, developing extreme cold tolerance and a tendency to rip out his coworker’s throats. He needed the iron from their blood because his was losing its hemoglobin. Icefish have none: oxygen dissolves better in cold water than warm, so they can survive in very cold water. Now, so I could accept psychosis (though that is probably even worse misrepresented in popular fiction than are genetics and genetic engineering) – say, toxic effects of his elixir. I could accept aplastic anemia or severe red blood dyscrasia or hemoglobin gene expression being turned off by insertion of a bioengineered vector – again toxic effects. But throw in cold adaptation sufficient for long-distance travel across the Antarctic at night PLUS a miracle cure for everything and the suspenders on my belief go pop-sproing! I can’t imagine history being presented, even as escapist entertainment, with such gross absurdities. (Though I am not an historian, and I do not know what torments historians suffer.) Why should SF!!