Snail mail

You've probably seen the recent news item about the Polish chap who received a priority mail letter 14 days after it had been sent. The letter had been posted only 11 km away. According to his calculations, a garden snail could have delivered it more rapidly than the Warsaw mail man.

What a silly thing to say. Doesn't he know that snails deliver lettuce?

Collateral damage

It's not my car. I wasn't driving. You can't prove anything.

Saltbush spectrum

Fragrant saltbush (Rhagodia parabolica) is rare in Victoria but you might not think that as you begin the Lerderderg Gorge walk at Mackenzie's Flat. There, saltbush forms dense stands on either side of the track.

The leaves and flowers are discreet and understated in two-tone grey-green but the fruit are as colourful as a bag of parrots. Rhagodia parabolica produces berries in a range of shades from white through yellow and orange to bright red.



At this time of year, silvereyes (Zosterops lateralis) stuff themselves silly on the fruit. They prefer red over other colours, apparently, but neither they nor the other frugivorous species appear reluctant to diversify. I can see their point. The berries all look delicious to me.

Seeds from different coloured fruits exhibit different germination characteristics. Plants pop up from red seed much more rapidly than they do from yellow. White seed has the greatest germination rate after emerging from the back end of a silvereye. (You can think it, but don't say it.)

This array all occurred a 50 metre stretch of the track.

Opisthostoma and the mad woman's knitting

Considering that this is supposed to be a snaily blog, it's been lamentably light on molluscs recently. Here's the first step to redress that deficit.

A couple of weeks ago, I posted this pic of Opisthostoma vermiculum, a recently described diplommatinid land snail from Gunung Rapat in Perak, Malaysia. The paper appeared in Biology Letters, which is not known for its publication of single species descriptions. So why was this an exception?

Well, the snail is a bit odd. And by odd, I mean that it gets around in the most bizarre shell in the history of bizarre shells.

In order to understand just how strange this animal is, it helps to visualize how a snail shell forms. Essentially, it's a tube coiled around an axis. Well, it's a tube that increases in diameter from start to finish but the basic idea is there. One tube and one axis.

Each whorl (a complete turn) partly overlaps the previous one, attaching to it for increased strength. Depending on the thickness of the shell walls, the degree of overlap, the diameter and the external ornamentation, a shell can be a lightweight shield covering only the really important bits or a capacious and robust fortress that protects the animal against a range of predators. And that's why crabs have such strong claws …

But I digress. Back to Opisthostoma vermiculum, which doesn't have to worry about being eaten by a crab.

This snail has multiple coiling axes. To achieve that, the shell whorls detach and reattach all over the place. It's like the mad woman's knitting.

To be absolutely accurate, whorl detachment isn't that rare. Despite the mechanical advantage of attachment, successive whorls aren't always cemented to the previous ones. In some species, the last whorl is a little free and easy, projecting in a different direction. This is common in other species of Opisthostoma and in Urocoptidae. It also occurs in the pupillid Gyliotrachela.

In others — a very small number — more whorls are detached, allowing the shell to grow as a loose spiral. Once again, it occurs in Opisthostoma and Blaesospira, among others. In these cases, the shell coils around a single axis, either sticking to that plan or only departing from it in the last whorl. The marine worm shells (Vermetidae) take it to extremes. What starts as a normally-coiled shell in the juvenile stage gets peculiar very quickly, developing into an irregularly coiled adult shell that's all over the place. More knitting. But vermetids are sessile and don't have to move. They could have rotating radar dishes and a windmill attached to them and it wouldn't matter.

Opisthostoma vermiculum is different. It lives on land and is mobile (on a small scale, of course), so its shell has to be both strong and shaped to allow movement. Too much decoiling would create havoc for a terrestrial snail. Or so you might think.

The shell starts off in the usual fashion with overlapping whorls around a central axis. So far so good. But then the whorl detaches and follows a second axis, which is almost at right angles to the first. The shell spot welds itself onto an earlier whorl, presumably for structural strength, and then rotates around a third axis. Another spot weld and it finally circles a fourth before finish off with a fancy collar around the mouth of the shell. Reattachment at those two points occurs without the building guidelines normally associated with shell development.

The authors say that the "coiling strategy is not only puzzling from an evolutionary perspective, but also hitherto unknown among shelled gastropods."

Or, as J.B.S. Haldane would have said if he'd spent more time thinking about snails,

… my own suspicion is that molluscs are not only queerer than we suppose, but queerer than we can suppose.

Reference
Clements, R., Liew, T-S., Vermuelen, JJ & Schilthuizen, M. (2007). Further twists in gastropod shell evolution. Biology Letters doi: 10.1098/rsbl2007.0602

Lerderderg Gorge: Mackenzie's Flat

Lerderderg Gorge State Park is less than an hour's drive from home but I'd never been there. (I've asked this question before but I need to ask it again — what on earth have I been doing with my time?). Anyway, to redress this appalling lack, I headed out to the Gorge last Friday with my botanist friend and we had a look at all of the plants and some of the animals.



The SP covers more than 14,000 hectares of eucalypt woodland. At the southern end, it's dry and rocky, with a number of rare and endangered plants. The dominant trees are blue manna (Eucalyptus globulus) and manna gum (E. viminalis) along the river and red box (E. polyanthemos) on the ridges. At the northern end, the tall forest is mostly messmate (E. obliqua) with narrow-leaved peppermint (E. radiata). In between is an interesting sequence of box and box – ironbark woodland, which seems to change rapidly from one type to the next.

The Lerderderg River rises near Blackwood and cuts a concertina of meanders through the hills until it joins the Werribee River on the coastal plain. The gorge is Lower Ordovician sandstone and mudstone shot through with veins of quartz. The sediments were laid down about 470 million years ago in a shallow sea.



Since then, it's been tilted and turned and uplifted by a succession of faults ...

... but has survived all that geological manhandling in remarkably good nick.

And there's gold in them thar hills.

Koalas are common here but we didn't see their furry arses wedged in the manna gums. This seems to be the pattern. I'm beginning to suspect they're hiding from us. Neither were echidnas or kangaroos terribly obvious but the wombats had made their presence felt. Well, one wombat, which had marked its territory with great enthusiasm. Like lots of other mammals, they warn off intruders with judiciously placed poo. Wombats take great care with the location, preferring to leave their boundary markers on logs and stones. How they manage some of those sites is difficult to comprehend. They're not the most acrobatic of animals … but maybe they have hidden skills.

Although we had no luck with the mammals, the birds were out and about in great numbers. Crimson rosellas chatted to each other in the woodland canopy, while the currawongs and white-winged choughs stayed on the ridges. Small flocks of silvereyes moved through the trees, feeding on the brightly-coloured berries of fragrant saltbush (Rhagodia parabolica). (More about that tomorrow.) They were accompanied by yellow-faced honeyeaters, striated pardalotes and numerous LBJs, all of which were no doubt thrillingly rare and unusual but remain unidentified. A sacred kingfisher kept an eye on us for a while, until a laughing kookaburra took over the surveillance.

More about the northern end of the park soon. In the meantime, here are some of the botanical beauties of the bush …

Fragrant saltbush (Rhagodia parabolica) is widespread in inland South Australia but is very limited in Victoria.

Mistletoe (Amyema pendulum) on yellow gum (Eucalyptus leucoxylon).

Native elderberry (Sambucus gaudichardiana) has edible berries but we left these for the birds.

Mistletoe (Muellerina eucalyptoides) on yellow box (E. melliodora). Its roots insinuate themselves along the branches in a slightly sinister way.

Forest germander (Teucrium corymbosum) occurs in the damper areas along the river bank.

Rock clefts provide protection for smaller plants including this purslane (Calandrinia)

Stonecrop (Crassula) is one of a handful of succulents in Australia.

Necklace fern (Asplenium flabellifolium)

One of these is not like the other ones

Little black cormorants (Phalacrocorax sulcirostris) are equally at home in fresh and salt water. Sometimes groups of a hundred or more gather on the rocks at low tide in Hobsons Bay but this little party was lined up on a cable over the Maribyrnong River at Essendon.

They were keen on grooming. (This one had a length of monofilament around its foot. I only noticed it after I downloaded the photograph.)


A solo little pied cormorant (P. melanoleucos) was hanging out with them.


I keep promising myself that once I get some free time I'll return to painting and drawing. These monochrome birds are just there to be rendered in some beautiful, glossy, green-sheened ink.


(BTW, I've been trying to think of a collective noun for cormorants. The best I can do is a diary of shags.)

Tower Hill

Tower Hill erupted about 32,000 million* years ago (give or take). When magma encountered water in the overlying rock, the superheated steam exploded, creating a shallow crater. (It must have been a hell of a shock for the Koroitgundidj people living there at the time.) Subsequent eruptions produced a series of low hills, which are now islands in Tower Hill Lake.


A narrow road passes a grey wall of tuff — volcanic ash — that gives an idea of how active the volcano must have been in its glory days. It doesn't do much anymore.


Although declared a national park in 1892, the crater was scoured by farming and quarrying. Within a few decades, it was almost devoid of native flora. When the state government began to revegetate the area, they had to refer to Eugene von Guerard's 1855 painting "View of Tower Hill" for an idea of its original condition. Extensive planting has encouraged the birds to return. Iconic fauna abounds — including emus.

Not so iconic fauna is also abundant. These fussy Theba pisana ignored all the other posts. This one must have had the best view.

Tower Hill is about 275 km SW of Melbourne, between the coastal towns of Warrnambool and Port Fairy. I'm planning to head down there again soon on a day trip.

_______

* Not surprisingly, that 'million' is a typo. No idea where it came from. Sorry for the confusion!

Nature Blog Network

Mike of 10,000 Birds has set up the Nature Blog Network the toplist for every species of nature blog. It's only been in operation a few days, but so far, 69 blogs have signed up, every one with nature on its mind. There's something for everyone.

The Light of the World

Renovating? You might like to check out this light switch featured on Pharyngula. It's been doing the rounds for a while but it's worth another airing. I'll leave it up to you to decide whether the image is safe for work.

There's a whole lot more atrocious religious 'art' at Jesus of the Week. Seriously, it's addictive.

Cape Bridgewater: cliff top saltmarsh

It's easy to think of salt marshes as being … well … just a tad dull. Expanses of green with only a few species of plants, none of which sent up bright and lively flowering heads. This lack of floral exuberance probably contributes to the enthusiasm with which salt marshes are cleared for housing developments. (Who cares? It's just a bunch of boring weeds. Well, the proud new home owners start to care when their bowling green lawns develop bald patches from acid sulphate scald. But that's another story.)

Coastal salt marshes develop on sediments just above the high water level of neap tides. They are still affected by spring tides, which inundate them periodically, but they dry out in between. As the plants grow, they impede water flow during spring tides. This allows water-borne sediment to settle. Over time, the deposits build up. Eventually they are high enough to be free of direct tidal influence.

But high for a coastal salt marsh is usually measured in centimeters not metres. Certainly not tens of metres. So the top of a cliff isn't where you'd usually expect to find salt marsh plants. At Cape Bridgewater, water seeping from the dune limestone combines with spray from the Southern Ocean to create just the right conditions.





How could anyone say this is a tad dull? Creeping brookweed (Samolus repens) covers the cliff top in a swathe of green. The tiny white flowers are almost luminous. I bet at night the salt marsh looks like the Milky Way.





Succulent beaded glasswort (Sarcocornia quinqueflora) grows with the brookweed. This species is common on salt-affected land. It forms extensive stands at Lake Corangamite and other inland lakes in western Victoria.





A second species, thick-head glasswort (Sarcocornia blackiana), also grows on the cliff top. That common name may be unflattering but there is a certain pudginess to the stems.



Although a few other species appear among the brookweed carpet, the plant diversity is low. Unlike the salt marshes as sea level, this one doesn't appear to be home to many invertebrates either. Were this by an estuary, I'd expect to find a few snails. No, not Theba but the miniature pulmonates Salinator and Ophicardelus. But because these snails lay their eggs in the ocean — and they don't tend to do a Christmas Island crab-style migration up and down the cliff face — there is no chance of them setting up a self-perpetuating population. Mind you, there wasn't any Theba either so that was good news.

And that concluded the trip to Portland. Not a bad haul for two days!

Jelly feast

In 2007, a 'bloom' of the giant jellyfish Nemopilema nomurai drove Japanese fishermen to distraction. Caught in trawls, the monster jellies (some up to 2m across and 200 kg in weight) caused problems by stinging fish, breaking nets and threatening to capsize vessels*. The fishermen had to fend them off with bamboo poles. Not only were the fish catches buggered but Nemopilema was not a good replacement for the lost harvest. The texture's not quite right, apparently. Not crunchy enough.

But whereas the jellyfish have been rejected at the ocean surface, a whole bunch of creatures on the ocean floor have been chowing down on the carcasses. A study of 138 dead jellies in the Sea of Japan revealed their importance as a source of organic matter in a habitat where the locals rely on bounty from above.

Nemopilema was popular with four species of scavengers: Pandalopsis japonica (shrimp), Chionoecetes opilio (snow crab), Buccinum striatissimum (ivory whelk) and Ophiura sarsii (brittle star). How popular? Ten kilogram chunks o' jelly were reduced by 30 – 50% in less than a day. And the fishermen top side say that they're not crunchy enough. It just doesn't make sense.

Reference
Yamamoto, J. et al. (2008). Transportation of organic matter to the sea floor by carrion falls of the giant jellyfish Nemopilema nomurai in the Sea of Japan. Marine Biology 153: 311 – 317.

_____

* By their weight in the net, rather than any co-ordinated and malicious intent. But I'd pay good money to see a film about a bunch of vigilante jellyfish roaming the ocean with revenge on their minds.

Cape Bridgewater: cliff tops

We pulled in at the car park overlooking Bridgewater Bay. There must have been … ooh, I dunno … fifty people on the beach sun-bathing, swimming and surfing, so we gave it a miss. The silver gulls and crested terns didn't seem all that bothered by the fuss.

A track at the top of the cliff starts at lookout and runs down to a seal colony, about two hours away. Behind the lookout, the sea box (Alyxia buxifolia) wason covered in red berries and the old man's beard (Clematis microphylla) had set fluffy grey seeds. Singing honeyeaters looked sleek and well-fed. (They're the zebras of the bird world — they always look as though the living's good.)

Bridgewater Bay

Sea box

Old man's beard

The dense vegetation on this side of the Cape differs from that at the tip, which projects into the Southern Ocean. On still, warm days, it's difficult to believe that there's nothing between the Cape and Antarctica, except thousands of kilometres of blue water. On cold, wet and windy days, it's a lot more plausible.

The Great South West Walk follows the edge of Cape Bridgewater. To the west, it takes walkers down to the shelter of Discovery Bay. We headed east until we lost the tourists. Most of them went no further than the Petrified Forest, so it didn't take long to escape them.

Below us, Australian gannets (Morus serrator) soared in formation a couple of metres above the waves. Hundreds of them, in twos and threes, plied a route between the colonies on Lawrence Rocks and Cape Danger to the protected waters of Discovery Bay. On land, silvereyes (Zosterops lateralis) popped up out of the thickets and zipped across the track to the next feeding place. Blue-winged parrots (Neophema chrystostoma) picked seeds from low vegetation. When we approached too closely, they would take to the air with fast wing beats and disappear into the Melaleuca. Not one of them sat still for a portrait. Contrary little so and sos.

Cushion bush (Leucophyta brownii) dominates the beach limestone at the start of the track. But it's not the only plant.

Pigface (Carpobrotus rossii) forms dense carpets — rugs, perhaps — between the grey cushions.

Had I not been with a botanist, I would have dismissed this dune thistle (Actites megalocarpa) as some crummy weed. I'm still not taken with it. Still, it's not there for my benefit. I'll just have to come to terms with that. What makes my dismissal even more pathetic is that Actites is a monotypic genus. So this is it. One species. That's yer lot. I'm working on warming to it.

Sea celery (Apium prostratum) is edible. Apparently. Yum!

Sand ixodia (Ixodia achillaeoides) is now grown for the cut flower trade.

Fan flower (Scaveola aemula) is a great garden plant but it looks even better in the wild.


I have never seen so many native wasps in one place at one time as I did on this Melaleuca lanceolata. I would have made a video but the soundtrack would have been nothing but swearing and squealing. Sure, wasps are not particularly ill-disposed towards people but they are possessed of ovipositors like stilettos. And as it was quite warm, they were flying around with great enthusiasm. One of them might have knocked me over. Discretion. Valour. All that stuff.

There were Theba here too. Sun-bleached shells were scattered all over the place but living snails were much patchier. Where they did occur, they were stuck to just about every type of low-growing plant. And some taller ones too, including coastal wattle (Acacia sophorae).

This low open heath wasn't the only vegetation type at Cape Bridgewater. At several points, water drained from the rocks, creating salt marshes on the cliff tops. More about in the next post.