A Windang Shindig

The Gong 151
#003 A Windang Shindig

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On a cool and blustery day in March, Salty, Keen Wasabi and I hiked around Lake Illawarra foreshore to the sandy arm of Windang Island. The island’s green top rises conspicuously from the lip of the lake. Anglers endure relentless plumes of spray on the seaward cliffs, each wave sending waterfalls cascading down deep flutes in the rock. Snorkelers proliferate in the summer, diving from ledges exposed at low tide, while swimmers wander up from Warilla Beach to survey the long and peaceful bay. The island is also notorious for sharks.

At 11 o’ clock the tide was at about 0.6 metres and dropping. Things that are usually submerged were becoming exposed. Keen and I dropped our nets and tanks on a rock ledge and waded out amongst the pools.

Soon we were walking on mats of Neptune’s Necklace (Hormosira banksii). This brown alga is made distinct by the string of olive-coloured beads that make up its thallus (body). Like plants, brown algae uses chlorophyll to photosynthesise and  absorb energy from the sun. Unlike plants, it also produces xanthophyll, a yellow pigment. This gives brown algae its distinct brown-green colour.

While at first it seems weird – after all, chlorophyll works perfectly well for plants – the secret of brown algae is where it exists in the ocean. Red light is bad at penetrating the ocean’s surface. Green light however penetrates deeply into the water. Because a thing’s colour is determined by the light it reflects (meaning green plants reflect green light) algae need to be differently coloured to absorb the light available to them beneath the waves. For Neptune’s Necklace, this means disguising its green chlorophyll with red pigment.

What I find fascinating about Neptune’s Necklace is just how well-equipped it is to maximise its light exposure. The alga is made up of multiple strands of beads called thalli. Each bead is made of a  spongey tissue filled with air and protected by a waxy coating. When submerged, the air makes the beads float, drawing them towards the surface, where there is more light. When the tide drops, the beads lay like a carpet across the rocks, their waxy coating preventing them from losing too much moisture.

b003_shells
Shells embedded in the island’s dirt wall.

Neptune isn’t the only one who fancies his algae. As we sat by twin rock pools on the low intertidal, Keen and I counted 135 Zebra Top Snails (Austrocochlea porcata) in and around the strings of beads. Interestingly, of all the species of snail in the pools, only Zebra Tops were found on the Neptune’s Necklace. Smaller snails seemed to prefer the shelter of the algae more than the larger ones, who preferred grazing on an encrusting brown algae on the bottom of the pools.

Up until last week, I kept five Zebra Tops Snails in my laboratory aquarium. They eat the slimy brown algae that is a fact of aquarium life, and it’s fun watching a snail licking glass.

Woe betide me, this week I am down to three Zebra Tops. The reason? Clever fish. Working together, two of my fish (Holly, a Black Drummer, and Dart, a Blackspot Sergeant) repeatedly ram the Zebra Tops until they come unstuck from the glass and tumble upside-down into the sand.

Like other marine snails, Zebra Tops have a tough disc called an operculum that they can draw over the opening in their shell, like shutting a door. My fish are quite unable to get past the operculum. But, as they learned, if the snail wants to right itself, it has to push its operculum aside and stretch its soft body around the top of the shell to grab a hold of something solid. When that is done, the snail gives a quick pull and flips around upright.

Holly and Dart wait until the snail’s soft body is exposed, and attack. In just a few strikes the fish have conquered a snail as big as themselves. This bringing down of the mammoth results in tank-wide excitement, as the other drummers rush in for a nibble and the crab dances out of his cave, claws waving.

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Scary-story-snail face.

On the beach, Zebra Tops have more insidious enemies than tiny fish. Seastars prowl for young snails. You will have seen seastars sold as trinkets and jewellery. Dried and bleached, they offer poor comparison to these active hunters.

A sea star’s underside is covered in hundreds of tube feet. At the end of each arm, there is a splay of probing fingers and a rudimentary eye. A seastar can move as swiftly as a snail or abalone. It crawls over its pray, wrapping it in powerful arms. It then everts its stomach, coating its prey in digestive juices. Finally the seastar draws its stomach and its melted pray back into its body.

One such predator on Windang Island is the Eight-Armed Seastar (Meridiastra calcar.) It’s obvious when these seastars are busy eating, as their central disc will be raised into a hump, the prey engulfed beneath it. While snails are high on the menu, Eight-Armed Seastars will also graze on algae, and I have even seen them feasting on crabs’ legs and fishes’ tails.

Perhaps one reason Zebra Tops choose to hide amongst the beads of Neptune’s Necklace is that it is not readily navigated by seastars. Seastars probably also have poor vision, and cannot tell a small Zebra Top from a bead.

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Anglers enticing sharks with their juicy backsides.

“The sale of souls to gain the whole world is completely voluntary and almost unanimous…but not quite.”

As we finished counting Zebra Tops (Keen felt sorry for some and rescued them from seastars. But echinoderms need to eat too!) we noticed a huge white and grey Pelican riding thermals rising from the hot exposed rock. Wind gusted hard over the island’s top, and the Pelican would surf thermals for a minute before lowering itself into the gusts and riding in a wide crescent out over the ocean. Seeming without a care in the world, it would then coast over the island and catch another thermal.

“Do you think it’s having fun?” said Keen.

“Looks like it,” I said.

We watched the seabird, a proud example of Australian Pelican (Pelecanus conspicillatus.) Its wings wobbled as it hovered on the thermal. Then – it dropped and swooped out over the waves. In moments it was back.

“It’s not looking for food,” I said, as the seabird hung suspended in the air. “And that does look like fun.”

Keen sighed. “I wish I had wings.”

We spent a while chasing gobies in rock pools, and then we were hungry, which meant it was time to go. On the return hike to the car we walked past the mouth of Lake Illawarra. The tide was starting to rise and the foreshore was wet and dark. It also appeared to be moving.

“Hey, crabs!” I had ditched my gear and was dancing amongst crabs in a second. “Look, Keen, soldier crabs!”

All across the foreshore, an army of perhaps ten thousand soldier crabs were digging out new holes above the waterline. In amongst the waves of smaller Mictyris platycheles were large Light-Blue Soldier Crabs (Mictyris longicarpus) looking like horses amongst foot soldiers. They were oblivious to us. By the drove they kept on digging, while others processed sand through their mouthparts, restlessly surging across the boundary of surf and sand.

Salty poked his nose into a crab’s back, and watched baffled as the crab burrowed in a spiral into the wet sand. In seconds it was up again, scuttling for higher ground. From the water a Pelican watched on idly, sailing as majestically as a brilliant white yacht. Storm clouds bathed the escarpment beyond.

Keen and I finished the journey to the car in high spirits. The world can be savage, it’s true. But from the snails sampling the finest delicacies of the sea, to the pelican surveying its kingdom, it is also a world of great joy and satisfaction.

Thank you Keen and Salty for a banger of a trip out of Windang Island. Thanks to you two, I’m finally able to present the first five Gong 151 species!

 

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#001 Neptune’s Necklace (Hormosira banksii)

Length: Up to 300 mm

Zone: Low intertidal

Sighted: Day, on rocky substrate in pools and low-lying channels

Locations: Windang Island, common

 

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#027 Zebra Top Snail (Austrocochlea porcata)

Height: Up to 25mm

Zone: Low intertidal

Sighted: Day, on rocky substrate and algae fronds

Locations: Windang Island, common

 

071_Light_Blue_Soldier_Crab_small.jpg

#078 Light-Blue Soldier Crab (Mictyris longicarpus)

Carapace width: Up to 25mm

Zone: Low intertidal (brackish water)

Sighted: Day, on border of sand and sea

Location: Windang Island (Lake Illawarra entrance), common

 

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#090 Eight-Armed Seastar (Meridiastra calcar)

Arm radius: Up to 50 mm

Zone: Low intertidal

Sighted: Day, on submerged rocks and rocky substrate

Locations: Windang Island, uncommon

 

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# 138 Australian Pelican (Pelecanus conspicillatus)

Wingspan: Up to 2.6 m

Zone: Shore

Sighted: Day, cruising on calm water or riding on thermals.

Locations: Windang Island, uncommon

 

Now it’s up to you. Get out into the Gong and meet some animals!

For the five species listed, we need to find:

  • Which locations they can be found
  • Their numbers in each location
  • Their interactions with other species
  • What they eat
  • What they do all day

You can join Salty and I for a day of discovering sea creatures on Saturday 8th April 2017 at Bellambi Beach. Some snacks will be provided. Bring a bottle of water, your camera, and let’s see what we find.

*Coming soon: Updated link to the 151 Field Guide*

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Author: Anneque D. Machelle

Anneque "Dangerpus" Machelle (rhymes with ranger wuss) is a rebel and a rogue from way out west. Strictly banned from interactions with other human beings, she spends her days amongst molluscs, dogs and lizards, whom she counts as her closest friends.

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