Even seaweeds get sunburned

Why is this green seaweed turning white?

Sometimes, we also come across seaweeds on our shores with black spots, discoloured portions, rotten bits.

Here's an article that may explain some of these sightings.

The article also shares findings of how some seaweed spores and germ cells can be hurt or killed by ultraviolet radiation. Thus changes in UV can affect the distribution of some seaweeds, and the animals that feed on them.

Even Seaweeds Get Sunburned
ScienceDaily 22 Aug 08;

It is red, it burns and itches: a sunburn on our skin. However, too much sun is not only bad for humans. Many plants react sensitively to an increased dose of ultraviolet radiation, too. Yet they are dependent on sunlight. With the help of pigments absorbing solar energy and light, plants produce their vitally important building blocks by means of photosynthesis.

However, this has its limits: too much sun means an over-abundance of energy and thus the destruction of the sensitive pigments. The result are black spots, pale leaves and rotten parts.

Since algae cannot apply sun lotion like we do, they develop their own strategies to protect from the sun: "A species of red algae, for instance, produces under increased ultraviolet radiation less red light-harvesting proteins, thus decreasing the absorption of radiation. The typical red colour of the alga fades and the plant gets white tips.," explains Prof. Dr. Christian Wiencke, marine biologist at the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association. "The algae additionally produce substances which react similar to melanin in human skins: mycosporin amino acids (MAA)." Melanin absorbs ultraviolet radiation and thus protects the human skin – at the same time, it gives a natural suntan.

The ozone layer usually absorbs the major part of the hard and harmful solar ultraviolet radiation of short wavelength. However, because of stratospheric ozone depletion, these dangerous rays increasingly penetrate to the earth's surface and therefore also to the seawater.

Extensive biological experiments are presently conducted on this complex of problems at the German French Research Base AWIPEV on Spitsbergen. "We examine the harmful effects of ultraviolet radiation on algae and their protective mechanisms," says Wiencke. The ultraviolet radiation particularly harms the algae's photosynthesis and their hereditary material. These organisms usually react with a decreased rate of growth or a reduction of reproductive success.

The spores and germ cells of the algae which drift through the water as unicellular organisms are particularly sensitive. Even small ultraviolet doses are damaging and inhibit their germination. "Our investigations show that the distribution of certain species of brown algae is inhibited by the climate of ultraviolet radiation. The algae are displaced into deeper water layers if ultraviolet radiation increases."

The research conditions on Spitsbergen are optimal for Wiencke and his colleagues: "We want to observe the development of marine coastal ecosystems in the face of global climate change. Not only an increased ultraviolet radiation plays a decisive role, but also the water temperature which has been increased by the greenhouse effect. This increase in temperature can particularly be felt on Spitsbergen, in the Atlantic sector of the Arctic."

Speaking up for our rare marine life

Yesterday, Chay Hoon's thoughts about our rare marine species was shared in the Straits Times. She spoke about the Bailer snail (Melo melo).and the beautiful basket star (Class Ophiuroidea)
Greater awareness of our living shores may help more understand and treat them with care. Bravo!

Second chance for Singapore to save its rare species
The rediscovery of 'extinct' wildlife serves to motivate nature enthusiasts
Kimberly Spykerman, Straits Times 22 Aug 08;

WHEN it comes to wildlife native to these shores, it seems people here just do not know enough, grumbles Miss Toh Chay Hoon, a 31-year-old nature enthusiast.

In her spare time, the accountant does her bit to introduce people to the flora and fauna here by leading nature walks on offshore islands such as Pulau Ubin and Pulau Semakau.

She recalled an incident at Changi Beach last year, when a beach-goer found a threatened species of marine snail commonly known as the Bailer Snail, so named because its large shell is said to have been used to bail out water from leaky boats.

She said with dismay: 'He was going to take it home and cook it - even after I told him it was an endangered species! People have to learn to appreciate animals in their natural environment.'

People here are not aware of the rich variety of animals and plants in these parts, largely 'because because they don't get out there and explore', she said.

And given that some animals native to these shores have staged a 'comeback' in recent years, nature enthusiasts like her believe it is time Singaporeans sat up and took notice of the creatures that share their environment.

Miss Toh, for one, is always on the lookout for a great find.

In June last year, she thrilled the local scientific community by spotting the multi-armed starfish called the Basket Star while on a pre-dawn trip to the coral reefs off Sisters Islands.

A relative of the common Sea Star, it had not been seen in waters here since 1896. Its distinguishing feature is the basket-like shape formed by its many arms.

Miss Toh said of her find: 'I never expected to see a Basket Star. Till then, the only one I'd seen was a skeleton at the Raffles Museum of Biodiversity.'

She left the fragile starfish where she found it, and came away with just memories and a few photographs.

full article also on the wildsingapore news blog.

Oil rig at Pulau Semakau to remain until Sep 08

Looks like the gigantic oil rig off Pulau Semakau will be there until Sep. It's been there since July.
[Update: a new Port Marine Notice No. 175 of 2008 dated 16 Sep extends the work period to 15 Oct 08]
What special marine habitats are near this location?

• The Pulau Semakau's intertidal walk trail and the location of TeamSeagrass monitoring sites (in the photo above, TeamSeagrass volunteers are on this walk trail).
  
• Singapore's first coral nursery, which is located near Raffles Reserved Anchorage where the oil rig is parked.

In addition to the oil rig, there's also a fish farm near the coral nursery.

from PORT MARINE NOTICE NO. 150 of 2008 dated 22 Aug 2008

OIL RIG “ESSAR WILDCAT” AT THE RAFFLES RESERVED ANCHORAGE

This is a revision of the Port Marine Notice No. 129 of 2008. The work period has been extended.

With effect from 22 Aug 08 to 15 Sep 08 at West Jurong Anchorage.Off-loading and loading of drilling equipment and maintenance works will be carried out onboard the rig. The work barges will be used for the transportation of the equipment to the shore facility. Safety boats will be in attendance during the entire stay of the rig at the anchorage.

Further general enquiries relating to the project can be directed to Mr Jimmy Nicol, the project manager, at Tel No: 91188208.

The area in yellow is the intertidal shore of Pulau Semakau.

In May 08, a new fish farm was set up at this location (insert in red box).
Here's a photo taken in Aug 08 of both the fish farm and the oil rig off Pulau Semakau.
In an earlier post on the wildfilms blog, a question was posed by Chin about this fish farm: "Is there any harms to the ecosystem in pulau semakau after the fish farm is being set up?will it eventually damage the coral reefs?"

To which budak kindly responded with these details:

I think you have to consider firstly the impact of the physical installation of the farm infrastructure (along with possible discharges from human or farm-related activities into the sea). Has the location of the farm been ascertained to have minimal impact on the nearby habitats? There is also the issue of pollution from the waste and uneaten feed dispersed into the surrounding sea by a high and dense population of captive fish.

Barramundi i believe is a species that occurs locally, but would the stock at the farm be from local sources or genetically-distant cousins from other regions? The risk and impact of fish escaping and also of pathogens crossing between the farmed fish and wild animals also needs to be considered. Add to that the oft overlooked issue that carnivorous species like barramundi don't help much in the overfishing crisis as wild 'trash' fish or other protein sources still have to be caught to provide feed.

Some links on marine aquaculture:

• Aquaculture on the FishWise website
• Nearly half of all fish eaten today farmed, not caught on the Food and Agriculture Organisation (FAO) website.

More links

Latest articles on aquaculture on the wildsingapore news site.

Our jellyfishes identified

Dr Tan Swee Hee of the Raffles Museum of Biodiversity Research kindly offered my photos as examples of our jellyfishes to Dr Michael N Dawson of the University of California, Merced. To my delight, Dr Dawson has kindly offered these tentative identifications. Thank you Dr Dawson!

It's great to put a name to the jellies we've seen, though we might not be able to pronounce most of the names (haha).

[Update on 26 Aug: Dr Dawson suggest some corrections after having a look at this blog entry. Thanks once again!]

[Update: First off, Dr Dawson points out that in jellyfish, 'tentacles' refers to stuff that is stuck to the edge of the bell. The other things that stick out from under the bell around the mouth are more properly called 'oral arms'. These terms have been amended in the entry below.]

The jellyfish above with orange oral arms and the white one below are both Chrysaora sp., Class Scyphozoa. Highly seasonal, when seen, many are seen on both the Northern and Southern shores. And then none seen again for some time.

The stings of these jellyfishes are very painful to humans. Chay Hoon got stung once during a dive and declared that she would rather hug a hydroid!

Elsewhere, the common names of these jellyfishes include Sea nettle (Nettle is a kind of stinging plant, so this name is a bit obtuse if you don't know the plant) and Compass jellyfish. Maybe it should just be called Ribbons of Fire Jellyfish or something equally more dire.


This may be Catostylus sp., Class Scyphozoa. We see this sometimes on Changi. As usual, when seen, usually in numbers and then none for a while.

From the Australian Museum's Wildlife of Sydney:

Catostylus mosaicus or Jelly Blubber is the most commonly encountered jellyfish along the Australian eastern coast and large swarms sometimes appear in estuarine waters. In Sydney waters, the Jelly Blubber's large bell is a creamy white or brown colour, but farther north it is usually blue. This is because the jellyfish has developed a symbiotic relationship with algal plant cells that are kept inside its body. These plants vary in colour from region to region. The algae photosynthesise, converting sunlight into energy that can be used by the jellyfish. The Jelly Blubber has no mouth but there are many tiny openings in its tentacles. The tentacles also have stinging cells that can capture tiny crustaceans and other plankton.

[Update: Dr Dawson says "To my knowledge, there is currently no evidence that any species of Catostylus is photosymbiotic with zooxanthellae. So, the colour variation has a different cause (I don't know what it is)". ]


This jellyfish was bigger than my hand and is Cassiopea sp., Class Scyphozoa. Also known as the Upside-down jellyfish, it does indeed prefer to be upside down; usually found with oral arms facing upwards and bell facing the sea bottom. If you turn one the 'right' way up, it will slowly turn itself back upside down. They are quite commonly encountered on Pulau Semakau.

From the entry on Cassiopea on wikipedia:

Cassiopea is a genus of scyphozoan jellyfish very commonly found in shallow mangrove swamps, mudflats, and turtle grass flats in Florida and various other similar environments around the world, where it lives usually upside-down on the bottom. Where found, there may be numerous individuals with varying shades of white, blue, green and brown. They have a mild sting since they are primarily photosynthetic, but sensitive individuals may have a stronger reaction. The stinging cells are excreted in a mucus; swimming over these jellies (especially using swim fins) may cause transparent, essentially invisible, sheets of this mucus to be lifted up into the water column, where they are then encountered by unsuspecting swimmers. The stings, appearing in the form of a red rash-like skin irritation, are notorious for being extraordinarily itchy.

The Cassiopea jellyfish is also called "Upside Down Jellyfish", because it lies on its back, so that the bell touches the ground. In this position it resembles a sea anemone. Sometimes this jellyfish is picked up by a crab (Dorippe frascone) and carried on its back. The crab uses the jellyfish to defend itself against possible predators.

[Update: Dr Dawson says some Cassiopea have a very 'sharp' sting, so be careful!]

Some times of the year, really gigantic jellyfishes are seen washed ashore on Changi.

This is one of two enormous jellyfishes we saw washed up on the shores of Changi. They were about 50cm in diameter. Dr Dawson says this one belongs to Order Rhizostomeae, but there isn't enough details in the photo to be sure which kind it is.


This jellyfish stranded on the Changi shore was about 40cm in diameter! That's Chay Hoon's foot in the top left corner of the photo. Dr Dawson says from the patterning on the bell, it may be Versuriga sp., Class Scyphozoa, but requires a closer look to be sure.


This may be Aequorea sp., Class Hydrozoa. From the Aequorea entry on wikipedia: Some common names of this animal include Crystal jelly. Aequorea victoria found off the west coast of North America is reported to be bioluminescent. The Singapore one in this photo was seen in the daytime, so we didn't see any bioluminescence.


This could be either Rhopilema sp., Class Scyphozoa or Acromitus sp., Class Scyphozoa (small details under the bell-shaped part of the animal needs to be examined to be sure). This is a small jellyfish, which I though looked very much like the next one. This shows that it's important to document all animals even if they look similar.


This is Acromitus, Class Scyphozoa. Sometimes, the waters at Chek Jawa are teeming with these small chubby jellyfishes which move in short bobs as they energetically contact their small bell-shaped bodies.

More jellyfish photos in this wildsingapore flickr set.

Have a look at Dr Michael N Dawson's fabulous Dawson Lab website with lots of photos of cool marine life from all over the world; as well as his awesome The Scyphozoan website with lots of info about jellyfishes in Class Scyphozoa.

Dr Dawson subsequently shared some detailed tips on how to photograph jellyfishes for identification.

Cyrene Reef: last sunrise trip

6am and we're all ready to go to Cyrene!This is the last morning trip to Cyrene for the year. How nice to have lots of new friends to share this fabulous reef with.

On the way there, Jani and Abigayle of the Blue Water Volunteers have a look at the chart of 100 Knobbly sea stars that Sijie and Chee Kong of the Star Trackers have so far included in their study. They're looking the star that Blue Water Volunteers adopted during Reef Celebrations!We make another safe landing thanks to Melvin. Poor Melvin fractured his toe but he still heroically brought us out to the reef.

As soon as we land, we see lots of sandy shore animals like sand dollars and sea stars! Cyrene is truly alive.

Although it is past sunrise, the day is ominously dark.As November and Marcus share about the 'Nemo' in her anemone, rain is starting to fall on the mainland. The False clown anemonefish (Amphiprion ocellaris) that lives in this Giant carpet anemone (Stichodactyla gigantea) was too shy to show itself. But we did see an anemone shrimp (Periclimenes brevicarpalis) at the anemone! We didn't see one in the last visits we made. How interesting!All around us, big black clouds are gathering. These ones over the industrial installations of Jurong Island.
Fortunately, there seems to be a 'hole' in the bad weather, right on top of Cyrene Reef! So we can continue with our little walk. Here's Jerald sharing about the Knobbly sea stars (Protoreaster nodosus) of Cyrene. Jerald and Vyna are doubling up both as guides as well as helping the Star Trackers to mark the locations of Knobblies with the big yellow flags.Andy and Sijie have found an interesting slug! This is Philinopsis sp., belonging to the Family Aglajidae also known as tailed slugs. It has a long, cylindrical body with a pair of 'wings' (called parapodia) which fold over the centre of the body as well as a pair of 'tails, one longer than the other. It has a tiny internal shell. Some species of tailed slugs eat bubble shell snails, hunting them by following their slime trail then swallowing them whole!
There's lots of interesting stuff to look at even in places that appear to be only bare sand! Here's a look at the creature that creates those intriguing coils of sand, the Acorn worm (Class Enteropneusta). Paul also spotted a swimming anemone (Boloceroides mcmurrichi) which was stranded on the sand. But it didn't swim when we gently put it back into the water.
A little further on and Vyna spots this interesting flatworm. This is not regularly seen and I'm not sure what it is.We stop many times to take a closer look at the animals, but have to push on as the tide is short today. And the weather continues to look ominous. We also see a living scallop (Family Pectinidae) along the way! But we didn't have time to watch it for long. At Labrador, when we had time, we saw it 'swim' with a clap of its valves!We rush off to catch a glimpse of the coral reefs before the tide (and weather) turned.Cyrene Reef is ringed by reefs at the edges and they are full of a bewildering variety of soft and hard corals and many different crabs, fishes, nudibranchs and other small animals that live there. Here's the team happily exploring the reef.

Abigayle and Jani have been exploring too and they saw a fish that looks like a sand diver! Belonging to the Family Trichonotidae, these long narrow fishes are said to hover in small groups above the sand. When threatened, they dive into the sand. Hence their common name.
Meanwhile, Sijie and Chee Kong and Andy are hard at work monitoring those amazing Knobblies (marked with the yellow flags). Today, they recorded 118 stars in about an hour!Behind them is a huge dredger that is doing works between Jurong Island and Pulau Bukom.
Here's the dredging working area (marked in red) from an earlier MPA notice.Besides this dredging project, Cyrene Reef may also be affected by the massive reclamation planned on the mainland (in red box) at the Pasir Panjang Port.
Vyna shares about the reefs as the group slowly heads back to the departure point. And another storm front is developing over the Southern Islands in the background. This one looks serious, and is unlikely to miss Cyrene.Marcus takes a few last photos as the weather looms again over Jurong Island.Just before we go home, Ling Ling spots this interesting peacock anemone (Order Ceriantharia). This animal has a columnar body topped with rings of tentacles, and outer ring of long tentacles, and inner ring of short ones. It builds a tube to live in, so it's sometimes called a tube anemone.As I was waiting for the others to come up to the departure point, I saw this little anemone. It looks somewhat like a small version of the Giant carpet anemone (Stichodactyla gigantea). But it was really small (about 5cm in diameter) and had white radiating lines. Hmmm?

As usual, the weather held until it was time to go home. Melvin quickly brought us off the reef and said the incoming storm looked like a bad one. We are now convinced that Melvin has god-like powers in keeping the bad weather away from us during our field trips.

With us today were new friends from the I want to go Cyrene facebook group: Charmaine, Gabriel, Tian Loong and Chun Fong; Ling Ling and Paul from NParks, Abigayle and Jani from Blue Water Volunteers.

The facebook group folks valiantly put up these fabulous blog entries to convince us that they should go to Cyrene. Thank you for your wonderful blog entries!
Charmaine Ho's entry: Cyrene to call our own with an update on her experience of the trip.
Gabriel Tan's web entry I want to go Cyrene Reef with an update on his experience of the trip.
Chong Tian Loong's blog entry I want to go Cyrene Reef
Chun Fong's blog entry Serene Cyrene

Regulars on this trip include Dr Chua Ee Kiam, our very own famous nature author and photographer; Chee Kong and Sijie of the Star Trackers; and from the Naked Hermit Crabs: Andy, Marcus, November, Jerald and Vyna.

We're taking a long break now as the tides will not be suitable for any trips to Cyrene for a while. We will miss this wonderful reef and hope it will keep well despite the many ongoing works around it.

More blog posts about this trip

• Marcus' poetic rendition of the day on his budak blog
• Vyna shares more encounters on her can you sea me blog
• Charmaine does a delightful account that makes me fall in love with Cyrene all over again on her Me(W)andering blog

More about Cyrene Reef on the wildsingapore website.

Erosion on Singapore's shores

A study of erosion at Sungei Buloh Wetland Reserve is being done.

Read more about it in today's article: Sungei Buloh erosion: How bad? Study on, by Tania Tan and Ang Yiying, Straits Times 19 Aug 08; on the wildsingapore news blog

Coastal erosion is an issue on many of our shores.

East Coast Park is one of the places where this is most obvious: this photo was taken in May 08.
What causes coastal erosion? What can and has been done about it?

Here's some old media articles about erosion on some of Singapore's shores.

Excerpts from Reclaimed land under threat, by Radha Basu The Straits Times 6 Mar 06; on the wildsingapore website

Severe erosion over the past few years has caused parts of the reclaimed shoreline along the East Coast Park and Pasir Ris to recede.

The Building and Construction Authority (BCA) told The Straits Times it has commissioned a detailed survey to study the extent of the damage and to recommend measures to help solve the problem.

Surveys mapping the physical contours of the beaches and surrounding waters are under way. The final report may take up to two years to complete, said a BCA spokesman.

One possible reason for the excessive erosion is that the breakwaters - stone and concrete structures built to protect the beaches - have not been as effective as expected.

When the beaches were first reclaimed, the elevated breakwaters were intended to protect the shore immediately behind them, leaving natural erosion to occur along the unprotected parts.

However, it now appears that in some parts of the beaches, including the Costa Sands area at East Coast Park, erosion may have occurred even behind the breakwaters, causing chunks of the shoreline to recede.

This could be because the height and force of the waves have been greater than anticipated. 'In areas, the waves could have gone over or around the breakwaters, causing portions of the beach directly behind these structures to erode,'

And here's a 2004 story about the erosion on West Coast Park from the habitatnews blog.

Worry over West Coast erosion
Tan May Ping, The New Paper 30 Jun 04;

RECLAIMED land in West Coast Park is slowly being reclaimed again - by the sea.

Soil erosion has left the shoreline in a sorry state. In the past two years, it has receded by at least 3m in some parts.

Park visitors and boatmen who work there are upset about this.

But Mr Teh Tiong Sa, a geomorphologist (someone who studies the evolution and configuration of landforms) said it's only natural that erosion occurs, especially in areas that have been reclaimed and are not protected from the waves.

He said the erosion is just as bad in parts of East Coast and Pasir Ris parks.

'It's a natural process. It becomes a problem only when people do not anticipate the erosion by leaving a buffer zone.

'Without the zone, infrastructure like walking tracks and barbecue pits built too near the coastline can be destroyed,' said Mr Teh, 59, a lecturer at the National Institute of Education.

In West Coast Park, several coconut trees have already fallen because of the constant pounding of the waves, and others look threatened.

The shore is littered with sharp boulders and all sorts of rubbish.

SEAWALL PLANNED

The authorities are aware of the situation and had planned to build a seawall at the end of last year.

But the work was postponed. It is now set to begin at the end of this year and is to be completed by late 2005.

A spokesman for the Building and Construction Authority told The New Paper that plans for the seawall had to be changed to accommodate the mooring of sampans there.

Letters complaining about the soil erosion have appeared in The Straits Times forum page.

One of the writers was concerned that children may accidentally fall into the gaps where the sea has taken bites out of the shoreline. That's a drop of about 2m in some places.

West Coast Park was set up in 1979, on reclaimed land. It is barely 1km long, stretching from the Republic Of Singapore Yacht Club to the shipyards at Pandan Crescent.

The rest of the park is well-maintained and has a large playground, cycling and jogging tracks, exercise stations and barbecue pits.

Boatmen who look after sampans there for a living told The New Paper that the problem got worse in 2002.

They used to live on the Southern Islands such as Pulau Sudong and Pulau Brani but were resettled to the mainland in the '70s. Some of them live on the sampans. They said they tried to fight the erosion about 10 years ago, by building a barrier along the coastline with driftwood and boulders.

The boatmen claimed that the park manager told them to remove the wood in 2002.

However, the National Parks Board (NParks), which employs manager, would not confirm this.

One of the boatmen, Mr Tan Ah Jin, 75, said: 'After we pulled the wood out, all the stones started to fall over.'

That, according to the boatmen, is when the erosion accelerated.

Mr Tan added: 'It's become dangerous for us to walk up and down when we need to get to the sampans.

'The place doesn't look nice anymore. Even the coconut trees have fallen down because of the erosion.

'We all hope the authorities will do something about this.'

Another boatman, Mr Wak Yakop Getim, 87, said a cordon was erected recently at the most affected stretch, but people could easily walk around it.

The cordon was extended after The New Paper asked NParks about the situation.

Madam Wu Yiqing, 36, who takes her 6-year-old son to the park, was happy about that. She said: 'It's very dangerous especially for young children. I really like the park but it could be better if they do up the shoreline.

'I don't let my son go near there now but it would be nice if he could play in the sea water.'

She said of the beach: 'It's very dirty and there's a lot of mud. If I want to go to the beach, I would still go to East Coast Park or Sentosa.'

No beach when seawall is built

MR TEH said those who are most likely to be affected by the building of a seawall are the boatmen.

'They would either have to be relocated or provisions would have to be made to build an opening in the seawall to allow the sampans to pass through,' he said.

A seawall is usually made from concrete and quarry stones. Building a seawall is one of the most expensive ways of preserving a coastline, said Mr Teh. But it is also the most long-lasting solution.

It can preserve the coastline but it also means there will not be a beach behind it.

Mr Teh said: 'The two don't go together. When there is a seawall, there won't be a beach because the waves carry sand away from the beach and it is not replaced.'

A spokesman for the Building and Construction Authority said it would build a 500m-long seawall.

The spokesman would not disclose the estimated cost of the project.

Din of dining urchins

Scientists in New Zealand have confirmed that undersea noise on their reefs are due to to the chomping of feeding urchins.

Sea urchins have five 'teeth' that they use to scrape on algae and other encrusting stuff growing on hard surfaces. The sea urchin has a skeleton which is basically a hollow sphere. This sphere amplifies the sound of their teeth scraping!



This noise may have a role in reef health!

The scientists also found that "reef fish and crab species swim towards underwater sound, concluding that noise generated around the coast plays an important role in guiding baby fish and crustaceans to a suitable habitat in which they can settle".

The Echinoblog earlier explained how Sea Urchins make a lot of noise when they eat with links to cool sound clips and more articles about chomping urchins.

Here's articles about these findings:

Noisy Eaters Are Cause of Mysterious Ocean Sounds
Dave Hansford in Wellington, New Zealand
for National Geographic News, 18 Aug 08;

If noisy chewing bothers you, never date a sea urchin.

New Zealand scientists say they have confirmed that the spiny sea creatures are responsible for a mysterious, twice-daily uproar heard underwater.

The 20- to 30-decibel noise is caused by the spiny sea creatures' teeth scraping on reefs as the hungry starfish relatives feed on algae and invertebrates.

Auckland University marine biologists Craig Radford and Andrew Jeffs solved the mystery during a study of ambient noise around northern New Zealand reefs.

The pair recorded two massive spikes in sound intensity each day: The first occurs just before dusk, the other before sunrise.

Radford said urchins had long been suspected of creating the din, but it took a series of experiments to confirm it.

"We put some urchins in a tank and got them feeding on algae, then we recorded them. The noise they were producing caused spikes at certain frequencies."

Those frequencies matched the sonic peaks the team had recorded at sea. The recorded frequencies also confirmed a series of earlier Australian experiments using Helmholtz resonance, the phenomenon of air resonating as it moves in and out of a cavity—as when you blow across a bottle opening to create a tone.

Radford said the nocturnal animals' hard shells produced just such a resonance as they fed with their five-toothed, calcium-carbonate mouths. An urchin's chewing apparatus is called an Aristotle's lantern, due to the ancient Greek philosopher's reference to the mouth's resemblance to a type of five-sided lamp.

Noisy Eaters

"The noise they make is the sound of those teeth scraping on the rocks," Radford said. "A large urchin will have a low resonance frequency, while a small urchin will have a higher frequency.

"When they emerge from their crevices at dusk, they're probably really hungry, munching away quite rapidly," he said, adding that the din drops off as the night progresses.

"They have another big feed before they go to sleep" at dawn, the biologist said.

On heavily fished reefs—where depleted fish stocks have led to an increase in urchin numbers—the noise was much greater than in reserves where fishing was banned, the researchers found.

Coastal noise of similar frequency and bandwidth has been recorded near the Bahamas; San Diego, California; and Australia.

Chris Tindle, a physicist at the University of Auckland, said the urchins made more noise on dark nights around the new moon.

"It's a huge increase—20 to 30 decibels—which is an increase of a hundred to a thousand times the background level."

Sonic Signposts?

Biologists believe the noise of reefs—not just the munching of urchins, but also the pops of snapping shrimps and the grunts of fish—acts as a beacon. The sound may guide larval fish and crustaceans, which hatch in plankton swarms many miles out at sea, to suitable habitats.

"They have to find their way back somehow," study co-leader Radford said. "They've got really impressive swimming abilities—7.8 inches [20 centimeters] a second for a 0.2-inch-long [5-millimeter-long] animal. But they need some kind of cue to swim towards."

In a featureless blue world, he said, "there are no visual cues. So we reckon it's sound."

Tindle, the physicist and marine sound expert, noted that fish larvae have been attracted toward sound in laboratory experiments.

"Whether they are attracted by sound from way out at sea, we still don't know. But we think sea creatures use the sounds coming from different directions to find their way around, to navigate."

Shrimp And Sea Urchins Make Noisy Guides
scoop.co.nz 15 Aug 08;

Snapping Shrimp And Feeding Sea Urchins Make Noisy Guides

Research that shows fish and crabs swim towards the source of underwater sound, potentially offering a technique for re-stocking depleted reefs, has won scientist Dr Craig Radford a prize in the MacDiarmid Young Scientists of the Year Awards.

Using an underwater listening device, Dr Radford identified snapping shrimps and feeding sea urchins as making the loudest sounds beneath the ocean. His study also showed underwater ambient noise around New Zealand’s coast gets louder twice a day with the sound of shrimp rapidly closing their claws and sea urchins scraping their teeth on rocks while feeding being major contributors to increased noise levels at both dawn and dusk.

Craig, who is based at the University of Auckland’s Leigh marine laboratory, is runner-up in the Understanding Planet Earth category of the MacDiarmid Awards, which are presented by the Foundation for Research, Science and Technology with Fisher & Paykel Appliances as principal sponsor.

Fish and crab larvae are frequently dispersed tens of kilometres out to sea and Craig set out to investigate how they get back to the coast. He found that reef fish and crab species swim towards underwater sound, concluding that noise generated around the coast plays an important role in guiding baby fish and crustaceans to a suitable habitat in which they can settle.

Craig says replicating underwater sounds could be a means of attracting fish back to depleted reefs and helping fish and crabs to flourish in reefs which have been slow to colonise.

He is currently completing a post doctoral fellowship with the University of Auckland, continuing research into how larval fish and crabs use underwater sound as an orientation cue. This includes trying to determine the frequencies they are listening to, how loud underwater sound needs to be for them to hear it and how far offshore they can pick up sound.

Reclamation works at Sentosa continues: MPA notice

The working period has been extended for reclamation and sea wall construction for the Sentosa Integrated Resort (IR).

CONSTRUCTION OF SEAWALL AND LAND RECLAMATION IN CRUISE BAY
from Port Marine Notice No. 148 of 2008 dated 18 Aug 2008

This is a revision of Port Marine Notice No. 52 of 2008. The working period has been extended.

Date: With effect from 5 Sep 08 to 31 Dec 08

Location: In Cruise Bay, off Sentosa

Working Details: The works include construction of a sea wall, piling, dredging and land reclamation within the working area.

Deployment of a silt curtain around the ferry terminal and removal of existing pontoons and access walkways will be carried out.

Crane barges and work barges will be used for piling works and transportation of equipment.

The barges used in the project works will be shifted by tugs operating in pusher mode. Safety boat will be in daily attendance for 24 hours throughout the duration of the operation.

For enquiries, please contact the project manager, Mr Chris Kelly at Tel: 9118 2802, or email: Chris_Kelly@macdow.com.au.

This is a view of works on these shores taken in Jul 2007.Links to more

• More background on the issues of reclamation on this shore.
• Other blog entries about Sentosa and reclamation there.

Changi under a strange moon

4am and we're on Changi. We notice something really odd about the moon. It was full yesterday. But today, it looked like a quarter moon. And it was slowly shrinking too!

It was Liana who shared that it was a lunar eclipse!

We didn't pay it much mind aside from taking a few photos, and headed off to explore Changi on what should have been a good low tide.What a wonderful find! A sea cucumber that looks like the unknown sea cucumber we saw at Cyrene Reef last month.Although it's a burrowing sea cucumber, it has a distinct underside. How odd! Kok Sheng says he's seen something like this on Chek Jawa too. That's great to know.This was another unidentified sea cucumber seen on the shore.Its tube feet emerge in rows along the body length and appear to end in rounded tips. Hmmm.I finally managed to get a clear shot of the pretty Warty sea cucumber (Cercodemas anceps) with its tentacles extended, well, sort of. I've never actually seen this animal with its tentacles fully expanded.Alas, we realise after a time, that the tide wasn't really going down. In fact, it seemed to be coming back in! Anyway, it was a good opportunity to explore the high shore, and take a closer look at our seagrasses. Changi has long, thin Needle seagrasses (Halodule univervis).As well as the beautiful Fern seagrass (Halophila spinulosa) and the oval-leaved Spoon seagrasses (Halophila ovalis).I took a really close look at the seagrasses and noticed many were covered in a fine lattice-like structure. Could these be bryozoans? Bryozoans are colonial animals that build a thin skeleton. These are my first photos of them, although I'm sure these animals are abundant on our seagrasses. I've just never looked closely enough at them!There were also really tiny snails that probably graze on the tiny algae that grow on the leaves, and clumps of what look like eggs.

Seagrasses form an important habitat, providing permanent attachment for small animals. Their roots stabilise the ground so that burrowing animals can shelter and avoid being swept away in the waves. All these tiny animals in turn form the base of a food chain for larger animals, including shrimps, prawns and fishes.
Among the seagrasses was this really tiny Biscuit sea star (Goniodiscaster scaber).
And a Dove snail (Family Columbellidae).
There was a tiny sea anemone too. This might be Stichodactyla tapetum, and not a small Stichodactyla haddoni, the more commonly seen large carpet anemones on our Northern shores. We shall send this photo to Dr Daphne and see if it's useful to her.There was also a very small patch of tiny Button snails (Umbonium vestiarum). The snails are really small so they might have only just settled into their sandy home.The bigger Button shells are occupied by tiny hermit crabs!
The hermit crabs are great fun to observe when the tide is not very low. Here's one in a spiral shell of a snail that I've yet to see alive.
Hermit crabs are often seen gathered in groups. Dr Dan told us that hermit crabs can smell when a snail has died. This smell attracts lots of hermit crabs who are always in the market for upgrading to a better shell. So a newly 'vacated' shell will often result in a gathering of hermit crabs.
Here's another pair of hermit crabs with what seems to be an empty shell. When one hermit crab takes the 'new' shell, another hermit crab may take its 'old' shell, which triggers more shell exchanges among the gathered hermit crabs. This shell 'musical chairs' may go on for sometime, because the animals often change their mind!

Before I could witness any swopping between these hermit crabs, the tide had come in!Oh dear. But I had a nice day out, and the others also saw lots of other interesting things such a dead shark (possibly it was still born), and a 'squeaky' clam, noble volute, sand stars, sea pens and other stuff. Kok Sheng shares more about these on his wonderful creations blog.

There were also sand dollars, more 'sea pencils' than I've seen on the last visits, and the big white sea urchins were still present in some numbers.

We wonder whether the lunar eclipse had affected the accuracy of the tidal prediction. On the other hand, these are among the very last of the morning tides for the year. The tides will soon switch to evening for the rest of the year. Usually, in our experience, during this switch over period, the tidal predications can be a little off in terms of height.

The lunar eclipse intrigued me. Here's what I found out about this event from space.com
A lunar eclipse happens when the earth gets between the sun and the moon. It is the earth's shadow that we see moving across the moon. Wow!

Today's eclipse was a partial lunar eclipse.

Eclipses of the sun and moon usually come in pairs. A solar eclipse is almost always accompanied by a lunar eclipse two weeks before or after it.

The next lunar eclipse will occur on 9 Feb 2009 and will favor Alaska, Hawaii, eastern and central Asia, Australia and New Zealand.

The next total lunar eclipse will be on 21 Dec 2010.

Read the Top 10 lunar eclipse facts on space.com to find out answers to questions such as why lunar eclipses don't occur every month, at every full moon.

As well as read about how lunar eclipses affected ancient civilisations and created myths. It must have been quite scary to see the moon being 'eaten' every now and then.

So unbeknownst to us, we were experiencing a special astronomical event!