Why you should dive Nitrox on your next liveaboard?

23/4/2022

What’s the difference between air and Nitrox?

The air we breathe everyday is as a gas made of 21% oxygen, 78 nitrogen and 1% other gas.
Nitrox, also called enriched air, is a mix of the same gaz but in a different proportion, we enrich the air with extra oxygen so the oxygen proportion is bigger. Its name: Nitrox comes from the combination of Nitrogen and Oxygen.
We refer to Nitrox according to its oxygen percentage, for example a Nitrox 32 contains 32% oxygen and is the most commonly used.

What are the advantages of using Nitrox?

If you remember your Open Water theory class, the amount of nitrogen entering your tissues is what limits the time you can spend at a certain depth.
The more nitrogen in the body, the more we risk a decompression sickness. Using Nitrox allows the diver to have less nitrogen in his blood within a given diving time, which gives Nitrox divers many advantages:

The ability to stay longer at a certain depth before reaching the same nitrogen blood level.
For example, if you dive at 30 meters, you could spend about 20 minutes on air before a decompression stop becomes compulsory, 30 minutes with a nitrox 32 and 40 minutes with a nitrox 36!
Having less nitrogen in your body also means your surface intervals could be shorter (which is a big advantage in some situation when you want to squeeze in 2 dives in a limited time).

I’m planning to dive with my friend who dives one air, what’s the point diving nitrox? Even if you follow the same dive profile as air divers, you will be far less tired then if you were diving on air and far safer as you will be further away from a risk of decompression sickness.
The nitrogen tissues desaturation is what tires you so much after a long dive. The less you have nitrogen in your blood, the less tired you will fill.

What are the disadvantages of using Nitrox?

The “depth level” notion is the main disadvantage of Nitrox: the less nitrogen in your nitrox, the more oxygen you breathe. Oxygen becomes toxic with depth and it is important not to exceed a certain partial pressure or you risk in water-convulsions (which may lead to drowning!) These events are extremely rare and easily avoidable if you follow the brief. Nitrox is safer than air if used within its limits.

Can I dive deeper with Nitrox?

It is generally believed that Nitrox is used for very deep dives, but the reality is that it is a gas allowing longer diving time in mid-deep waters, perfect for recreational dives between 20 and 30 meters deep.
The only thing you need to know to dive using Nitrox is that beyond a specific depth, the oxygen becomes toxic. Nitrox being rich in oxygen, it becomes dangerously toxic, faster (less deep) than normal air.
But don’t get scared, after your course, you will know very well what will be your maximum depth on any given nitrox mix and plan your dive accordingly to stay safe!

Can I dive longer with Nitrox?

Nitrox will make your NDL (no deco limit) time longer but if you breath through your gas fast, you will still need to ascend before being “out of air”. So it will make your dive longer only if you are good with air consumption. While Nitrox has many advantages, reducing your breathing rate isn’t one of them and you should not see any noticeable change on your air consumption when switching to Nitrox.

Where can we dive with Nitrox?

Nitrox is used everywhere in the world, and it becomes really advantageous when doing multiple dives a day such as on dive cruises.

Do I need another certification to dive nitrox?

Yes! Because of the danger associated with diving nitrox, which are different from the dangers of diving with air (which you have learned during your open water course), you will need to learn a few more things to dive safely with Nitrox.
The Nitrox course is the most taught speciality in the diving industry, not only it is the easiest and quickest diving course, it can be done without even getting wet.
On the MV Smiling Seahorse, we teach Padi Enriched Air Nitrox for 6000 THB. It can be easily done onboard in a few hours but can also be done online before coming through PADI e-learning. Don’t hesitate to get in touch if you have any questions!

Want to reed more fishy stories? Check our most popular blogpost!

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The hawksbill turtle: the critically endangered sea turtle

22/9/2021

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The hawksbill turtles, presentation of an endangered species...

While critically endangered, The Hawksbill Turtles are the most frequently encountered turtles on our cruises, today let's learn about hawk-billed turtle or Eretmochelys imbricata...

All Sea Turtles, are cold-blooded creatures, belonging to the reptile family, just like snakes, crocodiles or dinosaurs!

1. Where can you see Hawkbill turtles?
2. How to tell Hawkbill turtles from the others?
3. What do Hawksbill turtles eat?
4. Hawksbill turtle reproduction
5. Is the hawksbill turtle threatened?

Where can you see Hawkbill turtles?

Hawk-billed turtle, the only representative of the genus Eretmochelys, lives in the subtropical waters of the Atlantic Ocean, the Indian Ocean and the Pacific Ocean. It is therefore quite possible to cross it in the Andaman Sea, in the midst of coral reefs. In Thailand, they can be seen both in the North Andaman (Surin and Similan islands) and South Andaman.

Hawksbill turtles are amongst the smallest of the seven species of sea turtles. They measures between 76 and 89 cm and weighs an average of 40 to 69 kg.
As a migratory species, they have a wide range of habitats, from the open ocean to lagoons and even mangroves in estuaries. In the early stages of their lives, like other young sea turtles, they live a pelagic life, staying at sea until they mature enough to settle down.

Adult hawksbill turtles are mainly found in tropical coral reefs.

How to tell Hawkbill turtles from the others?

Hawksbill turtles and green turtles, are both commonly seen in the Andaman Sea and hard to tell them apart at first sight. Here are a few tips to differentiate them:

Hawkbill turtle VS green turtle: Sea turtle identification infographic

How to identify the Hawksbill turtle

Sea Turtle's face identification: Hawksbill VS Green turtle

Hawksbill turtles have a beak, while green turtles have a round face.

The hawksbill turtle has a hooked beak

The green turtle's beak is rounded

sea turtle identification, hawksbill head

Hawksbill turtle have 2 pairs of prefrontal scales

On top of their head, Hawkbills turtles have four little square in between their eye while green turtle have two. These squares are called prefrontale scales.

sea turtle identification, green turtle head

Green turtles have one pair of frontal scales

identify hawsbill turtle from the top of the head

Hawksbill turtles's nostrils are turned up

Green turtles's nostrils are a lot more forward

The turtle's nose is also a good differentiation factor: those of Hawksbills looks upward, on top of their beak while green turtle's nose is forward, on the front of their face. When looking at a tutle from the front you would see the green's nostrils a lot more.

Sea Turtle's Shell identification: Hawksbill VS Green turtle

The carapace of the sea turtles are also a good way to tell them appart. The shape of the green turtle is rounder with squales next to each other and a soft edge, while the hawksbill turtle is more hear-shaped with squales overlapping each other and the edge is serrated, like a saw.

Green turtle's shell has a soft edge and squales do not overlap

baby hawksbill on the left VS baby green turtle on the right

Hawksbill turtle shell has a serrated edge and squales overlap

Beautiful Hawkbill turtle by Franck Fogarolo

The carapace colour doesn't help identification but this carapace is serrated, means it is a Hawksbill

Sea Turtle's Flippers identification: Hawksbill VS Green turtle

It is not often easy to spot but Hawksbill turtles forelimbs have two claws on each fin, while green turtles only display one.

The second claw is fairly small though and hard to notice.

Hawksbill turtles front flippers identification

Hawksbill turtles have two claws on their front flippers

Hawksbill turtle VS Green turtle identification: belly shot

Green turtle Belly

Hawksbill turtle belly

If you have a photo of a turtle from bellow and you are trying to find out if it is a green or a Hawkbill turtle, the shape will be your best friend.
The Hawksbill turtle has a longer neck, and serrated carapace (looks closely in between the two back flipper) you may also see its beak!

What do Hawksbill turtles eat?

The hawksbill turtle is one of the few animals known to feed on sponges and is the only known spongivorous reptile. This diet make them very important to avoid sponges overtaking the reef.

Turtles do not have teeth, but a powerful jaw and a hooked beak allowing it to “tear” its prey.

Hawksbill turtle eating sponge on the reef

Hawksbill turtles are omnivorous, beside sponges, they can also feed on anemones and jellyfish, mollusks or sea urchins. Most of these are toxic but do not make them ill, it is however believed that their meat is poisonous to humans.

Small reminder: Turtles do not have teeth, but a powerful jaw and a hooked beak allowing it to “tear” its prey.

Hawksbill turtle reproduction

Like most sea turtles, Hawksbill live a solitary life meeting only for reproduction. This turtle mates and returns to the beach where it was born, every two or three years, to lay eggs...

The hawksbill turtle digs a hole in the sand at night where it lays more than a hundred eggs.
After about two months, these eggs will hatch. The little ones will then have to try to get back to the ocean quickly, at they risk of being eaten by birds or crabs!
Did you know? The temperature of the nest during the 60 days incubation will determine the sex of the litter! Cooler sand leads to more males hatching and vice versa.

Is the hawksbill turtle threatened?

Yes ! The hawk-billed turtle is now critically endangered. They are believed to be the most endangered of the seven species of sea turtle, with only approximately 8,000 nesting females left globally. Its beautiful carapace has been used by jewellers and for home decoration for thousands of years. Ghost fishing, by catch and sea trash are also a major treat to these gorgeous animals.

It is estimated that millions of hawksbill turtles died in the 20th century due to carapace trade. Additionally, hawk-billed turtle eggs are still eaten across the globe, and turtles themselves are killed for their flesh.

Plastic bag floating in the sea...

Not only do we destroy the reefs they feed on, but they cannot find a quiet beach to lay their eggs anymore and many sea turtles dye eating plastic.

It is estimated that one in two turtles has already eaten plastic, a plastic bag that floats in water can be easily identified as a jellyfish by the turtle but is a lot harder to digest...

You want to know more about Sea turtles?
Read this too

Green turtles have green flesh and other interesting facts about this wonderful sea turtle

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The corals of the Andaman Sea

8/9/2021

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Colourful fishes have always been a favorite to tropical sea divers but have you taken a closer look at the gorgeous coral species that inhabit the Andaman Sea?
Do you know what corals are? How coral grows to form the coral reefs (Planet earth largest living structures) and why they are so important for our planet?
Contrary to common beliefs, corals are animals, not plants and surely neither rocks!
What you see above is actually a group of animal living under the same roof... developing over time like any living thing.

How do coral reefs form?

Coral reefs release eggs and spermatozoa (gametes).
After fertilisation (meeting of a male and female gamete), a ciliated larva called planula is formed.
The larva will attach itself to a place favourable to its development and form a flat disc.
A polyp will form and then bud (each polyp secretes a hard exoskeleton, made up of calcium carbonate, as well as an internal limestone skeleton that remains in place even after the death of the animal), to give what we know today like coral.

The successive budding of the polyps makes it possible to continuously enlarge the coral colony which, over time, forms the reefs.

The reefs are therefore made up of colonies of polyp corals held together by calcium carbonates. Note that polyps alone could not live and reproduce without their symbiotic relationship with zooxanthellae algae. While the algae provides the animal with the necessary nutrients, the polyp releases carbon dioxide which allows the algae to develop and also to carry out photosynthesis which will give colour to corals in particular.

Here are the stages of the coral reef’s life cycle

Coral reef’s life cycle - coralworldvi.com

There are hundreds of species of corals! Most live in tropical seas with optimal conditions for their development: lots of light and a temperature between 25 and 30 ° C.

But then, how to differentiate coral species?

can you spot the stone fish on this nice coral reef?

The magnificent colours of the corals that we, divers, are lucky enough to admire, their shape or even their size allow them to be distinguished in particular.

Red, brown, yellow, green, blue, purple or even fluorescent ... the colour combinations of corals are infinite! Colours can often help divers distinguish one coral from another, but their shape is a better tell tail.

There are two main types of corals: Hard coral and Soft Coral

Hard coral species of the Andaman Sea

Hard coral are made of a rigid calcium carbonate (polyps' exoskeleton made out of limestone) and appear very much like rocks. When a polyp dies, their skeleton remains and new polyps grown on top of the last ones enlarging the coral one life at a time. Hence hard coral grows very slowly.
There are several categories of hard corals encountered in the Andaman Sea, each of these with many sub-categories and species.

Branching corals

Branching corals are made up of a multitude of branches often used as nurseries to keep the baby fish out of harmway.

Elkhorn & Staghorn Coral:

Elkhorn / Stahorn Corals resemble branched elk horns (Elkhorn corals) or deer (staghorn corals) which tend to protrude vertically with a large number of side branches.

Elkhorn / Stahorn Corals

Encrusting corals

Encrusting coral

Encrusting corals form a crust on a substrate by spreading over their surface and thus create a thin coloured layer.
This is the perfect place for christmas tree worms and encrusting shells to settle.

Foliose corals:

Growing outward and only attached to the reef from their center "trunk", Foliose corals are often compared to heads of lettuce.

Massive corals

With a very slow growth (from 0.5 to 4.5 cm / year), these round-shaped corals bummies constitute "the pillars" of most reefs, in the Andaman Sea and beyond! They can reach massive sizes like the multi million years bummies depicted bellow from the Burma Banks.

Massive corals

platygyr brain coral mussidae

Mushroom Corals

Mushroom corals are fairly solitary corals. They can be found on the sand and do not attach to other corals. Made up of a single polyp, mushroom coral can reach 25 cm in diameter.

Mushroom corals

Table corals

Table corals:

Table corals are easily recognisable thanks to their horizontal structure which gives them great stability and perfect hiding places for other animals of the Andaman Sea and a particularily appreciated nursery for butterfly fishes.

Bubble corals

Often mistaken for eggs, pollyps ressembles bubbles during the days which deflates at night to let the polyps feed. Despite their soft appearance, bubble corals have a "stony" structure and are hence classified as hard corals.

Bubble Coral, or Plerogyra sinuosa

Orange Cup coral

Another nocturnal coral with fleshy appearance, the orange cup coral is indeed a hard coral. It is classified as ahermatypic, because it doesn't contribute to building the reef.
In fact it is a pretty invasive specie which spread quickly favouring on rocky walls and chasing away sponges and hydroids.
The polyps retract during the day and "blooms" at night covering the wall with beautiful yellow
"flowers".
Next time you see them, make sure to look closely for the pretty yellow snails that feed from them.

Sun corals or orange cup coral

Cup corals are one of the most colourful hard coral specie on the Andaman Sea.

Soft Corals species in the Andaman Sea

Soft corals are easiest identified from hard coral because they do not have a hard skeleton. They also have 8 arms per polyp.

Carnation corals

Carnation corals are soft corals that love curants, their amazing vibrant colours make them some of the favorites for underwater photographers.

Richelieu Rock is famous for the purple coloured carnation coral that covers the best dive site in Thailand.

red whip coral in the front, bushy Carnation soft Coral behind and giant seafan in orange

Seafans

The Andaman Sea was gifted with several types of seafans, tall web-like fan structures in various colours. The most impressive is probably the Giant seafans (Anella mollis) which can reach 2 meters in diameter!

Giant seafan in the Andaman Sea

Why are corals important?

Not only are coral stunningly beautiful and giving the Andaman Sea its colours but they are so much more important than for background imagery!
1- coral feed small critters and fish that feed the bigger ones, no coral= no more fish!
2- 500 million people make a living from coral reefs: from fisheries to tourism
3- coral reefs can reduce waves by 95% and could save the coastline from the damaging effects of tsunamis and storms
4- Coral reefs are also the lung of our planet! Generating half of our planet's oxygen and absorbing about a third of the carbon dioxide generated from fossil fuels usage.

Coral reefs are in danger! Help us make them last longer!

Coral reefs have already been reduced by more than 50% and our generation might be the last one to witness one of our planet's greatest treasure before it disappear.

OUR ACTIONS now will determine if our children will see it too.

The Smiling Seahorse is commited to ocean preservation, when you go diving, make sure to chose and eco friendly operator to reduce your ecological footprint.

due to accelerating global warming, more and more corals no longer regenerate and see the entire reef die small little by little!

coral bleaching due to ocean warming is one of the many treats to coral reefs

The Smiling Seahorse's promises

to abides by Green fins principles
to encourage environmentally responsible diving practices
to reduce/ reuse/ recycle as much as we can, especially plastics
to offer reef friendly amenities: such as our refillable organic, reef-safe Soap, Shampoo and hair conditioner.
to ask all our employees to help in ocean conservation efforts
To support marine science research and clean up projects

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Where about are baby Whale Sharks ?

23/6/2021

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The mystery behind whale shark reproduction

Whale sharks life cycle is still an enigma, here is what marine biologists know so far about baby whale sharks

Whale sharks are the biggest fish in the oceans, their size implies slow growth rates and great longevity. Male Whale sharks reach sexual maturity in around 30 years (their adult size is rarely bigger than 8 meters). Females get much bigger but it takes them 50 years to be ready to conceive.

While they could live up to 100 or 150 years old and mother a few hundreds pups, this late development implies slower potential population renewal as most whale sharks will not live long enough to have a descendant.

They have to steer clear of a lot of threats such as fishing nets...before they get a chance to breed.

What do you know about their reproduction ?

The answer to this question: not much …. even by whale sharks specialists.

Ways sharks reproduce ociparus viviparous ovoviviparus

Shark have 3 modes of reproduction

There are three different modes of reproduction among sharks and rays (oviparity, ovoviparity and viviparity) and 1 variant (asexual reproduction)...

Oviparous species, like many other fish (as well as birds and reptiles), lay eggs.

Viviparous species give birth to live young, just like mammals: a placental links the developing embryo and its mother and feeds it in utero until its birth.

Ovoviviparous species also give birth to live young but do not have a placenta linking mum and baby. The embryo first develops within an egg, gaining nutrients from the yolk, it then emerges from the egg whilst still inside the mother who gives birth

Asexual: leopard sharks held in an aquarium have given birth after years of captivity!!!

Whale sharks are ovoviviparous and this is known thanks to a single pregnant female caught in nets in 1995 (nicknamed "big Mamma" ) containing 300 embryos in her utero at various stages of development. Some were still in their eggs, others already hatched, the biggest was 64 cm long.

So when Baby whale sharks are born, where do they go?

Where whale sharks go to give birth is still a mystery, it is believed that whale sharks are born between 40 – 70cm but surprisingly no diver has ever seen a whale shark under 2m longs and it is still unknown where they spend their time before reaching this size.

As it is one of the few places they can still hide in… it is believed that baby whale sharks are born in very deep water and spend the first years of their lives at depth.

Baby whale shark sightings are very very rare but they have been seen !

Only 21 baby whale sharks smaller than 1.5 m long have ever been sighted globally till this day, most were neonate captured as bycatch in fishing nets.

The latest Whale shark baby was found on the 15th of March 2020 and was 60cm long. This is smaller than the largest embryo found inside "big Mamma" in 1995, meaning this pup is either a small newborn or even neonate.

Taiwan 2013

80cm - Pakistan 2017

Given their size and swimming ability it is likely that the Philippine, Peru, India, Australia, Pakistan and Taiwan, where they were found, may be close to whale sharks nurseries !

60cm - Phillipines - march 2020

50cm- India 2017

38 cm- Philipines- March 2009

Watch a baby whale shark swimming off in this video:

If you liked this article, share it!

learn about adult whale sharks in this bespoke article:
All about whale sharks
And if you have something to add, feel free to leave us a comment below!

You want to learn some more about Marine life on our blog?

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Zebra shark: one of the cutest sharks in the indian ocean!

12/5/2021

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Meet the Zebra Shark also known in Thailand as Leopard Shark

1. Zebra Sharks or leopard Sharks?
2. Where can Zebra Sharks be found?
3. The Zebra Sharks diet: what do they eat?
4. Zebra Sharks reproduction
5. Zebra Sharks asexual reproduction...?
6. Are Zebra Sharks dangerous? How to approach them?
7. About Zebra Sharks conservation?

Zebra Sharks or Leopard Shark?

The most common confusion among divers concerns the Leopard Shark, very often confused with the Zebra Shark, which is frequently encountered when diving in tropical areas.

Both species have the particularity, in adulthood, of sporting a spotted coat like the African leopard.
However, the two species are biologically different and very easily differentiable.

On the left, the Zebra Shark is born with "zebra lines" which change into leopard-like-spots when they reach adulthood. Their Cylindrical body measure from 50cm at birth to 3.50 m when fully grown with prominent ridges along the flanks. Upped lobe of the caudal fin is very long.

On the right, the Leopard Shark has a unique spotted gray-dress an can measure up to 1.80m, so it is a bit smaller than its congener the Zebra Shark. It lives in the cold to temperate waters bordering the United States, from the Gulf of Mexico to Oregon. Its favorite areas of evolution are the turbid, shallow and rough areas of the seaside, the sandy bottoms and the rocky substrates of the kelp forests.
This lovely little shark is probably the reason why American divers call Stegostoma tigrinum "zebra shark" but the rest of the world (diving warmer water and hence never in touch with the triakis semifasciata) just call them "Leopard shark"...

Stegostoma tigrinum Zebra Shark AKA False Leopard Shark (adult)

Triakis semifasciata - Leopard Shark (Adult)

So what does Zebra Shark (or false leopard shark) look like when they are younger?
Rarely photographed in the wild, Zebra sharks look black with white zebra marking at birth and develop their "leopard" patterns after a few weeks.

Where can Zebra Sharks be found?

The Zebra Shark can be found in the shallow waters all around the Indian Ocean and West Pacific from South Africa to the Red Sea, from India to North Australia and from china to New Caledonia and Southern Japan. They usually hang out on sandy batches near coral reef where they can find their food.

Map of zebra shark habitat by Sharksider.com

The Zebra shark diet: what do they eat?

The Zebra Shark is known for its foraging habits; it feeds and moves mostly at night, foraging for crabs, sea urchins, small fish, snails, and other invertebrates hiding in holes and crevices. They have great whisker-like organs (barbels, in front of their snout, helping them seek out their prey). They are also equipped with smallmouth and strong gill muscles to snatch up prey but are not as strong as active fish hunter as many other sharks. They prefer to rest on the ocean floor during the daytime, where they can breathe and pump water through their gills while remaining motionless. When there are strong water currents, they might seem to be surfing as they adjust their fins to stay motionless in the open water.

Zebra shark reproduction?

Stegostoma tigrinum usually live a solitary life and only seek each other during the mating seasons. During courtship, the male Zebra Shark will follow the female, bite vigorously at her pectoral fin and tails, with occasions where he holds her fins down. These usually happen at the bottom, and a long time before, the male curls its body around the female’s and joins his claspers with her cloaca. The mating usually lasts about five minutes. Females lay about four eggs at a time, but some studies show they can lay up to 46 eggs over 112 days. The egg cases are usually between brown and dark purple, with fine hairs around, helping them stay anchored or secured when developing. Eggs may hatch in between four to six months.

zebra shark couple caught during their mating dance

zebra shark egg: Photo by Keith DP Wilson

Zebra shark asexual reproduction?

(CNN) A female Zebra Shark in an Australian aquarium has astounded scientists by producing live offspring asexually, three years after being separated from her long-term mate. [...] It is only the third documented case of a vertebrate of any species switching its reproductive strategy from sexual to asexual.
The shark had earlier reproduced after mating with a male, so it was shocking that it managed to lay fertilized eggs again after so many years without any sexual intercourse.
This asexual reproduction - which exist in other animals’ reproduction like spotted eagle ray and Colombian rainbow boa - had never been seen in sharks before now. Studies are ongoing to understand this phenomenon, but some scientists believe that it might be a natural adaptation to the lack of sexual partners.

Zebra shark can create clones!

Are zebra sharks dangerous? How to approach them?

Are Zebra Sharks dangerous?

Zebra Sharks are non-aggressive, they can be easily approached when underwater. Divers visiting the Koh Bon Pinnacle or Koh Tachai in Thailand as well as North Twin in Myanmar have a good chance to meet one of these fascinating sharks.

How to approach them without disturbing them?!
Zebra shark are relatively easy to approach but they will run away from you if you don't do it right!
Approach them from the side, where they can see you. Dont pass on top of them or approach them from behind, if you are in their "dead angle" they will swim away.

About Zebra Sharks conservation?

About the Zebra Shark conservation

Today, Zebra Sharks are endangered: humans are the driving factor that might drive extinction in the future. Usually, inshore fisheries use them for their meat, which is either salt-dried or fresh. The traditional Chinese delicacy also uses Zebra Sharks, particularly its fins, for making shark fin soup, a delicacy in China.

Is Zebra shark a fish?

All sharks are cartilaginous fish (their skeleton is made of soft cartilage, not bones). These fish all fall into the group of fish called the elasmobranchs (like rays).

A zebra shark and its beautiful blue eyes

A zebra shark poses for the photographer if correctly approached

ZEBRA SHARK CLASSIFICATION:
LATIN NAME: Stegostoma tigrinum (fasciatum)
FAMILY: Stegostomatidae
PHYLUM: Chordata
CLASS: Chondrichthyes

We hope you liked this blogpost and found the information you were looking for. Check out our Marine life section for more fun facts about Andaman Sea life!
What else do you know about leopard sharks? share in the comment section below!

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Nautilus can have sex for 30 consecutive hours and other fun facts on these incredible animals!

6/5/2021

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Nautilus is a cephalopod, a nearby relative of octopuses and squids. This creature can be found in the tropical waters of Indian and Pacific seas, close to the coral reefs, near depth areas of 300 to 600 meters. Nautilus are (like most marine species these days) affected by over-fishing and by the fact that their beautiful shells are sold as ornaments.

6 Fascinating Facts about Nautilus

Nautilus measure 20 to 25cm in average. Its shell is white to orange with brown zebra stripes. Internal side of the shell is pearly white.

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101 Nudibranchs of Myanmar

29/8/2020

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Welcome to the vibrant world of nudibranchs

For me nudi-hunting is like collecting stamps...
You always want to find new ones for your private collection.

I remember the first time someone pointed out a nudibranch to me during a dive, gesturing towards a rock and signalling “Look, something small”. What felt like minutes went by as I squinted and shifted focus trying to figure out what exactly I was trying to look at. Then suddenly a tiny piece of what appeared to be algae moved and I noticed it was actually alive! It couldn’t have been longer than a centimetre or so and was pink with beautiful blue and yellow tentacles sticking out all over its worm-like body and head. What WAS that thing? And how in the world had the dive guide seen something so minuscule and hidden?

Now, I am the type of diver who can usually be found hovering in one place for minutes at a time treasure hunting with my mask a short distance from the reef or seafloor. Many people don’t know that the biodiversity in a square meter of coral reef is unmatched by any other ecosystem on the planet, a rule to which the Andaman Sea in Thailand and Mergui Archipelago in Myanmar (Burma) are no exception. The regions are filled with a cornucopia of colours, shapes and textures that if you take your time and look closely you can find some bizarre little rarities that can bring a tear to your eye.

What exactly is a nudibranch?

Today there are somewhere around 3000 documented species of these incredible molluscs that can range from a mere 4mm to a hefty 60cm. Nudibranchs are invertebrates that spend a certain stage of development with a shell. They will always shed this shell at some point before adulthood. All nudibranchs are members of the sea-slug family, however not all sea-slugs are nudibranchs.

Egg ribbon of Hexabranchus Sanguineus nudibranch, aka Spanish dancer

These “sea slugs” are hermaphroditic which means that each individual has both female and male reproductive organs on the right side of their body. They can lay up to 25,000 eggs at a time in a mucous ribbon-like formation that will take roughly a week to hatch.

Because they have both male and female sexual organs, a pair can inseminate each others so that you have two pregnancies instead of one. However nudis still need to find a mate. They cannot impregnate themselves!
Nudibranchs are carnivorous and love to eat sponge, hydroids, algae, coral, anemones and even other nudibranchs. They can be found mostly in shallow reefs in warm salt water, but there are some species that live in deeper or cold waters and some can even survive the lower salinity of brackish water. They are found in great abundance at any of the dive sites of the Mergui Archipelago in Burma.

What is so special about nudibranchs?

Apart from their gorgeous colouring and their many shapes and sizes nudibranchs have some special tricks up their sleeves that really sets them apart.

Although they are small, they have developed some very industrious techniques to protect themselves. Many nudibranchs display bright colours for a multitude of reasons. Some practice what’s called aposematism which is colouration to suggest to predators that they aren’t tasty or can be toxic. This is a technique used by the Phylidiidae family that we often see in the Indo-Pacific.

Phyllidia coelestis

The Blue dragon only need to eat for the first few months of its life before they become self reliant!

Some nudibranchs that feed on the stinging cells of jellyfish or hydroids can actually recycle them and use them as weapons. Glaucus atlanticus or the Blue dragon nudi can be found floating near the surface and feeds on the nematocysts of the Portuguese man of war Jellyfish and similar species. It will eat the stinging cells and pass them harmlessly through their body where they can then be displayed on their skin or in appendages called cerata making them harmful to predators.

Some nudibranchs that eat sponge will also use the same chemicals that their prey use to defend themselves to make them taste foul to their own predators.
Some can also make their own chemicals (regardless of what they eat or where they live) to serve similar purposes or can even secrete an acidic mucous when disturbed.

Some nudibranchs will feed on plant cells and use them to create their own food sources. A particular group of sacoglossan sea slugs will eat certain algae found in soft corals and recycle their chloroplasts so they can create their own nutrients through photosynthesis. This means that once it has eaten enough it doesn't need to eat any longer. The algae in its body will use the sunlight to create enough nutrient for its host to survive.

Doriprismatica atromarginata nudi

One of the world’s most famous nudibranchs is the Spanish dancer or Hexabranchus sanguineus is also one of the world’s biggest growing up to 40cm long! These are nocturnal and can often be found during a night dive. If you are lucky you can even see one swimming in a mesmerising undulating movement. It is potently chemically defended and it advertises it with its bright red colour. They also often have small symbiotic emperor shrimp which ride along on their backs.

Hexabranchus sanguineus aka Spanish dancer

Emperor shrimp hitching a ride on a hexabranchus sanguineus

How do you identify a nudibranch?

Nudibranchs have complicated names which can be very daunting to someone just starting to learn about them. They often have common names which can be easier to remember but they can also cause confusion. For example, some people call the same nudi different names depending on where they dive and what the locals refer to them as. Sometimes a distinguishing feature that led people to give it a common name is not specific to that species leading different nudis to be called the same thing.
Using their scientific names is the best way to accurately identify nudibranchs even if it can be a bit of a mouthful. Taxonomy is the way we classify living things in biology and it is an intricate science. Basically speaking, plants and animals are divided into family trees that get more specific as you travel downwards eventually allowing you to name individuals.

4 main families of nudibranch

Instead of branchial plumes, Aeolid
nudibranchs are covered in appendages called cerata which increase surface area for gas exchange and also can be used to display ingested chemicals or stinging cells for defence.

There are 4 main Nudibranch families:
Doridoida, Aeolida, Dendronotida and Euarminida. The most common families are "Aeolids" and "Dorids" which each have specific identifiable features.

Dorids all have a distinguishable branchial plume on their back end which they use to breathe. Their mantles are often smoother and more regular shaped than Aeolids which are typically much spikier.

Anatomy of Dorid and Aeolid Nudibranchs

Understanding the difference between the different species is a great place to start but there are other things to consider when identifying a special slug you found on the reef. Looking at its body shape can be very helpful as well as colouration and any markings like stripes or polka dots. Also when in doubt there are many resources available to you like marine species identification books or public forums on social media.
Some of my favourites are ID Please (Marine Creature Identification) and Nudibranch Central on Facebook.

What kind of nudibranchs can we find in Thailand and the Mergui Archipelago?

The marine life in the Mergui Archipelago and Thailand are so diverse that it has something to offer to any diver. Macro lovers rejoice in Burma and especially those with an affinity for nudibranchs. Behold some mesmerizing little beauties that we have found on our cruises.