Harlequin Shrimps are a very flamboyant looking and a delight to see. There are two species of harlequin shrimps, namely the Hymenocera Picta found in Hawaii and Hymenocera Elegans found in Andaman Sea. They are commonly known as clown shrimp, painted shrimp and dancing shrimps.

The Harlequin shrimp is unlike other species in that it is a slow mover and not very agile. The beautiful bodies have stunning coloration with the body being a pinkish white or white with large purple edged pink spots. There may also be red and orange tones depending on the local environment.  The shrimps vary in size averaging between 2cm-4cm. The females are larger than the males and can be identified by the coloured abdominal plates. The male’s abdominal plates are white. It is believed that the vivid appearance of the shrimp is enough to deter predators. It also indicates that it may be toxic to eat as brightly coloured creatures often are. This is not the case with the shrimp. The two large flat pincers constantly move even when the shrimp is stationery, hence the common name “dancing harlequin shrimps”. The eyes are positioned on the end of stalks and the antennae are flattened, looking very leaf like.

Harlequin Shrimps are very shy and are found in mating pairs. They are monogamous and are very territorial usually covering an area of up to 10m square.  They are predominately nocturnal and will feed during twilight or under the cloak of darkness. During the day they are found in hiding places on a rocky or coral substrate.  This species of shrimp are rare and do suffer as a result of coral damage. The Indo-Pacific species is more common that the Hawaiian species, because over the years the latter has been actively collected for the aquarium trade.

Moulting occurs once a month. During this process the shrimp will hide until the new shell hardens. It is usual for simultaneous molting to occur. The molting also gives the opportunity for the shrimp to replace missing limbs, this may take more than one regeneration.  The mating couple will reproduce after the female as completed her molting process. She will lay between 100 and 5000 eggs per season and tends to them until they are hatched.

The Harlequin Shrimps are predatory carnivores. They are ruthless and extremely strong. The shrimps work as a team and detect their prey by scent. They live on a diet of starfish. Once the starfish has been located the pair will prize the arms from the rock and overturn it, thus rendering the starfish helpless.  The starfish may be 10 to 20 times larger than the shrimps. It has been known for the shrimps to drag the starfish to the lair where it acts as a living larder. It is kept alive by the shrimps feeding it.  The shrimps dine on the tube feet starting at the tips and working inwards to the centre plate, thus keeping their food source alive for as long as possible. Occasionally, a starfish may detach an arm or two to make an escape!!!! It is fortunate that starfish have the capability to rejuvenate their limbs…..

If you would like to know more about the identification of species why not sign up for on a  Underwater Naturalist Specialty Course, which will enhance your knowledge and highlight the key things to look for or a cruise on board MV Scuba Adventure or MV Scuba Fun for a chance to see these for yourself.

I was very excited to take this trip out during the “summer season” as tour leader on MV Scuba Adventure. All season the local sites from Phuket had been performing so well, with lots of great visibility dives and an abundance of marine life both (very) big and small. I also knew that during the high season the dive sites of Hin Deang and Hin Maung are awesome, but I didn’t know what to expect from a trip this time of year?

Scuba Adventure

… It was not a disappointment!

So here we go:

Day 1:

Shark Point – Great visibility to enjoy all the lovely soft corals, fans, sponges and tons of marine life including the odd leopard shark. Hi-light of the dive: a large marble patterned tiger tail seahorse.

Shark Point

Koh Bida Nok – Again tons of marine life, especially the trevally and schools of fusiliers, and a nice big hawksbill turtle at the start. Hi-light of the dive: absolutely the 10-20 black-tip sharks seen during the dive, especially getting up real close to 5-10 of them in the bay, before they finally torpedoed passed us.

Koh Bida Nok

Koh Ha Yai – A beautiful late afternoon dive to enjoy the caverns (known as the Cathedral) and swim-through’s. Hi-light of the dive: the view looking out at the silhouetted divers the from the back of the Cathedral.

"The Cathedral"

Koh Ha Lagoon – A comfortable night dive in the protected lagoon between islands 2 and 4. Our group explored the east side wall of island 2 and the sloping reef between. Hi-light: For me the macro life amongst the vivid soft corals on the wall, for others the giant barracuda following us!

Day 2:

Hin Muang – Oh my God! The visibility! We could see the bottom… and which ever side you are on, it goes down a very long way! Lot’s of life; and the soft corals looking bigger and more colourful than ever. Hi-light of the dive: All of it, in stunning visability. It was like a scene from the movie The Abyss but with the lights on! Diving – the best reason in the world to get up with the sun.

"Stunning Visibility"

Hin Deang – Awesome vis continued, we could even see the outer pinnacle from the main rock! Whichever way you looked there was marine activity and mild currents meant an easy swim to appreciate it all. Hi-light of the dive: Did I mention the large manta ray that made it’s way around the rock to the outer pinnacle!

"Manta Ray"

Koh Ha Neua – An early afternoon dive made the best of the huge purple soft corals on the southern side of this site. The shallow hard coral reef at the end of the dive was full of fish, whilst weaving in and out of the soft-coral coated rock channels rewarded us with nice nudi’s and a brilliant yellow tigertail seahorse. Hi-Light of the dive: A spotted eagle ray hovering over the purple soft coral field.

"Sea Horse"

Koh Bida Nok – With the currents reversed and an exciting dive the day before, we chose to go again from the other side of the island. This dusk dive showed us some more big fish (black-tip sharks), kuhl’s rays, mantis shrimps, morays, nudibranchs. Hi-light of the dive: I guess taking the time to see all the things we hadn’t noticed on the other dives – Bida Nok is one of the richest and most varied dive sites. Oh, and it being a dusk dive so some of us could visit Phi Phi Don and enjoy an evening on land.

Day 3:

Koh Bida Nai – Yet another sunny day, this early morning dive provided more sharks and a small school of big pick-handled barracuda. Hi-light of the dive: Swimming through the hundreds of fusiliers and trevally that hang out in the sunshine over the beds of stag horn coral, then back up the reef to the glittering chevron barracudas.

Koh Bida Nai

Anemone Reef – Of course anemones but also lots of colorful soft corals make this a beautiful pinnacle in good visibility… and it was! A turtle, lot’s of fish, little current, nudi’s and a few bamboo shark made it even better. Hi-light: A pale-yellow seahorse out in the sand (I like seahorses!)

Anemone Reef

Koh Doc Mai – A nice surprise… an extra dive thrown on to the end of the trip! This wall dive is awesome for macro – wonderful nudibranchs, ornate ghost pipefish, more bamboo sharks, all sorts of morays, this site can have it all. Hi-light: We got to dive again, ha!

Koh Doc Mai

Apart from the great visibility and relaxed diving (with it’s heart racing moments – sharks, manta, eagle ray), for me it was the wonderful variety of dive sites and marine life that made the trip one of the best. Also helping to make the diving awesome was that, during most of the trip, we were the only boat diving the sites… well, we were on the Scuba Adventure!

Scuba Cat Diving has been offering the Nitrox Enriched Air Specialty since ‘s introduction of the course in 1996. Once considered to be dangerous, it now is widely accepted and very accessible. Diving with Nitrox Enriched Air allows us to safely extend our bottom times and after all, time underwater is what it’s all about!

Since its introduction in recreational diving 1985, Nitrox Enriched air has slowly changed from being controversial to widely accepted. It is now our most popular Specialty Program and all our Daytrip boats are equipped with Oxygen Clean Compressors, which enables us to make Enriched Air available to all Nitrox certified customers.

Diving with Nitrox Enriched Air is most beneficial on dives between 18 and 30 meters. The reduced Nitrogen in the breathing gas means less Nitrogen loading and thus longer dive times.

What is Nitrox?

The air we breathe every day typically consists out of 78% Nitrogen, 21% Oxygen and 1% other gasses. In simple terms, Nitrox Enriched Air in Scuba Diving is any breathing max with an oxygen percentage exceeding 21%. The most popular mixes are EANx 32 (with 32% oxygen) and EANx 36. For recreational diving, breathing gases enriched to 40% oxygen are acceptable and up to 60% with Semi Closed Rebreathers.

Most scuba equipment, including regulators, BCD’s and dive computers are compatible with Nitrox Enriched Air up to 40% when they come from the factory, however you should check the manufacturer’s guidelines.

The normal air we use in scuba diving mainly consists out of Nitrogen (approx. 79%) and Oxygen (approx 21%)*.  Dive tables and computers are based on calculation of theoretical Nitrogen loading. This loading is expressed in Foot Sea Water (fsw), which is directly related to the Partial Pressure of Nitrogen. So, as most divers already know, the nitrogen loading is based on the depth of the dive and the amount of time we spend underwater. Besides these two elements, the third factor that determines our nitrogen loading is the percentage of Nitrogen in the gas we breathe.

In Scuba Diving, Enriched Air Nitrox is any gas mix with more than 21% oxygen. Our body doesn’t use the extra oxygen in the mix, but we do benefit from the reduced Nitrogen. The reduced nitrogen will reduce the partial pressure of nitrogen when we dive and reduce the nitrogen loading, thus extending our bottom time.

Nitrox Enriched air was first introduced as a recreational breathing gas in 1985, which caused major controversy among Scuba Diving experts. It took another 11 years before it became widely accepted with ‘s support of Nitrox Enriched Air as a recreational breathing gas and its introduction of Educational Material and the Nitrox Enriched Air Speciality course in 1996.

Most dive centres have Nitrox Enriched Air available and some boats have Nitrox available onboard.

Scuba Cat’s MV Scuba Adventure, includes several free Nitrox fills on every trip to allow longer dive times. MV Scuba Fun and MV Scuba Cat both have the facility for Nitrox on board meaning that you can take your Enriched Air Diver Specialty during your diving with us no matter which boat you are on. The course is available as a Elearning course, so you can complete the theory from your own home and enjoy the diving on your vacation.

The Similan Marine Park is located 70km west of Thailand Phang-Nga province. This group of islands is considered to be one of the top dive destinations in the world, mainly due to the clear water that surrounds the islands.

Similan was derived from the Malay work for nine “Sembilan” as the little archipelago is made up of nine islands. The islands do have local individual names, but are usually referred to by their respective numbers from North to South.

The Similan’s were designated as a National Park of Thailand in 1982 and cover an area of 128km2, which includes Koh Bon and the two rocky outcrops of Shark Fin Reef and Hin Pusa.

In 1998 an extra 12km2 of area was added when Koh Tachai was added to the park, which is now a total area of 140km2, of which only 15km2 is land.

Most of the islands are uninhabited with the exception of Islands 4, 8 and koh Tachai, which have national park offices located on them.

With the nine islands you get a wide variety of experiences, activities and stunning views, there are white sand beaches and massive boulder formations.

Underwater there are amazing coral gardens and diverse marine life ideal for all divers.

The topography differs between the eastern and western sides of the islands. The east side consists of sandy bottoms with wide and colourful soft and hard coral fields that slope down to 40m in some areas. They have gentle current and make for easy diving.

The west side is characterized by large, stacked granite boulder formations which create tunnels and archways with impressive scenery. Currents here can be unpredictable which can make the diving more challenging for beginner divers. But this side is exposed to the open sea and provides good opportunities to spot big pelagic life.

Island 1               Koh Hu-Yong

The second largest island lies 8km south of island 4, it has the largest white sand beach of the Similan National Park which is located on the north side of the island. The beach is a protected area and has a Turtle hatchery, you need special permission from the forestry department to enter this island.

Island 2 and 3     Koh Pa-Yang and Koh Pa-Yan

These two islands are also protected, their topography is granite boulders with mountains and cliffs, no beaches. At resent all the first 3 islands are closed to diving in an effort to preserve the underwater environment. The most southern dive sites are the rocky outcrop of Shark Fin Reef and the submerged site of Boulder City.

Island 4               Koh Miang

The island has a marine park office, camping, small bungalows and a fresh water supply. There are 2 beaches, Haad-Yai or Princess beach on the north and Haad-Lek or Honeymoon beach to the East. There is a trail that runs between the two through the forest. Also on the island is a view point where once you reach the top has a spectacular view of the south islands of the Similans, the trek to get there is a little energetic though.

Islands 4 and 5   Koh Ha and Koh Hok

These two islands are located to the East of Island 4 and are the smallest in the group. The landscape underwater is spectacular with both fringing reef and boulder formations.

Island 7               Koh Pa-Yu

The island has a combination of granite formations and sand beaches. The East side of the island is now closed to diving, but the north and west sides offer rocky pinnacles as dive sites which are covered in soft corals. Again these sites are open to the ocean so currents can be encountered along with the bigger pelagic life.

Hin Pusa

Is located between islands 7 and 8 and is a group of boulders known as “Elephant Head Rock” as the shape resembles the head of an elephant. The site is recommended for experienced divers due to the depth and current.

Island 8               Koh Similan

Is the highest and largest of the islands and has a marine park office and camping in the North of the island at Donald Duck Bay. It is also where the famous Sail Rock is located which is a symbol of Similan. The view from the Rock shows the North part of the Similans. There is no diving on the west or East side of the island, leaving only the North area available.

Island 9               Koh Ba-Ngu

The island has no beach, but is a favorite with divers due to the scenery underwater, it has a mix of coral reef and rocky outcrops.

Koh Bon

The island is North east of Similans, with no sand beaches it is a limestone island with an unusual “hole” which traverses the island on the west side caused by sea erosion. The most popular dive is the ridge where a cleaning station for Manta Rays can be found.

Koh Tachai

This is most Northern part of the Similan Marine Park.  The island has a beautiful white powder beach where the park office is located. With many dive sites including a plateau to the south it is a popular dive destination.

Richelieu Rock

Although not part of the Similan marine park this is often dived on the same liveaboard trips. It is actually part of the Surin Marine Park and is located between the mainland and Surin islands. It is a submerged pinnacle know for it colourful soft coral and rich diversity of life, which can include the smallest creatures such as ghost pipe fish and sea horses to the largest of whale sharks and Manta rays.