All divers interested in critters sooner or later will get interested in crustaceans. Some of the crustaceans are considered “must see” items, such as harlequin shrimp, tiger shrimp, several of the extremely small shrimp recently found here in Lembeh, emperor shrimp and a host of other shrimp. The keyword here is shrimp. Crabs on the other hand seldom elicit the same interest from divers. However, many crabs have at least as interesting life styles as shrimp, and many are also colorful and attractive, such as the amazing xeno crabs.
As those of you that have read my earlier posts might already understand, one of the aspects I find the most interesting when diving is the close symbiotic relationship between many marine animals, where one animal provides another animal with living quarters. Most crabs are free living and do not show symbiotic relationships to other animals. In contrast, here in Lembeh some really fascinating examples of symbiosis between crabs and other animals can be studied.
First of all, unknown to me until my last visit, there is a crab that quite violently excavates a hole into a soft coral and then lives there. It doesn´t seem to matter much what kind of a soft coral it is. This crab is extraordinarily hard to find, as it most of the time is totally buried into the coral. It comes in a couple of color varieties, which seems to some extent be related to which host they inhabit. This of course indicates that the crab sometimes will be outside its hole and walking around on the coral, using the color to blend in, but despite looking a lot for the crab I have never found it outside its lair.
The second crab on my list does a similar, but less violent, excavation into the rope sponges littering the sea floor in dive sites such as TK. This crab does not disappear into the sponge but at least during daytime it clings to the sponge, fitting into the excavation it has dug so tightly that ii is nearly indistinguishable from the sponge.
Third on my list, and a crab that I always look for but very rarely find, is the Xenia crab (not to be confused with the Xeno crab). This crab lives its life in between the polyps of some of the species of the pulsating Xenias soft corals.
Fourth are the swimming crabs living their whole life on a sea cucumber. These crabs are very flat, and have hooks on their legs. They use these hooks to attach their legs to the skin of the sea cucumber, and with the help of their claws they are able to pull the skin of the sea cucumber partly over them selves, thus being very hard to find for a predator. When they get tired of life on the outside of the sea cucumber, they actually hide themselves inside the ass of the host. Next time you see a sea cucumber, take a look up its butt. There just might be a crab looking out on you from the inside!
Fifth, and probably the most beautiful of the symbiotic crabs, are the soft coral crabs, or candy crabs as they are known as. These tiny crabs have small hooks on their exoskeleton where pieces of their host Dendronephtyid soft coral will be attached. The crab will also color match itself to the coral, so finding those crabs are best left to an experienced guide.
Finally, and maybe in many ways the weirdest and most special of the crabs here in Lembeh, are the Xeno crabs. These crabs live their whole life on a single wire coral, where they attach polyps from the wire coral to their exoskeleton, thus decreasing the risk that any fish will pick them of the wire coral.
Interestingly enough, very little is known about the details of any of the symbiotic relationships I have described here. Without doubt there is a career for a PhD-student interested in cool crab life styles waiting to be done. It is quite evident that some of the crabs incur a cost for their hosts, but it could also be that the hosts in some way has a benefit from its lodger. The quantification of costs and benefits for those relationships is probably quite hard to do, but wouldn’t it be the dream job of all!
Being an animal is being filled with protein and fat! That is probably the scariest fact small animals have to face. Protein and fat is on the whole extremely uncommon in nature. Compared to the ubiquitous carbohydrates, which plants just require some sun and some fancy chemistry to create, protein and fat is really hard to come by. Carbohydrates are also readily available to any one interested (if you don’t believe me, take a look out of your window and you will se all the green stuff we call plants, all consisting mainly of carbohydrates). The flip side of the availability of carbohydrates is that they are terribly hard to digest, and once digested, rarely in themselves meets the dietary requirements of higher animals. Protein and fat, on the other hand, is easily digested, and, once digested, more or less meets all requirements animals have for different substances to build parts of their body as well as fuel the whole system. As an inevitable consequence, protein and fat will be very rare, and once in place, will be protected by it´s owner a lot, as death is the most likely effect of loosing substantial amounts of a protein and fat investment.
The inequality between the availability and quality of different food substances is one of the major drivers of evolution. After all, animals, consisting of sought after ingredients, that get eaten will by definition have lost out in the evolutionary game, from which there is no second chance. Obviously this will put great pressure on small, slow, easily devoured prey to do something about the risk they face. Enter one of the most painful animals I have ever met, the fire urchin!
Fire urchins are essentially slow, ball shaped meals of protein and fat in a package that is easy to catch. Obviously, evolution had to do something about this, or fire urchins would have been extinct a couple of minutes after they evolved. Fire urchins did not get their name in a random draw of cool names for urchins. As everyone that have had contact with them know, a sting will lead to a burning sensation, that will continue for quite some time. There is no doubt that getting stung will be a stern warning to never ever touch anything remotely similar to a fire urchin again. Fire urchins have venomous tips on their many spines, and the spines are quite brittle, breaking of when embedded in a clumsy victim, prolonging the pain to several hours. However, unlike it´s most venomous relative, the flower urchin, stings by a fire urchin is rather highly uncomfortable more than an imminent danger.
So is this entry all about fire urchins? No, essentially it is all leading up to some the animals enjoying the defenses of the fire urchins. A number of crustaceans live all their adult life on fire urchins. First of all, and in many ways the most characteristic of those, are the zebra crabs. The striking dark brown and white colouring of the zebra crab and the weird and unusual shape of the carapace makes it really easy to recognize it. Zebra crabs also occur on false fire urchins and on flower urchins.
The fire urchin squat lobster on the other hand is much harder to find. It ´s colours blend in very well with those of their host. The squat lobsters also tend to perch low on the urchin and can easily be overlooked.
Probably the most sought after of the crustaceans living on fire urchins are the Coleman shrimp. Coleman shrimp will almost always be found in pairs. They clear the spines from a small area high on the urchin where the pair can be found. Coleman shrimp feed on the soft tube feet and tentacles of the sea urchin, which does not seem to be severely harmed. Being very confident of the protection the shrimp gain from the venomous spines of the urchin, Coleman shrimp are excellent and very attractive subjects for photographers. Take care, though, not to get too close to the urchin, as fire urchins move pretty quickly being an urchin, which could have painful effects it you are to concentrated on getting the perfect picture of the colourful pair of shrimps!
On todays morning dive at Nudi Falls i found this cool crab. It is a very weird looking elbow crab whose colour and shape strongly remind of a skull – even though the shape is not really human … rather the one of the stereotypic Alien. So i will call it Alien Crab (i am sure it has another name). After i made sure, that this is not a dead crab or a piece of rock with a strange shape (i did the poke test and it moved …) i started to look for the eyes, but the shady areas, where a “skull” would have had the eye cavities did not contain any eyes. I finally spotted them right over the mouth – two yellowish spots under the inner borders of the “skull-eyes”. The crab was about 1-2 cm in size and i found it sitting on a small rock … after the photo session on this sponge, i placed it back on its rock.
Lembeh Strait is a Muckdiving paradise – and it has many interesting habitats to offer. Algae, Sand, Rubble, Coral, Rocks and Sponges. This week i took 3 nice photos with different animals all living on the same type of sponge – i just realized that, when going through my pictures of this week. There are many other cool critters living on those sponges, but i just thought i share these that have been taken within some days.
There is a Paaron Shrimp, that really blends in with the sponge and not only mimics its colour and shape, but also its surface pattern. Then there is a sponge mimicing Nudibranch, that is laying eggs and a carrier crab that is decorating its back with a piece of xenia coral (polyps are retracted in this picture).
Today is boxing day – so what could be a better Critter to write about than the Boxer Crab (Lybia tesselata, Pom Pom Crab or Mosaic Boxer Crab). But not only does its name fit the date. It is also a very popular Critter here in Lembeh – specially if you keep in mind that it is “just” a crab and not a Frogfish or an Octopus.
Its most distinctive feature are its “Boxing Gloves” – stinging anemones that it collects and holds on to for feeding and protection. If threatened it raises its protective anemones and waves with them like a boxer or a cheerleader (which gave the Boxer Crab also the name Pom Pom Crab). The second feature of the Boxer Crab is its attractive colour pattern of white, black and orange.
They grow to about 2 cm across from leg to leg and are specially attractive when they carry eggs: They are poppy red and held by the crab on the bottom of its carapace (see picture).
Boxer Crabs live – like many crustaceans – very cryptic: they stay hidden under rocks and coral debris. So if divers want to see Boxer Crabs, they have to CAREFULLY turn over rocks to find them. So the don’t touch anything rule has to be bent a little bit to turn broken coral bits – but it is better to leave this up to your dive guide! Usually you’ll find several of them in one area and none in another one – they have a very special preference to their habitat.
Best places to find Boxer Crabs in Lembeh: California Dreaming, Batu Merah, Angel’s Window, Yiko Yansi, Sarena Besar.
Best time to see: All year round.
Photo Tips: 100 mm Macro – good to have a buddy or dive guide to make sure the crab does not disappear in a crack while you are focussing.
It is quite amazing that even though i already work in Lembeh for several years, i can still find new things – and this is why i love this place so much. Yesterday we went to our second morning dive at Tandu Rusa to look for two little Shaggy Frogfishes and a Painted frogfish. On my way back to the boat i found this little Crab in between the rubble. It is white, thorny and has not only the shape but also the size of a pearl. A Pearl Granulate Purse Crab (Heteronucia perlata). Not really a Critter that people have on their whishlist when they come to Lembeh – but still a very beautiful Crab. And the cool thing is: The more you start searching for things that are weird and wonderful, the more new stuff you find.
This week we did a lot of housereef diving here at NAD Lembeh and found many cool things – squids, shrimps, nudibranches, Lembeh Sea Dragons, Stonefish, Spearing Mantis, Twin Spot Gobies, Double Ended Pipefish, Sponge Crabs, Baby Baracudas and much more. The day before yesterday i went for another housereef dive in the late afternoon to take some pictures and it turned out to be the wrong timing: visibility was very very bad. So i put on my Subsee +10 Diopter and started looking for Super-Macro Subjects and found these cool Coral Crabs.
At first i didn’t realize how cool they were … only after the first few shots i saw the nice colouration between the eyes and the spots on the legs. So even if the visibility was bad, i came back with pictures of something that i never photographed before.
For everyone who wants to shoot them: They are virtually everywhere on our housereef – living in the branches of staghorn coral.