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!
Well, as Lembeh must be the frogfish capital of the world, and frogfish are some of my favourite critters, I think that frogfish actually merits another blog entry. So here it is.
Frogfish are probably most known for their built in bait, an illicium or “fishing rod” that is topped with the esca, the worm- or shrimplike lure it self. The illicium and esca are formed from the foremost rays of the anterior dorsal fin, and can be moved in different directions in front of the mouth when prey comes close enough.
Frogfish belong to the family Antennariidae in the order Lophiiformes, which among others also include the supercool deep water anglerfish with lures that are shining with light. With a few exceptions, the most notable being the Sargasso frogfish, frogfish are mostly shallow water fish, living among rubble, sea weed, coral heads and other underwater structures that can aid the frogfish in hiding their outline from prey and predators.
In Lembeh strait a number of species are found. I have seen eight or nine species in Lembeh, but there are probably one or two more around.
Frogfish are notoriously hard to determine to species. Many species come in different colors, so color is at best a weak clue to what they are. Colors seem to change with background, making camouflage excellent, but on the other hand not helping very much in species determination.
A combination of habitat, body shape, and, maybe most important, characteristics of the lure can most often be used to at last narrow it down to a couple of likely names. A few, however, such as the hairy frogfish with it´s wormlike lure and the warty frogfish with it´s warty exterior are very characteristic and often easy to name. Others, such as the hispid, the painted and the giant (also called Commersons) frogfish are not to hard to determine if the lure is visible.
Then there are a number of frogfish with lures that are hard to see and quite similar markings that I find pretty hard to determine to species underwater.
And finally, Lembeh is home to at least one undescribed species, which has not been named by scientists yet.
The lure of the frogfish indicates that frogfish are specializing on fish as prey. With a few exceptions, fish is exactly what frogfish eat. When a small fish comes close to the frogfish, the lure is waved in an enticing way in front of the mouth of the frogfish. The prey fish will often be conned into believing that it is the luckiest day in its life, which most often is the last feeling the prey fish will have. When the prey comes close enough, the frogfish extends its enormous mouth, inhaling a lot of water and a small, and highly likely very surprised, fish. The mouth movement of the frogfish is so quick that scientists have problems explaining how that speed is even possible.
The teeth of frogfish are very pointed and directed backwards towards the interior of the mouth. Thus, anything caught by a frogfish will have a really hard time escaping, while the direction of the teeth will allow the frogfish to move the prey inside the mouth. Frogfish are extremely elastic, being able to swallow prey as large as themselves.
Frogfish have three ways of moving. First, like most fish, they can swim through the water column using their caudal fin. They can also use a water jet by expelling water through the small gill openings behind the pelvic fins. Finally, frogfish can more or less gallop over sandy bottoms, in a rather ungraceful running motion resembling what a cross between a sea lion, a football and a horse would look like in full speed.
So, now I am of running an ecology/photo course in the Red sea. Those of you that follow this series will probably have the next entry available in a couple of weeks.
I posted the following picture of a yellow lipped sea krait, Laticauda colubrina, on a couple of web sites after my last visit in Lembeh.
Among comments, several was so sure of the extreme danger I was subject to while taking the picture that they felt it worthwhile to actually write and advice me not to get that close to such a deadly creature, or the second most deadly snake in the world as one comment described it. That is of course very considerate, and I appreciate that to me unknown people actually worry about my well being, but in this case it is not really warranted. In my day job I sometimes handle snakes, and while I am pretty careful handling most terrestrial venomous snakes such as pit vipers, I am pretty relaxed about the underwater snakes, or at least sea kraits.
That said, most marine snakes have extremely potent venom. So am I an idiot without any consideration of danger (think James Bond meets Chuck Norris), or is there more to the risk of being close to a snake than just the potency of the venom per se?
Well, first of all, humans are extremely bad at doing rational risk evaluations. One relevant example in the context of diving is of course the risk of being killed by a shark, which is many orders of magnitude less than other risks, such as the risk of being killed in a traffic accident, we accept daily. Even toasters are on a global level far more dangerous than sharks, but I have yet to meet a person that questions my sanity when I put toast in a toaster. Not so when I give talks on marine ecology, when I show pictures with sharks, the audience more or less always are pretty certain that a miracle saved me from being torn to pieces by the shark, even if it is a picture of white tip reef shark, being below hamsters or rats on my list of dangerous creatures!
Still there is the issue of the potency of the marine snake venom? How should that enter into a rational risk evaluation? The risk of actually being hurt, or even dying, of a particular snake´s bite is the product of a number of factors. Included in those factors are the risk of meeting the snake, risk of being bitten once having met the snake, risk of the bite actually penetrating the skin, the risk of being envenomed once being penetrated by the fangs, the amount of venom being transferred once being envenomed, the potency of the venom and the size and health status of the person being bit. So how does the banded sea kraits, such as the yellow lipped krait pictured here, score on such a calculation.
The risk of meeting the yellow lipped sea krait (or chance, from my perspective) is quite high. I see them approximately every 25th dive in Southeast Asia, so if one does a fair amount of diving, one will definitely run into the snakes. The risk of being bitten once having met the snake is extraordinarily low on the other hand. The only information I have on bites by the sea kraits is that fishermen entangling the snakes from nets have sometimes been bitten. Also there is some anecdotal evidence that the snakes can be aggressive if they feel that their way to the surface is blocked (they breathe air as all other snakes). Sea kraits have rather small teeth, so given that most divers wear wet suits, a bite would rarely if ever penetrate the suit. I have no specific information on the rate of envenomation once being penetrated, but many snakes do not use their costly venom very often in defensive actions. Also, given that venom is transferred, there seems to be quite some variation in the amount injected.
The potency of the venom in general, however, is very high for sea snakes. Finally, I am big and quite healthy. So, in conclusion, for yours truly, the combined risk of being killed by a banded sea krait seems to be quite low. Of course your calculation might differ markedly, so do not take this blogg entry as anything else than an example of my very own way of accounting for risk.
It should also be emphasised that there are many other sea snakes that scores much higher on the aggressiveness and tooth size factor above. At least one of those looks very much as the banded krait, so mistakes in identification can be made even by very experienced herpetologists. So even if the kraits are very docile, it might overall be good advice for most people to be a little bit careful around sea snakes.
We’ve got lots of Critters around the Lembeh strait at the moment, but Blue Rings are still present in good numbers, and to be honest they are one of my favourites. I went on and afternoon and night dive to try a new camera, and he also came back with some video too. Here you go:
During the dive I saw a few other things as well, but as a good lesson to all you photographers out there, keep your gear organised and take care of it after your last use! There were a few technical difficulties with my strobes so not so many photos 😉
I was diving with Johan, who is back with us again after we found him working in a textile shop of all places (shouldn’t have left to another operator at the start of the year, silly boy!). Stenley is private guiding, as is Paulus. and then Joni, Indra, Abner and Marnes are also busy. We have a new guy Steven, more on him later.
On the night dive i was struggling with my new setup so stayed out of the way on the Sand (ie i was pretty much lost). Johan found some harlequins that Joni had found earlier in the day and also a Bumblebee shrimp which im pretty upset to miss!
Hopefully i’ll be in the water again soon, until then!
Today i was lucky enough to find this little critter: Gnathophyllides mineri – the Urchin Bumblebee Shrimp. It grows to about 1 cm in size and lives on the Cake Urchin (Tripneustes gratilla). The cake urchin has spines and sticky arms – which collect rocks, leaves and pieces of plastic or whatever else is laying on the seafloor. So to find these shrimp you first have to take the decoration of the sea urchin. And then, if you are lucky, you can find the Urchin Bumblebee Shrimp holding on to one of the spines of the urchin. Compared to other Urchin shrimps, the Gnathophyllides mineri is not longer (rather the opposite), but thicker.
Rating Critters is a very subjective thing, but i have to say, that the Bornella anguilla is for me something like the “Queen of Nudibranchs”. For her cool shape, her nice colours and the absolut fantastic swimming behaviour – she moves her tail like an eel (therefor the name) and swims at a speed you would never think a nudibranch is be able to reach. So i was very delighted to find one on today’s morning dive … i screamed into my regulator and watched it for about 45 minutes. Whenever it started to get annoyed by my flashes it just started swimming off into another direction. A unbelievable dive. But even more unbelievable was, that – after not having seeing a Bornella for the whole year – i found another one on the second dive 😉
On todays morning dives we had several highlights such as Banded Tozeuma Shrimps, Bumblebee Shrimp and other rare Critters – but the funniest thing were these two painted frogfish hiding in a purple sponge. They where in the famous rubble patch at TK1. First there was one of them on each side of the sponge – so our guest could watch & shoot them from both sides. But then the smaller one crawled under the sponge towards the bigger one. From the side of the bigger frogfish you could then see the smaller one peek around the “Benkile” (Sangihe language for “Bum”) of the bigger one. Everyone started laughing immediately and it was still a big topic afterwards on the boat 😉