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Posts Tagged ‘commensalism’

Commensal Bryaninops gobies

For some reason certain animals are on the “cool” list that everyone wants to see and photograph and others are placed on the “not so cool” list and get ignored by most divers and photographers. Scarcity and cuteness seems to be two important factors determining the popularity of an animal. Despite not really ticking either the scarce or the cute box, due to their interesting life style the gobies of the genus Bryaninops have a long time been on my favourite list, and I more or less never pass a wire coral without checking it out for a goby or two.

Goby on wire coral

Few other divers seem to find them very interesting, so I mostly get to have the wire corals and the gobies more or less for myself. This time in Lembeh, Paulus, my excellent guide, knowing about my interest in parasites, in the beginning of my stay showed me a couple of Bryaninops with the characteristic copepod parasites that many of these gobies carry, with the gobies living on other animals that I did not normally associate the gobies with.

Goby with a heavy load of copepod parasites on sponge

During the weeks I stayed, I found gobies on a lot of different sedentary animals, more or less always colour matching the animal the goby associate with.

Goby on soft coral

The Bryaninops gobies are found as commensals on different coral groups as well as sponges, sea squirts, sea stars and even on Halimeda algae.

Goby on Halimeda algae

The pelvic fins of the gobies are more or less adapted to be a disc capable of sucking the goby to its host during currents.

Goby on sea star

They never move far from their host, and can often be seen moving quickly around on the surface of the host, feeding on small zooplankton drifting by in the current.

Goby on tube sponge

Being commensal means that the interaction between two animals are neutral for one of the, in this case the host. The other partner, in this case the goby, of the interaction receives some benefit of being in a commensal relationship. There is no doubt that commensal gobies receive benefits by living on their hosts. The gobies settle as small larvae on their hosts and change colour to match the host during ontogeny.

Goby on soft coral

Obviously such a colour match leads to some kind of concealment for the goby which otherwise has no protection against predators. When detected the gobies also use their hosts as hiding place, moving quickly to the other side of the host.

It is, however, not really clear that the hosts are unaffected by the interaction. At least one of the species, the common and wide spread wire coral goby Bryaninops yongei, lays their eggs on a patch of the wire coral where the gobies have cleared the coral from living polyps. Thus, at least in this case, it is unlikely that the coral is not negatively affected, and the relationship then should rather be classified as a parasitic interaction. On the other hand the goby might protect the coral from coralivores, thus mitigating the cost of the lost polyps somewhat.

Goby tending eggs (the black spots beside the goby) on soft coral

Many new species of those gobies are now being recorded by goby experts from different parts of the world. The diversity of commensal gobies in Lembeh is probably quite high judging by the number of different gobies of slightly different shapes I saw on a number of different hosts during my two week stay, and I would not be surprised if there was one or two undescribed species among them. It will require a goby specialist to really understand what species are present here in Lembeh, so at least I, not that much into goby taxonomy, will have to enjoy the active and often quite beautiful fish without really knowing what specific species it is. On the other hand, with many other groups of high diversity in Lembeh, that happens quite often here, so one just have to get used to it!

Probabably Bryaninops yongei

Symbiosis and commensalism

On my day job part of my time is used to teach ecology for undergraduates in biology. Maybe not such a surprise, many of the best examples of interactions between species that I use in my teaching come from marine ecosystems. This is especially true when dealing with symbiosis theory.

Symbiosis means “together living”, and describes animals or plants living together with a tight relationship with each other. It is reserved for animals or plants of different species, but the exact definition is under some discussion. I will use it in its general sense, including obligate (the different species need each other) and facultative (at least one species affects the other species, but the interaction is not essential for either). Used in this sense, symbiosis includes commensalism, mutualism and parasitism. Today´s entry will be on the least exciting of the three, commensalistic interactions.

Emperor shrimp feed on the bypassing substrate and do not harm their sea cucumber host, gaining protection by living on the unpalatable sea cucumber.

Commensalism describes the relationship between two organisms where one organism benefits without affecting the other. Many such examples are found in marine environments. One likely example is the small porcelain crabs residing on soft corals. The porcelain crabs get a perch to sit on and protection among the arms of the soft coral, while the soft coral is unaffected.

Porcelain crab on Dendronephtya soft coral

Another example would be the gobies that live on many other animals in the sea, often changing colour to closely resembling their host. It is likely that the host in most circumstances are rather unaffected by the gobies seeking shelter.

Commensal goby

Commensal goby

The gobies and the porcelain crabs exemplify commensalistic interactions where one species lives on the other species, which is a true symbiosis. They are probably also more or less obligate, as predators quickly would kill both gobies and porcelain crabs without the shelter of the hosts . Commensalism doesn´t have to include symbiosis. This was clear when we were in a slight current on Hairball, watching a box crab rip a smaller crab to pieces. Box crabs are messy feeders, so a lot of the bits and pieces of the crab were swept down current out of reach of the box crab. However, it was not just lost, as a couple of big flounders quickly placed themselves behind the crab and ate the morsels coming with the current, benefitting the flounders without harming the box crab.

Box crab with waiting flounder

Finally, one part of the pair can already be dead when the commensalistic interaction takes place. Hermit crabs, having to find shelter for their soft anterior parts, need empty shells in order to hide the unprotected part of their body. Different snails provide these shell after the snails are dead, which means that the hermit crabs are benefitted by the presence of snails, while snails are unaffected by hermit crabs.

Hermit crabs fighting over shells

Fire urchins and their inhabitants

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 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.

Fire urchin spines

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.

Zebra crab

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.

Fire urchin squat lobster

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!

Coleman shrimp

Creature Feature: Emperor Shrimp

The Emperor Shrimp (Periclimenes imperator) is a commensal shrimp and a member of the Palaemonidae. Sounds strange, but looks really beautiful: Characteristic is its attractive red, white and purple colouration and its commensalism. The Emperor Shrimp can be found on several species of Sea Cucumbers and Nudibranchs (for example Risbecia tryoni, Cerathosomas, Spanish Dancers, Melibes and others). Usually they pick relatively big nudibranchs. Emperor Shrimps can be up to 2,5 cm in size and always stay on their host.

Best places to find Emperor Shrimps in Lembeh: Basicly any Divesite with sandy bottoms (for shrimps on sea cucumbers and Nudibranchs) or also rubble (for shrimps on Nudibranchs).

Best lens to shoot Emperor Shrimp: Any Macro Lens from 60mm (shrimp or shrimp with background) to 100mm (shrimp only) – or even diopters & teleconverters (for super close ups).