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Fluorescence and bioluminescence

When I arrived in Lembeh this time it was just after Christmas. However, I was up for another Christmas treat. Simon here from NAD had ordered a bunch of cool stuff from Nightsea, strobe filters, filters for the lens and a cool pair of yellow spectacles, which waited for me here.  I have now tried this system during my stay and will in this blog give a short overview over what I learned from shooting it. But first of all I want to give a brief explanation over what fluorescence is, and why we can find it in nature. BTW, the complete system is available for rent here in NAD if you wish to try it out.

Fluorescent hard coral

Fluorescent hard coral

First of all, fluorescence is often confused with bio-luminescence. Bio-luminescence is found in more and more animals, and in a number of mushrooms as well. Well-known examples are those of plankton giving of light when disturbed, deep-water organisms with light organs, mushrooms glowing in the forests, fire flies and for northern areas glowworms. Bio-luminescence is the emitting of light involving a chemical reaction. Very generally, the light emitting substance is a protein called luciferin, which emits light through a chemical reaction catalyzed and oxidized by an enzyme, called luciferase. Thus, a chemical provides the energy fueling bio-luminescence, using oxygen in the process.

Bioluminescing mushrooms

Bio-luminescing mushrooms

Fluorescence, in contrast, is the emission of light where energy from one (or on rare occasions two) photon excites an electron into a higher energy orbital. After a short time, the electron will return to its former level, emitting the excess energy as light of another wavelength. No oxygen will be used in this process, as the light emittance is fuelled by the energy in the photon. Many different subjects in nature fluoresce. Despite that, we can seldom see the fluorescence, as the emitted light level is low, or in wavelengths we cannot detect. One notable exception is the red or orange anemones that we sometimes can se in much deeper water than red and orange colors from sunlight penetrate water. Despite being fairly poorly understood on a biological level, fluorescence is used in many applications, from mineralogy, oil detection, microbiology and forensic work.

Fluorescent hard coral

Fluorescent hard coral

So why do things bio-luminesce or fluoresce? Bio-luminescence in marine systems is used for at least three widely different purposes. Most of the deep-sea bio-luminescence seems to be used in order to attract prey.  Second, a number of fish living in the zone deep enough for a little light to get through, use bio-luminescence to counter shade the ventral side of them, so shading against the faint surface light can not be used by predators to find prey. Third, and maybe most speculative, it is thought that small crustaceans that bio-luminesce do so to deter small predators. Why would small predators be afraid of light? Well, if a small more or less translucent predator eats a bio-luminescing crustacean, the small predator will light up and attract the next step upwards in the food chain, increasing small predators risk risk of being killed them selves.

Fluorescent lizardfish

Fluorescent lizard fish

What is the point of fluorescence in marine systems? For a number of shallow water cnidarians, mainly the ones using zooxanthellae for their energy input, fluorescence has been suggested to be a way to control excess levels of sun exposure, limiting the damaging effects of uv-light.

Fluorescent hard coral arm

Fluorescent hard coral

Both proteins in the coral itself as well as chlorophyll in the zooxanthellae associated with the coral may fluoresce. The available evidence, however, does not really support this theory.

Fluorescent hermitcrab

Fluorescent hermit crab

A number of other animals fluoresce. Some crustaceans, such as the anemone hermit crab fluoresce. Also some bristle-worms, fish and cephalopods fluoresce. There seems to be no reason for these animals to fluoresce, so much fluorescence simply seems to be a side effect of other processes in living creatures. Whatever the cause of fluorescence it really is quite magical to see the different sources of fluorescence light up leaving the rest of the surroundings pitch black when diving. Try it out, it is an experience I am sure you will not forget!

Fluorescent anemone

Fluorescent anemone

What did I then learn from shooting this system? A to me very surprising fact is that people are not wildly enthusiastic over the results! That might of course be my results that are lacking. Furthermore, the best results, bleak as that may be, are when there are more than one fluorescent color in the picture. Third, and maybe most important is that it is a lot of fun to try it! I look very much forward to try it on coral reef sites such as in the Red sea as well as on land in rain forests. In a month or so I might get back to you with results from that.

Octopus camouflage – how does it work?

Meat, being high quality food, is a scarce resource in nature. The available amount of meat for any consumer is many orders of magnitude less than the amount of vegetation that is available. If you don´t believe me, just take a look out the nearest window and do a quick calculation over how much animal weight and how much tree or other plant weight you see out there. With notable exceptions such as my home area (where all you will see right now is a lot, and I mean a lot! of snow) and a camel market in the middle of a desert, meat will be extremely scarce and often not even around. Where I sit right now I see probably hundreds to thousands of tons of trees. I see one (very annoying) fly representing available meat.

_MG_1896

Octopus are essentially soft globs of meat living in a world where meat in general is extraordinarily scarce and needed. Octopus will face a never-ending struggle to keep their meat to themselves, and not let anyone else use it for food. It is no wonder that octopus have a number of defenses to actually accomplish monopolizing their meat. Once being seen by a predator, octopus have several defenses. First of all they will try to escape, either by swimming quickly away from the predator or by getting into a small crevice or hole that the predator cannot penetrate. Second they can let go of an ink cloud in order to confound the predator, or, best-case scenario, have the predator attack the ink cloud as the octopus escapes. Third, some octopus can let go of limbs when threatened much like lizards loosing their tail, leaving the predator with a meal but keeping most of the octopus unharmed. Fourth, some octopus can use warning coloration advertising a highly venomous bite when threatened.

Young algae octopus a couple of seconds later

Young algae octopus a couple of seconds later

However, octopus go a long way to keep from having to use their active defenses. they do so by blending in in the environment, that is being camouflaged, in a way that is highly efficient and also very adaptive. One problem with using camouflage in general is that camouflage is site specific. Once out of the area the camouflage pattern is adapted for, the camouflage stops working. A Swedish soldier in his very efficient camouflage for Swedish winter conditions would, if transferred to tropical rainforest, stand out as a huge boil on the forehead of Naomi Cambell! As octopus are highly active, they have to be able to adapt their camouflage to changing environments, which they solve in a way very few other animals do.

Young algae octopus a couple more seconds later

Young algae octopus a couple more seconds later

Texture and color are the two major components of an environment that a camouflaged animal must handle. Octopus handle texture in an impressive way. They can change from looking like a smooth coral to a piece of broken rubble in a matter of seconds. They do this by using muscles in their outer layer of skin, using their very acute eyesight to map an exact picture of the surrounding environment in order to match the texture of the environment with that of the outer surface of the octopus. Some octopus can go from smooth to looking like a hairy piece of decaying sea floor in mere seconds.

Young algae octopus yet some seconds later

Young algae octopus yet some seconds later

Octopus are even more impressive when handling colour matching of the environment. First of all, their sense of sight is excellent, enabling the octopus to know what they have to match. Second, the outer layer of octopus skin has a number of different specialized skin cells, which can change the colour, brightness and reflectiveness of the octopus. These cells are under control of the nervous system of the octopus, enabling extremely fast responses to outer stimuli.

In this way, octopus and many of their allies can live their life being highly successful despite inhabiting a very dangerous environment.

Sex change – without surgery!

Few humans have gone through a sex change. Changing sex in humans is a major effort, involving long-term counselling, surgery and medical treatment. Very few other terrestrial vertebrates, if any, change sex during their life cycle. In contrast, in the underwater world, sex change is very common. And this sex change does not involve any surgery, any hospital stay and any medical treatment. How do marine animals change sex so easily, and why do they change sex in the first hand would be reasonable questions to ask.

First of all, in many animals sex is not determined by chromosomal factors. Thus in many reptiles such as sea turtles the temperature during egg development determines what sex the offspring will have.

The sex of hawksbill sea turtles is determined by the temperature during egg development

The sex of hawksbill sea turtles is determined by the temperature during egg development

In marine systems, non-chromosomal sex determination is mostly a consequence of social rank or, in some cases size, which in itself may be correlated to social rank. Thus most wrasses, basletts and groupers start out as females while large individuals turn into males, while anemone fish start out as males, and, typically, only the largest individual in an anemone changes to being female. In both sex-changing groups, all individuals have both testis and ovaries, but at the most one of those are active at a given time.

This subdominant spine cheek anemone fish is still male, and will continue as male until its larger partner dies.

This subdominant spine cheek anemone fish is still male, and will continue as male until its larger partner dies.

Why change sex then. The sex change from female to male is more or less exclusively seen in species where males keep harems or gather in communal mating areas and fight for dominance over females. In such species, it is utterly pointless (with one exception that I get back to in a later blog) to be a small male. As small males do not get any matings, and few individuals reach sized large enough to dominate other males, it makes a lot of sense to start out life as female to ensure participation in the reproduction. Only if an individual for some reason has a better than average life will it reach sizes large enough to change sexes. Such a sex change, when large, will give access to many females and will be very successful in terms of offspring production.

Fairy baslett that reached a size and a social status making it possible to change from female to male

Fairy baslett that reached a size and a social status making it possible to change from female to male

The sex change from male to female does, to my knowledge, only occur in species with strict monogamy. In fish, as in most animals, large individuals will have more excess energy to put into sex cells. As the miniscule sperm cells are cheap to produce, and eggs are many times larger and much more energetically expensive to make, it makes a lot of sense for a monogamous pair to let the larger individual be a female and the smaller a male. Obvious examples of this are the anemone fish, where typically only one individual is a female and at the same time the largest individual in the anemone, while the rest of the resident fish are males. Only when the female dies will the former second largest change sex and become a female.

Large female and small male false clown anemone fish

Large female and small male false clown anemone fish

Finally, some species have no sex determination, but lives life as both sexes. Such animals are called hermaphrodites. A well-known example from land is the common earthworm. The classic example from marine systems is the nudibranchs, where every individual is both male and female. When nudibranchs mate, both partners transfer sperm and both have their eggs fertilized.

Hermaphroditic nudibranchs transferring sperm to each other

Hermaphroditic nudibranchs transferring sperm to each other

Why good things can be bad.

In every documentary I have seen and book I have read about Lembeh, it is stated that the waters of Lembeh are exceptionally productive partly due to the currents that bring nutritious water through Lembeh strait regularly, partly due the black lava sand more or less defining Lembeh that leaks nutrients into the water. It is easy to envision that such an environment with loads of biological production would be very nice to live in for the creatures inhabiting the strait.

Wire coral gobies, feeding on plantkon that is swept through the strait by currents

Wire coral gobies, feeding on plantkon that is swept through the strait by currents

Surprisingly enough, evolution seems to have been working overtime  in Lembeh, partly shaping the foraging skills of the animals here, but even more obviously perfecting their skills of evading predators. Why is the pressure on prey animals tougher here in the seemingly benign waters of the strait than in other less productive environments?

Lizard fish with the elongated fin rays of a former sand diver in Lembeh

Lizard fish with the elongated fin rays of a former sand diver

Mathematical models of predator and prey populations give us the answer.  For every population there will be a maximum number of individuals that the environment can provide for. This number is called the carrying capacity of a population. If one increases the carrying capacity for a prey population, the prey population will increase the number of offspring that is produced. However, if there are predators around, predators will take advantage of the increase in the reproduction of the prey population, and the predators will increase their population size, leaving the prey at a low but very productive density. Thus every prey individual alive will be faced with a much higher risk of being killed by a predator than in a less productive environment, setting the scene for evolution to try out more and more bizarre and elaborate ways for the prey to survive the onslaught of the predators. Obviously there will be competition between prey on being safer than anyone else which will feed evolution with a drive to use whatever genetic variance giving anyone an advantage over conspecifics or individuals of other species.

Soft coral crab with an almost unbelievable camouflage on its soft coral host in Lembeh

Soft coral crab with an almost unbelievable camouflage on its soft coral host

Why stay here then? Is there really anything good at all living in productive environments then given that you as prey face a never-ending threat from predators? Well, it turns out that the alternative is just as bad. In prey populations that are controlled by food availability rather than predators, prey will reach densities where the food resources are heavily used and most everyone is on the verge of starving to death. The sad truth about being an animal in nature is that, with very few exceptions, you either live a life where every day is a constant struggle to make ends meet, feeding on the very scarce resources not already being utilized by someone else, or you live in constant fear of being torn in pieces by something bigger and fiercer than you are! Sucks, doesn´t it!

Shrimp seeking refuge in anemone

Shrimp seeking refuge in anemone

Luckily for me, as I really enjoy exquisite examples of prey adaptations to evade predators, many prey animals in Lembeh will be on the “lots of food around, but holy smoke it is scary here”  end of the scale. Every dive here will give even a first time diver in the area many examples of what living in such an environment does to prey animals. Also, as a nice side effect, the strait is littered with predators, which we will get back to in a later blog.

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