When I visited Lembeh in September/October there were flamboyant cuttlefish around in numbers that I have never seen before. On more or less every dive, we saw one or more flamboyants. Blue ring octopus were not as common, but still there was hardly a day when we didn´t see them. This is very much in contrast to the situation now, at least considering adult octopus and cuttlefish. We have seen some, but while still here, they are not nearly close to the densities experienced in September/October. Where did they all go?
Actually, cephalopods, the group that octopus and cuttlefish belong to are quite short-lived. Not only that, they only reproduce once and then die! This pattern of reproduction, where an individual grows for almost all its life, mates and then die, are called semelparity.
Other animals continue living after reproduction and produce other litters some time after. Such a strategy, with multiple reproductive events after the onset of maturity, is called iteroparity.
The answer is that all life histories, that is the allocation of energy over time, consist of trade offs. Food is seldom unlimited, and if it where, time or developmental rate would limit the options available for an animal. The first ting that needs to be realized is that reproduction, having offspring, is expensive. Experiments have time after time verified that reproducing individuals of a lot of different species die earlier than non-reproducing individuals. That is the first trade off, choosing between a long life or offspring. And having no offspring is a fundamental screw up in nature, as your genes get lost for the future, so choosing long life rather than reproduction is not an option for animals looking for success in life.
The second trade off is that costs are related to the effort that is put into reproduction. Everything else equal, the more offspring that is produced, the less survival or future growth rate an individual will experience.
The third important trade off is that an individual need to keep significant amounts of energy reserves in order to survive over long time in the future. Up to around 90% of the energy budget might have to be allocated to future survival if that is the goal. Thus, an individual can produce a vastly higher amount of offspring in one reproductive event if no energy is saved for future survival. Thus, if an individual irrespective of reproduction faces quite high mortality rates, it could obviously be advantageous to “go all in”, reproduce with all the effort you can, and save nothing for a very uncertain future. And that is exactly what cephalopods do, invest all they got in one single “big bang” litter instead of saving themselves for another day.
The cool effect of that here in Lembeh is that there now are quite a number of minute, fully colored flamboyants around. The young flamboyants are really cool, brightly colored and have a lot of attitude.
Prey are well adapted to evade predators, and predators are correspondingly well adapted to catch prey. For most of us it is pretty reasonable to accept that such adaptation happens by natural selection, leading to long-term evolution of animals, making them better to either catch prey or evade predators, whatever end of the food chain you happen to be on. Thus natural selection affects traits such as foraging efficiency or anti-predator behaviours that lead to longer lives, quicker growth rates and, both directly and indirectly, higher reproduction rates. Most of my earlier blogs have more or less built on the assumption of natural selection affecting adaptations of animals.
There is another kind of selection, sexual selection, that is a little bit harder to understand. Sexual selection is the process where traits that directly affect the likelihood of securing a mate is changed over time, leading to the evolution of traits that sometimes seem to act contrary to natural selection in that sexually selected traits rather decrease life expectancy and growth rates. There are many examples of traits governed by sexual selection on land. Bird song, brightly colored males in many birds and lizards, antlers on deer and males adapted for fighting other males for access to females are examples that we all can relate to. It is thought that sexual selection in terrestrial systems are well as important as natural selection in shaping many aspects of populations and also a major force in driving speciation.
Are there examples of sexual selection in marine animals? Well, such examples are without doubt not as obvious as on land. The most obvious is dimorphism between sexes, that is that the two sexes differ in size. Many fishes, such as many species of wrasses and groupers, have males that are much larger than females. Males of such species secure their mating by either fighting with other males for mating rights or showing of to females in order to make the female choose the performer. This is certainly a sexually selected character. Some crabs seem to have very large males as compared to females, and that could be related to mating coinciding with female molting. Males can detect this molting some days before it actually happens, and try to protect “their” female from other males. Thus large males will be able to fend of smaller males, thus monopolizing pre-molting females.
When females are lager than males, it is very seldom a sexually selected character. In most marine monogamous species with a size difference between the sexes, the female will be the larger. This is not due to the female competing for mates, as the pair is monogamous, but rather that size affects egg production positively much more than size affects sperm production. Thus, in many cases, it makes sense for a monogamous pair to consist of a large female and a small male.
Another possible example of a sexually selected trait could be the extraordinarily long “nose” that some xeno crabs have. I have no idea if this is correct, or even if “nose” length of xeno crabs are related to sex, but is could be.
Otherwise, I find it surprisingly rare with clear sexually selected traits in marine animals. It could be related to the mating methods many marine animals use, where sex cells are released into the water and is more or less anonymously left by themselves to find a suitable cell to fuse with. This method of mating somewhat precludes mate choice or mate competition, thus making the force of sexual selection very weak compared to that of natural selection. I will get back to mating methods on reefs and reef-near areas in a later blog.
Whenever you visit the same dive area several times, some dive sites seem to consistently deliver more than others, and, correspondingly, some less than you would wish. Here in Lembeh my favorites are the Aer Bajo sites and Hairball, where many uneventful starts of dives have been turned around to glorious experiences. The different TK sites on the other hand have for some reason not really caught my interest that much, despite that if I really think hard I actually have seen some really neat animals there. My expectations for yesterday´s morning dives were less than stellar, as the first dive was in Nudi retreat (coral dive, why??) and TK 3. Nudi retreat delivered a couple of cool Xeno crabs as well as a beautiful soft coral crab, which was fine, and perfectly OK. Happy with that. TK on the other hand, in the words of a well known dive resort owner, just kicked the balls out of any kind of negative feeling about that site.
Paulus, my dive guide for the day, first found a weird flat crab buried into the rope sponges that are so common in TK (pictures coming in a later blog). Just after that a great Janolus nudibranch posed nicely,
followed by a number of “commoner” nudis, and a beautifully colored devilfish, showing of its pectoral fins.
A couple of minutes later in a small patch of rope sponges and debris, two beautiful frogfish and one common sea horse were found.
That was just the start. After that, less than 5 meters apart, a flamboyant cuttlefish was hunting,
a hairy frogfish came walking by, and, finally,
a coconut octopus did his (or her) amazing show with a couple of beautiful shells, hiding, digging, watching me and walking around with the shells.
So, TK, I am officially sorry for my negative attitude. TK after this climbs significant steps on my favorite dive site list. Simultaneously, my wow for this trip of concentrating the photo shooting to a few of the best subjects on each dive, was blown to pieces. But what can you do, this was like letting kids loose in a candy store, Danes loose in a beer pub, Djengis Khan loose in a village of pacifists or Simon loose in a camera store!
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.
Lembeh is a very good place for seahorse hunting. Not only does Lembeh have several “proper” seahorses, which is medium-sized fish, looking like a seahorse should look like but also at least three pygmy seahorses, a number of pipefish and the almost iconic Lembeh sea dragon as well as their relatives, ornate ghost pipefish and the sea moths.
The coolest and maybe best known feature of the seahorses and pipefish is that the males takes care of the eggs. Why is this such a big deal? Well, as we define the two sexes, males produce tiny mobile sex cells called sperm numbering gazillions, while females make a few energetically expensive, immobile sex cells called eggs. Thus, males can get to father a lot of offspring by getting their sperm placed in contact with eggs, while females are limited to much fewer offspring. Of course the mean number of offspring for the two sexes will be the same, indicating that some males have great success, and others none, while females have much less variance in their number of offspring than males. Also, in most cases, as females have a large investment in each mating, females may often be more motivated to invest in offspring.
Not so among seahorses and pipefish. Seahorse and pipefish males, for some reason, are the caretakers of the eggs during development. In seahorses eggs are transferred to a pouch on the males abdomen and the male there fertilizes the eggs. Eggs are kept in the pouch until they hatch and the small seahorses, that look like miniature versions of the adults, are expelled by the male by contractions of the pouch. Pipefish on the other hand, do not have a pouch and “glue” their eggs to either their abdomen or to the base of the tail. As most seahorses and pipefish are monogamous, it does make sense for the pair to let the male take care of the eggs and juveniles, as the female then can invest all surplus food in a new batch of eggs. As far as I know, little is known about the sex roles of the pygmy seahorses, but researchers are currently working on both their ecology and their systematics.
Ghost pipefish females in contrast take care of the eggs. The eggs are held between the pelvic fins of the female and held until they hatch. The male, often much smaller than the female, hangs around and waits for the eggs to hatch.
Quite common here in the strait are the sea moths, close relatives to the seahorses. They are almost always found in pairs, with the more distinctly coloured male leading their walk around their territory in search of food.
Finally, it is interesting that there still are both a number of known but scientifically undescribed species, and news species that are found on a continuous basis. In the north Sulawesi region the Pontohi seahorse and the Lembeh seadragon have been found during recent years. It is highly likely that more species will be found here in the years to come. In fact, the first of the pygmy seahorses were found not too long ago by a sea fan researcher, that took a sample of a particular sea fan into his laboratory, and there much to his surprise, saw the small, pink Bargibanti seahorses swim around the fan.
Frogfishes! Always fun to see and wherever they are found often the stars of the local diving critters. Lembeh delivers frogfish in so many shapes, sizes, and colours, that you could spend a week or more just checking out the varieties here in the strait. Well, maybe not shapes as most are more or less shaped like a hybrid of a ball and a fish, with the expected agility of such a creature! The last two days, we have seen painted, spotfin, giant, warty, hispid and striated frogfish and the striated has shown both it´s shorthaired and longhaired version.
So what are frogfish? All frogfish are small to medium sized sit and wait predators, that tend to find a more or less species-specific spot where their specific camouflage can be used. As an example giant and painted frogfish are most often found in or next to sponges, where the frogfish blends in in an amazing way with the colour and texture of the sponge. Another example is the hairy frogfish, which most often will be found right next to small colonies of corals with long tentacles on their polyps, giving a surprisingly efficient illusion of the frogfish being part of the coral colony.
Making the illusion even more thorough, frogfish do not have gill covers like most other fish, but expels the water flushing over their gills through small holes at the base of the pectoral fins. Thus no moving gill covers will alert any predator or prey that there is a rather tasty or dangerous, depending on perspective, frogfish just in front of you.
Frogfish, or anglerfish, which is their proper name, use their famous fishing rod called an illicium that is tipped with a lure, a so-called esca. The lure is waved in front of the mouth of the frogfish and, as the frogfish itself blends in with whatever it is sitting on or next to, passing fish cannot believe their luck when they see such a tasty morsel being available. The passing fish will approach and try to catch the lure, but will soon find itself in the stomach of the frogfish. In contrast to the sluggish and otherwise slow life style of frogfish, they actually are able to perform one of the quickest movements in the animal kingdom. The extension of the mouth and subsequent inhalation of water is over in milliseconds, often giving an illusion of pure magic when one observes a small fish in front of a frogfish suddenly just not there any more!
This afternoon’s dive will partly be spent in search of the elusive Randall´s frogfish. This small species is very cryptic, spending most of it´s time in rubble or clumps of dead sea weed. It is really hard to find, so luckily we can have a try tomorrow again. And the day after! The good thing about looking for almost impossible stuff here in the strait is that you will see so much cool other stuff while trying, so it is highly likely that we more or less will forget whatever it was we started out with looking for!
As a colorful contrast to the black or grey sands in Lembeh strait, nudibranchs of different sizes, shapes and colors are plentiful here. The vivid colors of many of the nudibranchs such as those of the Risbeckia are clear messages to predators that the nudibranchs are very nasty food items, filled with poison from the cnidarian prey of the nudibranchs.
It makes a lot of sense to announce the danger of eating the nudibranchs, as they get no help from the poison once ingested, despite killing of the predator in the process. The clear colors send a powerful message to would be predators that it is not worth even trying, letting both prey and predators take care of their own business without being harmed. These kinds of signals, where bright colors give a message of a horrible fate to a predator-to-be are called aposematic signals.
Some of the other very venomous animals, such as the flamboyant cuttlefish, the mototi octopus as well as the blue-ringed octopus that we currently see every day here in the strait are perfectly sized prey for may of the carnivorous fish feeding in the sands. However, given that these cephalopods themselves try to catch fish, a constant aposematic signal would complicate life for the blue-ring and the flamboyant scaring of the prey. The solution is to turn the aposematism on when threatened and turn it of again when the danger leaves, as shown here by a mototi octopus.
Thus, both flamboyant cuttlefish and blue-ring octopus are at the same time both among the most camouflaged and the brightest colored animals here in the strait, vividly demonstrated by the flamboyant cuttlefish flashing strong colored circles or waves of vivid colors when agitated and blending in with the rubble in an amazing way whenever left in peace.