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.
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!
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.
This is my fourth trip to Lembeh in just 2 years. I do dive a lot of other places in the world, but my favorite place is this narrow strait with a big harbor in the middle of it. With just a couple of exceptions, all the other visitors here in the resort this week have also been here before. So what is it that draws not just me bot also lots of other people here time and time again? After all, the world is full of nice dive spots with clear blue waters, nice beaches and colorful reefs right on the coast. As most people in the dive world know, Lembeh will not give you that. Not that there are no corals in Lembeh, actually there are a couple of surprisingly healthy hard coral dive spots here, but for Lembeh aficionados, those dive spots are preferably left alone in hunt for the real treasures of the strait. And the real treasures are in some sense the total opposite of dives on blue water coral reefs. In a rather murky setting, on dark lava sand with bits and pieces of “stuff”, some of it of natural origin and the rest with clear traces to the villages and the harbor at the coast of the strait, the weirdest, hairiest, most camouflaged and simply butt ugliest creatures found on earth dominate. There are of course some really beautiful creatures here, such as many of the nudibranchs or the quite common candy crabs on the Dendronephtyids
but the real stars are the multitude of octopus, frogfish, snake eels, scorpion fish, stone fish, carrier crabs, urchins and other uglies that just a mother and a muck diver could love, or maybe just a muck diver.
On todays morning dive we found two of my absolute favorite scorpion fish, a big female and a small male Ambon scorpion fish waddling around and looking like an innocent piece of sea weed with no mean plans for small fish coming close. A small cardinal fish happened to do just that, which was the last thing the little fish ever did. With their enormous mouths, Ambons as well as all the other scorpionfish take in a huge amount of water in their mouths containing the small slightly careless small fish. The water is expelled through the gills and the fish is retained in the mouth and subsequently swallowed. If one hangs around for a little time after the catch, it is quite common to se the prey wiggle around inside the scorpionfish for a little while before actually dying. It is highly likely that the main evolutionary pressure leading to the amount of amazing camouflage seen here in the strait is that the sand bottoms here simply is so barren that a sit-and-wait predator such as scorpionfish would be out of luck catching food in this environment if they didn´t look like some thing. Thus, algae covered coconut husks, roots from trees falling in the strait, clumps of disintegrating sea weed and other similar debris have been the model evolution has tried to simulate. And Lembeh really is the place that shows evolution succeeding. Without a good dive guide, most of the really interesting animals here would continue their lives without ever being seen by divers. Butt ugly as they are, it is hard not to be amazed at their adaptation to the stark landscape they live their lives in.
So here is the first instalment by the brand new guest blogger at NAD! My name is Bent Christensen, an avid underwater photographer visiting Lembeh for the fourth time in two years, and already planning my next trip! On my day job I teach ecology at a swedish university and run a small media company focused on coral reef and rainforest ecology, guaranteeing me trips to exciting and warm places when my home in Sweden closes down in darkness, snow and temperatures way below zero.
What is around right now in Lembeh then? As always when coming here, something new is showing up. Currently a lot of nudibranchs, many of them small, are around right now. Even the excellent guides seem to be somewhat uncertain on the name of some of them, and that is a feat considering the thousands of dives the guides have done here in the strait. There is also a lot of baby frogfish now, with around five to ten being spotted on each dive to day. The blue-ring season got a jump start yesterday, with three different blue-rings seen on one dive. Flamboyants are around, both big adults and some coming right from the egg. Mimics and wunderpus are seen, but that more or less would be expected, as are pygmies of different kinds, devilfish, xeno crabs, pom pom boxer crabs, stargazers and all the other usual suspects rare most places but quite easily seen here.
The year is almost over and it was another great day of diving here in Lembeh Strait: we had Tiger Shrimps, Hairy Shrimps, Frogfishes, Blue Ringed Octopus, Coconut Octopus, Pipehorses, Seahorses and lot’s of other cool stuff. I specially liked this nudibranch. First, because i don’t know what it is (please comment if you do) and second because it looks so funny with its two different rhinophores. It was about 1 cm in size and in 5 meters depth in the rubble … just one of the various uncommon nudibranchs i have been seeing here recently.