Critter getaway in Bangka

Mangrove view

Mangroves at Bangka Island

At the moment I am back in Lembeh Strait for what will be the last visit to Indonesia during my PhD. So I am making the most of it, enjoying every moment and taking time to visit friends spread out across the archipelago. A few days ago I went to Bangka Island to visit Sophie and Simon, who own Nomad Divers, a very pleasant small dive resort. I wrote about Bangka before, so check it out here if you want to know what the island is all about.

I enjoyed a few very relaxed days, playing (and losing ) board games, teaching their kids how to behave badly and philosophising about science while enjoying gin-tonics. But I also got to appreciate the abundant critters that live in the mangroves and jungle of Bangka Island. Those few days of not working (not a single dive done and no computer in sight), and just enjoying nature reminded me why I fell in love with the tropics in the first place. The beauty of Indonesia (and much of the tropics by extension) is that there is so much wildlife all around you, as long as you just keep your eyes open…or just get plain lucky.


Tarsier in the ceiling! I never realised how long their tails were…

On my first night, while we were catching up and sharing stories about science hobbits, a small tarsier decided to have his dinner in the restaurant. These small primates are rare and vulnerable to extinction, they are only active at night and are usually very shy. If you want to see them in the wild, your best bet is to find yourself a good guide who knows where they roost during the day, so you can see them waking up and moving out to hunt when night falls. Just seeing one is great, having one sitting just above you, while eating a gecko is dumb luck and freaking amazing. For Sophie and Simon, this was a first in 4 years on Bangka!


Nomnomnom. Tarsier (Tarsius Tarsier) eating a gecko (Hemidactylus frenatus) in Bangka Island

There was plenty to see by day as well. I had a great time wandering through the mangroves, looking around for interesting crittersAs you may or may not know, mangroves are important nursery areas for all kind of fish, so it was no surprise to see lots of baby snappers, damsels and other small fish darting around in the shallows. But there was a lot more, loads of mudskippers (skipping around in the mud, as they do), kingfishers in the trees, and the always busy fiddler crabs in the intertidal zone.


Two male fiddler crabs facing off

Fiddler crabs are colourful little crabs, and are named for the males’ disproportionally large claw. One claw is small and used like any other crab uses its claws, the huge claw is used to show off (what did you expect?). The males wave their big claw around to get the attention of females, and to ward of other males encroaching on their territory. If you  ever find yourself in a mangrove with plenty of time on your hands, I can highly advise watching these little guys at work for a while, it’s pretty captivating and highly entertaining.

While I didn’t go into the jungle, there were plenty of little lizards to spot while strolling along the beach or heading to my room. Apparently, there are quite a few snakes to find in the jungle, and legend has it there’s even deer around, maybe I’ll have to bring shoes next time and go have a look.  If mangroves or jungle or jungle trekking aren’t your thing, you can always just chill out, have a beer and watch the geckos on the wall eating bugs or fighting each other. The tropics really are accommodating for any life style 😉


Sophie and Max enjoying the ocean view

Ocean pretenders: Eat or be eaten


Algae or  a pipefish pretending to be algae?

At some point or other, all of us have pretended to be something that we are not. From trying to look old enough to buy alcohol as a teenager, to keeping your head low and pretending to be a pot plant in the corner of the office when the boss is looking for someone to take notes during a meeting. Some people might pretend more often than others, people might have good reasons for wanting to look like someone (or something) they are not, and some individuals might have less than innocent intentions when hiding their true identity. The same thing happens in the oceans but the stakes are usually higher than (trying to) look cool with a beer, or the tedium of having to take notes. A critter’s skill at pretending often means the difference between getting dinner or being dinner…

The ocean-pretending I am talking about is more commonly known as camouflage and mimicry. The terms are frequently mixed up or even assumed to be synonyms, but they are two different concepts. To distinguish between the two, it helps to know that the goals of camouflage and mimicry are opposite from each other. Animals using camouflage are trying very hard not to be seen, like you trying to be a pot plant instead of a potential scribe. Mimicry attempts to do the opposite: wanting to be seen, while hoping observers will believe you are someone else, like our teenager bluffing he’s old enough to drink.

Usually when biologists (who know their shit) talk about camouflage, they are thinking of mobile animals that are pretending to be objects or animals that don’t move; these objects could be plants, rocks, sand, sponges, etc. When those same biologists talk about mimicry, they mean active animals that pretend to be different species of active animals. But that is just the start of it, the obvious question is why? What are the reasons behind camouflage and mimicry? As a rule, fish don’t like alcohol, so there must be some other cunning plan.

For camouflage it boils down to two options: defensive or aggressive. People tend to intuitively understand defensive camouflage: hiding so you don’t get eaten or killed. Two ocean examples are seahorses pretending to be seafans or crustaceans looking like sponges. Aggressive camouflage is when an animal tries not to be seen, so it can eat unsuspecting animals coming closer. Frogfish are masters at this, so are most scorpionfish, and many other species. It is perfectly possible for an animal to use both defensive and aggressive camouflage at the same time. Think about the human version: soldiers wearing camouflage do not want to get shot, while aiming their guns at the enemy.

Mimicry has similar uses, depending on what the animal mimics. Unlike camouflage, mimicry needs a distinctive “model species”, which is imitated by the “mimic”. Depending on the nature of the model and the mimic, we distinguish three kinds of mimicry. Batesian mimicry has a dangerous model, but a harmless mimic. Mullerian mimicry has a dangerous model and a dangerous mimic. The last type, Peckhamian mimicry, has a harmless model, but a dangerous mimic.

Batesian mimicry can be compared with our teenager trying to buy alcohol. He might try to look like the real deal, but really is not. A great ocean example is the (non-toxic) baby pinnate batfish (Platax pinnatus), which look like a toxic flatworm. Or baby sea cucumbers pretending to be toxic nudibranchs. Predators assume the mimic is toxic, so they avoid eating it, good news for the mimic!

In Mullerian mimicry both mimic and model are “the real deal”.  This is very common in nudibranchs of the Phyllidiidae family. Most species in this family are very toxic and they all look very much alike. When a predator tries to eat one species, he’ll learn to avoid the other similar looking species as well. A bit like the leather-clad members of different motorbike gangs which look equally dangerous to outsiders. The bikers can tell the difference between other gangs, but I would advise against picking a fight with any of them.

Peckhamian or aggressive mimicry happens when the mimic pretends to be a harmless model, usually to get close to prey. This method is used by predators like dottybacks, who pretend to be harmless damselfish so they can get close enough to juvenile damselfish to eat them. A (purely hypothetical) human example could be a person living in a fancy white house, who pretends to be a silly orange clown, but in reality is a dangerous would-be dictator. As it turns out, land is no different than the ocean: the animals that believe in the illusion are most likely to suffer from it.

Best of Dauin_Lizardfish eating Dragonet

Aggressive camouflage in action: this dragonet failed to see the lizardfish hiding in the sand.

High school teaching intermezzo

Last month I had to make a short and unexpected trip back to Belgium. In the short time I was there, two friends who are high school teachers decided to enlist my services to teach a few guest classes. So I (rather surprisingly) ended up talking to a bunch of 14-to-16- year-olds about how great weird fish are.

To say that this was a different crowd to my usual audience (scientists, enthusiastic divers, etc.), would be a bit of an understatement. Communicating about the ocean with teenagers living in a big city, most of which have never snorkeled in their lives, was a refreshing challenge. How do you get high school kids whose main interests are.. (what are they even?) to listen to stories about fish?

Turns out the trick is….the same way as getting most other people’s attention: by piquing their interest with stories about gore and sex,  and cool videos. Not of the gore and sex (that wouldn’t be allowed in high school I think). Showing videos of hunting frogfish, or of flamboyant cuttlefish wandering around definitely worked better than just pictures. Not-so-much to my surprise, telling stories about the aberrant mating habits of fish and comparing it to teenagers’ normal school interactions with the opposite sex also seemed to get their attention. So much actually, that it inspired me to write the sex under the sea post from last month!


Not my usual setting – teaching in a high school in Belgium

Valentine special: Sex on the sand

In the aftermath of valentine’s day, I figured a post about nautical naughtiness was suitable. Popular media such as romantic comedies, reality tv-shows or more dubious videos available on the internet might have you believe that a moonlit fondle on a tropical beach is the highlight of romance. They are, however, very much mistaken! Late night walks on the beach turning into passionate, steamy scenes of desire and lust are in fact the best way to discover that sex and sand really don’t mix well. No matter how hard you try, sand will get where you absolutely don’t want it to get. But for creatures that spend their entire lives on soft sediments there is no way around it. They have no choice but to deal with the gritty truth that is sex on sand. As you can imagine, this blog is not going to be a pretty story, but if you think you can handle it, here is how things go down in the muck…


A small male frogfish (Antennarius pictus) risking his life to get closer to a larger female

Getting started with one my favourites, frogfishes, immediately proves my point on how difficult romancing is on the sand. As in humans, competition for females is fierce, but competition is made worse because frogfish are usually quite rare, so there aren’t many females around. The result is that males will often stalk a female for multiple days or even weeks, waiting until she might be ready to mate. This is a very risky strategy though. At best, the larger female will reject a male by pushing him away or swimming off. At its worst, the grumpy female might decide to eat the male! It sure would make Tinder a lot more exciting if this trend would catch on in humans. Have a look at a cannibalistic frogfish below (Video by Albert Kang).

When the female frogfish is in the mood however, the male will gently put its pectoral fin on her belly when they’re almost ready to mate. He’ll prod her until she’s ready, at which point the female swims up, partially pushed by the male, and releases her eggs. The male then releases his semen over the eggs, after which the now fertilised eggs drift off, forming a sort of raft until the young frogfish hatch. The attentive blog-reader will have noticed that frogfish also avoid the sand when mating, clever! Here is a rather explicit video of two hairy frogfish in action (video by BlueWaterLife1)

Unlike frogfish, the blue ringed octopus wastes no time on small talk or courtship. Male blue ringed octopuses just pounce upon any opportunity, inserting their hectocotylus (scientific slang for “penis-arm”) in any other blue ringed octopus they encounter. The problem is that males unfortunately can’t tell the difference between males or females. So they will try any octopus and only know if they hit the jackpot or got themselves into a rather embarrassing situation until after attempting to copulate (not unlike some drunk male tourists in dodgy bars in Thailand or the Philippines). The unfortunate males on the receiving end don’t seem to take it too badly and do not react aggressively, preferring to wait passively until the mistake becomes obvious. The females however are more feisty and tend to finish the act by “forcefully pulling the males from their body“, occasionally attacking or even killing and eating the males (is it me or am I seeing a trend here?). The actual deed takes on average 90 minutes, but I think we can all agree it hugely lacks in romanticism.

Best of Dauin_Blue ringed octopus_small

A blue ringed octopus on the prowl. For what I don’t know, and turns out neither does he…

Best of Dauin_Seahorse thorny_MDB

Male Thorny seahorse (Hippocampus histrix) showing off its pregnant belly

Seahorses are more romantic, forming stable couples that sometimes stay together for life. The couples greet each other every morning by doing a little dance. When mating their dance gets more elaborate and ends up with both fish swimming up in the water-column and doing the act at the highest point of their dance. But then it gets a bit kinky, as it is the female who penetrates the male! She deposits her eggs in the male’s pouch, who then fertilises the eggs, gets pregnant and gives birth to baby seahorses. Shortly after giving birth the couple mates again (within as little as 30 minutes for pygmy seahorses!), and the males gets pregnant all over again. No rest for these little guys!

At least for nudibranchs life is a bit simpler, there is no such thing as a male or female nudibranch, since they are both at the same time. It is believed that being hermaphrodites (simultaneously male and female) is an adaptation to being rare and not being able to move very far during their lifetime. After all, you wouldn’t want to spend half of your life on your own, getting increasingly horny, to then finally meet a single other individual of your species and find out you can’t reproduce with them. So when nudibranchs mate, they usually get pregnant and make the other one pregnant in one go, talk about efficiency. Being efficient at mating does not mean mating is a boring occasion. Nudibranchs are some of the most deviant critters in the ocean. They occasionally indulge in mating aggregations (aka orgies),  S&M (most of their penises have backward pointing spines), mating with different species than our own (a slug’s a slug), and some species even practice protandry (adults mating with juveniles). But it gets even worse….


Nubibranch sex: These Gymnodoris nudibranchs clearly show how both animals penetrate each other at the same time

Some species amputate their own penis after mating, mostly because pulling out is just too much effort with those backwards pointing spines. They do have spares and the amputated penis regrows, so no harm done. In what is probably one of the most bizarre cases of sex on the sand, a species of Siphopteron-slugs uses a part of its forked penis to stab its partner through the head during mating! You read that correctly, they use an adapted penis to stab each other in.the.head while having sex. Not the mouth, not any other orifice, the head, right above the eyes. As if that’s not enough, they even inject prostate fluid into the head as well. A process beautifully coined as “cephalo-traumatic secretion transfer”. Call it what you want, this stuff is a bit too kinky for my liking. Oh, and the reason why? You guessed it…we don’t know, although researchers have suggested it might change the behaviour of the receiving slug, go figure…

As you see, sex on the sand is a lot more complicated (some might argue interesting) than in more conventional places. Try to remember that during your next romantic walk on the beach.