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.







Surveys: What do we actually do?

So far I have mostly been writing about muck diving, critters, dive sites, but I haven’t really explained how researching all of this works. What do we get up to when we are diving? Do we look at weird critters and think “that’s pretty cool!” or do we actually do something more?

Perks of the job: Air ajo 3, one of the survey sites

Perks of the job: Air ajo 3, one of the survey sites

First off: Yes, Luke and me very often think, talk and even shout under water about how very cool our critters are. We do however, try to get a bit more scientific than that. Since May this year we finished nearly 200 transects on 20 different sites, besides that we have also been collecting sediment samples and we took many, many pictures of the bottom of the sites we surveyed.

Running a transect

Running a transect

Surveying sites by running transects (we are actually doing “belt transects”, but that’s a technicality that’s not important now) is a way to try to tell how many fish there are in that area. The idea is to have a fixed measuring unit, so you can compare your counts to other sites. It would not make sense to just swim for a while, counting fish if you don’t know how much area you have covered. Without a measuring unit you might swim 500m in one dive, 300m on the next one and 900m in yet another one, making comparisons impossible. One way to deal with this, is by simply taking a measuring tape with you so you know how much you area you have covered. Before you do this, you have to decide how long your transects will be and how far away from the tape measure you will count fish. This way I know that with every transect, I cover an area of 50m2, and per site I investigate 500m2 of seafloor(10 transects).

Doing this on every site we investigate allows us to make comparisons. For example, at one site I found 3 Scorpionfish, but at another site I found 35 Scorpionfish. Since I used the same methods (both covered 500m2), I can conclude that there really are more Scorpionfish in one site than the other.

Benthic cover???

Benthic cover???

This obviously does not explain WHY there are more fish on one site than another. To try and explain some of the differences, we gather data on a few other things per site. Besides noting the depth we found species, we look at a few more environmental factors that might vary. The main two are benthic cover and the actual sediment. Benthic cover is just a fancy way of saying “stuff that covers the bottom”, to investigate this we take multiple photos of the bottom at each transect. Afterwards the photos get analysed to decide how much of the bottom was sand, algae, coral,…

Initial sediment drying

Initial sediment drying

Sediment sampling is a bit more intensive. First step is easy, scooping up about sand at each transect under water. Next the samples have to be dried, packed and transported to the lab. In the lab it all gets wet-sieved, dried again, and then I can start the actual analysis. By the end of this month we will have collected about 200 samples, each of which take about an hour to process (+48 hours drying time). So a lot of hours of playing with sand ahead of me, let’s just hope it results into something useful 😉

Sediment collecting

Sediment collecting