Guest blog: Big brother is watching – Spying on the secret lives of endangered seahorses

Louw_CroppedIt’s time for a new guestblog, this one is by the amazing Louw Claassens. Louw is a South-African marine scientist at the Knysna Basin Project and a member of the IUCN Seahorse specialist group. She studies one of the world’s most endangered seahorses, part of her work involves studying their behaviour, which recently resulted in a very interesting publication (go check it out!). In this guestblog she gives you the most important findings of that paper and shares some fantastic video footage. Enjoy!


A big part of ecological research is based on observations – where do animals occur, what do they eat, what do they do. Some of these questions can be answered by using standard scientific methods e.g. a population survey can tell you where animals occur (although why is a whole other kettle of fish!). The tricky part sets in when you want to find out what an animal is doing. Conventionally, this entails going to the animal in question and watching it (sounds pretty simple, right?!). But it is here where observational effect (the act of observing has an effect on behaviour) and observational bias (researcher bias as to expected behaviour) creeps in.

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I spy with my little…GoPro? (Photo: Louw Claassens)

One of the 21st century solutions to these observational problems, is using cameras to study animals, and we are now even able to use cameras to study animals under water (thank goodness for relatively cheap action cameras such as GoPro’s!). Most fish research uses cameras to look at fish diversity, abundance, and habitat use – with limited work on actual fish behaviour. One of the reasons for this is probably owing to the highly mobile nature of most fish species.

So, is there a place for action cameras in fish behavioural research?

We focused on seahorses to answer this question. The conventional way to study seahorse behaviour entails getting in the water and watching the seahorse go about its business. Or, getting some seahorses and conducting observational research in the lab. The first method is problematic owing to two reasons: 1) Observer effect (the seahorse might act differently when you are watching it), and 2) seahorses move quite slowly most of the time, so detecting a behavioral pattern is quite difficult. Not even to mention the costs and time involved in doing this. The latter method might make sense, but it is well known that animal behaviour in captivity is rarely authentic.

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A very well camouflaged Knysna seahorse (Hippocampus capensis) (Photo: Louw Claassens)

Our aim was to test the efficacy of using video cameras to study the natural behaviour of a seahorse, and we had the perfect opportunity to do this! During a recent population survey of the endangered Knysna seahorse (Hippocampus capensis) in the Knysna estuary (South Africa) we found a stable population within a residential marina estate. The seahorses were found to use artificial Reno mattresses (wire cages filled with rocks). We had the seahorses, we had a relatively protected area to deploy cameras, and we had a sturdy structure to attach the cameras to.

In the first instance, we wanted to see if seahorse behaviour changed throughout the day e.g. between the morning, midday and afternoon. To add to this, we had an opportunity to see what happens to seahorse behaviour during the busy December holiday season. To do this, we used boat noise as a potential stressor (as occupancy of the residential marina estate increases from ~30 % to 100 % over the holiday period).

Video: Aggressive behaviour in the Knysna seahorse (Hippocampus capensis) – main action starts at 0:45.

But first we had to see if cameras successfully captured seahorse behaviour and if they could be used in behavioural assessments. We conducted a short trial period to test this, and found that 49 % of footage recorded contained seahorses. Using this data, we created an ethogram (a catalogue or table of all the different kinds of behaviour or activity observed in an animal) for H. capensis:

  • Feeding: the seahorse is actively searching for prey animals.
  • Irritation: identified by increased clicking and tail adjustments.
  • Moving from holdfast to holdfast: seahorse moves around without any feeding behaviour in-between.
  • Interaction: interaction behaviour can either be between a male and female as part of courting or between seahorses of the same sex and might entail aggression.
  • Stationary: seahorse remains completely still.

Video: Knysna seahorse (Hippocampus capensis) feeding

The next step was to deploy the cameras throughout the day (morning, midday and afternoon) and across the longer time periods (Pre-holiday, Holiday and Post-Holiday). To assess behaviour we used 10-min video sections as a sample and timed all observed behaviour for a single focal animal during the sample.

We recorded hours of footage, of which 57 hours contained suitable footage of seahorse behaviour. Seahorses spent 82 % of their time feeding and we noted courting behaviour exclusively in the morning. This courting behaviour entailed grasping of the female’s tail by the male in an attempt to position himself face to face with the female, followed by swaying movements. We also found that seahorses were more visible and fed more during the morning. There were no differences between the behaviour of males and females.

Graphic footage! Video of a cormorant catching a seahorse (H. capensis)

We observed quite a few cuttlefish, rays and cormorants, but only noted predation by the latter (check out the video above!). Seahorses were also observed happily living side by side with octopus, although octopus are known to eat seahorses in Australia. We also noted some other curious fish, like our temperate butterfly fish (Chaetodon marleyi) (video below) – can you spot the seahorse?

A cold water butterfly fish (Chaetodon marleyi) checking out Louw’s GoPro setup

When we looked at behavioural changes across the longer-term periods, we noted a decrease in visibility and feeding activity of the focal seahorse, with an increase in irritation behaviour, during the holiday period. No courting behaviour was noted during the holiday period – which is a bit concerning, seeing that this species breeding season is from September to March.  Feeding activity and seahorse visibility increased again during the post-holiday period.

So, what does all this tell us? Action cameras are pretty useful in studying natural behaviour of seahorses. Recorded footage can be watched on fast-forward mode which enables a clear view of the behavioural pattern of the animal (something that is quite difficult to see whilst diving, as these guys move so slowly). For H. capensis, it was the first time that natural behaviour was studied, and we gained some valuable information with regards to feeding and interaction behaviour. In addition, it seems that boat noise has a negative effect on the natural behaviour of this species – an aspect which does need further research (preferably, a controlled experimental approach is needed here, to control the vast number of confounding factors that might have played a role!). The use of cameras in natural seagrass habitat also needs to be tested, as visibility might be problematic in dense vegetation.

In the past, the world of underwater research was exclusively meant for the eyes of the researcher/diver. Now, we are able to bring what we experience to the surface and to the lay person. And perhaps the real power of doing this is to create and instill that love and passion for the underwater world that all divers and water lovers have, in all people. I mean, who cannot fall in love with two seahorses doing their morning courting dance?

The secret sex lives of seahorses: mating dance of the Knysna seahorse

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Answering questions

During the last three months, I have been lucky enough to be based in Lembeh Strait in Indonesia. While most of my time there was spent writing, I also managed to get a fair few dives in so I wouldn’t forget why I started this PhD-project in the first place. What motivated me to go back to university after 7 years of working across the world, was curiosity about the marine life I love so much.

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What is a Bobbit worm’s (Eunice aphroditois) place in the food chain?

While working as a dive instructor, I would constantly wonder about what I saw. Why did certain animals only appear in some spots or at certain times of the year? How long do frogfish/pygmy seahorses/other-fish-of-choice live? Do camouflaged fish choose a place to live depending on their own colour, or do they change their colour depending on where they live? What eats nudibranchs? What do nudibranchs eat? …? A few guide books offered answers to some of my questions, but most remained unanswered. Over the years, it slowly became clear that the answers were not locked up in some dusty university-dungeon or inside an even dustier professor’s brain. The truth is, science didn’t know the answers to many of the questions I had.

Many divers would be astonished by how little we really know about the ocean. As anyone who has heard me talk about my research will tell you, I answer a lot of questions with “I don’t know”. Even many of the most basic questions still haven’t been answered. There is a lot of great research going on, but there is even more ocean out there to be studied. When it started to dawn on me that hardly anyone was trying to find the answers to my questions, I decided to try to find them myself.

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Why do frogfish (Antennarius spp.) yawn?

Of course it wasn’t as quick and straightforward as I write it here. But in the end (mostly through stubbornness and dumb luck) I managed to get myself into a project where I could spend multiple years trying to find out some answers myself. Turns out finding answers isn’t as easy as you’d think! But it also turns out that it is an even better way to spend one’s time than traipsing across the world as a dive instructor. The result is that after 3 years I have answered a fraction of my initial questions, while simultaneously tripling (quadrupling? quintupling?) the number of questions I had in the start!

What I am planning to do with those new questions is a matter for another post, but this final field trip definitely motivated me to keep searching for answers…

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Do Ghostpipefish (Solenostomus spp.) change sex? These are 3 males together

 

Growing up

Growing up isn’t always easy, going from the playful life of a child to become a (seemingly) functional adult takes blood, sweat and tears. Anyone reading this blog who longingly remembers the awkward changes your body goes through puberty, please feel free to share in comments below whether it was the pimples, the voice changes, gangly limbs or any other similar affliction you’d like to get back in your life. I am fairly confident the comment section won’t be overly populated. If you think growing up was hard for you or any other human, take some time to consider how much more extreme becoming an adult is for fish.

As you or may not know, most fish start their life as transparent larvae, floating through the blue. Once they are large enough to become proper fish, they “settle” on the reef. This settling is the first big growing up fish have to do.  Forget about years to grow from a baby into a teenager. Typically within less than 2 days, the freshly arrived larvae change colour and massively grow in size. If you think changing colour and doubling in size within a month isn’t hard enough as a childhood, consider the following. Over 50% of baby fish arriving on the reef get eaten within the first two days of arriving on the reef! Talk about a bad first day at school…

Childhood might be the most dangerous time for fish, but that doesn’t mean puberty is any easier. While we humans complain about acne and high pitched voices, fish have got other things to cope with. Many fish change colour again as they become adults, which is a minor nuisance compared to the fact that some radically change shape. Good examples are batfishes, which start by looking like leaves or flatworms to then turn into a relatively boring plate-looking fish.

Shapeshifting is peanuts compared to a process many fish have go through during puberty: sex change. Many fishes are born as one sex, but will turn into the opposite sex as they grow up. The best known example are clownfishes, which are all born as a male, but turn into females later in life. Including this process would have made “Finding Nemo” a much more interesting film in my humble opinion. Other species, such as parrotfishes and wrasses are born as females, but then turn into males as they grow up. While surprising to most people, the whole sex change thing is actually very common in the ocean.

Part of growing up in humans is learning to appreciate different kinds of food: whether it’s vegetables, olives or alcohol, children like different things than adults. The same goes for many fish species. Frogfishes for example start by mostly eating small shrimp, and then evolve a more delicate palate including fish like seahorses, lionfish, or pretty much any other fish that fits in their mouth. Interestingly, for frogfish growing up can mean that you start of as prey for a fish, but turn into a predator for that same fish once you’re big enough. Conclusion: growing up can be difficult for any animal, but some have it worse than others.

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…

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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.

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

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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….

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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.