It has been quiet on the blog, mostly because I spent a few weeks recharging my batteries in Europe. But it’s action time again now and there is lots of cool stuff going on! So a short blog to bring you up to speed.


Getting ready to hop into the Silfra fissure

The last weeks I’ve had the pleasure of exploring some new places in Europe and meeting up with friends I had’t seen for too long. One of the highlights of the trip was that I’ve finally managed to snorkel Silfra fissure in Iceland. Silfra is a gorge in the Thingvellir national park, a rift valley between the North American and Eurasian tectonic plates. So snorkeling in the Silfra fissure means that you are basically snorkeling between two tectonic plates, and it’s quite the experience. Besides being very cold (it was -12°C outside and 2°C in the water), it has the coolest topography and amazing visibility, up to 100m!


Silfra Fissure landscape

The Europe trip ended with a visit to the University of Tubingen, where I met up with people that do some exciting research on fish biofluorescence. The lab does some very cool work, like investigating how fish see the world, whether or not they can see fluorescence, etc. It was very interesting to talk with them and learn about their research, and fun to share my work with them.

Which brings me to what’s happening my research. I am now at the very last push of my PhD, with less than 3 months to go before submitting my thesis. There is still work to be done, but I’m happy that multiple papers are currently in review, and will hopefully be published this year. Two of those papers will be of big interest to scuba divers and photographers. One of them might even cause some commotion all the way into zoos and aquaria. I will share them here as soon as they have gone through the review process.

Lastly, some really exciting news about future work. Last month I received a grant from the Mohammed bin Zayed Species Conservation Fund to run a project that will benefit one of the world’s most endangered seahorses. Together with my friend Louw, which you might remember from her guestblog, we will be looking at new ways to detect the endangered Knysna Seahorse (Hippocampus capensis). Louw and me will be collaborating with the TrEnD lab in Perth to make a difference in the conservation of this beautiful critter. This project will start immediately after handing in the PhD, so I will be able to share new critter insights for a while longer.

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The endangered Knysna seahorse (Hippocampus capensis) – Photo: Louw Claassens


Guestblog: Frogfish history

IMG_0737This is the second guestblog by Daniel Geary, resident marine biologist  and frogfish-enthusiast at Atmosphere Resort in Dauin, Philippines. You can read his first blog here. In this new guestblog Daniel explores the history of frogfish research and provides an introduction to a few common and not-so-common frogfish species.

There are many places across the globe where divers can see frogfish, but the Philippines (especially the Dauin area) is one of the best frogfish destinations of them all. I have personally seen thirteen species in this country, including 11 species here in Dauin. Sometimes we will see over 30 individuals on a single dive! It is not uncommon for some of the frogfish to stay on the same site for over a year, especially Giant Frogfish. Another great destination for frogfish is Indonesia, especially Lembeh, Ambon, and also some places in Komodo. Generally, if there is good muck diving, there is good potential for frogfish action. Australia also has some unique frogfish species, as well as the Caribbean, where there are a few places with reliable frogfish sightings.

Although frogfish are relatively well known critters to divers in the Indo-Pacific, this has not always been the case. Stories of frogfish and their accompanying drawings and sketches have existed for hundreds of years, with encounters spanning the globe. The first ever documented frogfish comes from Brazil. At some point before 1630, a drawing was given to the director of the Dutch West India Company. A woodcut was made from this drawing, and that woodcut was published in 1633. The first color drawing appeared in 1719, published by Louis Renard, an agent to King George I of England. He published a collection of color drawings of Indo-Pacific fish and other organisms and some of these represent the earliest published figures of Indo-Pacific frogfish. One was called Sambia or Loop-visch which translates directly to “walking fish.”

photo 1 - louis renard

First colour drawing of a frogfish – Louis Renard 1719

Albertus Seba and Philibert Commerson were two important scientists in the 1700s when it comes to frogfish. Seba believed frogfish were amphibians and tried very hard -incorrectly of course – to prove that they were the link between tadpoles and frogs, although anyone who has seen a baby frogfish knows this to be false. Even though he incorrectly identified a few nudibranchs as juvenile frogfish, he was still able to identify two species, the Hairy Frogfish (Antennarius striatus) and the Sargassumfish (Histrio histrio) during his studies. Commerson was the first scientist to focus solely on frogfish. He was a botanist and naturalist employed by the King of France and he described three species from Mauritius (Painted Frogfish – Antennarius pictus, Giant frogfish – Antennarius commerson, Hairy Frogfish – Antennarius striatus).

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Commerson’s drawing of the hairy frogfish – Antennarius striatus

There have been plenty of identification problems when it comes to frogfish, even today.  Frogfish colorations and patterns are highly variable, so it is nice to know people have been struggling with frogfish identification for hundreds of years. Albert Gunther, a scientist who attempted describe the different species of frogfish, said in 1861 that “[their] variability is so great, that scarcely two specimens will be found which are exactly alike…although I have not the slightest doubt that more than one-half of [the species] will prove to be individual varieties”. He listed over 30 species, but only 9 of those species are still accepted today. Since 1758 there have been over 165 species described and over 350 combinations of names. Currently there are around 50 accepted species, roughly one third of the total species described.


Painted Frogfish – Antennarius pictus

This is the most abundant frogfish species in the Indo-Pacific. They can be identified by having 3 distinctive spots on their tail. They prefer to live near sponges, rocks, ropes, mooring blocks, and car tires. They can grow to a maximum size of around 15 cm.


Painted frogfish (Antennarius pictus) with its typical three tail spots

Sargassumfish – Histrio histrio

This is the species with the largest distribution. They can be found in floating seaweed or debris as well as anchored seaweed and other marine plants. They can reach a maximum size of around 15 cm and are often sold in the marine aquarium trade.


Sargassumfish (Histrio histrio), a surprisingly good swimmer that lives on floating seaweed

Psychedelic Frogfish – Histiophryne psychedelica

This is one of the rarest frogfish species. They are only found in Ambon, Indonesia at a handful of dive sites, usually at around 2-3m hidden in rock crevices or in coral rubble.


“Snooted” picture of a psychedelic frogfish (Histiophryne psychedelica)

Giant Frogfish – Antennarius commerson

This is the biggest frogfish species, reaching lengths of more than 40 cm. They prefer to live on sponges and have two large spots on their tail, as well as lines coming from the eye and enlarged dorsal spines.


Giant frogfish (Antennarius commerson) resting on a sponge. Note the two tail spots

Ocellated Frogfish – Nudiantennarius subteres

This frogfish species is the “newest” frogfish species. Originally thought to be a new species, it turns out this species is the previously described, relatively unknown “Deepwater Frogfish”, although the lure is incorrect in the original drawing. It was thought that the adults lived deep and only the juveniles were found in the shallows, but  adult mating pairs of this species have been seen at less than 10m depth. They grow to around 5 cm.


Typical coloration of the Ocellated frogfish (Nudiantennarius subteres)

New publication: Parasites on the Great Barrier Reef

This is blog is a story about more than just a new publication, it is also the story of how I became a full time marine biologist. The publication might have come out only last month, but its story began more than 5 years ago on an expedition site in the Philippines…

It is on that site where I met my good friend Eva, who asked me at the end of the expedition if I wanted to join her on the Great Barrier Reef (GBR) for a couple of months of fieldwork. At that point I had no idea that we would be studying cleaner wrasses and parasites, but who would say no to such an offer?

Male adult Gnathiid parasite

A male gnathiid parasite

So November 2012 found Eva and me in a tiny plane, on our way to Lizard Island while  enjoying the amazing views over the GBR. The fantastic research station on Lizard Island would be our home for more than three months while we were conducting a series of experiments designed by Dr. Lexa Grutter, one of the world’s experts on cleaner wrasses and fish parasites.

Lizard Island

Lizard Island in the Great Barrier Reef

The experiments we were doing are part of a much larger project that’s been ongoing since the year 2000. The base of the project are 16 small patch reefs, half of which have had their cleaner wrasse removed from the start of the project, and the other half was left alone. To make sure the “removal reefs” stay cleaner wrasse-free, they are regularly checked for new cleaner wrasse, which are removed when found. This amazing setup makes it possible to see how reefs without cleaner wrasse are different from reefs with cleaner wrasse.

Eva and Hemigymnus

Eva and one of our “Hemis” (Thicklip wrasse / Hemigymnus melapterus)

Our particular experiment was designed to test if the number of gnathiid parasites (basically the mosquitos of the sea) were different when there are no cleaner wrasses on a reef. Cleaner wrasse eat the parasites off fish, but it’s unclear if they eat that many that it has an effect on the total number of parasites on coral reefs. The best way to count parasites is by using living fish as bait, Eva and me used the beautiful thicklip wrasse (Hemigymnus melapterus – aka “Hemis”). Our lovely hemis were put in traps which were placed on the different reefs for 12 hours. The traps are specifically designed containers that let the smell of fish out, and would allow parasites to enter, but not to escape.

We did two main sampling periods, each three weeks long, centered around the full moon. During sampling, our daily routine was to get up well before sunrise, collect the fish that were put out the night before, and deposit a new batch of fish. The main part of the day we would collect the parasites from the traps, and tend to our Hemis and their aquaria. At sunset we would collect the morning traps + fish and deposit a new batch of traps + fish. The days ended with collecting the daytime parasites. I can say in all honesty that I haven’t done such a tiring, but simultaneously exciting fieldwork experiment since.

End of traps celebrations

The end of a big experiment: time to celebrate!

The work we did provided only half of the data, more data was collected from similar experiments conducted by other colleagues, using different fish species. Afterwards there was a lot of lab work done by yet other collaborators, who counted and identified all the parasites. Only then could the data by analysed and written up. Sometimes experiments are quick and easy, sometimes they take a massive team effort!

Sentinel trap reef

Parasite trap on the reef

So the results are in now, and they are very cool. The main story is that when cleaner wrasse are present on a coral reef, they indeed have an effect on how many parasites infest fishes. But… The effect only happened by day, and only for big fish species such as our thicklip wrasses. For smaller fish species like damsel fish, there was no difference whether or not cleaner wrasse were present on the reef. Also very interesting is that cleaner wrasse only have an effect on the parasites that are active by day.


What does this all mean? In short, it seems to indicate that cleaner wrasse not only directly remove parasites from fish, but they do it so efficiently that it keeps the parasite numbers down in the areas where they clean fish. This is in turn good news for all the other fish on the reef, as living in an area with less parasites is much better for your health than living in a place full of parasites. Just think about it, how much would you enjoy living in a mosquito-ridden swamp? This experiments shows that cleaner wrasse are at least partially responsible for removing the mozzies from your swamp!

This paper means more than that to me, it means very fond memories of tiring sampling sessions, crazy-pants parties, beach runs, sunset drinks, meeting some fantastic people,… But more than that, the work involved made me realise how much I enjoy doing research, and it is what made me decide to pursue a PhD in marine science. So being able to write a blog about this paper while I am in the final stages of writing up my PhD thesis very much feels like things have come full circle.


New publication: Finding fluorescent critters

Great news! I can finally share the reason why I was playing around with fluorescent torches for the last three years. The main biofluorescence paper I have been working on was published two weeks ago in the journal Conservation biology, happy days!

Previously I have written blog posts about funky biofluorescing fish, publications on frogfish that might be using fluorescence to attract prey, or just some funky fluo pictures to keep you you entertained. This particular story is about why I started working on biofluorescence in the first place and how the results of the research might help to protect little critters.

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Biofluorescent painted frogfish (Antennarius pictus)

As anyone who has ever tried to find small or camouflaged critters during a dive will be able to tell you, the little guys are pretty hard to find! This isn’t just a problem for a dive guide who wants to show pygmy seahorses or small frogfish to his divers, it is also a very real and well-known problem for marine biologists trying to study them. Finding these “cryptic” critters might be a headache for divers, but there is much more at stake when you are trying to collect data about critters that might be endangered with extinction.

If you are trying to figure out if an animal is endangered, the obvious first thing you want to know is “how many of them are out there?”. All good and well when you are studying elephants or giraffes, but slightly more tricky when you’re studying pygmy seahorses or a tiny goby that’s less than 3cm long! Not finding any pygmy seahorses or gobies could just mean that you didn’t look hard enough.


Biofluorescent moray eel (Gymnothorax zonipectis)

Scientists have three different ways of coping with this issue:

  • First option: Ignoring the problem by not counting small, cryptic animals when doing surveys. After all, if you weren’t looking it’s only normal you didn’t find any.
  • Second option: Adapting standard “visual surveys”. Usually by going slower or looking harder at a smaller area than when looking for big fish. This way you find more cryptic critters, but a lot still depends on how good a researcher is at spotting small fish.
  • Third option: (you might not like this one) Using chemicals that either stun or kill all the fish in a small area, after which all the fish are collected and counted. This method is very efficient and gives a good idea of which fish were living in that area. Unfortunately using methods that kill fish are not ideal, especially when you might be dealing with rare species.
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Two fluorescent seahorses (Hippocampus subelongatus)

This is where biofluorescence could come in to help. If you are confused about what biofluorescence is, definitely check out this post or this website. But briefly, biofluorescence happens when fish first absorb light and then reflect it in a different colour. Importantly, biofluorescence is  not the same as bioluminescence, where animals produce their own light.

So what has biofluorescence to do with finding cryptic fishes? A few years ago, a paper was published that stated that biofluorescence is common in camouflaged fishes. The work looked into evolutionary history, but the main idea triggered a little light bulb. I had previously seen coral researchers use biofluorescence to find baby corals (which are tiny, transparent, and VERY hard to see), so I wondered if the same technique could be used on cryptic fish.


The same bandtail scorpionfish (Scorpaenopsis neglecta), with and without fluorescence

So I decided to test it as a part of my PhD. I was very lucky to get support from multiple divecentres which helped me to go fluo-diving all across Indonesia and the Philippines. In the last 3 years I did over 200 dives observing, investigating, counting, and cursing fluo-and non-fluorescent fish. The results are published here, but the answer is: Yes, you can use biofluorescence to count cryptic fishes.

The vast majority (87%) of cryptic fishes I tested showed biofluorescence, compared to a small fraction (9%) of the non-cryptic fishes. A cryptic fish is 70.9 times more likely to be biofluorescent than a non-cryptic one! When comparing normal surveys with fluorescence surveys, I found three times as many triplefins (a small cryptic fish species) when using fluo surveys than during comparable normal surveys.

What was also really exciting (to me at least) is that I discovered that pygmy seahorses are fluorescent as well! Using fluorescence I found twice as many Bargibant’s pygmy seahorses than without the fluo torch. As if they weren’t cute enough already, these little guys are fluo pink when you look at them with the right tools!

Fluorescing seahorses are not the only reason why I am excited about this new publication…although it probably plays a bigger role than it should in order to call myself a serious scientist 😉 The great thing is that this is an easy and cheap technique that could help researchers study and conserve small fishes more efficiently than before. And in the end, that’s what it’s all about for me, making sure the oceans remain an amazing place full of critters to enjoy looking at…

Solenostomus cyanopterus_Fluo_MDB

Robust ghostpipefish (Solenostomus cyanopterus) are biofluorescent too!