Leafy seadragons: Australia’s favourite fish

In a recent poll organised by the Australian Society for Fish Biology and Lateral Magazine, the Leafy Seadragon (Phycodurus eques) was voted as Australia’s favourite fish. This exquisite critter definitely deserves its place at the top, to celebrate it amazingness I wrote a blog about it. This blog appeared originally as an article in Lateral Magazine, you can find the original version here.

According to the popular stereotype, marine biologists spend their careers diving on colourful coral reefs, cuddling dolphins, and wrestling sharks. Unfortunately, the truth is a lot more mundane; we are more likely to spend our days diving into data analyses, cuddling too many cups of coffee, and wrestling grant proposals.

But sometimes we get lucky enough to work with animals that exceed the wildest stereotypes. Studying marine life is always exciting, but some animals are so unique they just stop you in your tracks; they make you thank your lucky stars for not listening to your mother when she said ‘marine biologist’ was not a real job.


Two leafy seadragons. Photo credit: David Harasti

For me, the ultimate awe-inspiring fish is the leafy seadragon (Phycodurus eques). “Leafies” only occur in temperate waters off southern Australia, and they are, to say the very least, unique animals — the kind that makes you wonder whether evolution had a stroke of brilliance or just a stroke. Seadragons belong to the Syngnathidae family, which also includes seahorses and pipefishes. Even in a family that is known for their oddly-shaped members, leafies stand out big-time.

These beautiful fish have the head of a seahorse and the body of a seaweed, with flamboyant leaf-like protrusions that wouldn’t look out of place at the Carnival in Rio de Janeiro. Leafy seadragons defy the idea of what a fish should look like.

Maybe that is why they are so popular with fish enthusiasts all over the world. Scuba divers fly halfway across the globe to dive in the cold waters off southern Australia, hoping to catch a glimpse of them. In the few public aquaria that display them, including Melbourne Aquarium, leafies are one of the absolute crowd-pleasers. For fish-lovers, this Australian endemic fish is at least as iconic as kangaroos or koalas.


Leafy seadragon. Photo credit: Tony Brown

Despite their popularity, we know surprisingly little about leafy seadragons. Adult leafies are one of the largest members of the Syngnathidae family, with adults measuring up to 35cm. Like seahorses, male seadragons carry their mating partner’s fertilised eggs; unlike seahorses, they do not have a pouch. Instead, females lay their eggs on the underside of the male’s tail, where they remain until hatching.

Leafy seadragons depend on kelp and seagrass beds as their habitat, where they blend in supremely well to avoid predators. Unfortunately, these habitats are in decline all over the world, including in Australia, caused by coastal development and potentially climate change. As a result, seadragon population numbers are decreasing, although the species is currently not considered to be endangered.


Admiring a Weedy seadragon, a close cousin of the Leafy seadragon. Photo credit: Greg Lecoeur

One would assume that the decreasing population numbers of a unique Australian emblem would inspire multitudes of researchers to study it. Strangely, this is not the case. A search of the scientific literature suggests that nobody has studied them in the wild for almost a decade. This lack of research on evolutionary distinct marine critters is unfortunately not unique to seadragons. It extends to many other species that do not fit in the ‘food’, ‘danger’, or ‘Pixar-famous’ categories in which landlubbers like to divide marine life. If so little attention is paid to the struggles of Australia’s most recognisable and charismatic fish, then what hope do other species have?

Time will tell what the future holds for the leafy seadragon. I, for one, am doing what I can to ensure generations after ours will continue to have their minds boggled by this incredible animal. If you care about seadragons, one way to help is to join citizen science projects such as iNaturalist or Seagrass Spotter. These projects collect observations from divers and snorkellers, directly helping scientists better understand and protect these animals and their habitats.

A short note about this blog: Two weeks after the poll I was awarded a research grant by the Sea World Research and Rescue Foundation to study the seadragons using eDNA. Hopefully the results that will come out of this research will help to better understand and protect these beautiful fishes.

Video: PhD fieldwork compilation

During my PhD I spent almost a year doing fieldwork in Indonesia and the Philippines. Besides conducting all kinds of serious science, I also entertained myself by filming some of the amazing marine life I encountered.

Now that the thesis has been submitted, I have finally taken the time to put a video together that should give you some idea of what life was like in the field. All footage was either filmed by myself or by Luke Gordon.

Critters in the deep

Some of you might have noticed the exciting news last week that the third species of seadragon has been filmed in the wild for the first time. Others, not living in Australia might now go “Huh? 3rd species?” or even “Huh? Seadragon?”. Which is completely fine, they are very cryptic species and it makes me feel like I can teach people something new 😉 The special thing about this new critter is that it lives in deep water, so I figured it was time to look into what critters are to be found below where divers can go.


Ruby seadragon (Phyllopteryx dewysea) (Source: WA Museum)

Let’s start with this new seadragon species, the Ruby seadragon (Phyllopteryx dewysea). It was described in 2015 and is found only in deep waters in the south of Australia. It is a cousin of the Leafy and Weedy seadragons, but mostly differs from them in the fact that it lives a lot deeper: below 50m. Besides the very exciting fact that there is a third species, it is also very interesting to see how it differs from other seadragons. The Ruby seadragon is ruby red, which is a great colour to camouflage yourself in deeper water. Unlike its cousins, the deep species does not have any appendages (the fancy frills so typical for the other seadragons). The explanation is once again pretty simple, there is not enough light for plants to grow in the environment it lives in, so it does not need the frills to resemble plants and maximise its camouflage. Another difference is that this new species has a tail that can wrap around objects, which the other dragons do not have. Have a look at the Ruby dragon in the video below:

We will stay with the pipefish and seahorse family for more deep species. Pygymy seahorses are a favourite for many divers, but what is virtually unknown is that there are no less than 2 species of pygmy seahorses that have never been seen alive and only live in the deep! The Bullneck seahorse (Hippocampus minotaur) and Hippocampus paradoxus (does not have a common name yet) are very mysterious species which we literally know nothing about. The Bullneck seahorse is only known from a couple of individuals found below 60m while trawing the bottom. The other species was discovered at 100m also using bottom trawling, only 1 animal has ever been found. They are a bit bigger than the shallow water pygmy seahorses (4cm to 6cm) and might live on gorgonian seafans or on bryozoans. Both of the species have only been found in Australia, the Bullneck seahorse in the southeast, H. paradoxus in the southwest of the country.


Larger Pacific Striped Octopus (Source)

Octopus are amazing animals, not only because most of them look cool and are very intelligent, but also because they show some really interesting behaviour. Divers are used to seeing species like mimic octopus or coconut octopus on the sand in shallow water, but some species venture much, much deeper. Larger pacific striped octopus (LPSO) can be found all the way down to 300m. They live in the eastern Pacific Ocean, in places like Panama and Nicaragua. Despite being an extremely interesting species, the LPSO has still not been scientifically described. Unlike most other octopuses, this species seems to like living in groups, sometimes of up to 40 animals. LPSO are beautiful animals that behave differently from other octopus species. They mate “beak-to-beak”, where other octopuses seem to prefer mating from a distance, or mounting on top of each other. Unlike shallow water octopuses, the female LPSO does not stop mating after it lays its eggs. Instead they keep on laying new eggs and mate with other males for much longer. There is good news for octopus-enthusiasts, this species does not only live in the deep sea, it can sometimes live shallow enough for scuba divers to be able to reach them.


Details of the Larger Pacific Striped Octopus (Source: Caldwell et. al 2015)

It would not be possible to talk about deep critters and leave out frogfish. Most non-divers only know about the existence of deep-water frogfish (although they might call them anglerfish) and not about their shallow cousins. I guess the scene in Finding Nemo with the big-toothed, bioluminescent anglerfish has got something to do with that. But in case there is any doubt, the shallow water frogfish and deep-water anglerfish are related. They all belong to the order of the Lophiiformes. The deep-water species generally look quite scary, with large teeth, dark colours and beady little eyes. Which makes me love them even more 🙂 Two interesting adaptation for the deeper species: they often show bioluminescence (produce their own light) to attract prey, which shallow species don’t do (although they might use biofluorescence). Another thing some species do, is mate in a very peculiar way. The males are a lot smaller than the females, once they find each other (which is rare in the deep sea), the male will attach itself to the female with its jaws. Over time, the male and female fuse together, the male basically becoming a parasite that receives all its nutrients through the female. This has major drawbacks for the male as well, since it will slowly shrivel up and become not much more than a pair of gonads attached to the female, serving no other purpose but to provide semen when she is ready to mate. Life in the deep…it’s quite something.


A deep-sea anglerfish (Caulophryne pelagica) (Source: National History Museum

If anything, having a closer look at deep-water critters has made me very curious about what else is out there. Searching for those elusive pygmy seahorse is something that got me particularly interested. I might have to become a technical diver after all, just to go find the little guys.



Halfway there. (Already???)

It’s been a while since the last blog post, partially because I have been travelling a lot these last weeks. The main reason is because I have been busy finishing up the last of my fieldwork. I have been on the road for fieldwork for more than a year now, and collected all the data I needed for writing up my thesis. As I am writing this, I once again realise I am more than halfway through my PhD, it has gone so much faster than I could have imagined when I started at the end of 2014.

So far I’ve had a great time during my PhD. It is exhilarating to dream up a project, work hard for it and then actually get to do the project as well. Over the last 18 months I have visited and dived some absolutely amazing places, from the cold Swan River in Perth to amazing coral reefs in Raja Ampat and Komodo, to world class muck diving in Dauin and Lembeh. On those dives I have seen more critters than I would’ve dared to hope and also finally got to see some elusive ones I had never seen before. Finding species like Rhinopias, Hairy shrimp, Wunderpus, etc made the work even more rewarding than it already was.

Synchiropus picturatus_3_MDB

Another first time: the Picturesque Dragonet (Synchiropus picturatus)

The most rewarding part of doing this PhD though is learning a lot of new things. Some of them were really practical, like how to write a grant proposal or how to organise a long-term fieldwork session. Luckily I also got valuable insights in what I am actually studying. I have gotten a good understanding of soft sediment ecosystems, have gained insights of the social aspects of dive tourism, played around with biofluorescence, got to observe diver behaviour, and so much more. I will learn even more when I actually start analysing the bulk of the data, which is why I am very much looking forward to the next year and a half.


At work in Dauin

Some  general  trends that are already very clear, most importantly that there still is so much that we don’t know. The soft sediment ecosystems (=sand areas) I work on are a lot more diverse and full of life than what is currently assumed. We hardly know anything about the species that have evolved to live in these environments. We don’t know how long they live, how the communicate, how they reproduce, if they are threatened or not, … What we do know is that they are very important for local communities who can make a living of these ecosystems, either through tourism, fishing, or other means.

Which brings me to the people who have been crucial to this project. I have had the pleasure of meeting and working with a lot of great people. During the last two years I have also felt how the dive industry is not always just about making money. While for some it might be just about dollars, most people sincerely care about the environment they work in and want to protect it. I’d like to say a big thank you to everyone who has helped me with fieldwork. Notably Luke for being a splendid science hobbit, Dragos and his family for giving me a place to crash in Philippines, and Anne-Sophie and Fabien from Safari Bali for getting me on multiple liveaboard trips in Indonesia. The list of divecentres that helped me out is extensive, a massive thank you to these guys as well: Atlantis Philippines, Atmosphere,  AzureBlack Sand Dive Retreat, Critters@Lembeh & Lembeh Resort, Froggies, Geko Dive Bali, Nomad Divers Bangka, Safari Bali, Scuba Seraya, Sea Explorers Philippines.

The next half of this PhD will be mostly spent at my desk, analysing data and writing up results. But I do have a few things planned to prevent myself from getting bored. I am writing this blog from Hawaii, where I will be attending the International Coral Reef Symposium, the world’s largest conference of marine biologists that do work on coral reefs. During the next week more than 2000 coral reef scientists will be presenting their research, networking, and discussing the future of coral reef research. I am joining the madness to present the results of my biofluorescence research. An update of the conference will be posted on the blog in a few days!


A fluorescent Western Australia Seahorse (Hippocampus subelongatus)