New publication: Critter diversity on the sand

It turns out that moving halfway across the world and diving into a new job is more time consuming than I expected, so I haven’t been keeping up with the blog recently. I’m slowly starting to get more organised and in the coming weeks I will try to catch up with summaries of papers that I’ve published recently.

The paper “High diversity, but low abundance of cryptobenthic fishes on soft sediment habitats in Southeast Asia” was published almost a year ago in the journal Estuarine, Coastal and Shelf Science. It was one of the key papers of my PhD and describes the diversity of critters on sandy habitats in Indonesia and the Philippines.


If you have ever been muck diving it won’t come as a surprise to you that there is some very exciting marine life to be found on sandy bottoms. When you mention places like Lembeh Strait, Anilao, or Dauin to keen divers – especially photographers – they either get lyrical about the amazing pictures they took there, or will tell you about their plans for visiting any of the above places to go see some crazy marine life.

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Species like this painted frogfish (Antennarius pictus) are popular with muck divers

In fact, the popularity of these sandy critters is so great, that the divers visiting Southeast Asia for muck diving bring in more than $150 million of revenue each year, supporting thousands of sustainable jobs! With so much money and jobs involved, it would be normal to expect researchers and conservationists to be interested in knowing which animals live on tropical sandy slopes. Unfortunately, that assumption would be wrong, surprisingly little is known about soft sediment (=sandy) habitats in the tropics. Even basic knowledge such as which animals live where is often unknown.

Luckily things are changing! Scientific interest in “cryptobenthic species” – the small, camouflaged critters this site is all about – is definitely increasing, with excellent work being doing on coral reefs by colleagues from across the world. We are starting to understand just how important they are for coral reefs and how very diverse cryptobenthic species can be.

What I am interested in though, is what is going on with the critters that live away from reefs. Are the critters living on the sand as diverse as those one coral reefs? Which species are most common? What causes species to live in one area, but not another? To answer these questions I set of with my good friend Luke for a 3 month dive survey trip that took us to Lembeh Strait, the north coast of Bali, and the sandy slopes of Dauin.

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Surveying soft sediment critters in Dauin. Photo: Luke Gordon

During our survey dives, we not only counted and identified the fish we saw, we also measured a bunch of other factors that could have an effect on the presence of critters. We wanted to know whether depth, benthic cover (growth of algae, coral, sponges etc), or the characteristics of the sediment played a role in which species we found.

So what did we find?

One of the most interesting results is that the diversity (number of species) of cryptobenthic species was very high, higher in fact than the cryptobenthic fish diversity on many coral reefs! In contrast, the abundance (number of individuals) was much, much lower than what is found on coral reefs. To put it in perspective, if a normal coral reef would be an aquarium with 300 cryptobenthic fish of 15 different species crammed inside, soft sediment habitats would be the same aquarium with 30 fish of 16 species.

When looking at environmental factors, one of the most important factors that influenced where species lived, was the characteristics of the sediment. For small critters it makes a big difference whether the sand is powdery fine, or coarse like gravel. There seems to be a middle ground where the size of the sediment seems ideal for many critters. The tricky part is that the characteristics of sediment are in a large part determined by other processes such as currents or wave action. For now it is too early to conclude whether critters are found in these places because of the type of sediment or because of other factors that shape the sediment!

The amount of growth on the bottom played a role as well, particularly when algae or sponges were present, which makes sense as it offers variation in the habitat and potential hiding places for some species. Depth differences played a minor role in some regions (Daiun, Bali), but did not make a real difference in Lembeh. The limited effect of depth could partially be due to the fact that we did not survey deeper than 16m (university diving regulations are quite restrictive). It would be a great follow-up study to compare with deeper depths, as I am sure they will give very different results.

What does it all mean?

This study was (as far as I know) the first one ever to investigate the cryptobenthic fish in soft sediment habitats. The unexpectedly high diversity and very low abundance means there is a lot more  species out there than what was assumed, but that we have to look much harder to find them. I mostly see our results as a starting point to guide further research. We have only uncovered a fraction of what is out there and are not even close to really understanding how tropical soft sediment systems function. While this provides an exciting opportunity for scientists like me to new research, it also means that we do not yet know how environmental threats such climate change or overfishing will impact  species living on soft sediment. We do not know yet if the species that muck dive tourism depends on need protection, or how to best protect them if they do.

Whiteface whaspfish

We might not know yet what the future holds for sand-specialists like this whiteface waspfish (Richardsonichthys leaucogaster), but I am hoping to find out!

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New research project: diversity in Wallacea

A few weeks ago I wrote about starting an exciting new project at the University of Leeds. At the time I didn’t go into details, but now that I’m a few months in and I am starting to understand what is going, so it’s time to enlighten you as well.

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Coral reef critter research coming up!

For the next two years I’m part of a team that will study marine biodiversity on coral reefs in central Indonesia. The overarching goal of of the project is to improve the management and conservation of coral reefs by discovering how impacts such as pollution or overfishing change the way coral reefs function. After all, the best way to start solving a problem is by properly understanding it.

Obviously, there’s a lot more to it than the lofty big goal as the title of the project indicates: “Gradients of marine biodiversity and linkages with eDNA across the Wallacea Region”. There are two components to the project: traditional visual surveys and environmental DNA (“eDNA”) surveys. We will use both methods to create ecological networks and see how they differ when they are threatened by different impacts.

At this point you might be asking a few (logical) questions:

  • Where is the Wallacea region and why do you go there?
  • What is eDNA?
  • What is an ecological network?
  • Why should I care? I came to this site to read about critters!

The Wallacea region is the central part of Indonesia, from Lombok eastward almost all the way to Papua, and up all the way to Halmahera (check out the map below). It was named after Alfred Russel Wallace, the scientist who, together with Darwin, developed the theory of evolution. The region represents an interesting boundary area where fauna and flora from the Asian and Australian continents meet. So it is home to some amazing wildlife, but also to a large human population that depends on natural resources to survive. The marine diversity in the region has not been studied very well (except for a few local exceptions), so finding out how healthy the marine ecosystems are is quite important.

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The Wallacea Region

Environmental DNA (eDNA for short), is a relatively new method to detect species. I have written about it extensively here if you want a long explanation and background. The method detects tiny fragments of DNA in the water column that are shed through poop, mucus, etc. By filtering and analysing a scoop of water, we can tell what animals (and plants, microbes, etc) live in the water nearby. It’s pretty powerful and very exciting, but still needs a lot of additional testing to know just how precise it is compared to other survey methods.

I will then build ecological network models with all the data we collect. The easiest way to imagine what those are, is to see them as a different kind of food web. Where food webs focus on who eats who, we are more interested in who lives close to who, and who interacts with who. In the ideal situation I will include all the information on fish, corals, algae, invertebrates (crabs, sea stars, etc.) in one big model which will show how they rely on each other. More importantly, it will also show what happens with the networks if sites are overfished or polluted and how that differs from untouched sites.

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Example of an interaction network on land, figure by Bohal et al. 2013. Source here.

So yes, my job for the next few years is less critter-focused than before, but it doesn’t mean I will be ignoring them! Besides the obvious fact that there’s a lot of cool critters to be found on the coral reefs I’ll be visiting, I am still involved in a few very cool projects on the side. It’s too early to go into details, but more seahorse and seadragon work is coming up, and even some exciting pygmy seahorse news as well! I’ll regularly be posting updates on the Wallacea project, as well as more critter features, so stay tuned 🙂

Wondering about mimics?

I have been meaning to write a blog about the Mimic octopus (Thaumoctopus mimicus) and Wunderpus (Wunderpus photogenicus) for ages, but inspiration has eluded me until I was revisiting some of my earlier research on charismatic muck dive species. Both the mimic octopus and the wunderpus are very popular with critter enthusiasts, but we know surprisingly little about them. Time to change that or at the very least tell you some of the things we know about them!

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A wunderpus (Wunderpus photogenicus) checks out my camera

If you’re not a diver or you have never heard of them, the Mimic and the Wunderpus are very (very!) funky species of octopus. They have a wide range of interesting behaviour, they look amazing, and both are found on sandy habitats in the tropics. What they also have in common is that both were only recognised as new species fairly recently (2005 and 2006).

Just by reading their scientific names you could imagine these are not your average cephalopod. The wunderpus’ species name “Wunderpus photogenicus” says it all and  is probably also one of the easiest scientific names to remember (except maybe for the brilliantly named “Boops boops“). “Thaumoctopus mimicus” tells you that this particular species is good at mimicry, even for octopus standards.

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Mimic octopus (Thaumoctopus mimicus) foraging on the sand

Both species live on soft sediment (mostly sand) habitats and they have evolved to be perfectly adapted to this lifestyle. They live in holes in the sand, are small, have longer arms than your average octopus, and their colours are quite drab. There are a few subtle physical and behavioural differences between the two though.

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Wunderpus partially in its hidey-hole

One of the things I noticed is that their hunting strategies vary slightly. Wunderpus have more extensive “webbing” between their arms than mimics and they use this webbing when hunting. Crabs are a favourite prey of wunderpus and they catch them by spreading their mantle (the “web” between their arms) over rocks, holes, or other objects like a big parachute. They then use the tips of their arms to poke the crabs out of their holes, after which they run into the parachute-web and are easily collected with one of the other arms.

Mimic octopus seem to forage more actively and (in my experience) use the parachute-technique less often. Instead they poke their long arms into holes in the sand, scaring out any critter that’s in there and then grabbing it directly. This means that mimics spend even more time moving over the sand than wunderpus do, which might be why they evolved some very particular behaviour.

Mimic

Trying to mimic?

Whenever you search for information about the mimic octopus, one of the first things to come up is that they mimic all kinds of other animals. Unlike other octopuses, it does not just mimic colour, but also the behaviour of up to 6 (or 8 or 12 depending on who you ask). The question is, does a mimic really mimic? Their mimicry is supposed to deter or fool predators or prey, but I wonder if this is really the case, or whether we are over-interpreting things from our human perspective.

Many of the behaviours that have been called mimicry could also be explained by simple logic or physics. Take for instance the idea that they mimic toxic flounders/soles while swimming. Yes, they do look very similar when they swim, but it is also a fast and energy-efficient way to swim over any flat area. Which is undoubtedly why this type of swimming is used by most octopus species living in the sand. Another example is the lionfish-mimic, which could also be explained as a way to look as big as possible when threatened. It’s a very common tactic used throughout the animal kingdom, and if you happen to be an octopus with long arms, you’ll look like a spiky lionfish when spreading them out. Other behaviours can similarly be explained, but I wouldn’t want to bore you with long lists right now.

Does this mean they do not mimic or that I am just a mopey cynical bastard who refuses to be amazed by a fantastic animal? Of course not! I love mimics and they show some  of the most extraordinary behaviour in the ocean. It just means that I want to learn more about them to find out what causes it.

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Close up of a mimic octopus

To study them properly, you first need to be able to tell the wunderpus and mimic octopus apart though! These critters look very similar (stripey), so it’s easy to get confused. Here is what to look for:

  • Arm patterns I: The black/white patterns on the arms of Wunderpus are very sharply defined, compared to more blurry with the mimic. Imagine the patterns on the wunderpus were drawn by a German painter using a pen and ruler, and the ones of the mimic by me with some crayons.
  • Arm patterns II: Mimic octopus have a continuous white outline along the border of each arm. The wunderpus does not have this, instead the band-pattern continues across the border.
  • Head: Mimics have a “U-“-shape on the back of their head, where wunderpus have a white patch.
  • Colour: Wunderpus usually have more of a red/brown colour shade to them than mimics, which are almost always black and white. Careful though, they can both change colour so this is not the best way of telling them apart.
  • Behaviour: The hunting behaviour I described earlier is a hint, though not always consistent. From my experience, wunderpus live in areas where the sand is more coarse (gravelly) than mimic octopus, which could also explain why they have slightly different hunting methods.

Finally, because you made it this far, here is a video I took of mating mimic octopus in Indonesia:

Closing one chapter and opening another

It is time to share some very big news. My time in Australia has officially come to an end and I am starting a new and exciting chapter on the other side of the world. From April onward I will officially become a “Research Fellow in Quantitative Tropical Marine Ecology” at the University of Leeds in the UK. In other words, for the next two years I will work as a postdoctoral researcher on a very exciting new project.

I will write about the new project in more detail soon, but right now I am feeling a bit nostalgic about the past 6 years of living and becoming a scientist in Australia .

End of traps celebrations

Celebrating the end of an experiment on the Great Barrier Reef

I arrived in Australia as a dive instructor, thinking I’d be there for a few months to help out a good friend with a research project on cleaner wrasses in the Great Barrier Reef. Working and living on Lizard Island Research Station gave me the chance to meet some amazing marine scientists passionate about their research. More than anything else, the people I met there are what pushed me in the direction of becoming a marine scientist.

A series of fortunate events lead me to Perth and I somehow managed to convince Professor Euan Harvey that taking on a semi-nomadic beach bum for a student would be a great idea. To this day I still do not know if  Euan was being very wise or very stupid, but once I got my foot in the door of the Fish Ecology Lab it took them about 6 years to get me out again.

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The amazing team of the Fish Ecology Lab, all of you will be missed!

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Happy sunset drinks by the beach

While I never planned on spending a long time in Australia, it didn’t take me long to appreciate the beauty of the place. Western Australia in particular is basically a Europe-sized playground for people who love the outdoors. I can’t count how many camping trips, dives, surf sessions, ocean swims, hikes, … I’ve done in recent years and I still haven’t seen half of what I’d want to see. Some of the highlights that come to mind include camping on remote beaches, diving with seadragons, snorkeling with sea lions, and sunrise surf sessions with friends. I won’t even begin to write about the many wine tasting sessions down south 🙂

I was lucky enough to meet some amazing people along my journey. Almost without noticing it, I built up a group of colleagues and friends. I love the typical Australian easy-going, honest (sometimes in-your-face) style of communication. Even if it could not be more different from what I was used to in Indonesia (or even Belgium). The people more than anything is what make or break a place, and I will miss the ones I left behind in Perth dearly.

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Exploring the coastline in southern Western Australia

When I arrived in Australia I never expected that it would become a second home, but that is exactly what happened. The people, the wildlife, the landscapes, all of it have found a spot in my heart, and I am grateful for my time there. I am very much looking forward to starting a new chapter, if it’s even half as good as the last one it is going to be fantastic.

lucky bay

See you next time Australia!