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 🙂

New publication: Flash photography impacts on fish – To flash or not to flash?

The final paper of my PhD thesis has just been published online in the journal Scientific Reports. The paper, titled “Behavioural and pathomorphological impacts of flash photography on benthic fishes” explains the effects of typical diver behaviour while photographing small critters such as seahorses or frogfishes.

The paper itself can be a tad technical, so with the help of two co-authors (Dr. Ben Saunders and Tanika Shalders), I wrote this summary of the research, which was published first at The Conversation (original article here).


We all enjoy watching animals, whether they’re our own pets, birds in the garden, or elephants on a safari during our holidays. People take pictures during many of these wildlife encounters, but not all of these photographic episodes are harmless.

There is no shortage of stories where the quest for the perfect animal picture results in wildlife harassment. Just taking photos is believed to cause harm in some cases – flash photography is banned in many aquariums as a result.

But it’s not always clear how bright camera flashes affect eyes that are so different from our own. Our latest research, published in Nature Scientific Reports, shows that flash photography does not damage the eyes of seahorses, but touching seahorses and other fish can alter their behaviour.

Look but don’t touch

In the ocean it is often easier to get close to your subject than on land. Slow-moving species such as seahorses rely on camouflage rather than flight responses. This makes it very easy for divers to approach within touching distance of the animals.

Previous research has shown that many divers cannot resist touching animals to encourage them to move so as to get a better shot. Additionally, the high-powered strobes used by keen underwater photographers frequently raise questions about the welfare of the animal being photographed. Do they cause eye damage or even blindness?

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Does flash harm fishes? Photo: Luke Gordon

Aquariums all around the world have taken well-meaning precautionary action. Most of us will have seen the signs that prohibit the use of flash photography.

Similarly, a variety of guidelines and laws exist in the scuba-diving community. In the United Kingdom, flash photography is prohibited around seahorses. Dive centres around the world have guidelines that include prohibiting flash or limiting the number of flashes per fish.

While all these guidelines are well-intended, none are based on scientific research. Proof of any damage is lacking. Our research investigated the effects of flash photography on slow-moving fish using three different experiments.

What our research found

During the first experiment we tested how different fish react to the typical behaviour of scuba-diving photographers. The results showed very clearly that touching has a very strong effect on seahorses, frogfishes and ghost pipefishes. The fish moved much more, either by turning away from the diver, or by swimming away to escape the poorly behaving divers. Flash photography, on the other hand, had no more effect than the presence of a diver simply watching the fishes.

For slow-moving fishes, every extra movement they make means a huge expense of energy. In the wild, seahorses need to hunt almost non-stop due to their primitive digestive system, so frequent interruptions by divers could lead to chronic stress or malnutrition.

The goal of the second experiment was to test how seahorses react to flash without humans present. To do this we kept 36 West Australian seahorses (Hippocampus subelongatus) in the aquarium facility at Curtin University. During the experiment we fed the seahorses with artemia (“sea monkeys”) and tested for changes in their behaviour, including how successful seahorses were at catching their prey while being flashed with underwater camera strobes.

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The aquaria were the seahorses were housed during the experiment

An important caveat to this experiment: the underwater strobes we used were much stronger than the flashes of normal cameras or phones. The strobes were used at maximum strength, which is not usually done while photographing small animals at close range. So our results represent a worst-case scenario that is unlikely to happen in the real world.

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West Australian seahorses (Hippocampus subelongatus) in their aquarium at Curtin University

The conclusive, yet somewhat surprising, result of this experiment was that even the highest flash treatment did not affect the feeding success of the seahorses. “Unflashed” seahorses spent just as much time hunting and catching prey as the flashed seahorses. These results are important, as they show that flashing a seahorse is not likely to change the short-term hunting success (or food intake) of seahorses.

We only observed a difference in the highest flash treatment (four flashes per minute, for ten minutes). Seahorses in this group spent less time resting and sometimes showed “startled” reactions. These reactions looked like the start of an escape reaction, but since the seahorses were in an aquarium, escape was impossible. In the ocean or a large aquarium seahorses would simply move away, which would end the disturbance.

Our last experiment tested if seahorses indeed “go blind” by being exposed to strong flashes. In scientific lingo: we tested if flash photography caused any “pathomorphological” impacts. To do this we euthanised (following strict ethical protocols) some of the unflashed and highly flashed seahorses from the previous experiments. The eyes of the seahorses were then investigated to look for any potential damage.

The results? We found no effects in any of the variables we tested. After more than 4,600 flashes, we can confidently say that the seahorses in our experiments suffered no negative consequences to their visual system.

What this means for scuba divers

A potential explanation as to why flash has no negative impact is the ripple effect caused by sunlight focusing through waves or wavelets on a sunny day. These bands of light are of a very short duration, but very high intensity (up to 100 times stronger than without the ripple effect). Fish living in such conditions would have evolved to deal with such rapidly changing light conditions.

This of course raises the question: would our results be the same for deep-water species? That’s a question for another study, perhaps.

So what does this mean for aquariums and scuba diving? We really should focus on not touching animals, rather than worrying about the flash.

Flash photography does not make seahorses blind or stop them from catching their prey. The strobes we used had a higher intensity than those usually used by aquarium visitors or divers, so it is highly unlikely that normal flashes will cause any damage. Touching, on the other hand, has a big effect on the well-being of marine life, so scuba divers should always keep their hands to themselves.

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Look, take pictures, but don’t touch!


NOTE: I realise that this is a controversial topic in underwater photography. If you have relevant questions, comments, or thoughts you want to share, feel free to add them in the comment section below. If you are interested, I would highly advise you to read the original research paper via this link. The paper is open access, so anyone can read and download it. If you have specific questions about the paper, you can always contact me via email here.

Marine biodiversity in Oman: Mini-blog 3 – Workshop time

The Oman fish biodiversity trip I am currently doing is nearly over. We spent the last days in a workshop at the Sultan Qaboos University in Muscat. The workshop focus was on “Bridging the gap between marine resource managers and research institutions in Oman and Australia”. Besides our team, the workshop was attended by Omani researchers and government officials, international researchers working in the region, and even by marine students from the university.

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Participants to the workshop at Sultan Qaboos University

With such a varied group of attending researchers and presenters, talks were bound to be interesting and go beyond the work I am familiar with. The first day focused on seas around Oman, its diversity and natural history. Since this was my first visit to Oman and I know very little about its marine life, there was a lot of interesting new information to absorb.

The Omani seas are fascinating for many reasons, but one of the things that really stuck with me was how big the environmental differences are in a relatively small area. The north of Oman has seas that get very hot, with a high salinity and a very different fauna and flora than the southern areas. The south of Oman has coral reefs, but also has a strong cold upwelling each summer. This upwelling is so strong that temporary kelp forests grow here in summer! I did not get to dive there this trip and the kelp has already disappeared this time of the year, but it would be fascinating to come back and dive in the Salalah area.

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Hussein Al Masroori talks about designing solutions to reduce ghost fishing by lost fish traps

The second day of the workshop moved from natural history to new monitoring techniques, and explored some of the regions nearby Oman. There was a thought-provoking (but sad) talk about the heavy impact of coral bleaching in the Arabian Gulf. Water temperatures in the summer of 2017 reached up to 36°C, and some areas lost more than 90% of coral cover! Our team members also presented some of their personal work, Joey talked about eDNA, Darren about monitoring biodiversity in the Red Sea, and Chris talked about how cryptobenthic fishes could be used a sensitive measure of changes in reef health.

In an interesting discussion afterwards, it became very clear that collaborating across different countries is more effective than just working as a loner. When experts in certain fields can share their work and skills with researchers that may not have the infrastructure or cannot get the training in the country they work, everyone benefits. Local researchers often have a very extensive knowledge and valuable insights that visiting researchers just don’t have. As visitors, we can offer a new perspective and stimulate new ideas to help push the boundaries of knowledge.

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Sultan Qaboos University. Photo source: www.squ.edu.om

People like Joey and Alyssa, who stimulate these kind of collaborations, are the ones that (in my humble opinion) will make the biggest difference to marine science. Not just to improve our understanding of the ocean, but also to improve how we can sustainable use the ocean, or protect the areas and species that need it most.