New publication: Critter diversity on the sand

September 14, 2019September 14, 2019 / Maarten De Brauwer / 1 Comment

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.

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.

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!

Sediment characteristics play an important role in where critters are found

Luke collecting 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.

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!

Guestblog: Frogblogging – insights in the world of frogfishes

October 18, 2017October 18, 2017 / Maarten De Brauwer / 4 Comments

This month’s guestblog is written by Daniel Geary, the resident marine biologist at Atmosphere Resort in Dauin, Philippines. It’s safe to say that Daniel is very passionate AND knowledgeable about frogfishes. He’s been studying them for years in Dauin and even wrote (and teaches) a PADI speciality course on these awesome critters! In this blog he gives a taste of some of the many ways frogfish are fantastic and deserve a closer look.

Longlure frogfish (Antennarius multiocellatus) from Florida

Frogfish. You have probably heard of them, and if you’re a diver you might have seen one or two before. You have definitely swam right past a few of them without knowing they were there. Although most of them have a face only a mother could love, behind this outer layer exists a well-adapted, expert fisherman with amazing camouflage capabilities. They are more than just a lazy, camouflaged blob that sometimes doesn’t change location for a year.

Frogfish are anglerfish, although they are what I call a shallow, less ugly version of anglerfish. They have a rod and a lure that they actively fish with when necessary. Their fins look like limbs that somewhat resemble those of a frog. They must inhale water though their mouth to then push it out of their gills which aids in locomotion. Frogfish are experts at changing color and can change color multiple times, usually to blend in with their surroundings. Normally a full color change takes about 2 weeks, but frogfish have been witnessed to change color in under ten seconds when disturbed by divers’ bubbles and needing to switch to a different coral.

The same giant frogfish (Antennarius commersoni) changing colour in two weeks

There are around 50 species of frogfish, with a new species or two being described every few years. Frogfish can be found worldwide in tropical and subtropical waters (but not in the Mediterranean). Some species are only found at a handful of dive sites, others are only found in one country or continent. A handful of species are found in the majority of the warm water areas, but only the Sargassumfish is found worldwide. There have been a few occasions where Sargassumfish were found all the way up in the cold waters of Norway and Rhode Island – way out of their preferred habitat, but they live their lives floating in seaweed and/or other debris and are at the mercy of the ocean currents.

Sargassum frogfish (Histrio histrio) often wash up on the shore of the Atmosphere housereef, when they do, they get released back into deeper water

Painted frogfish (Antennarius pictus) using its lure to attract prey

Frogfish are ambush predators which is why they seem to be so lazy. The less they move, the better predators they can become due to algae, coral polyps, and any other organisms that use the frogfish as habitat. I call this being lazily efficient, or efficiently lazy. Frogfish will make minimal adjustments to their body positioning before they begin to lure prey, although sometimes the frogfish are so camouflaged that they don’t need to actively attract prey. Frogfish swallow their prey whole by opening their mouth and creating an instant vacuum since the volume of the mouth increases up to twelve times the original amount. This means frogfish can swallow their prey whole in six milliseconds. They feed on a variety of organisms, depending on where the frogfish lives. Generally they like small fish like cardinalfish, shrimps and crabs, and sometimes other frogfish. They can comfortably swallow prey that is their own size, and with a bit of effort they can swallow prey up to twice their size, although this can result in the death of the frogfish if the prey item is too large and gets stuck in their throat. Frogfish do not have many predators, but they are sometimes preyed on by moray eels, triggerfish, and lizardfish. Flounder will sometimes suck up juveniles from the sand and fishermen in the Philippines have been known to capture and eat Giant Frogfish.

This giant frogfish (Antennarius commersoni) bit of more than it could chew and did not live to tell the tale. Photo taken at Apo Island

Frogfish egg raft

Frogfish have been known to eat each other if they get too close, especially after failed mating attempts. A male will approach a female when she is bloated with eggs. He will do his best to show off for her, which includes expanding his fins to their maximum sizes, rapidly opening and closing his mouth, as well as violently shaking his body. At this point, the female either accepts him or tries to eat him. If accepted, he gets to stand next to the female, which is the frogfish equivalent of holding hands. Once he is ready to mate, he will start again with his flashy moves, but this time bouncing around the female. Sometimes he has to physically swim her off the substrate to mate, other times she is able to swim on her own. Once they are a meter or two above the substrate, the female releases her egg raft, causing her to spin rapidly. The male then fertilizes this egg raft, also spinning rapidly. Both the frogfish then return to the bottom as the eggs float off into the distance. The eggs will hatch a few days later and become tiny planktonic frogfish babies, which will continue to float for a month or two until they are big enough to settle in the substrate, change color, and begin their lives as adorable frogfish.

A male (red) painted frogfish (Antennarius pictus) trying to convince the female (yellow) to mate

Stay tuned for more frogfish insights coming in December, where I’ll write about the history of frogfish research and describe a handful of frogfish species, including a potentially “new” species. Until then, keep an eye for frogfish on all your dives, especially if you’re in warm water.

Fluo time

November 27, 2016November 27, 2016 / Maarten De Brauwer / 2 Comments

If this isn’t the first time you’ve read this blog, you probably know I am interested in the phenomenon of biofluorescence. I’ve previously talked written about what it is and what it might be used for. In the near future I’ll be tell you all about the details what I was actually doing. But I realized I haven’t shared any pictures recently that show just how beautiful and otherworldly it can be. So here is a random selection of fluo shots I took over the last two years. Enjoy!

A bubble snail (Hydatina physis) photographed in Lembeh Strait, Indonesia

Thorny seahorse (Hippocampus histrix) in Bima Bay, Indonesia

West Australian Seahorse (Hippocampus subelongatus) in Perth, Australia

Amazing coral in Raja Ampat, Indonesia

Reptilian Snake Eel (Brachysomophis henshawi) in Amed, Indonesia

Lizardfish (Synodus sp.) in Lembeh Strait, Indonesia

Cockatoo Waspfish (Ablabys sp.) in Lembeh Strait, Indonesia

Sea spider (Pycnogonid sp.) in Tulamben, Indonesia

Painted frogfish (Antennarius pictus) in Lembeh Strait, Indonesia

Juvenile Painted frogfish (Antennarius pictus) in Dauin, Philippines)

Barred moray (Echidna polyzona) in Nusa Kode, Indonesia

Using SMURFs to catch baby fish

April 27, 2016April 27, 2016 / Maarten De Brauwer / 1 Comment

Luke and I have been in Dauin for a few days now. We are here to investigate the recruitment of cryptobenthic fish. If you’ve read this blog before, you’ll know that I am interested in camouflaged, small critters that live on the seafloor (=cryptobenthic). You might not, however, have heard about “recruitment”. This is the term used to describe the process of larval fish (which usually swim in the open ocean) “settling down” on the reef. When fish larvae settle, they change rapidly from small, transparent, weird oddballs to colourful reef fish. Or in the case of the critters I study, to camouflaged weird oddballs.

Larvae and adult Sargassum Frogfish (Histrio histrio) Source: http://nfchroniclesnoaa.blogspot.com

There are many reasons why I would like to know more the recruitment of the species I study. The most important one is that nobody really knows why some of these baby fishes show up where they do. If you don’t know this information, it is really hard to protect the right places that would be a suitable habitat for baby fish. Another reason is that this process is vastly different from anything we see on land, making it fun and challenging to try and figure out what is going on.

So how does one best study tiny baby fish? In the case of my critters, looking for the small adults is already hard, so how do you even begin to try and find the even tinier versions? The slightly disappointing answer is: “We don’t really know”. There are multiple techniques to find new recruits or larvae that are about to settle down (light traps, visual surveys, crest nets, …). But most of those don’t seem to be very effective for camouflaged critters. One method did show promise in a study in the Caribbean, the benthic “SMURF”. If at this moment you are imaging little blue creatures with scuba tanks, catching baby fish with lassos and you don’t want to spoil that mental picture, please stop reading now.

SMURF at sea (Photo Luke Gordon)

Since you’re still reading, I can now disappoint you about my SMURFs, they are not the ones you have seen on tv (no ethics clearance possible). SMURF stand for “Standard Monitoring Unit for Recruitment of Fishes”. It is a mesh-basket you fill with any substrate you want (pebbles, sand, coral rubble, plastic,…) which you then place in the ocean for a set time. After that time you collect the basket and see how many baby fish were attracted to your unit. Not quite the blue man-option, but you are the one who kept reading.

Luke and me made a whole bunch of units, which we deployed around Dauin. To deploy the units we had the help from my supervisor Euan Harvey, who decided to drop by to see what we are up to in Philippines. Euan is an expert in remote sampling using video cameras, but he definitely seemed to enjoy setting up experiments on baby critters as well. This could be due to the fact that on his very first muck dive here, we found Flamboyant cuttlefish, Blue-ringed octopus, a bunch of Frogfish, Ghostpipefishes, Seahorses and loads more critters.

Euan photographing Ghostpipefish (Photo Luke Gordon)

This is the second time I am trying this experiment, the first attempt was thwarted by the ocean. Conditions are looking better now, so with some luck the units will survive the next weeks. By the end of the SMURF-project, we will hopefully know if this method works well for the species I study. With some luck, I will even be able to tell you if baby cryptic fish prefer sand, pebbles, or rubbish. The method can then be used in the future for other people wanting to study the recruitment of cryptic species, so we can start to unravel some of the bigger questions about these poorly studied animals.