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.

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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:

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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.

Guestblog: Frogblogging – insights in the world of frogfishes

IMG_0737This 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.


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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.

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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.

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

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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.

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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

 

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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.

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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.

Poll: alternative muck diving terms

voteAfter the recent blog about the history of muck diving I received some interesting suggestions about alternative names to describe the activity. Because this is a democratic blog, it’s time for a poll! Tell me (and the rest of the world) which name you prefer and who knows, it might just catch on!

While less talked about than the term “muck diving”, a few people suggested the world needs a fitting name for muck dive enthusiasts (maniacs?).  In bird watching the most fanatic bird watchers are called “twitchers“. I reckon finding an appropriate term for those divers that love nothing more than finding new critters could be interesting.

I have been offered some suggestions, but feel free to add others. For the sake of inspiration, the name “twitcher” actually stems from the nervous behaviour of a well-known bird watcher in the 50s and 60s. So feel free to make fun of your photograph happy critter-enthousiast dive buddies 😉

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Muck-enthusiast in action (can you see the black hairy frogfish?