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Living fossils of the mesophotic

July 7 2018

We're on a mission to study feather stars over the depth gradient from shallow to mesophotic depths. We focus on the intimate relationships between them, their infestors and predators.

July 7 2018


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Mission Underway

There’s life at depth, a lot of it too!

Our tec team have filmed over 20,000 feather stars in video transects spanning coral reefs in the upper mesophotic zone (between 30-70 m), called ‘mesophotic coral ecosystems’ (or MCE). From these videos we can identify our eight superstars and see how many other feather stars live there. To our surprise, comparisons with transects from shallow reefs (surface to 30 m depth) reveal similarities: feather star communities are equally diverse, but more of them are found in shallow reefs. However, while we do see overlap, some species are rare in the shallows and others are completely unique to MCEs!

You might wonder (because we did too): how can a world so rich exist in this deep and dark place? Changing light penetration is key to orchestrating the shift in communities we see from shallow to deep. Whereas shallow reefs receive total light penetration, light struggles to access the mesophotic zone (found at 30-150 m depth; ‘meso’ means middle, ‘photic’ refers to light), and none reachs past this zone to the deep sea (deeper than 150 m; called ‘aphotic’, ‘a’ = no, ‘photic’ = light). Because of this, light dependent coral, algae, other organisms can still be found in MCEs, but not deeper. Note, however, there is life in the deep sea too (even coral reefs spanning several kilometers, like in shallow and mesophotic zones!).

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Life after fieldwork: where the real magic begins!

Life doesn’t stop after completion of fieldwork, this is where the real magic behind science begins! After two months of diving to the seafloor, spying on our superstars and their inhabitants, we have gathered a tremendous amount of data. Now we take ‘dry days’ (sit at our computer rather than the bottom of the ocean) to create graphs that highlight patterns hidden behind the vast sea of numbers we’ve generated.

So, what do these graphs tell us? How intimate is the relationship between feather stars and their micro-world? If you recall, we played a little game of Magic Cup, shuffling shrimp and lobsters from one feather star species to the next, some had different colours, others had the exact same - we wanted to see if they would go back to their original host. The graphs unveil a remarkably close relationship between squat lobsters and feather stars, and one that isn’t so clear for shrimp. They tell us squat lobsters are picky when it comes to selecting a forever home, with the majority returning back to their exact host after a matter of hours (we call this ‘individual fidelity’). Shrimp on the other hand show ‘species and colour fidelity’ (not individual fidelity), only reshuffling themselves if the exact colour of their new home doesn’t match theirs. It seems feather stars might in fact be a perfectly engineered home after all, providing inhabitants with everything they desire in a safe haven.

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Voodoo gases that keep us sane at depth

Things get a little bit tricky in terms of gas once you start breathing it deep. For these dives our tec team need to consider not only narcosis (principally from nitrogen, which blurs the mind, much like on a good night out with friends and several bottles of wine), but also the fact that 21% Oxygen (i.e. air) becomes toxic deeper than 57m. As a general rule, dives beyond 50m require ‘trimix’ – a gas mix of Helium, Oxygen, Nitrogen. Adding Helium to the mix allows our tec team to reduce the amount of Nitrogen in the gases they breath at depth. They also carefully blend these gases to reduce oxygen content thereby lowering the dangers of Oxygen toxicity. This week's dive to 65m at Unity Point, for example, was on a blend of 18% Oxygen, 30% Helium and 52% Nitrogen. As previously discussed these dives require long decompression: 26 minutes at 65 requires more than an hour ascent switching from the gas they breathe at depth (trimix, also known as ‘back gas’) to first 50% and then 100% oxygen. 

We get creative with gas blending

As we use a partial pressure blending system it can be hard to get the final few liters out of large tanks of our precious (expensive) Helium stores, but a craftily put together system using pipes, plastic bags, duct tape and a faucet allow the tec team to get Helium directly into the compressor, and blended back gas. This success was greeted with unbridled happiness that this plan (referred to as ‘trash bagging’) actually worked!

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I'd like to help out!
Chino Corpus 09157563958 | 09177327174chinocorpus@gmail.comDirector | Cinematographer

Feather star fingerprints

Keeping track of hundreds of near identical individuals seems like a cruel mind game, but fear not, some of our superstars have ‘fingerprints’ just like you and I! If you were to flip over a feather star and look at its centrodorsal (the middle part of its body where all arms radiate from) you would notice darker patches - a pattern reminiscent of an inkblot. At a glance they seem very similar from one specimen to the next, but stare at them long enough and distinct patterns form that help us differentiate one individual from another. We rely on photographs of their centrodorsals, which we match to its identical twin from the day before, to relocate the individual and then note findings specific to it. As our experiments go on we find ourselves becoming masters at this memory game. Here are some examples of the fingerprints we work with. Are you able to find the matching pairs?

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I'd like to help out!
Chino Corpus 09157563958 | 09177327174chinocorpus@gmail.comDirector | Cinematographer

Not so sessile after all - they crawl and swim!

We’ve talked previously about our swift moving escape artists (infestors), but what about our superstars? Most assume feather stars are sessile creatures, they look like a plant after all and, if undisturbed, they live on the same perch (a rock, piece of coral, anything they can grasp) for most of their lives – which is great for relocating individuals for our research! BUT they do have the potential to crawl or swim away from a predator (and our experiments). They do this surprisingly quick too! How does their physiology enable them to move so freely? Feather stars have ‘mutable connective tissue’, a ligament that they actively control, allowing them to coordinate complex movements, on multiple arms, at the same time. For example, feather stars stiffen this tissue to remain in their feeding posture against a strong current, and relax it to autotomize arms when nibbled on by a fish or other predators. These ligaments are also responsible for their highly coordinated swimming strokes: first, a short burst of alternating arms moving up and down, then the arms gather to form a parachute for the slow fall to their new perch. Here's a video of their mesmerizing dance caught on camera (by Caters Clips)!

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I'd like to help out!
Chino Corpus

09157563958 | 09177327174

Director | Cinematographer

Our bittersweet love affair with Mesophotic reefs

One key reality in SCUBA diving is the deeper you go, the shorter you stay! Unless you’re technical (‘tec’) diving. Staying within prescribed ‘no decompression limits’ (meaning that at any point of the dive it is relatively safe to surface) severely shortens your time at depth, and in our case, make it impossible to survey sites much deeper than 30 m. Thanks to tec diving, Tadhg and Angela (our ‘tec team’) can plummet safely and for long periods of time to our deep sites (30-70 m). But this comes at a cost: unlike recreational diving, the tec team does not have direct access to the surface without risk of decompression sickness (remember those tiny bubbles that cause big problems?).

Copious gas needs

Breathing under water is our (every marine scientists’) dream superpower! Until that comes true we must bring a SCUBA (Self-Contained Underwater Breathing Apparatus) tank full air to explore the seafloor. One tank typically suffices for a short and shallow dive, but not for a tec dive. The longer and deeper our tec team ventures into the deep, the more gas they need to carry to ascend slowly, stopping (‘decompressing’) and waiting several times on their way to the surface. By doing this, they eliminate gases that have quickly accumulated in their tissues, which then leave their body gradually rather than like a well shaken Champaign bottle ready to pop! To decompress, the tec team bring up to four tanks filled with various mixtures of gas (note: Oxygen becomes toxic at depth - another layer of complexity to diving that deep). In short, gas needs is where our bittersweet love affair with mesophotic reefs began!

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Master blender/underwater clown – meet Tadhg (‘Irish man’)!

Known around MCP for his witty jokes and outgoing personality, it’s safe to say that this ‘Irish Man’ is a fan favourite. It’s not all fun and games though, he’s often found working hard behind the scenes, blending gases (requiring several hours of cautious work) so he and Angela can venture to deeper parts of our dive sites to survey feather stars who live there. This realm, known as ‘mesophotic’ depths (deeper than 30 m, shallower than 150 m), is severely under explored because of the challenges involved in accessing them. For example, to dive to 60 m (dubbed ‘upper mesophotic’) Tadhg uses some serious problem solving and mathematical skills to calculate the exact volume and ratio of Helium, Oxygen, and Nitrogen we need to breathe at depth and during our ascent to keep us at the bottom for long enough to finish our surveys and surface safely without any gas or decompression issues (aka build-up of small bubbles in our tissues that could cause big problems at the surface).

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Perfectly engineered (feather star) metropolis

Our team’s eagle-eyed vision (we wish!) can spot the tiniest of squat lobsters (generally less than 5 mm long), ghostly shrimp (some are translucent), burrowing fish, and near invisible worms… all of whom mirror the colour and patterns of their home so perfectly that they are often only detectable when/if they squirm away when awakened by us. That’s why we’re often seen tickling our superstars underwater!

If you recall, we chose our eight superstars because of their vastly different morphologies. In theory, these dissimilarities help increase habitat complexity in a coral reef system (aka. provide a wider array of homes for potential inhabitants, like infestors, to choose from). By surveying the feather star metropolis we can see how good they are at contributing to complexity. Our surveys tell us they’re masters at it! For example, one individual can house as many as ten inhabitants from many different forms of life (snails, flatworms, and sea slugs to brittle stars, sea cucumbers, and lobsters). There’s no telling what you’ll see beneath this perfectly engineered metropolis!

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Hard worker (not just because her favourite dive site is Unity Point) - Introducing Charlotte Matthews

Committed to exploring the micro-world of feather stars, Charlotte spends hours under water staring at their undersides! She (and the team) have surveyed nearly 3000 feather stars over five vastly different dive sites, inspecting every part of their body for a combination of injuries (regenerating and missing arms) and infestors to see if the two are related. Her treasure hunt (of infestors) doesn’t stop there, every day she fights ripping currents in Unity Point, surge and waves in Malatapay (her two favourite sites!) just to have a peek at this feather star metropolis. As you can imagine this work requires a lot of intimate contact with her specimens so Charlotte can often be seen carrying out her safety stop with remnants of feather star arms clinging on to her. She has even been known to sport the tip of a feather star arm as a fashion accessory for her hair.

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An ocean-worthy cage

Building an ocean-worthy cage is not that easy, even Google has no answer on how to do this.

When Google fails, we get creative and improvise. In just a few hours Raffy and Ceasar build the carcass (a 1m x 1m x 0.5m frame) out of thin pieces of bamboo and for two days we tie slats of bamboo (acting as prison bars) to this carcass. Admiring our blistered fingers (sure sign of hard work?) we realize “mesh is best”. It’s much less tedious to sew mesh to the frame than each individual piece of bamboo, and water can circulate through it to feed tiny food particles to our superstars living inside the cage while also keeping escape artists (like our squat lobsters and shrimp) locked in.

The ultimate test to our newfound fitness is lugging the awkwardly large and heavy cages through 150 m of choppy surface water and securing them to the seafloor. After two months of experiments, strong currents, animals growing on/eroding them, and scientists tugging at them daily, the cages have survived and become one with the ocean (they look and smell like one!).

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Presenting Rob Hechler: Canadian undergraduate student, lover of cuttlefish…and wearer of Tuque’s in the scorching Philippine weather!

With a knack and enthusiasm for all things digital, we knew Rob would love working with the expedition’s copious amounts of video transects. He and the team are collecting 100s of shallow- (0-30 m) to deep-water (30-60 m) transects, and he’s patiently analyzing them all! Here's a picture of Rob slowly filming all of the feather stars along a 50 m underwater line transect. By following this line and filming at a fixed height above the seafloor (see the object dangling from Rob's hand and hovering a few inches off the seafloor?), he knows exactly how much area he has covered, making it easier for him to compare patterns of who is where at different depths. While no one questions his scientific abilities, some do however wonder about Rob’s decision to bring a multitude of sweaters, jackets and fleeces to a country where temperatures rarely dip below 30oC but he stands by his decision, occasionally even resorting to wearing a Tuque (Canadian term for a knitted winter hat)!

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Our home away from home – meet Marine Conservation Philippines

A not-for-profit organisation entirely dedicated to conserving marine habitats in the Philippines…and kindly going out of their way to make sure our research needs are fulfilled.

SCUBA diving boot camp

It was Marine Conservation Philippines (MCP) who made sure our dive team would be “research ready” in time to collect data. By their third week at MCP, Charlotte, Mikalyn and Rob were indeed that thanks to their dedicated drill sergeant, Dan (MCP’s Lead SCUBA Diving Instructor), who put our eager students through a rigorous underwater boot camp, including swimming through hoops underwater (backwards too!), hovering (sometimes upside down) above the seafloor while composing a novel (or nearly that) for Dan - all critical skills needed to record data under water.

Technical and deep diver boot camp

Meanwhile Tadhg and Angela (project leads) underwent a special boot camp of their own – a technical and deep diver boot camp. Diving deeper than 30 m brings on extra danger, requiring complex technical gear, gas mixtures, extensive technical dive training (more about this later on in the blog!), and once certified, practice. Soren (MCP Founder, Technical Dive Instructor extraordinaire, also dubbed Michael Phelps at times) is our saviour/mentor in this aspect. He has taught us everything we know and provided the shiny toys needed to successfully complete all surveys in the upper mesophotic zone (30 – 60m depths) and when one of us temporarily falls ill, mesophotic surveys continue, thanks to MCP technical divers who step in to help (thanks Ashley!).

Cages and their secret ingredient

Finally, we reveal the secret ingredient to our cages: the careful handicraft of Raffy and Ceasar, MCP's multitalented Dive Technician and Handyman. Our crinoids would be lost without them (literally).

MCP staff are not only there to provide technical support, but also, for 4-6 months of the year they are our family and home away from home. Learn more about MCP here:

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Introducing (w)undergrad Mikalyn: organizational and visual mastermind with priceless underwater facial expressions

We’ve told you a little about the animals we’re studying, our experiments and research sites, now we reveal the team making all of this possible. First up is one of our undergraduate research assistants, Mikalyn! Exaggerated facial expressions are key to storytelling in synchronized swimming, a skill that translates well in SCUBA diving. One glance at synchronized swimmer Mikalyn’s face reveals all about the status of her squat lobster/shrimp-host experiments. Mikalyn is delving into the world of community relationships by looking at infestor fidelity, to keep track of who is where in her cages she must carefully memorize the distinguishing features of each individual she works with. Outstanding organizational skills and visual memory allow her to seamlessly plow through a large number of replicates (she already has 120) in just a few weeks!

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Our complicated love-hate relationship with Unity Point

WHACK! That’s the sound of Unity Point hitting us straight in the face. This dive site -known for its fast flowing currents and thousands of feather stars- offers a perfect all you can eat buffet for our gluttonous feather stars. While our superstars love this, we don’t. Research here is a test of our patience and dive skills (maybe also a great workout?). Imagine swimming a 50 m pool length (essentially our transect) against a ripping current. That’s only half the battle because back on land we have to analyze the transects to see who and how many are present there (otherwise known, in ecology, as community distribution and abundance), so a 15 minute analysis (e.g. Dauin, another dive site) can quickly turn into an impossible task, taking hours (up to 4 hrs!!) to finish as feather stars are found by the thousands! We now feel fully prepared to take on our opponent. Til we meet again, Unity Point.

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Angela, this is fascinating!! Great work and a real pleasure to follow. I wish we could find a way to share this with students in Quebec. Thinking about that.

Thank you Donna! We could have a little video conference/tutorial with your students at some point. That would be fun! Thank you for reading and following :)

Feather star = big ball of Velcro!

The name “feather star” gives the illusion of something soft and fluffy, but in reality they are big balls of Velcro! In fact, their pinnules (branches off the main arm) mimic the shape of a Velcro bristle. A necessary part of their morphology that they use for capturing small particles in the water. Their Velcro like properties has also earned our superstars a bad reputation among divers. An accidental encounter with a feather star results in forever picking pinnules and arms off of your wetsuit/hair. Does this property inhibit our research? Yes, it does. Remember how we meticulously amputated a fixed number of arms off feather stars in our regeneration experiments to then calculate arm growth? This is thought to be affected by number of arms re-growing simultaneously, so arm hemorrhaging could skew our results. Not to worry, we’ve finally defeated this ball of Velcro, now used to our advantage to transport (up to 10!) specimens to their temporary homes.

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Anyone know how to “Wrasse proof” a cage? Because I need it.

We all know life is multifaceted and complex, it turns out infestors and their feather star hosts aren’t immune to this. Recently, shrimp and squat lobsters have been mysteriously disappearing from our cages. Nothing to worry it’s just a few individuals, it’s not detrimental to our experiment. But still we’re scientist (detectives?) so we feel compelled to solve this case. This week we had a momentary stroke of genius while thinking of our results and concurrently watching fish darting in and out of our cage. Our latest results tell us infestors show high fidelity to their host - they never leave their feather star, when moved they return quickly. After a brief literary investigation, we find out one fish in particular, a floral wrasse, happens to feed on small crustaceans (like our shrimp and squat lobsters)! Mystery has been solved but the problem persists and the wrasse continue to dine at our catered buffet.

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Preparation Stage

This week we have been setting up our infester experiments. We installed a large cage on the seafloor that has been subdivided into eight compartments. Here we house pairs of feather stars that are infested and uninfested with squat lobsters and shrimps. We trick the lobsters/shrimps by transplanting them to different hosts – some are very similar to their initial home, while others are vastly different. We track their movements to record host, colour, species fidelity. Stocking the cages with infested feather stars has not been an easy feat because feather star squat lobsters and shrimps are masters in disguise. Their specific colour patterns precisely match that of their host, allowing them to blend seamlessly into their feather star (or what we call a micro-habitat). Here are a few photos of the specimens collected this week. Can you spot the infestor? Any luck? We’ve zoomed in on the infestor, but still they are hard to see because these little guys are often less than one centimeter in length and well hidden with patterns and colours mimicking their host. Our first experiment testing individual host fidelity is due to begin soon! We'll keep you posted on the riveting activities of feather stars and their infestors, as well as the other experiments and observations that are due to begin in the next few weeks.

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Another aspect of our work consists of monitoring arm regeneration in our eight superstars. Here, we meticulously amputated four or more arms off 100 individuals, mimicking an injury caused by a fish, sea urchin, or other predator. Our animals feel none of this pain (we promise!), in part because they can’t feel pain (feather stars have no central nervous system like we do), but also because autotomy (self-amputation and regeneration - a magical power I wish I had!) is a natural process used by feather stars to escape fatal injuries. By sacrificing a few arms, the individual can swim away relatively uninjured from a hungry predator. This part of the experiment requires a lot of time and patience. We sit and wait for the arms to grow back (regenerate) less than a millimeter per day. We’re interested in any possible variation in growth between the eight species, and test what factors, like nutrient availability, temperature, depth and type of feather star (species), could be responsible for this dissimilarity in growth rates. Here's a picture of some regeneration in one of our feather star, at last! And the temporary home of our amputees.

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Our research much resembles a game of ‘Where's Waldo?’, in which we try to spot well camouflaged infestors, like shrimps, lobsters, snails, etc., that live among feather stars. By experimenting on these host-infestor relationships we can better examine the morphological and behavioural plasticity of infestors. For instance, we are testing host-specificity of small squat lobsters and shrimps that have uniquely adapted to living within the feather star’s arms and cirri (the fingers feather stars use to cling to their perch). In the images below we show two examples of such infestors: a shrimp (white), squat lobster (orange), and fish (brown and white) hiding in their feather stars. If you look closely, this fish has no fins - it has 100% adapted to living/slithering around on it's feather star host! Concurrently, we are documenting infestor and feather star species distribution over the depth gradient (from shallow to mesophotic coral reefs) to capture community patterns, resemblance across the bathymetric gradient, but also to try to understand factors that correlate with arm injuries in feather stars - one of which might be these inhabitants (shrimp, lobsters, etc.). Basically, we want to know who lives where, and, if absent from a locality, why? Here's a picture of Charlotte carefully examining the underside of feather star Capillaster multiradiatus during one of our surveys.

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Hello mesophotic lovers! We are back in the Philippines and continuing our research on the spectacular feather stars (or technically known as ‘crinoids’) that live here. This year we’re looking into multiple aspects of the native crinoid species’ ecology from shallow to mesophotic (30-150 m) depths. With three new research assistants from the University of British Columbia (Charlotte Matthews, Mikalyn Trinca Colonel, Rob Hechler) our team (led by Tadhg O Corcora and Angela Stevenson) is hoping to document observations from multiple depths and different sites along the East coast of Negros Oriental, Philippines, as well as conduct in situ (in water) experiments. The diversity and abundance of feather stars here, in the Philippines, is simply outstanding! Because we are interested in contrasts between species, our projects only focus on the eight most morphologically different species. Here are our superstars for this year's expedition, which you’ll see plenty of over the next few months!

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Expedition Background

We're on a mission to reveal host-infestor relationships over the depth gradient, from shallow to mesophotic depths.


We're entering a truly exciting time for mesophotic exploration. Happy to be following along here!

Thanks David!