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“Birth” announcement from a Maui Reef – Can you identify this baby fish?

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Spring is here!


Spring on Maui means that whale season comes to a close, the water starts to warm up, corals begin releasing their eggs and sperm into the water during their annual spawning events, and new baby fish begin to settle out of the plankton onto the reef.


The spring and summer months are prime months for baby fish settlement. These fish have spent weeks or months as larval fish developing up in the plankton, and when the time is right they leave the plankton and seek an appropriate reef to begin their life as juvenile fish.



Sometimes these settlements of fish number in the thousands or even – in historic years such as 2014 – in the millions of a single species. But the vast majority of fish species settle in smaller numbers with no fanfare, without our awareness. They are tiny, and they remain tucked into crevices in the reef until they are large enough to be less vulnerable to predators and until they are better able to defend themselves.


It is so rare to see these new arrivals – those that have literally just dropped out of the plankton the night before or two nights before – that it is almost like witnessing a birth when you see one!


baby puffer 2735IMG_2735 for blogI was in the “birthing room” today during a dive. As I reached out to pick up a stick on the sand, a tiny black thing darted a couple of inches. It was so tiny and so unremarkable that I hadn’t even noticed it. At first I thought it was a squid, but as I looked more closely, it appeared to be a tiny pufferfish.


At half-an-inch in length, this little guy already had the shape and proportions of an adult pufferfish. He had delicate fins in the right proportions and he even had an exquisite, tiny version of an adult pufferfish mouth. Any pufferfish parents would surely have said, “He’s perfect!”


He was so dark though, and appeared to have no distinguishing color or marks, that I never thought I would be able to identify the species of pufferfish he was.


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However, as I photographed him, over a few minutes, he turned lighter and lighter in color, revealing markings that gave away his identity! At less than the size of a dime he is an almost perfect miniature of an adult!


Can you identify which species of pufferfish this little guy is? Click here to find out if you’re right :-).



The Life and Times of a Humpback Whale Barnacle


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Last week we were treated to an unusual find during one of our dives off of Maui. There on the sand was a strange, black, partially-circular object composed of radially symmetrical segments. Was it plastic? Metal? With that symmetry, surely it was man-made.

But no, we’d seen something like this a few years before – it was part of a whale barnacle! Ten feet away from it we found its other half.



Every winter we keep our eye out for these lucky finds. Sometimes we find them soon after they have fallen off. If that is the case, the underside of the barnacle is covered with black whale skin (this one even had the flesh of a different species of barnacle, a gooseneck barnacle, still attached to it). If we find one months later, it has been picked clean by marine organisms.

barnacle undersides for blog

Left: Whale barnacle found (in two pieces) soon after falling off a whale, showing black skin embedded in barnacle (60 mm). Right: Barnacle found months after falling off of whale, picked clean by marine organisms. Photo: P. Fiene.


Until this year, all the barnacles we’d found had been intact. This one was unusual in that it was broken into two pieces. We don’t know exactly why. But, it allowed us to see – and not just read about and imagine – one reason the barnacle’s white shell stays so firmly attached to whales during the thousands of miles of migration, during their spectacular breaching, and through all sorts of sometimes violent male-on-male aggression. More on that later.


A humpback whale can have up to a thousand pounds of these barnacles attached to it! This may sound like a lot, but when compared to how much a whale weighs (35-40 tons), hundreds of pounds of barnacles on a whale is comparable in weight to, say, an aloha shirt and slippers on a human. And these are not just your garden variety barnacle. They are Coronula diadema, a species of acorn barnacle that lives only on whales, primarily humpback whales.*


whale barnacles on tail-A.Schwanke

Barnacles live on many parts of a humpback whale, from the throat area to the pectoral fins to the tail as seen in this photo taken off of Maui by Andy Schwanke.


Barnacle species that have evolved to live on whales are treated to a constant flow of water from which they can strain food particles. The barnacles position themselves in the places on the whale that experience the best water flow characteristics. It is believed that the barnacles are generally not harmful to the whale and might possibly even be beneficial in some cases as a defense or in competition between males.


Just how do these barnacles get on the whale to begin with? Adult whale barnacles are hermaphrodites. They fertilize the eggs of adjacent barnacles with a (proportionately) very long penis. The fertilized eggs develop into larvae which are then released into the water in the Hawaii wintering grounds. After further development as free-swimming larvae in the ocean, they are able to detect chemicals given off from the whale’s skin.** These chemicals cue the tiny larvae to settle on and attach to the whale’s skin, metamorphose into juveniles, grow, and secrete an incredibly sticky cement that tightly bonds them to the whale. Next, they begin to produce six vertical calcarious plates which will fuse to become the formidable circular shell that the animal will live within.


This shell is not solid material though. Cavities are built into the shell all around its circumference. These spike-shaped cavities pull the whale’s skin into them as the shell grows.*** The whale and the barnacle shell are then almost locked together. Because this barnacle was broken in two we were able (with the help of a Dremel tool) to actually see these cavities for the first time. And, as expected, they were filled with black whale skin! Skin also grows up around the base of the shell, leaving it firmly embedded and making it reportedly very difficult to dislodge.

barnacle crossxIMG_2299editwith arrpws

Arrows show where black whale skin has been “pulled” up into cavities in the barnacle’s shell. Photo: P. Fiene.


Given that the barnacle animal is cemented to the whale and given the interlocking-shell-and-skin configuration, it is a wonder that they ever come off. But they do!


Well-known researchers Mark Ferrari and Debbie Glockner-Ferrari have studied humpback whales in Hawaii for 39 years. They have first-hand knowledge of whales losing barnacles while in their Hawaii breeding grounds. Mark recalls that in 1987 they saw a yearling on separate occasions approximately a month apart. Because this individual was lethargic they were able to approach closely enough to actually see the barnacles and document their disappearance. He estimated that about 50% of the barnacles were lost during this time. And the reason they could tell that barnacles were being lost is because when a barnacle falls off, a perfectly circular scar is left, as you can see in this photo they provided below.

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Whale head showing adult barnacles and circular scars where barnacles have fallen off. Also showing many juvenile barnacles growing around the eye and all over the body. Maui, Hawaii. Photo ©Mark Ferrari, Center for Whale Studies, under Federal Permit #538.



Some of the reasons barnacles fall off have to do with male whales using their barnacle-encrusted pectoral fins as weapons in competitions with other male whales. They might also be knocked off when whales slash at tiger sharks or false killer whales in defense, something Mark and Debbie have witnessed themselves.


But most seem to fall off after about a year as part of a natural cycle. A French researcher reported that humpbacks taken by whalers soon after they had arrived in Madagascar for the winter season had large barnacles attached, but by late winter the whales had no barnacles. Instead the whales had barnacle larvae beginning to attach. By spring, the whales had small adult barnacles.* Photos taken in Hawaii seem to corroborate this approximate year-long life cycle. Scars show adult barnacle loss, while tiny new barnacles can be seen beginning to grow, as in the photos below and above.


Whether they are genetically programmed to die after about a year or whether some environmental factor in their breeding grounds causes them to die is, to my knowledge, not known. Could it be that Hawaii’s semi-tropical waters don’t supply the right (or enough) food, are too warm, harbor diseases (predators,  parasites?) or have insufficient available oxygen for the adult barnacles? Could UV radiation be too intense? Could the whale slough more skin or experience an altered immune response (in turn affecting the viability of the adult barnacles)? Perhaps some of these factors have been examined already but I could not find such studies in my search.


2-21-06, 38 Barnacles CU color, (c) MJF-CWSfor blog

Adult barnacles and juvenile barnacles growing on a whale fluke. Maui, Hawaii. (Long, fleshy gooseneck barnacles can be seen growing on the sides of the white whale barnacles. Photo ©Mark Ferrari, Center for Whale Studies, under Federal Permit #393-1772-01.


Considering the millions of pounds of barnacles that travel to Hawaii on the bodies of the humpback whales, and that many of them are falling off here, it seems surprising that to find one while diving is so rare. But when a barnacle falls off, the odds of it occurring in water visited by divers is small. Divers dive in such a tiny fraction of ocean waters, and usually in water shallower than most whales frequent. When you add the small size of the barnacles to the equation, it begins to make sense why such a find is considered a treasure.


barnacle eating


If we do find one, it is always fun to have our divers guess what it is when we get back on the boat and can talk about it. It isn’t often that they guess correctly. They are faced with what looks like a radially symmetrical white shell with a hole in the center. Most people, if they have to guess, think it is a seashell (a mollusk) of some kind. In fact, even scientists thought they were mollusks until 1830. But a barnacle is actually a type of crustacean – a relative of crabs and lobsters. In fact, if you look at the diagram to the left, you can see that the animal looks somewhat shrimp-like.




whale statue Aug. 7, 2014 smallerlong

This confusion is artistically captured in the form of the almost life-sized whale statue in Kalama Park in Kihei.





opihi on whale statue

If you look closely at the belly of the whale in the photo to the right, the artist has sculpted not barnacles, but opihi (limpets) attached to the whale! My mind had to do a little flip-flop the first time I saw this. But it’s understandable. Whale barnacles are a strange life form – and few people will ever have the opportunity to find one on the bottom of the ocean, much less see one attached to a humpback whale in the sea.




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Whale barnacles as viewed from above. Broken barnacle on left was found soon after falling off of whale and still has some animal tissue (opercular membrane) visible in the center. Barnacle on the right was found long after falling off of whale. Photo by P. Fiene.


Finding a whale barnacle is the closest some of us will ever come to “touching” a whale. We can’t help but view such a find as good luck. Knowing that this barnacle has traveled thousands of miles on a humpback whale and has fallen off in the exact spot where we are crossing its path is nothing short of spine-tingling.





Written by Pauline Fiene. Photos as credited. Mahalo to Mark Ferrari and Debbie Glockner-Ferrari for sharing their first-hand accounts and documented sightings, as well as wonderfully illustrative photos. Thanks also to Andy Schwanke for use of his whale tail photo and to Cory Pittman for his helpful comments.


*Scarf, James, E. Occurrence of the barnacles Coronula diadema, C. Reginae and Cetopirus complanatus (Cirripedia) on right whales. Sci. Rep. Whales Res. Inst., No. 37, 1986.
**Nagota, Yasuyuki and Matsumura, Kiyotaka. “Larval development and settlement of a whale barnacle” Biol. Lett. 2(2006): 92-93. Print.
***Newman, W. A. and D. P. Abbott 1980. Cirripedia. Stanford, CA, Stanford University Press. Intertidal Invertebrates of the Central California Coast: 504-535. 

Coralline Algae Target Phenomena – What makes those bull’s-eye patterns underwater?


This being National Archery Day (in addition to the much more significant Martin Luther King Day), I decided to finally look into and try to understand something that we see regularly underwater, but that has puzzled me my whole diving career. That is: patterns that look like archery targets which grow on shaded vertical rock walls underwater.

Coralline Target cropped 640 Makena Landing

A Coralline Algae Target with thin rings. Approximately 12 inches in diameter. Makena, Maui. Photo: P. Fiene


I guess I knew early-on that these concentric circles were a type of seaweed called crustose coralline algae. What are coralline algae? They are a group of red algae composed of fused plant filaments that have calcareous deposits within and between the cell walls. The crustose coralline algae look like a thin crispy layer, usually pink or purple, covering the surface of a rock.


In my mind all these years, the striking white concentric circles were the crustose coralline algae, and I paid no attention to the uninteresting background. My eyes saw only the white rings.


But I had it all wrong! The living part is the purple-pink background! The white rings, it turns out, are where the coralline algae has been killed. To finally learn this is poetic justice because I have always been amused when my divers think that bright white coral colonies are extra beautiful, when in reality they have just been killed and the white is the bare coral skeleton.

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Coralline Algae Target with thicker rings. About 12 inches in diameter. Makena, Maui. Photo by P. Fiene


This white ring disease (or complex of diseases?) was named “Coralline Target Phenomena” by Smithsonian coral reef scientists Mark Littler, Diane Littler, and Barrett Brooks in a short paper they wrote for Reef Encounters in 2007*. In the paper they proposed that the white rings are caused by an unknown agent (a bacterium, group of bacteria or other pathogen) that kills the pink coralline algae filaments in discrete concentric strips leaving just the white calcareous part exposed.


They did not have the opportunity to observe a target over time, so they made an educated guess at an explanation hoping that it would elicit information from colleagues. Whatever the agent causing the disease, they hypothesized that the pathogen kills a strip and then “leap frogs” over living tissue to infect ever-larger bands as the circle increases in diameter.


I contacted one of the authors, Barrett Brooks in the Botany Dept. of the Smithsonian, to find out if he knew of any new studies or information on the subject. He replied, “The phenomenon is still entirely open for study. No one, to my knowledge, has focused additional study into the matter.”


He also offered some additional comments to clarify what is known and not known: “Although bacteria were found present in the targets, they could be a result of some lethal activity, and maybe not the cause. How microbes work on reefs is a huge hole in our knowledge. I’m not entirely sure of the cause proposed, nor am I sure that there is only one cause. There is a range of “targets” from small diameter/thin bands, others large with thicker bands. It certainly looks like the bands travel/radiate outward, but who knows… The full answer is still out there.”

Coralline Algae Target - thick rings 640

A Coralline Algae Target with thick rings. Makena, Maui. Photo: P. Fiene


Next in my search for a possible explanation I asked marine biologist Cory Pittman and he offered this tentative hypothesis for how the bands might form:


“Assuming the cause is microbial (not necessarily bacterial – the bacteria could be secondary to an initial infection by something else), I wonder if the pattern might result from an interaction between a microbe and a defensive response by the algae? Assume, for the moment, that the agent colonizes a new patch of its host algae (cyst landing, contact with a vector…) establishing an initial point of infection. A colony spreads out from that point killing the underlying algae. The algae around the colony respond by ramping up production of a defensive chemical until it reaches a high enough concentration to suppress the growth of the microbes. The microbes respond by entering a migratory phase and “crawling” forward until they arrive at algae that hasn’t built up enough of the defensive chemical to resist them. Then, they start to consume tissue, again, until the next band of algae builds up resistance. With repetition this forms the target pattern. Meanwhile, the older, resistant bands of algae may begin to slowly overgrow the dead portions..


That would be analogous to how some terrestrial plants respond to attacks by insects. Neighboring plants sense chemicals released by the attacking insects (or the infected plant) and respond by producing defensive compounds that would be too metabolically expensive to produce all the time, but serve to check the spread of the insects ‘when needed’.”


Coralline algae target - thicker rings both  arrows

Photo taken at Makena, Maui by P. Fiene

The photos taken in Hawaii provide some clues regarding the progression of the disease over time. First, at the center of the target the coralline algae shows some re-growth over the dead white rings (yellow arrows) indicating that those rings have been there longer and the coralline algae has had time to recover.


Both green micro-algae and young starts of foliose brown (or red?) algae that colonize the dead surfaces are more prominent on the inner rings (black arrows) than on the outer rings, mirroring the progression of the disease and also suggesting that it takes some time (perhaps a matter of weeks?) for the “targets” to reach their full size.


Coralline Algae Target close-up-Makena Landing copy

Photo taken at Makena, Maui by P. Fiene.



In our Hawaii photos, the coralline algae surrounding the inner rings is often starting to regrow as indicated by the fine white edges (green arrows). The coralline algae around the outer rings shows no such white edge/active growth.






Coralline Algae Target with pink arrows- CP

Photo taken at Hekili Point, Maui by Cory Pittman


Also, some portions of the dead surface in the outer rings still retain faint pink pigmentation (pink arrows) suggesting that those patches have recently died. Again, this emphasizes the progressive formation of the “targets.”







In addition to determining the cause of the “targets,” there are many other intriguing questions to address, such as exactly how quickly the bands are formed, what keeps the targets from expanding to more than about a foot in diameter (in Hawaii), do the other species of algae that colonize the dead surface have any influence on the process, does anything relevant happen at night (just in case something else but a microbe is involved)…

With our curiosity now piqued, we will be keeping our eye out for “targets” to monitor and photograph over time.


by Pauline Fiene


*Mark M. Littler, Diane S. Littler, & Barrett L. Brooks. 2007. Target phenomena on south Pacific reef: strip harvesting by prudent pathogens? Reef Encounter 34:23-24.

Transparent Moorish Idol recruit – How long does it take to become opaque?


As Hawaii’s divers and fish-watchers are well aware, this summer will go on record as the largest settlement of juvenile fishes (recruits) recorded in historic times. Estimated millions of Blacklip Butterflyfish, thousands of Yellow Tangs, and hundreds or thousands of individuals of numerous other species settled out of the plankton on reefs on Oahu, Maui, Molokini, the Big Island and most likely other islands as well.


The settlements are not over yet, however. As of mid-September, recruits of some species are still settling. As our dive guide Warren Blum puts it, “We’re receiving new products all the time.” One of these “new products” is the Moorish Idol.


As divers, it is incredibly rare for us to see a reef fish in the first few days after it has settled on the reef. Most species, when they arrive, are transparent and/or silver, and hide down in the reef, some emerging only at night. During this time they undergo what is called transformation, where they become opaque, add color, and can change dramatically in body shape and fin length. Normally, by the time we notice new recruits, they have their color and look like juvenile fish.


Because Moorish Idols are comparatively large when they settle out of the plankton (about 3 inches), and because they are more likely to be out during the day before they have fully transformed, we get to see them while they are still partly transparent. From a distance a newly-settled Moorish Idol looks somewhat like an adult Moorish Idol with its pale night colors (think the-world-before-color-TV).

newly settled Moorish Idol fro blog

A recently-settled Moorish Idol (left) and a transformed juvenile (right).


But up close it becomes evident that the fish is actually transparent and we can see its spinal column right through its body!! This is advantageous for avoiding detection in the open ocean, but it is not ideal for life on the reef, where it must be visible in order to claim a territory or attract a mate (and where a transparent body would render it the ultimate wallflower!).

Moorish idol close-up

Recently-settled Moorish Idol, Sept. 6, 2014. Body is mostly transparent and spinal column is visible.


We were lucky to photograph one of these new arrivals over a period of days. Not only was it transparent with some opaque silver inside it, but its body was differently shaped than an adult. And already it had encountered predators which had taken bites out of several of its fins. This was actually a bonus for us because when we went back the next day to find out how much it had changed, we were able to find the exact individual, among the several that had settled on this particular section of reef, by looking for its unique pattern of bites.

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Recently-settled Moorish Idol on Sept. 6, 7 and 8 (left to right)




We have often wondered how long it takes for a newly settled transparent fish to transform into its adult colors, and now we have a much better idea. While we don’t know when this individual arrived or how transparent it was the day it arrived, we know that on Sept. 6 we could still see through it. The very next day the spinal column was less visible and the day after that the fish was completely opaque in that area. Along with the color acquisition, the dorsal fin became dramatically shorter and the snout became more developed – an impressive, almost magical transformation, especially between the first two days we saw it.

Two weeks later, although the fins were healing and filling in, this individual fish was still identifiable by bites and tiny color markings. It was still residing over the same small patch of reef. As an adult, it will have a larger range, but for now it is staying right where it settled after spending months in the plankton. One of the very lucky few to do so.

Young and adult Moorish Idols

Left: “Our” young Moorish Idol on Sept. 23, 2014. Right: What a full grown adult looks like

Part Two – Juvenile Blacklip Butterflyfish (Chaetodon kleinii) swarm divers and turtles in competition for food

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The arm of Ed Fingers gets picked by juvenile Blacklip Butterflyfish. Puu olai, Maui. Aug. 27, 2014

Strength in numbers is not a phrase that applies to the recent settlement of estimated millions of Blacklip Butterflyfish (Chaetodon kleinii) at Molokini and off the south coast of Maui. This many fish compete mightily for the limited amount of available food. We didn’t realize how serious the competition was until we had the opportunity to observe these masses of fish in two completely different habitats separated by 3 miles.


Molokini is a little volcanic cone that sits 3 miles off the coast of Maui in about 300 feet of water. Because it is so far offshore it is often exposed to currents and sometimes upwellings, both of which bathe the island in food for plankton-eating fish and invertebrates. Thus, the estimated millions of Blacklip Butterflyfish that settled at Molokini in July and August and September of this year (see Sept. 2 blog post) have been well-provided for by virtue of Molokini’s geographical position. They have distributed themselves roughly evenly around the crater, finding habitat all around it, and feed by picking the abundant plankton out of the water a few feet from the protection of cracks and crevices in the rock and reef.


The Blacklip Butterflyfish that settled along the coastline of Maui, however, have not been able to distribute themselves evenly because much of the bottom is flat, open sand. The sand provides no shelter so they have been forced to congregate over the isolated rocks and reefs. In addition, these Maui areas do not receive as much current, and therefore planktonic food items, as does Molokini. Such high concentrations of fish mean that competition for the limited plankton around these rocks is fierce. Yes, they are plucking tiny planktonic animals out of the water, but in addition they are performing a behavior that is very unusual for fish – juvenile or adult. They are swarming over us, picking who-knows-what off any exposed skin, dive gear and camera equipment.


once in our lifetime to send

Victoria Martocci is swarmed by juvenile Blacklip Butterflyfish. Puu olai, Maui. Aug. 27, 2014.


Leslie's hand with butterfliesIf you remember the old (and effective) Johnson’s Wax TV commercial for OFF mosquito repellent you will be able to picture what diving during this time has been like. In the commercial when the man puts his untreated arm into the terrarium of mosquitos they immediately swarm his arm. This has been the scenario at certain rocks off of Maui. As soon as we come close enough to the rock these youngsters swarm us, looking for any part of us that might be edible.


Ann and JD

Ann Quinn and JD Brill hold still while juvenile Blacklip Butterflyfish pick at their masks. Puu olai, Maui. Aug. 14, 2014.


Of course, we are not the only visitors to these rocks. Turtles, which are used to receiving some attention from several species of adult fish who clean their shell of algae and organic matter, are swarmed as well.

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blacknoses on turtle face for blogCompetition for food drives them to us. The ones that are bolder and more willing to approach large animals such as turtles and divers might be rewarded with more food. But they could also be exposing themselves to greater danger by moving farther away from their shelter. The ones that stay near the rock – perhaps they miss out on a good food source, but they may also be safer from predators. Interestingly, on days when there was current on these rocks, the fish were up in the water feeding and not at all interested in us. The current was presumably bringing them all the food they needed.


whole turtle being cleaned

It has been six weeks since they began swarming us and as their numbers decreased, so did the frenzy of unusual behavior. They stopped swarming divers and turtles, perhaps because there was enough food in the water for their reduced numbers. Or, perhaps as they get older, like many animals, they lose the fearless behavior and become more cautious.

While it lasted it was a wonderful experience out of the norm – to have fish coming to us instead of fleeing from us! In 35 years of diving in Hawaii we have never seen swarming behavior like this.

And if you’re wondering what it looked like from the turtle’s perspective….

inside the mask







Text and photos by Pauline Fiene


We would be so interested to hear if anyone else has observed behavior like this from a species of reef fish.


Part One – Massive numbers of juvenile Blacklip Butterflyfish (Chaetodon kleinii) settle at Molokini and in south Maui


Have your eyes ever beheld so many individual things that they felt full? That is the way my eyes felt three weeks ago while diving off of Molokini and south Maui. They felt so full that I actually had the sensation they were itching.


This is because on July 8 thousands of juvenile Blacklip Butterflyfish (Chaetodon kleinii) appeared overnight on reefs at Molokini and parts of south Maui. A month later on Aug. 4 another “shipment” arrived bringing the numbers into the estimated tens of thousands. And then a week later on Aug. 11, there was another astounding settlement which seemed to bring the numbers into the hundreds of thousands or millions. And these really were three distinct events. One day we were diving and everything was normal. The next morning, we descended and it looked like this:

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Hundreds of thousands of juvenile Blacklip Butterflyfish (Chaetodon kleinii) settled at Molokini in the summer of 2014. Photo: Pauline Fiene


Yes, it is an exceptional summer for numbers of newly settled juvenile fish (called recruits) of many species throughout the Hawaiian islands – various surgeonfish including yellow tangs, goatfish, other butterflyfish, parrotfish, trumpetfish and others. But, massive numbers of Biblical proportions seem to have occurred only with the Blacklip Butterflyfish, and have taken place mainly at Molokini and off the Makena area of Maui (with large, though not this massive, numbers reported in north Kohala on the Big Island and on the north shore of Oahu, and few to none in West Maui, Kihei or Maalaea, the Kanaio Coast of Maui or the island of Lanai).


Not wanting to use the word ‘Biblical’ lightly, I thought I’d try and put a number on this incredible event. So, I took the photo of a section of reef at Molokini (above) and estimated the linear distance in inches contained in the photo. I then counted the number of fish visible in the photo and arrived at 16.8 fish per linear inch of visible depth. And then I multiplied 16.8 by the estimated number of inches around the outside rim of Molokini and along the inside of that same rim. The number…….. are you ready…….. was over 1.7 million Blacklip Butterflyfish.


This estimate is based on the number of fish that could be counted in the depth range visible in the photo (about 20-40 feet). The fish actually extended more than four times as deep – down to 170 feet in places, potentially doubling or tripling this number. The estimate also does not include those distributed throughout the center of the crater. On the other hand, although the fish numbers appeared similar around the entire outer rim and along the inside, the surface area of acceptable habitat might not be as high in every part of the rim as it is in the photo. So obviously, this must be considered a rough approximation. When the tens of thousands of Blacklip Butterflyfish juveniles off of south Maui are included (another rough estimate based on a photo count – photo below), a safe statement to make would be that at the peak (the week of August 11) there were probably in excess of two million Blacklip Butterflyfish juveniles in the Molokini and south Maui areas that we dive (Wailea and Makena).


What on earth could cause such an epic show of nature’s ability to procreate?

Two of the most likely contributors to such numbers are the survival of an unprecedented number of larvae, and currents which concentrated and then brought the larvae near the islands.


final Tess' spawning diagram whiter sharper


Understanding larval survival requires knowing about the life cycle of most reef fish. A pair of adult fish release their eggs and sperm into the water at precisely the same moment and no parental care follows. Within a couple days the fertilized eggs hatch and tiny transparent larval fish only a few millimeters long emerge to develop for weeks or months. This takes place up in the water, not on the reef where the fish will eventually reside. This is also where the vast majority of them die.* This summer, however, for reasons unknown, massive numbers of larvae survived.



larval Chaetodontid 28 days post-hatch, 6mm

A larval butterflyfish 28 days after hatching from the egg. It is only 6 mm long. Used with permission from Frank Baensch (

The larvae that make it through that critical period of 2-3 days post hatching, will, when developmentally ready, detect the proper habitat on the reef by smell or sound or other signal. They will swim down to the reef, often still in a partially transparent form, tuck into a crevice in the reef and begin to take on the colors of the juvenile fish. This process, called metamorphosis, is almost completely under the radar as far as we divers are concerned. We do not see the larvae up in the water and we very rarely see the transition stages once they settle on the reef. By the time we notice them, they are juvenile versions of adults.



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A juvenile Blacklip Butterflyfish, about 30 mm long. Photo: Pauline Fiene

The juvenile Blacklip Butterflyfish, however, appeared overnight, as fully formed juveniles. Instead of arriving on the reef as larvae, scientists have learned that a minority of species metamorphose in the plankton and arrive on the reef as juveniles. This strategy might have been key to the massive scale of the Blacklip Butterflyfish settlement here on Maui. Most larvae have an internal clock ticking, so that when they are at the right developmental stage they have a limited window of time to detect suitable habitat and swim to it. If currents do not bring them close enough to a reef habitat that they can swim to, they die, unable to find shelter and the food they require. But, because the Blacklip Butterflyfish apparently has the ability to metamorphose into its juvenile stage in the pelagic environment, and because it is a plankton eater (and not dependent on eating algae or sponge or invertebrates, etc), it can survive longer in the planktonic environment, giving it a few more days for currents to bring it close enough that it can swim to the reef environment that it needs.


In addition to larval survival and “helpful” currents there are other factors that could have played a part in this wondrous settlement of juvenile Blacklip Butterflyfish. Some of these are fertility of the adults that spawned the eggs to begin with, sea conditions such as temperatures that are favorable to the eggs and developing larvae, plentiful food for the larvae, low predation on the larvae and probably other factors which we do not even know about yet. Most likely, this once-in-a-lifetime event was a fortuitous combination of two or more of these factors.


Whatever the reason, these fish are, unfortunately, probably not here to stay. Conditions in the plankton were clearly excellent for the larvae, but their requirements as adults living on a reef are completely different. Just a week after the August 11 settlement, the numbers had decreased slightly. Previous large settlements have shown that numbers continue to drop, most likely through predation and competition for a limited food supply.


blacklip butterflyfish, Maui

Thousands of Blacklip Buttterflyfish settled in the Makena area of Maui. There are over 2,400 fish in this photo. Photo by Pauline Fiene


You could dive your whole life and never be witness to an event like this. In the memory of this generation of Maui divers, obvious settlements of exceptional scale have happened only three times in the past 30 years on Maui: 1984 with Fantail Filefish (Pervagor spilosoma – estimated at tens of thousands); September 2008 with Blacklip Butterflyfish (tens of thousands) and our current July-August 2014 Blacklip Butterflyfish settlement in the probable millions.


Events such as this one are a great opportunity for us to learn about the life cycles of marine animals that determine how our reefs are populated. Life cycles which are happening all around us all the time, but not in a way that we notice – until it makes our eyes itch.

by Pauline Fiene

You can read more in Part Two –

Juvenile Blacklip Butterflyfish (Chaetodon kleinii) swarm divers and turtles in competition for food


*A 2014 paper (V. China, R. Holzman. Hydrodynamic starvation in first-feeding larval fishes. Proceedings of the National Academy of Sciences, 2014; 111 (22): 8083 DOI: 10.1073/pnas.1323205111) reports that 90% of fish larvae die from what the scientists call hydrodynamic starvation, which is the inability to eat due to the viscosity of the water preventing the larva’s ability to propel itself forward. The water drag on such a tiny 3 mm larva keeps it from being able to lunge at and inhale the planktonic food, so it starves.