The Coral Triangle

Anemonefish and demersal egg-laying strategy

Eggs on the reef: Anemonefish reproduction

By The Coral Triangle No Comments


It was several days past full moon and the tiny eggs were almost ready to hatch. The reproductive pair of anemonefish’s hard work of defending the eggs against predators and aerating them with their fins was about to pay off. Soon, thousands of tiny fish larvae will hatch and drift into the open ocean; the job of the parents would be complete.

This is part of the life cycle for anemonefishes. They belong to the group of marine fishes that practice demersal spawning, a strategy where females deposit or attach unfertilized eggs onto the substrate that are subsequently fertilized by the males. Female anemonefishes nip away at edge of the oral disc of their host anemone to expose a small patch of substrate upon which to attach their eggs. Males fertilize the eggs and it is there that the eggs begin their development into a new anemonefish. It can be hypothesized that having demersal eggs reduces the risk of eggs getting eaten while developing in the open water, cast ashore, or damaged by abrasion. Parental care often consists of nest building, nest cleaning, fanning, and guarding. The eggs incubate for about a week and after hatching, the tiny fish float in the ocean as part of the plankton pool where they will further develop. After about a week developing in the open ocean, they will return to the reef and seek out an anemone in which to dwell.

Clark's anemonefish fans and defends its eggs

Adult anemoenfish…

Tiny anemonefish almost ready to hatch

Thousands of tiny…

Comet (Calloplesiops altevelis)

A comet in the ocean

By The Coral Triangle No Comments


In my lifetime, I have seen only two comets, one was Halley’s comet in 1986 and the other was today while free-diving on a reef around Limasawa Island in Sogod Bay, southern Leyte. Comets (Calloplesiops altevelis) belong to the lesser-known family of fishes called devilfishes (order Plesiopidae), but why it gets this name is still a bit of a mystery to me.

A comet in Sogod Bay, Leyte, Philippines

Comets are often secretive and hover in front of crevices where they can hide if disturbed

Comets are probably the most popular of the seven species in this family; their remarkable color and shape have made them a highly prized fish in the aquarium trade. It has been suggested that the white spots against a black body and false eye on the back mimic the white-spotted moray eel. It may further this rouse by exhibiting the unusual behavior of facing into a crevice with its rear end facing out. Males do this especially when guarding their eggs. For years I have been hoping to see one of these cryptic and secretive fish and today was my lucky day!

Kurt's coralblenny from northern Busuanga, Palawan, Philippines

Reef Fishes from the Philippines

By The Coral Triangle No Comments


The title of this post reads like it will be a boring list of the 1700-plus species of tropical marine fishes that are found in the Philippines. Don’t worry; it is not about all of the reef fishes from the Philippines, but rather just some of the ones that can only be found in the Philippines (or found in immediately adjacent waters not politically associated with the Philippines). That list is an exponentially smaller subset of the master list of fishes, and for me, a more interesting one.

It would be safe to say that less than 3% of the total numbers of marine fishes in the Philippines are classified as endemics (or have ranges that extend into immediately adjacent areas but are in waters not politically associated with the Philippines). The beauty for snorkelers or divers who lust for larger and larger ‘fish-lists’ (equivalent to the life-list that avid birdwatchers compile) is that several of these fishes are easily accessible and often fairly common if one knows where to look.

Both the twinspot coralblenny (Ecsenius bimaculatus) and the hookfin cardinalfish (Osterhinchus griffini) are found throughout the Philippine archipelago, and outside of the Philippines, have only been recorded in waters along the northern tip of Borneo. The twinspot coralblenny is a small fish (up to 6 cm in length) that perches on top of coral colonies or boulders. They are usually solitary and feed on small marine organisms. A good and patient eye will usually spot one, especially on semi-protected or seaward reefs. A type location for the twinspot coralblenny is Anilao or Bohol. The hookfin cardinalfish is one of the larger representatives of the cardinalfish family. They can grow up to 15 cm in length. Their defining feature is a curved second dorsal fin and yellowish to reddish fins. Unlike coralblennies, they prefer silty or weedy habitats where they hover near crevices in the reef or amongst macroalgae like sargassum seaweed. A type location for the hookfin cardinalfish is in El Nido or Taytay Bay in Palawan.

Twinspot coralblenny from the Philippines

The Twinspot coralblenny…

Hookfish cardinalfish from El Nido, Philippines

The hookfish cardinalfish…

The real prizewinner for those looking to add range-restricted fishes to their fish-list is Kurt’s coralblenny (Ecsenius kurti). Kurt’s coralblenny is a greyish fish (6 cm) with three distinct, black lines and black-and-white spokes around the iris (see header image above). What makes it special is that it is known only from Palawan, Philippines. Northern Palawan, to be exact. Like most coralblennies, they perch on top of boulders or corals on shallow reefs. To find these little fishes, visit the reefs around the remote islands of northern Busuanga. The house reefs at Club Paradise or El Rio y Mar are great starting points. As we marvel and promote high diversity, we also must take a moment to admire marine life that is less prolific. In a way, all marine life started out as endemic to some place, before they sent their offspring to populate new areas…

male jawfish holding eggs in its mouth

Male Jawfish assume the role of motherhood

By The Coral Triangle


Finally! The right place, right time…but wrong lens. Ah, the same old story, but I can fix that with a morning visit to locate my subject again. Would I find it? I had better, I have wanted this opportunity for a long time. The very next morning, I asked the resort to bring me back to the reef where I systematically covered as much ground as I could while still making sure I wouldn’t overlook him. There! There he is. A male dendritic jawfish (Opistognathus dendriticus) with hundreds of tiny eggs in his mouth!

Male seahorses, pipefishes, cardinalfishes, and jawfishes belong to a very unique club whose membership merely requires them to play the role traditionally assumed by the mother that of carrying fertilized eggs to term. Egg-carrying strategies that males employ include eggs that are kept inside brood pouches, eggs that may be attached to the underside of the belly, or eggs that are retained in the mouth.

Male cardinalfishes and jawfishes incubate their eggs by holding them in their mouths, a strategy called mouth brooding. Females lay an egg mass and after fertilizing them, the male takes the eggs into his mouth and incubates them
for several days or up to several weeks for some species. During this time he does not eat, and his activities are restricted to juggling the eggs in his mouth to aerate them. Upon hatching, the juveniles usually remain in the same area as their parents, but receive no further parental care.

While the advantage of these strategies can be appreciated—providing a higher level of protection for their eggs during development—the reason for the males assuming the role of egg carrier is not well understood. It has been suggested that the female, who invested heavily in egg production, can now rest, which may result in the ability to reproduce more often. Given that they provide no parental care after birth and that few
will survive, perhaps mating more often increases the chances that more of their offspring will survive.

Jawfish eggs develop within the mouth of their male parent

A clutch of jawfish eggs…

Dendritic jawfish holding eggs in its mouth

Male jawfishes…

Brittle star hitchhiking on a hairy jelly, Lobonema smithii

Brittle stars hitching a ride

By The Coral Triangle No Comments


The odd relationship between brittle stars and hairy jellies

I am always excited for our Palawan, Philippine snorkeling trips. One never knows what to expect as the chances of seeing anything from the largest fish to the smallest invertebrate! On this trip, however, we encountered a group of organisms that does not inspire excitement from our snorkelers.

Bacuit Bay, El Nido, Palawan faces the South China Sea (West Philippine Sea). Except for a few islands that stand guard along the western perimeter of the bay, it is open to receive anything that is brought by winds and tides. Every few years, the bay experiences an invasion of some of the larger of the tropical jellies, hairy jellies (Lobonema smithii).

hairy jelly, Lobonema smithii

Hairy Jellies…

Their name derives from the thick tentacles that cover the entire bell. Sometimes referred to as a cannonball jelly, the bell can reach almost a meter in diameter, and with the trailing tentacles included, can exceed over a meter in length. Though a bit intimidating, they generally are not harmful as their sting is almost non-existent.

What’s most interesting about them is not necessarily their size or beauty (they come in a variety of pastel colors) but the hitchhikers that they bring. It is still a mystery as to how the brittle stars (often dozens are on each individual jelly) find their way onto their pelagic host. My guess is that, as larva, seek out the jellies (using some sort of chemical sensory to track them down), and upon settlement grow into the adult. What is known is that brittle stars not only gain protection from the jelly, but also get a free ride from the open ocean to their ultimate habitat: under rocks and boulders on the coral reef. How do they know when to leave their host? It is also my guess that brittle stars abandon the jelly while it is near death and with no longer having the ability to swim, rolls helplessly along the reef.

Brittle stars on a hairy jelly, Lobonema smithii

Brittle stars…

This fascinating migration compliments the awe at seeing dozens of brittle stars entwined in the tentacles of the jelly or crawling over the massive bell. For our group of snorkelers, fear of these jellies was immediately conquered by the desire to simply swim with these giants and marvel at their beauty, size, and, yes, their hitchhikers.

Sebree's dwarfgoby, coral triangle adventures

Biodiversity and the Coral Triangle, part 2

By The Coral Triangle No Comments


In the first part of this discussion, I defined the Coral Triangle and focused on physical barriers (vicariance) as a major force that drives the high diversity of marine life in this region. Part two will address another important ecological feature of this region that significantly contributes to the incredible diversity of marine life that we see…

Habitat diversity in the Coral Triangle extends far past the myriad of general reef environments such as coral reefs, mangroves, or seagrass beds. When factors such as depth, exposure to sunlight, exposure to waves, or turbidity are introduced into the equation, the number of habitats increases exponentially. As habitats set the stage for niche availability, the more habitats there are, the more potential niches are available for exploitation. Furthermore, organisms themselves set up potential ‘micro’ habitats. For example, large boulder corals (Porites spp.), prefer shallow, semi-exposed reef environments. There are several smaller organisms like gobies (the header image is a Sebree’s dwarfgoby, Eviota sebreei), coral hermit crabs, coral scallops, and Christmas tree worms that have adapted to living on this type of coral and to the environment in which the coral thrives.

Other corals, such as club or brush coral (Pocillopora spp.) that have preferences for areas exposed to heavy wave action, likewise have an exclusive complement of smaller organisms, but given the different type of coral and habitat, these organisms are different than those that live with boulder corals. Leopard blennies, guard crabs, and yellow-spotted scorpionfish are examples of inhabitants of Pocillopora corals. Translate this approach to the over 500 species of coral that exist in the Coral Triangle, and the potential niche availability increases by orders of magnitude. Extend it further to include all of the 30 phyla of animals, and the availability of niches seems almost limitless. What makes the Coral Triangle so special is that it seems that almost every available niche is, indeed, already filled. Fortunately, nature is dynamic, and with change come new opportunities for exploiting a new niche.

Wayag, Raja Ampat, Indonesia, Coral triangle adventures

The Coral Triangle’s incredible diversity derives from…

Coral scallop, Porites, Coral triangle adventures

A coral scallop…

reds-spotted guard crab, coral triangle adventures

A red-spotted guard crab…

Pyrosome floating in open water in the Philippines

It’s a Pyrosome…or maybe not!

By The Coral Triangle One Comment


Updated March 8, 2015Original <Back in 2009 I encountered a really strange creature while snorkeling off of Cabilao Island, Philippines. It was long and tubular (about a meter and a half long and 20 cm in diameter) with rings consisting of tiny pink balls along the entire length of it. I honestly had no idea what it was, and things like a jelly, salps, an egg case, trash, and several other absolute guesses crossed my mind. Unfortunately, I couldn’t find anything that looked close enough to it and moved on to other things.

Longitudinal view of a pyrosome

Pyrosome or squid egg case?

Flash forward to, well, today. Today I read about a rare encounter with a pyrosome, and upon looking at the pictures and video (which can be seen here) knew immediately that this was my mystery organism I had encounter five years ago!

Pyrosomes (order Pyrosomatidae) are related to salps, a type of pelagic, colonial tunicate. The entire colony is made up of thousands of individual zooids fixed in a gelantinous material called the tunic. In this photo, the stomach of each zooid can clearly be seen as the tiny pink balls. Each zooid is responsible for filtering the water for its primary food item, phytoplankton, and reproduction. Pyrosomes are bioluminescent and often flash a blue-green light visible from several meters away. It is this behavior that earned them their name, Pyrosoma (from pyro=fire and soma=body).

Pyrosomes drift in the upper depths of tropical seas but remain pelagic, and, thus, why people rarely encounter them. Some scientists even go as far as referring to them as unicorns of the sea, given they are so rarely seen they almost fall into the ‘mythical beast’ category. As snorkelers and divers we often feel it is a privilege to have intimate encounters with the myriad of marine organisms that inhabit coral reefs. In this case, I feel very lucky as well!>

UPDATE: The internet as a resource comes through again. As I wrote above, I had no idea what it was and only made the connection when I read an news piece about an encounter with a similar organism off Ticao Island, Philippines. The next day, I got an massage on my facebook account from a fellow that said he was told this is the egg case of a deep water squid called a rhomboid (or diamondback) squid (Thysanoteuthis rhombus). After searching, I am inclined to agree, though with only the smallest of reservations due to the fact that I have not had the chance to really investigate this on a detailed level (e.g., looking at the eggs or zooids through a microscope to see if they were, indeed, the former or latter). During my initial encounter, an egg case was on my shortlist of suggestions and though I still leave the absolute identification to those who are better informed about deep water squid or pelagic tunicates, I feel more confident hanging out in the camp with those that identify it as an egg case.

The gelatinous tunic with individual zooids

Tiny stomachs of zooids or eggs?

Individual zooids of a pyrosome

Pink eggs or zooids. It’s hard to tell…

marine biodiversity, coral triangle, fishes, coral

Biodiversity and the Coral Triangle, part 1

By The Coral Triangle No Comments


Biological diversity, or biodiversity, is essentially all of the variety of life in all of its manifestations, including the totality of genes, organisms, and ecosystems at all levels of biological organization. In most and simpler contexts, marine biodiversity refers to the number of different species inhabiting the sea. The Coral Triangle is a geographical term used to describe the region that possesses the world’s highest levels of marine biodiversity. The roughly triangular-shaped area encompasses waters surrounding the countries of the Philippines, Malaysia, Indonesia, Timor Leste, Papua New Guinea, and the Solomon Islands.

Map of the Coral Triangle from Marine Life and Natural History of the Coral Triangle by Lee Goldman and Ethan Daniels

The Coral Triangle

As the name implies, the parameter for inclusion in the Coral Triangle revolves around the total number of scleractinian corals (hard corals) in a given area. Any country or region with a body of water that contains more than 500 species of hard corals gains entry into this elite club. As it turns out, the boundary line embracing the coral-rich areas is shaped like a triangle. But as tropical marine fish experts started to look at the spatial patterns of fish species, the familiar triangular-shaped pattern that defined the area with the highest levels of coral diversity was true for fish diversity as well. Although the number of marine fishes is not a consideration for entry, areas within the Coral Triangle tend to have more than 1200 species of fish with recent surveys yielding closer to 1500 species for places like Raja Ampat and the Philippines. The Coral Triangle, in terms of marine biodiversity, may be easy to describe, but it is much more complicated and interesting to ask why this area has so many species compared to other areas in the world.

The answer to why areas like the Coral Triangle harbor the world’s highest levels of marine biodiversity begins not with the individual organisms, but with geologic processes that began hundreds of millions of years ago. Plate tectonics, continental drift, and the advance and retreat of glaciers gave rise to the theory of vicariance. This theory postulates that physical barriers to reproduction appear and disappear at random and can disrupt gene flow between populations. The advance and retreat of glaciers is the most tangible and recurring example. Glacial periods have encrusted the earth with ice at least 21 different times over the past several million years. It is believed that approximately every 140,000 years, glaciers gradually grow and recede as the result of small changes in the orbit of the earth around the sun. When glaciers advance over continental landmasses a concomitant drop in global sea levels occurs due to huge volumes of water changing from a liquid to a solid. During the most recent Ice Age, sea levels dropped by an estimated 120 meters. Such a drastic change over a short period of geologic time quickly transformed large tracts of ocean floor into dry land.

The diagram depicts the uncovered land mass (brown) based on the last ice age (c. 20,000 - 11,700 years ago) that tied up enough seawater in the ice sheets to lower sea levels up to 120 m.

The diagram depicts the uncovered land mass (brown) based on the last ice age (c. 20,000 – 11,700 years ago) that tied up enough seawater in the ice sheets to lower sea levels up to 120 m.

In areas where seas are relatively shallow, the impact of this change would have dramatically affected the geographical distribution of many species. For example, during those times, the landmasses that comprise the islands of present-day Borneo, Java, the Philippines, and Sumatra were physically connected to the Asian continent. This newly formed ‘land bridge’ enabled terrestrial organisms to migrate extended distances, but would have impeded dispersal of marine organisms, effectively separating species’ populations and stopping gene flow.

This type of species ‘splitting’ is referred to as allopatric speciation, and it is recognized as probably the most frequent method by which new fish and invertebrates evolve in the Coral Triangle. Also known as geographic speciation or vicariance, allopatry occurs when a physical or ecological barrier, such as an island, deep water, or even an oceanic surface current, separates a breeding population. The resulting hurdle prevents sexual reproduction and the exchange of genetic material among members of the now isolated populations. Over successive generations, the genetic composition of each group will change, eventually manifesting as distinct species no longer capable of producing viable offspring by interbreeding.

Though barriers that separate species are an important driver for speciation, another key factor supporting high levels of biodiversity is the availability of ecological niches, which is defined as the physical location where a species or population lives and how that species responds to the distribution of natural resources. In effect, a niche refers to how an organism makes its living. It is important to point out that a fundamental tenet of ecological theory stipulates that organisms cannot occupy the same niche, or make their living the exact same way. The lavish array of fish and invertebrates inhabiting the Coral Triangle inevitably competes with other individuals of the same species and different species for vital resources. Natural selection, as the mechanism for evolution, states that some individuals within a population will be more successful at competing for resources and more apt to reproduce than others, thereby hinting at the benefits of adaptive change over time. Niche diversity, or the number of ways different organisms make their living, in the Coral Triangle is astronomical. This is likely due, in part, to the diversity of marine habitats, the limited availability of nutrients, and the stable environment combined with high amounts of solar energy; the latter two further facilitating the abundance of symbiotic interactions.

Coral hermit crab, acropora, solomon islands

Ecological niches are defined by the combination of a physical location and how the organism responds to and uses natural resources. For example, coral hermit crabs (Pagurita spp.) reside in the abandoned tubes of feather duster and Christmas tree worms (order Sebellida) that are found only in species of hard coral. Strong competition on the reef contributed to their retreat into this permanent refuge where generations successfully adapted to utilize available resources. In this case, hiding in the coral caused an adaptative response that resulted in the loss of their shell and the evolution of their antennae into apparatuses for capturing plankton.