Thoughts about corals, coral reefs, and coral reef conferences

Hanauma Bay now and in the 1960s

Last week I was in Honolulu participating in the 13^th International Coral Reef Symposium (ICRS).  It was, for me, a time for reminiscing.  I was a student at University of Hawaii in the 1960s and was a participant at the 2^nd ICRS on the Great Barrier Reef in 1973.  A couple dozen of us old-timers were together again in Honolulu.

Honolulu, like most places on this planet, has changed a lot since the 1960s.  While Kauai’i is known as the garden isle, and Hawai’i is called the big island, Oahu is apparently now termed the traffic island, and with good cause.  Places I knew in the 1960s were radically transformed by new streets, overpasses, and high rise buildings.  In downtown Waikiki, there are places where it is hard to recognize you are by the ocean, and most of my favorite 1960s hangouts are long gone.  The old Hawaii is very hard to find in today’s Waikiki.

On the other hand, I managed to hop on a shuttle the day before the conference started, for a snorkel in Hanauma Bay.  Hanauma Bay, on the southeast corner of Oahu just a short ride east of Waikiki, although with way more traffic than I remember, was one of my favorite places in which to spend a Sunday when I was a student.  It cost nothing (a real plus in my financially straitened circumstances), and I knew of several spots up on the low cliffs to the north of the bay, where there was room to put down a towel or two, away from all the sand and all the tourists.  (Interesting how the newcomer to a place so quickly gains disdain for those who only visit for a week or two!)  A few steps down and an easy entry to the water was possible, with no need to swim out over the backreef filled with dreaded tourists, and through the reef itself.  The coral was healthy and abundant and the fish were plentiful and varied.  I spent many Sunday’s alternately soaking up the sun and soaking up the reef at Hanauma Bay.

Hanauma Bay Nature Preserve from the cliff-top parking lot.  The site labelled ‘Witches Brew’ in this map from the Honolulu Parks and Recreation Department is an area of turbulent water and strong currents out beyond the location where I snorkeled.  Don’t head there – it’s a long paddle out for the lifeguard to ask you to return closer to the beach.  The ‘Toilet Bowl’ site is similarly off-limits.  (I wonder why they label them on their map?)

This is Hanauma Bay on the day I visited.  Photo © Joerg Wiedenmann

There were many schools of Manini, Acanthurus triostegus, grazing over the substratum.
Photo © Hanauma Bay Snorkel Tours

And other surgeonfishes as well, such as these Acanthurus guttatus.
Photo © Hanauma Bay Snorkel Tours.

I am very happy to report that underwater, outside the reef, Hanauma Bay looks just as I remembered it, although the fish seem a bit larger, and less afraid.  Hanauma Bay has been lucky.  It became a marine protected area in 1967, shortly before I left Hawaii.  But with park status, and a booming tourist industry, it became used more and more heavily.  There were some early management failures.  Some extensive manipulation of the habitat inside the reef, plus the import of sand from Oahu’s north coast provided more places to swim and sunbathe, but at the cost of some living coral. Lack of regulation led to enormous numbers of visitors (as many as 10,000 per day), cars parked everywhere, and fish being fed human snacks in the shallows.  Beginning in 1990, steps were taken to rectify the overuse and fish feeding, and good management since has enabled the corals and fish to recover and remain healthy and abundant.

To achieve this good management there have been some extensive changes above high tide.  A large, paved parking lot now exists along-side the highway at the top of the cliffs.  It fills early most days and extra cars are turned away.  From the carpark, you pass through a gate after paying your $7.50 entrance fee and proceed to a mandatory 5 minute video screening that conveys such elementary messages as to not stand on the coral, nor swim out to sea.  Mixed in with these important messages (many tourists have no idea what is alive and what is just rock on a coral reef) is some information on how Hanauma Bay was formed – it is an extinct volcanic crater with one side eroded out – and what coral reefs are.  From the video screening, you are free to head down the hill, on foot or by tram.  At the bottom, there are showers and toilets, a rental place for snorkelling gear and lockers.  No fast food, or food of any kind down at the bottom, although you are welcome to bring your own.  Finally, there is the beach, the reef, and the ocean.  I noticed fences preventing people from walking out along the cliff bases on each side of the bay – my ‘secret’ sunbathing spots are now out of bounds.

Visitors are counted as they pass through the gate en route to the video screening, and there is a limit on numbers at the beach at one time.  Additionally, the park is closed completely each Tuesday.  Hanauma Bay now gets about a million visitors a year, and around 3000 per day, but the management of numbers (and activities) has allowed its animals to thrive.  The mongooses are brazen and well-fed; they are quick to find lunches in backpacks left on the beach by snorkelers.

On my visit, I went straight to the right-hand end of the beach, then snorkeled out through the reef.  The area outside the reef on that side of the bay was the best, in terms of fish and corals, in the 1960s, and seemed just as good, or better – in terms of fish size – than I remembered.  It was wonderful to know that a reef location could be so apparently unchanged.  Far too many reefs are now feeble images of what they used to be.  I also went in again briefly on the left-hand side.  The coral is less abundant in this more wave-exposed section, and it was so also in the 1960s; I don’t remember enough to say how it compares today to the 1960s.

Me, strictly incognito behind a mask and snorkel, enjoying Hanauma Bay.  Photo © Joerg Wiedenmann

The 13^th International Coral Reef Symposium

The 13^th ICRS attracted some 2500 reef scientists and managers from around the world.  There were about 14 concurrent sessions of papers being presented, from 8 am to 6 pm (Americans are masochists), and what seemed like thousands of posters, row upon row, detailing other studies.  As is typical of such conferences, I found plenty of papers to listen to, and plenty of conflicts – you cannot listen to two or three different talks being given in different rooms at the same time no matter how skilled you are in using your social networks and electronic devices.  I also found I was discovering old colleagues right up until the final day, and failing to find people after agreeing to meet at a particular time and place (sometimes my fault).  The week went very quickly.

The 13^th contrasts dramatically with the 2^nd, held from June 22^nd to July 2^nd, 1973 as we cruised the Great Barrier Reef aboard the MV Marco Polo, a clapped out cruise ship with a surly crew that seemed engaged in some sort of internecine warfare most of the voyage.  There were about 350 people on board, only 264 of which were scientists.  The organizers – the old and mysterious Great Barrier Reef Committee which I helped transform into the now vibrant Australian Coral Reef Society about a decade later – were forced to open the cruise up to non-scientists interested in an opportunity to cruise through part of the GBR simply to break even.  This was my first ICRS.  I shared a 4-person cabin, deep in the bowels, with Yossi Loya, the Israeli coral ecologist, Professor John Morton of University of Auckland, an older scientist towards the end of a distinguished career, and a mad keen diver from Brisbane who woke us all up early the first morning as he clanked and clunked, putting weights onto a belt and otherwise checking his dive gear in the middle of the cabin floor (I rolled over and went back to sleep).  There were two concurrent sessions of papers given under less than ideal conditions in lounges meant for drinking and partying, and we stopped every now and then for field excursions.  Some of us younger scientists spent a fair bit of time in the small bar at the stern and up around the funnel on the top deck; the senior scientists on board, especially those who had organized the conference, appear to have spent lots of time jockeying for position in the nascent hierarchy in our field.  Looking back, as well as some interesting science and the field trips, I remember the friendships that were formed.  A friendly rivalry emerged as we GBR natives watched bemused as the Discovery Bay (Jamaica) clique strutted their stuff – Jeremy Jackson complaining frequently that the excursions were not getting him to places where he could dive deep; we GBR natives believed there was plenty to fascinate in depths less than 100 ft.  It was all a long time ago, but it was good to see Yossi, Jeremy, Rupert Ormond, and coral biologists Jim Porter, Michel Pichon and Peter Glynn again at the 13^th ICRS.

Perhaps unwisely, I did not give a paper at this year’s ICRS, but I did participate in an event for the community in which I talked about how amazing coral reefs really are.  Here I lurk in the background.  Photo © Huffington Post

Field excursions barely featured in Honolulu, and there were few opportunities to gather in bars.  Still, to my delight, the range of papers presented in Honolulu seemed, if possible, even broader than at the 12^th ICRS, held in Cairns, Australia in 2012, and way broader than what was presented at the 2^nd.  I had feared there would be so much focus on bleaching, ocean acidification, overfishing and pollution that there would be scarcely room for talks on any other topics.  But I was wrong.  There are sizeable numbers of scientists asking interesting questions of coral reefs from many different perspectives.

There were whole sessions of talks on the microbiome of corals, on the genetic and molecular details of the symbiosis between corals and their resident algae (these symbionts live inside the cells of their host corals), and on corals living in extreme environments.  There were also sessions on the paleohistory of coral reefs, on the ways in which local culture can be used by effective social scientists to build better management of reefs and coastal waters, and on effective strategies for designing and managing marine protected areas.  There was a poster, by Jessica Nowicki, a student at James Cook University, Australia, detailing the neural pathways used in pair bond behavior of the butterfly fish, Chaetodon lunulatus, and showing they use the same brain centers as do pair-forming birds and mammals — we really are all related!  There was also a session titled ‘The use of genomics, proteomics and transcriptomics in coral reef studies’, but since I have only the vaguest notion of what those three words mean, I stayed away from it.  Some old dogs can be taught only some new tricks.

The breadth of topics and approaches was very evident in my own particular interest re the connectivity provided to reef communities via larval dispersal.  In 1955, Jack Randall (who, at 92 years, received a major award at the 13^th ICRS) recorded in his PhD thesis how he had observed late-stage larval manini (a surgeonfish, Acanthurus triostegus) one evening from the stern of his sailboat moored in the Ala Wai Yacht Harbor (within sight of the convention center where our conference was held, though now devoid of small sailboats with graduate students living aboard).  They were swimming into the harbor against the falling tide.  On this basis he concluded that, contrary to accepted opinion at that time, at least the final stage of return to the reef habitat was an active decision made by the larval fish.  Given that manini (like all other surgeonfishes) spawn in midwater on the outer edge of reefs, and produce eggs which hatch into minute larvae that are pelagic for about twelve weeks, this observation was an enormous dent in the paradigm that assumed larval fish were at the mercy of currents which sometimes brought them back to reefs.

Not a manini, but another surgeonfish, this Naso larva will become opaque and pigmented over the next 12 hours or so, will radically alter the length of its gut, and its teeth, and begin to eat algae instead of plankton.  Most surgeonfish larvae are about 1.5 cm in length when they return to reefs.  Photo © Colin Wen.

Over the past 60 years, and particularly over the last 15 years, we have made great strides in first confirming that the manini was not the only reef fish to make active decisions about finding reef habitat, and then detailing how this feat was accomplished.  Along the way, we have discovered that not only do reef fishes return actively to coral reefs, and to the ‘correct’ habitats within reefs, but that to a surprising degree they actually return home.  Early descriptive field studies have been bolstered over the years by sophisticated tagging studies and behavioral studies, and a full range of these was on display at ICRS2016.  Along with numerous studies that used chemical tags or genetic parentage analysis to track from where, or from which parent fish, individual juveniles had come, there were reports of larval fish responding to the odor or the sound of reefs, and lots of reports of the ways in which age or condition of arriving larvae interacted with conditions at the reef to determine how well the newly recruited fish survived.  Some of the latter concerned what happens when larval fish return to a reef degraded by bleaching, but most were looking more generally at the suite of interactions that determine success in getting into appropriate reef environments.  Still, after 60 years of effort we still do not know how the larval fish know what to look for or what to respond to in their journey back home.  Maybe we will never know the answer – why questions are always the most difficult ones.

Among the more surprising papers dealing with larval dispersal was one given by David Williamson of James Cook University.  David told how they had been able to use genetic parentage analysis to unambiguously link collected juvenile coral trout (Plectropomus sp.) to adult parents collected as much as 254 km away.  While some coral trout return to reef habitat as little as 200 m from where their parents live, others disperse over 1000 times further during their month-long larval period, proving that for this commercially and recreationally important species, the pattern of zoning within the Great Barrier Reef Marine Park does function as intended – protected sites harbor fish some of whose offspring seed fished locations as much as 200 km away.

I’m not surprised that coral trout species ( here Plectropomus maculatus).  Disperse during larval life in excess of 200 km from the spawning location.  I’m flabbergasted that it proved possible to sample intensively enough to be able to use genetic tools to locate the parents for a larva that had travelled this far.  Photo © P. Mantel.

Another surprising paper was given by Océane Salles, doctoral student at CRIOBE, the French research facility at Moorea, French Polynesia.  Based on field effort over 10 years in Kimbe Bay, Papua New Guinea, she and her colleagues have been able to use genetic parentage analysis to build a geneology for the clownfish population around tiny Kimbe Island.  Clownfish, Amphiprion percula, at Kimbe Island exhibit quite high levels of “self-recruitment”, meaning the larval fish produced there return to reefs around the island at the completion of their 11 day larval life.  As much as 60% of juveniles collected around this tiny island in one year are found to be the offspring of adults living there.  Miraculously (in my opinion), Salles and her colleagues have been able to use genetic evidence to build a five-generation geneology containing 502 founders at its base and including 990 parent-progeny links, spread over 121 families.  I don’t believe this has ever been done in any other marine fish species.

Now scientists have been able to not only confirm who Nemo’s parents were, but his family tree back five generations.  Well… that is if Nemo is one of the young clownfish (Amphiprion percula) living at Kimbe Island.  Photo © Jack Randall

As well as reports of connectivity in fish populations, there was a whole session devoted to soundscapes on coral reefs, and how these vary with reef condition.  Reef sound is likely important as a settlement cue for larvae of other reef creatures beyond reef fishes.  I also heard an interesting paper on odor cues given by graduate student Narrissa Spies of University of Hawaii’s Kewalo Marine Laboratory.  It concerned her studies of planula larvae of the coral, Leptastrea purpurea.  Under laboratory conditions, these larvae respond positively to the odor of adults of that species when choosing settlement sites.  Maybe we will one day learn that corals are also capable of behaving in clever ways to get back home after larval life.

The behavior of corals

This brings me to my final topic of the day.  For too long I have maintained that coral is ‘just habitat for fish’.  Tongue in cheek, I have advocated this view on more than one occasion just to see my coral-loving colleagues bristle.  But it comes from a deep-down prejudice in favor of animals that behave, animals that are actively doing things I can watch.  And mostly, corals just sit there, being corals.  Nothing really wrong with that, but I find it difficult to get emotionally engaged by most corals.  It’s the way I am.

Still, in an effort to acknowledge that corals can be amazingly cool beasts themselves, and that I do understand why so many reef biologists are enamored of corals, I offer the following.  I also do this because I am becoming more and more convinced that we will never succeed in encouraging people to care sufficiently about coral reefs to demand real climate action to protect them if we do not awaken people to their wondrousness, their sheer majesty as examples of just what life can create, given a chance.

Fungia fungites, a solitary coral, is one of a number of related species that occur as single individuals, lying unattached on the seafloor on Indo-Pacific reefs.  Normally they appear as in this photo, with their tentacles retracted.  When they behave, they put their tentacles out and look quite a bit different.  Photo © J. Messersmith.

Last week I saw a photo of a mushroom coral species (Fungiidae) posted on Twitter by @BioGraphic, a California Academy of Sciences outlet.  It links to a 6 minute video which was not tracking very well the day I looked at it.  Narrated by Pim Bongaerts of University of Queensland, the video includes some time-lapse photography of corals behaving and some deep reef sequences on the Great Barrier Reef.  The Fungia appears about a third of the way through and goes through its repertoire consisting of flipping over when turned upside down, and removing sediment covering its body.  A two-trick coral.  Earlier there is a short sequence of two corals fighting, using their nematocyst-armed tentacles to thrash away at each other.  (Judy Lang, who first discovered interspecific coral aggression in the 1970s was also at the ICRS meeting in Honolulu.)

Perhaps the most famous example of coral behavior is the mass spawning which occurs reliably on one or two nights near the October or November spring tides on the Great Barrier Reef.  Mass spawning occurs in all coral reef locations, at times characteristic of each region, but seems more broadly multi-species, and more strongly massed on single nights here than in some other locations such as the Caribbean.  On the GBR it is reliable enough that dive operators schedule special night dives to see the corals spawn.  Discovered by Australian graduate students in the 1980s, mass spawning is a process whereby large numbers of species synchronize their spawning activity to a single night each year, likely as a way of swamping egg predators and ensuring that some of the eggs survive.  Massing around the largest spring tides of the year is a trick also employed by a number of other marine creatures to synchronize spawning activity – when you rely on releasing your sperm or eggs into the current, it is very adaptive to all do so at the same time!  Mass spawning events are a silent expulsion of eggs, sperm bundles, or (for brooding coral species) young larvae, one by one.  These products drift silently upward towards the surface with fertilization taking place along the way.

Mass spawning has been filmed so many times now (here is an example), usually with symphonic background music, that it is ‘old hat’, and I have personally always considered the idea of diving during such an event somehow slightly x-rated.  (On the other hand, I once stumbled across a lagoon full of sea cucumbers (Holothurians), all busily synchronizing their spawning to the ebbing tide, standing on their heads, tails high in the water column, shedding eggs and sperm – the most amazing behavior any of them had exhibited that month, and somehow more amusing than x-rated.)

Spawning sea cucumbers, showing more behavior than they have exhibited all week!
Photo © Kevin Deacon

But I digress.  The coral nervous system is a modest affair.  No brain, not even a decent ganglion.  Just a diffuse ‘nerve net’ of neurons with their axons and dendrites connecting via synapses to form a web of neural tissue across the colony.  There is a little bit of an attempt to be more organized in a ring of especially well-interconnected neurons surrounding each polyp’s mouth, but that is about it.  So fighting with the neighbors, removing sediment from your back, flipping over when on your back, and synchronizing your spawning to coincide with that of your neighbors is actually pretty amazing.  But there is one more piece of coral behavior to talk about.

Dendrogyra cylindrus, the pillar coral, is a large Caribbean coral, the sole species in its genus, in a small, 8-genus family, the Meandrinidae, restricted to the Caribbean except for two rare species in the Indian Ocean.  When I see Dendrogyra, it reminds me of what are called, in my part of the world, sentinel pines.  Sentinel pines, usually White pine, stand tall above the surrounding canopy; they are the very few trees that were not cut for one reason or another when the land was logged in the late 1800s.  They tell us just how magnificent our forests once were.  Dendrogyra occurs as stout pillars 10 to 20 cm in diameter rising as much as 2 meters above their base; they stand similarly tall against the ‘canopy height’ of most corals on the reef slope.  Apart from standing out like sentinel pines, or perhaps like saguaro cactus, they are distinctive in that their polyps usually have their quite long tentacles out and waving about in the daytime.  This gives them a fluffy or furry appearance.  Caribbean reefs have very few coral species, but Dendrogyra cylindrus is distinctive and interesting.

Dendrogyra cylindrus has the most rapid nerve net among corals and reacts rapidly to being touched.
Photo © Paul Humann

Dendrogyra has one of the fastest nerve nets among corals.  Fast in that communication between neurons is very rapid.  When other corals have their polyps extended, touching three or four causes those particular polyps and a few neighbors to rapidly withdraw their tentacles.  It’s a good defense against having your tentacles bitten off by some browsing fish.  But when you touch a few polyps on Dendrogyra, the retraction response is almost instantaneous and spreads across the entire colony in the flick of an eye.  And as the polyps retract into the safety afforded by the skeleton, the overall color of the colony changes, becoming much whiter.  The first time I inadvertently triggered this response, I nearly dropped my regulator as the coral flashed at me; as a startle trigger, it is very effective, and I have no doubt that fish and perhaps crabs are just as startled as I was.  Wait a couple of minutes and slowly the polyps come out and recommence feeding.

Well, there you have it.  Putting these examples of behavior together, we see the corals of the world as pretty limited, but then, they are, after all, fastened firmly to the substratum (except for the Fungiids) and possessing nothing resembling a brain.  On that basis, I think they do pretty well.  Some of their more mobile relatives among the jellyfishes and the siphonophores do quite a bit more, but that is another story.  For now, we just need to remember that when we stress reefs and cause corals to bleach, we are harming vast numbers of living, behaving creatures.  They really are not just slimy rocks.