April 16, 2012

A dead coral city of vagabonds and tyrannosaurs. From the surface, our reef dive on Aitutaki, Cook Islands looked like it was going to be wonderful. A vast expanse of complex coral cemented the bottom, disappearing into the distance in the classic ridges and channels of a growing reef. But as we descended a different picture slowly emerged…this reef was not alive.

True, the coral skeletons were still there, a complex, interdigitated mosaic of branching and plate-like and mounding species. But 99 out of 100 coral colonies were dead. They were entombed by a layer of crustose coralline algae that covered all the native coral color and left a ghostlike pall of dull chalk color. The reef was still inhabited by fish – but not the normal kinds. There were no damselfish or planktivorous chromis, trigger fish, hawkfish or butterfly fish. But large numbers of algae-eaters were there, tiny surgeonfish and small parrot fish. Living like vagabond children in a dead and abandoned city, they picked their way through the silent towers of coral, picking at any fleshy algae that might grow on the mausoleum surfaces. And these fish were stalked by fearsome predators – huge moray eels like tyrannosaurs lurked in passageways ready to pounce on unwary vagabonds. Groupers stalked the channels and hid in plain site waiting for prey as the coral city around them steadily decayed.

One bright jewel gleamed just ahead – and as we swam toward it, we could see it was a fair sized giant clam, nestled between coral skeletons on a very deep ledge at 95 feet. I was slightly in front, but turned to see our dive guide Dawn pull out his knife and slice the clam off the reef. Alarmed and uncertain, I couldn't figure out how to ask by sign language what I wanted to know. "Was he moving it? "I wondered, maybe to a shallower site where it's internal algae could gather more light? But Giant clams were a delicacy in the Cook Islands and Dawn was a 100% native Cook Islander. "Was he planning to take it and eat it?" I couldn't be sure, and kept an eye on the clam…and on the reef.

What had happened to the coral here? A coral reef this extensive or diverse spoke of a vibrant and growing coral community within the past 5-10 years. In fact, the culprits were still there. Crown-of-Thorns starfish plastered themselves across some of the few living coral colonies, consuming the thin layer of living tissue, and leaving behind a stark white dead skeleton as a sign of their predation.

Crown-of-Thorns have plagued Cook Island reefs for years, ripping through coral reef communities over and over, reducing them to pavement. Places where the starfish starve and die, the corals can begin to grow back (see the Coral Kindergarten blog), but places where they hang on, they act to prevent any coral regrowth by preying on the young colonies.

Crown-of-Thorns outbreaks have come to many of the high islands of the Pacific, and to some of the low atolls. Strong freshwater run off from land, especially form poorly used agricultural and commercial land, fertilizes the coastal seas around a high island, and bolsters the populations of baby starfish. At first the young starfish remain hidden in a healthy reef, but then they emerge – 3 inch multi-armed predators against which corals have no defense. When thousands of them emerge on a reef, the outbreak spells doom.

Near the end of our dive, Dawn dropped the clam at the boat anchor and used his knife to dislodge dozens of starfish while we explored the shallows. But dislodging starfish hardly hurts them: it takes a serious effort to kill a Crown-of-Thorns. Time is the only antidote to this problem…waiting for the starfish to die off naturally and the corals to regrow. Of course if the outbreaks come faster and faster, then there is not enough time for recovery between outbreaks. This is why pigs are the best friends of starfish…pig farms on land wash so much waste into the water that the coastal ocean chemistry changes, and starfish babies are favored. Other poor land use practices contribute to the mess, easily seen in the brown, sediment laden water in a tropical stream after a heavy rain.

There was little enough to see on this dive that my mind turned to thinking about how to fix this problem. And wondering if I should hide Dawn's Giant Clam so he couldn't ascend to the boat with it. For the reef, the only hope lay in the corals recovering from healthy corals elsewhere - and the kind of baby coral re-growth we had seen in the Coral Kindergarten on Rarotonga. Keeping enough coral alive in the backreef, where starfish seldom venture, to be parents of the next generation would be one tack to take. Our experiments here might help with this.

As the signal flashed among us to head up to the boat, I warily watched Dawn re-collect the Clam. But he ambled off a few yards and found a place to nestle it into the reef, angling it up to face the sunshine that could power it to grow into a behemoth clam. Back on board our dive boat, he was surprised we had been worried…of course he'd preserve such a jewel.

We chose a more hopeful scene for our surface interval…the giant clam farm and coral gardens of the nearby back reef. There maybe we could find the parents of the next generation of corals that the dead reef behind us so sorely needs.

Photos:
Dawn, our dive guide on Aitutaki points out a back reef garden.
Dead dive on Aitutaki, Lauren descends onto a previously thriving but now 99% dead reef.
A giant clam soaking up the sunlight on Aitutaki.
All photos by S. Palumbi

April 12, 2012

Tanks for everything. My daughter and dive buddy Lauren couldn't understand why I was lighting a match under the oven broiler after lunch time in our little beach house in Rarotonga. And then why I was carrying the coral stress tank electronics into the kitchen, wiping them down and placing them gingerly on the stove. "You're broiling the stress tank?" she asked.

"No," I replied, "that would be silly. I'm using the broiler to warm up the oven and then putting stuff on the stove top to dry it out. Perfectly normal use of an oven."

The stress tank had been reconstructed with its new voltage converter, and then a deluge had soaked everything. Before much rain dripped deeply into the electronics, I was drying it all and hoping to bring it back to life. A few hours of gently drying later, and after a shift in tank placement under a part of the outside roof now known to be leak-proof, the tank was re-built and functioning again. One chiller power supply was dead, but even that might come back to life eventually.

It was three days till the end of our Cook Island trip, and data finally started to flow. I used the stress tank to test small coral fragments collected from a back reef area near Black Rock in eastern Rarotonga: they surprised me by surviving 32 degrees Celsius. I was surprised because the area is awash in waves from the forereef and does not appear to heat up much above 28 degrees. So, I imagined these corals would not resist 32 degrees because they rarely experience it. Even so, they have limits, and further use of the stress tank in the last few days on Rarotonga showed they began to seriously suffer at 33 degrees - and could not survive even a brief exposure to 34 degrees. Here were the stress tank results: 32 degree survival – 34 degree death.

Life on the reef crest

 

Rarotonga corals are not as heat resistant as Ofu corals. On Ofu most corals were at least partially resistant to 34 degrees Centigrade, and were stress free at 33 degrees for 2 hours. Ofu, in American Samoa, is quite a bit closer to the equator than Rarotonga and also sees generally warmer water. Especially in back reef Ofu habitats, the water heats up to 34 degrees and higher. So, coral heat resistance follows generally geography: an equatorial area has about 2 degrees higher resistance than one further from the equator. Of course this is just one comparison from a pilot experiment, and there may be other differences between the Cook Islands and Samoa that account this the change. But the results mirror some very early studies done in the 1970s in a few places. And the results whet our appetite for more information.

The best idea will be to conduct these stress tank studies as close to the equator in the Cook Islands as we can and then move south island by island till we get to the cooler waters of Rarotonga. The islands are far apart though, and only one of the northern group, the black pearl farming atoll of Manihiki, has regular air service. Instead, we talked with master Cook Island navigator Tua Pittman about a slower but better expeditionary route. A fleet of newly made Polynesian Voyaging canoes, under Tua's guidance and built by the Okeanos Foundation, is making it's way towards Samoa for the 50th anniversary of their independence in June. After the Festival of Pacific Arts in the Solomon Islands in August, one of these canoes will return home to Rarotonga. Tua suggested a route for a future voyage that would take a canoe, newly equipped as a science lab and classroom, all along the Cook Island chain from south to north and return (the return route demands a major detour SW and back, tacking against the prevailing NW winds). Along the way, coral scientists could test the reefs and sample parts of the world that have literally never been visited by science. And for the inhabited islets, we could bring educational materials and teachers and the old art of canoes. A hybrid of modern internet and ancient Polynesian worlds.

Perhaps all this was born of too much enthusiasm for long conversations with people on Rarotonga: Tua and Teina Rongo and Edwin Pittman, watching the sun set on the lagoon behind the reef in Rarotonga and imagining the value of knowing where in this dusting of coral islands the strongest corals live. The Cook Islands is designing the world's largest marine protected area, and may be poised to set up a protected zone in the southern islands that could be an important refuge for corals when the oceans heat up due to climate change. The waters there now are a bit cooler than more equatorial islands, and our tanks show the corals can withstand water a bit warmer than usual. A protected area that preserves reefs from local harm and that houses heat toughened corals might be a place corals could survive the next century. To have Polynesia corals and culture survive together would be a fabulous goal and a journey worth taking.

Beach house in Rarotonga – we set up the stress tank lab under the roof behind the picnic tables. At least three crowded beach barbeques went on alongside the operating tanks, a combination of natural science and Cook Islands' social engagement.

 

 

Beach sunset in Rarotonga – taking time out from barbeque meetings and stress tanks to walk the beach at sunset.

 

 

 

 

Map of the Cook Islands and Oceania, showing the proximity of Ofu and Rarotonga. The left hand map shows a possible route laid out by Tua Pittman for a Polynesian canoe to trace a path from the southern Cook's to the northern group and back.

Steve checking the stress tank in Rarotonga on the last full day of our trip.

 

All photos by Steve Palumbi, maps from GraphicMaps.com

April 7, 2012

Rarotonga Records has everything for the coral scientist. In front of the store, racks of tourist clothing frame a chalked sign announcing that TVs are now $380. Inside, shelves to the ceiling store electronic parts, DVDs, extension cords, flip flops, and…voltage converters. I bought one here seven days ago to power the coral stress tank, and it failed to deliver enough power. Another one might not quite do the job either, but I needed to try. We came here directly from the airport after returning to Rarotonga from Aitutaki – hoping to turn around the tank's failure there.

"All out, sold out, all gone!" was the reply, "everybody bought one the day you did." Meaning there was only one to begin with.

This was bad news since I knew that no one else on Rarotonga sold voltage converters.

"None?" I asked, rather uselessly.

"None! All out!"

My mind started down the path to Plan C…how was I going to manage to run the tank? This was bad…when I heard, "Of course, there is that big one down there…but nobody ever wants that."

"A big one? I asked, "where?" Down on the bottom shelf at the front of the store sat a hefty grey metal box with 'Salvation' written all over it. It was a machine-shop grade voltage converter and it's heavy weight spoke of the hopefully huge transformer inside it. It's weight and size told me I was never getting this box off the island, so I tried renting it for a week. No good, the savvy shop keeping saw a chance to sell something he'd kept (from the tarnish on the metal) on that lower shelf for years.

Fair enough. Sold. We carried it home to Paloma's house near the Rarotonga Airport.

I cleared off a spot along the countertop of the outdoor, tin-roofed picnic area that had seen many family beach barbeques. I restrained myself from going too fast, and I methodically set up the coral tank…LED lights, pump, heater, chillers, the micromanaging brain. I plugged them all into the new voltage converter, filled the tank with fresh water as a test, and carefully through the switch on the Big Volt Converter.

The brain woke up, flashing its normal indicator lights. The LEDs came on! The pump started! The chiller fired up! We had lift off and the tank was alive again!

Drenching downpour started immediately, and I saw all the places in the tin roof with gaping holes and gushing rainwater. Right over the outdoor electrical outlet and the stress tank! An electrical shock later, I was turning off the power to the main switch with a plastic handle dish scrubber, and frantically gathering up the tank electronics to get them out of the rain. This was not the best way to start Rarotonga experiments on coral heat resistance, but all along I was very happy to have finally everything I needed to do the experiments right.

Now if I can get the rainwater out of the voltage converter…

The savvy shopkeeper at Rarotonga Records. photo by Lauren Palumbi
The stress tank finally on a proper diet of 120 volt power, and under a better roof. photo by Steve Palumbi

April 5, 2012

The stress tank is not happy. Sitting in a perfect spot in our little house on Aitutaki, it will not run correctly. Instead, it is driving me crazy. The tank's brain is basically a micromanager, the worst boss you could think of, wanting to know every second exactly what is going on and telling its subordinates (a chiller and a heater) minute by minute what to do. It turns out that being a micromanaging monster takes a lot of energy, and the brain of our stress tanks sucks down more power than I thought. So much that the voltage converter we got for it, that turns 240 volt Cook Island power into 120 v power needed by the stress tank, is barely enough. It can run the brain, but much to my dismay it doesn't have enough wattage left over to run the heaters, chillers, pumps and lights.

Now what? (This might be a pun if you are inclined to think that way). Until I get an extra converter, we bump to plan B.

First, I give up on the lights I brought…they are special LED bulbs and drawn a lot of power. The bulbs cannot take 240 volts but the light fixture can. So I replace my LEDs with 240 volt, 60 watt bulbs. These double as heaters too, since regular bulbs put out a lot of warmth. This is very good since I can't get the heater to function at all. The recirculating water pump is the only thing that the main brain will power. Enough is working for a test.

In go the corals, collected for this pilot run at a stunning back reef beach near the end of the old Aitutaki runway. Scattered mounds of Porites corals and a variety of branching corals grow in clumps just a few yards off the beach. Swimming directly out from there to the reef, perhaps a 300 yards away, we pass across gardens of corals and small fish, interspersed with sand channels and old reef rock. I can find all the species I want here – the same ones I had tested while I was in Ofu last week. Four little branches of each coral come back to the beach in a plastic ice cream container nestled into the storage bin of a small motor scooter we rented. I strap a 5 gallon carboy of seawater to the back of the scooter with bungie cords. And within an hour of setting out from the house, I am back with all the makings of our first coral stress test.

I run it at 33 degrees, quite a bit higher than the Aitutaki back reef temperature of 26 degrees. This should tell me if these corals are heat resistant: Ofu corals take this temperature easily. But the tank simply does not cooperate. It heats up too fast and too much, and the brain can't deliver enough power to the chiller. So, I have to turn the chiller on when the tank heats up and turn it off when it is too cool. Though I have a microprocessor in the tank brain and another in a laptop connected to the tank, I spend the day plugging the chiller in and out, in and out, in and out.

The result is a tank that cycles from 33 to 34 and back again. I can't stabilize the temperature much better than that manually. But I complete the experiment, running Aitutaki corals for 4 hours on this cycle, taking out one branch from each species each hour and adjusting them slowly to normal temperature. The results: …unusable. Between the odd light bulbs and the irregular temperature, all I can tell from this experiment is that these corals are unhappy. Because the equipment is behaving differently I can't compare the results to Ofu, and that is the purpose of this expedition.

Back to the drawing board. I have to fix the lights and get the brain enough power to do its micromanaging job. Nowhere on Aitutaki is there another voltage converter – I've looked in the only hardware store. I will have to go diving instead, and wait to get back to Rarotonga, where there is a guy who may have the right thing.

April 3, 2012

The Coral Kindergarten. We made an exciting discovery on our first dive, one that made us smile through our regulators, and extend the dive to make sure we were right about what it was we were seeing. We found a coral kindergarten in Rarotonga.

From about 35 feet deep to 75 feet, there were young, newly growing corals everywhere, up to about the size of a saucer growing on old dead coral boulders and bare coral stacks. Every square yard or so there was a young colony growing, laying down a good base of attachment to the surface and then sending up tentative branches from the center. And there were a variety of coral species in the nursery.

People do not flock to Rarotonga for the fabulous reefs – it's a beach crowd that wanders along the shore. The dive shops are struggling and the corals here are well known to be mostly dead. The cause was an unfortunate triple whammy. The first disaster was long ago – an eruption of crown-of-thorns starfish in the early 1970s. Thousands – millions – of starfish appeared on Rarotongan reefs and ate the coral (an unusual choice for any starfish but the Crown of Thorns, which finds tiny polyps encased in slime-coated rock appealing). The reefs recovered from this in about ten years according to local coral expert Dr. Teina Rongo. The second whammy was another crown-of-thorns outbreak, but this one was followed by series of powerful typhoons that churned up the corals into a pile of broken crockery. These disasters left a scarred dead zone of coral rock from which the reefs have yet to recover.

Reef dives show this history. The bottom is littered by broken and overturned coral heads and plates, with wide swaths of bare limestone rock where corals used to live. Large, live colonies are restricted to rare lumbering Porites mounds, a type of coral that even the crown-of-thorns disdains as dinner.

But in an unlikely place just east of the biggest town in the Cook Islands, among the coral stacks and sandy canyons a reef is trying to regrow from baby corals. Two things stand out as major reasons why this place might be re-growing. The water is clear – even on a bad day for diving. We dove the morning after a torrential rain, and most other spots along the coast were murky with runoff. But this site retained the clear blue water and glimpses of sandy bottom that divers love to see. Corals love it too, and thrive in clear water that lets in lots of sunlight. The second important factor is that the old coral, though dead, was not covered in a fur of algae, but was scraped clean by parrot fish, surgeon fish, sea urchins and other algae eaters. Coral babies cannot settle down and grow on algae-covered rock. They need a clean nursery – and the fish are the nurses of this neonatal shore.

Good water and fish = new coral. At least on one place in Rarotonga.

Next: why are there still fish some places in Rarotonga? Poison is the answer.

Coral recruits from Rarotonga – the next generation grows up. Photos by Steve Palumbi.

March 26, 2012

The triumph of Randall: Ofu's weather alternated between scattered sun and roaring rain but Randall, the concrete artist of Ofu, had his runway repair crew on the job between squalls. There was a challenge – could the new concrete be laid by Thursday morning so that the plane could land Saturday? "Yes," said Randall. "No," said Joe, the plane's pilot, and the race was on.

My stake in this was that a flight from Ofu was the first of a set of planes to Rarotonga in the Cook Islands. That I am writing this in the Aukland Airport means that the flights are in progress and that Randall triumphed.

The Cook Islands are east of the islands of Samoa. They lie halfway from Ofu to Tahiti, and stretch from near the Equator to about as far south of the Equator as Hawaii is north. A bare couple of thousand kilometers as the whale swims. And the next destination in our Tough Trek, our expedition to find the strongest corals.

But whales don't swim from Samoa to the Cook Islands directly (they go back and forth via their feeding grounds in Antarctica). And I don't fly directly either. I have to go from the Samoan to the Cook Islands either via Auckland (3000 miles west) or LA (5000 miles east). I chose Auckland, so here I sit.

Randall hates rain on his concrete. "It ruins the finish," he revealed. And he has trained his crew to produce a concrete surface to exacting standards. In the intermittent storms, plastic sheeting maintains the sheen, but that can only go on after a respectful amount of time has passed for the surface to cure a bit. And the runway was finished Thursday.

True to his promise, Joe flew in Saturday, the small plane careening left in a wind gust and landing first on its rear left wheel. Balancing on this one ballet point, Joe roared down the runway on Ofu, missing all the new concrete patches, as if to say he still didn't believe they were set. We waited for a few large bales of frozen fish, loaded the plane, said our goodbyes to Rachael, Lupita, Nikki, Pierre and Francois, left tragically behind to spend a few more weeks on the Ofu reefs searching for the reason corals are so tough there. And we powered into the air for the first 50 mile flight on a 7000 mile hop to Rarotonga.

March 24, 2012

Map of Survivors. The stress tanks have been running for five days straight now on Ofu, and we have 138 small tubes with a ½ inch coral fragment bathed in alcohol as preservative. Each tube tells us what that coral's reaction was in the tank, and the result is a picture of what would happen here during a bleaching event.

Bleaching events are a perfect storm of calm winds and hot weather, with the relentless tropical sun heating up the upper surface of the sea. Normally waves break up the surface, and more importantly, they deliver water across the top of the reef to the lagoons behind. Without those waves, the withering sun can bake the corals with excess heat and light.

Our heat lamps and computer controlled heaters do this job for us, and deliver a measured dose of coral bleaching conditions in a small tank. And so each coral fragment we place in the tank comes out somewhere between bleached-white and healthy-brown, and the ochre rainbow at the end of the experiment tells us who are the survivors.

Some species are tougher than others, and fragment by fragment we are trying to build a list of the tough ones and the not so tough. And weak species growing in a tough place can be a surprise…the corals that manage to live in hot back reef areas may well be conditioned to those conditions, or have inherited the right genes for the job. The whole map of coral resistance to heat is being built day by day, tank by tank, species by species and place by place. No one has tried this for about 35 years, so we have a lot of work to do.

FIGURES: The portable coral stress tank set up and creating simulated coral bleaching conditions on Ofu, American Samoa. A set of 10 coral colonies (from top to bottom) tested four times each (from right to left) in the stress tanks. The two middle rows were heated to 34° C (about 94°F). For some colonies, that temperature was high enough to cause bleaching – shown as a whitening of the coral branch from its normal nut-brown color. (Figures by Steve Palumbi)(click on image to see 2x).

YouTube Video

March 22, 2012

First video from the field! Marine Biologist Steve Palumbi shows how he is looking in the backreef lagoons of Ofu in American Samoa for corals that have the highest heat resistance. Are these the ones that will survive global climate change? YouTube Video

March 21, 2012

We arrived on Ofu 36 hours ago and already we have learned three things. First, the corals we mapped and tagged last November are thriving, and the electronic meters that we left on them, to measure temperature and pH, have been doing their jobs: logging the conditions that each of these corals have seen. The batteries in them lasted until just a few days ago, according to the data we have downloaded just today, and we now have a record of the heat and acidity that these individual corals have seen in their natural environment.

The second thing we have learned is that corals that normally see higher temperatures can deal with our experimental coral stress tanks better than corals that usually see lower temperatures. I did the very first run of the stress tank yesterday, right after landing on the tiny airstrip that Ofu boasts, delivered by veteran pilot Joe Faiai thanks to the American Samoa government plane. It took about two hours to get the tanks set up, and plunge into the lagoon for the first time in months, to see what our corals had done.

We have gotten to know these corals on this reef. Some have been tagged, numbered and mapped for seven years. Coral AH09 is the biggest of our species, a table top coral that sits like a dowager Queen at the entrance to a channel in just 4 ft of water. Almost 7 ft across now, she grows exuberantly between every visit. Then there is the much more humble coral AH06: perched at the edge of a sand channel, barely 2 ft across, it barely grows except to crankily replace whatever small branch we take when we sample it.

My favorite are the 100s – AH100, 101, and 102 – not for their size or color, but for their placement, right behind the reef crest in a washing machine of waves and currents. Finding them is always a fabulous challenge of frantic swimming in 12 inches of water in 4 foot waves, being swept at breakneck pace along a pavement of reef by curling breakers. And once found, the challenge is to stay there for the minute it might take to place a buoy on them or take a sample, or take a picture. Most of the pictures I have of them are blurry because I am usually being washed away at the time.

The third thing we have learned so far is that I will have a difficult time getting off Ofu to get to Rarotonga. We landed amidst a surprising collection of construction equipment – and as soon as the engines of the plane were lost in the distance (after Joe took off again), the jack hammers started. Joe had said when we landed, and I asked about our return flight on Saturday "Sure, see you then. But talk to Randall".

Randall as it turned out has other plans. He runs the construction crew that is busily ripping up the runway that I need Joe to use. The idea is to replace the broken bits with fresh, beautiful concrete (Randall is a concrete artist, though he may object to being known widely that way). The problem is that the concrete will be poured Thursday and not be set well enough to land a plane on until Sunday. So far, Randall seems willing to try to get all the concrete poured tomorrow – if the sun shines. But nobody rushes the concrete artist of Ofu and I am casting around for other plans.

Figures: The Queen Victoria of corals, AH09 in Ofu. The least blurry picture I have of coral AH102, taken before being washed away off the reef crest.

March 16, 2012

Why, you ask, do we want to find the world's strongest corals? The short answer: global safety net.

Hundreds of millions of people depend on reefs – among Earth's most productive ecosystems – for fish and shellfish to eat. For many families, reefs put food on the table or a few dollars in the wallet when budgets are tight or jobs end. Steve Hall of the World Fish Center calls this a socio-natural safety net. The safety net fails when the corals die, and the fish fade away.

Elsewhere, local villages depend on corals to fuel a hefty tourist trade and keep storm waves at bay.

Beyond their practical value, corals are simply mind-blowing. They are wonders of the living world, primitive layers of tan tentacles that grow enough hard rock to build whole archipelagoes, and engineer structures that overtop the pyramids. Their colors and forms and diversity exceed our imagination. The thousands of species that live within reefs are the most intensely colored living paintings you will ever see.

Yet corals are dying fast. Buried by dirt, poisoned by pollution, smothered by algal weeds, corals have died on about a quarter of the world's reefs. Climate change threatens a third of corals with extinction by raising temperatures and ocean acidity.

Our work has found that some corals can survive the heating and bleaching that others succumb to. What if we found these strong corals and protected them in a grand alliance with political leaders of reef nations around the world? It would be a profound step forward. It might just give us enough time to solve the deeper problems of human

FIGURES: A school of surgeon fish at the Ofu lagoon. Health reefs have a lot of fish, which help maintain corals by eating fast-growing algae. The palette of corals and colors on a healthy Ofu reef. Photos by Steve Palumbi

March 14, 2012

How do corals react to climate?

Suppose you are 1000 years old and glued to the ground. Whatever environment you chose 1000 years ago when you were a wee coral larva is the environment that you had to grow up in. And over 365,000 good and bad days, you had to survive every single day – living through whatever the waves and sun and sand and ocean brought you. Corals in your high school class might have died over the years because they could not react well to a particularly hot day, but you survived.

And now the environment is changing, getting hotter year by year. And the ocean is becoming more acidic. How do you survive the NEXT 1000 years?

Animals can react to climate change in three ways. MAAD. They can Move. They can Acclimate. Their populations can Adapt. Or they can Die. Obviously, corals cannot Move. We'd prefer if they did not Die. That leaves Acclimate and Adapt. And that is what our expedition is meant to uncover – which corals have acclimated and adapted already to hot temperatures, where are they found and what do we do with them?

Figure – the oldest coral in the Samoan Islands, a huge Porites colony estimated to be over 2000 years old. Photo courtesy Rob Dunbar.

March 13, 2012

What's special about Ofu? In addition to being the site of the U.S. National Park Service's only park south of the equator, it boasts a backreef lagoon with very special properties. Reefs grow 100 – 1000 m out in front of the shore on many coral islands. Behind the reef itself is a region - between the crest of the reef and the shore - called the backreef. (If the backreef is a flat zone of very shallow water it is called a reef flat. If it has deeper pools, these pools are called lagoons.)

On Ofu, the backreef has a set of pools 4-10 feet deep, washed by waves that come over the reef at high tide. But at low tide, the pools calm down and their glassy surface reflects the clouds from above and the corals themselves from below (Pictures). The low tides at Ofu often come during the middle of the day, and when this happens, the pools heat up to 32-34 deg C (90-93 deg F).

We started our search for the world's strongest corals at Ofu because the backreef lagoons were too hot for corals to grow well – supposedly. But they were full of corals that seemed to be very healthy. In fact, they were growing faster than the same species do elsewhere. One question was whether these corals really were heat resistant, and if so WHY they were. But a second question was whether all corals could be this heat resistant or whether these Ofu corals were unique.

This started us preparing, last year, to measure heat resistance at Ofu, and to take this show on the road to other reef locations.

March 12, 2012

The back reefs of Ofu Island are a tropical paradise, rich green peaks rising around turquoise lagoons. The tides wash in and out slowly, making the water as warm and pleasant as any tropical tourist could ask for. But these warm waters are also an important training ground, the corals that live in these lagoons are constantly exposed to temperatures high enough to bleach and kill most reefs. Mass coral bleaching events across the globe have caused scientists to worry that these coral reef habitats are at risk of dying out as climate change raises ocean temperatures. On Ofu we have found corals tough enough to live high above their normal bleaching temperature. On Ofu, we are trying to understand how these corals have found a way to survive. But a bigger question looms: do these tough corals live elsewhere?

Our main research tool is our coral stress tank – a computer-controlled aquarium that lets us heat seawater to a precise degree. We place corals from different reef locations in these tanks, ramp the temperature up over the course of a day and record which of the corals bleach. You can watch us build and use the tank at Stressed Out Corals.

On March 18th, we will take our newest tank to American Samoa and test run it there, where we already know where the toughest corals live. From there we will take the tanks on the road for the first time into the rest of the Pacific. We will travel to Rarotonga in the Cook Islands, a place where normal ocean temperatures are lower than in American Samoa. The final stop is the 'almost-atoll' of Aitutaki, a small island north of Rarotonga. We'll test if the tanks work on these corals and if we can find evidence for tough corals in the Cook Islands.