Merry Youle's blog

Room at the Top

It is simply common sense. Look around you at any familiar ecosystem and you'll see that there are few top predators, lots more prey, and still more vegetation for munching. This seems intuitive because we know that at each trophic ("feeding") level, the organisms eat many times their own weight in food, roughly ten times their weight. It takes many mice to feed one hawk. Only 10% of what is consumed becomes new biomass that can then pass on up the food web to the next higher level. About 90% is spent in just staying alive. 

But there are an awful lot of sharks at Kingman Reef. So how does this common sense apply to a pristine coral reef ecosystem? For simplicity, let's picture a reef as having just four trophic levels. At the bottom are the primary producers, those being the photo-synthesizing algae and bacteria. Next level up are the herbivores—the fish and the invertebrates such as sea urchins that graze the algae. Next are the small predators that prey on the grazers, and at the top the large-bodied predators such as sharks, travally, and groupers. Since only 10% of the food eaten passes on up to the next level as biomass, this means that every pound of shark swimming about represents at least 1000 pounds of algae, 100 pounds of grazers, and 10 pounds of smaller predators. These approximations are minimums because there can be more mouths between the algae and the sharks, each taking their 90% cut.

The Microbial Landscape

by Forest Rohwer, head researcher on the Microbe Team

Most of the life on a coral reef is microbial. When we look at corals through a microscope, we see that each coral has about 10 million Bacteria on each square centimeter of its mucus-covered surface. There are another million Bacteria in each milliliter of seawater. The number of viruses here is even more impressive—about ten times as many as Bacteria, or at least 100 million per square centimeter and ten million per milliliter. The microbes are everywhere on the reef. The sand, the algae, the fish, and even the sharks are all heavily colonized by microbes.

So what do these numbers add up to for a place like Kingman Reef? The approximate area of Kingman Reef is 80 square kilometers (800,000,000,000 square centimeters). Doing the math, this calculates out to 8 × 1018 Bacteria on the reef surface. If we assume an average water depth of 10 meters, there are an additional 8 × 1020 Bacteria in the water at Kingman. While these number are unfathomably large, they are still a gross underestimate because we assumed that the reef is a flat plane, which it most definitely is not. The mounds, branches, fronds, crevices, and cracks make the total surface area much greater, and all of that surface area is covered in microbes.

The Microbes in the Field: Halloween

by Forest Rohwer, head researcher on the Microbe Team

Pre-coffee and half-asleep this morning, I opened my cabin door and was assaulted by a giant (3 ft) black spider. Apparently The Fish didn't have enough to do last night so they decided to try to kill off Alan or I with an early morning heart attack. The ship is now decorated with a Jack-O-Lantern, a sparkling pink skeleton (picked out before departure by my 5 year-old daughter Willow), and the spider.

Up to this point in the cruise, The Microbes (Katie Barott, Tracy McDole, Mark Vermeij, and I) have been supporting deployment of the CBAT tents. This included their initial set-up, as well as putting in the plumbing to gather water samples. These waters samples are taken back to the ship and processed so that we will know the concentration of dissolved organic carbon (DOC) and nutrients in the tents, and can correlate this with other measurements such as algal growth rates. In theory, the DOC levels should go up during the day when photosynthesis is happening and DOC is released into the water, and then should drop back down at night as the microbes eat the DOC. We aren't actually taking dark samples on Kingman because of the distinct possibility of getting eaten by the abundant sharks that swarm in the evening. We did try to get one of The Fish to go retrieve some samples during the hours of darkness, but they were strangely circumspect in this regard. We'll get night samples at one of the less pristine reefs.

A Most Useful Useless Reef

Charles Darwin saw a world that was dynamic, changing, evolving. On his voyages in the Pacific he was struck by the geology of the myriad islands and doughnut-shaped atolls there. He was the first to connect the dots and realize that they all represented snapshots taken at different stages in a geological progression. Each had been born as a high volcanic island that became encircled by coral reefs. Over time, the islands eroded and the sea floor sank (subsided, in geology speak), while the corals continued to build the reefs upward to stay in the sunlit zone. Eventually, the land disappeared beneath the waves, leaving only a reef as a clue to its past.

Kingman Reef is one such relic. By the time humans arrived in the Line Islands, only about three acres of land remained, all of which is awash most of the time. Without land suitable for settlement or airstrip construction, and lacking guano deposits or other usefulness, Kingman has been left alone—actually avoided as it poses a hazard to shipping. Being useless, it has proven to be extraordinarily useful for coral reef researchers today.

More of Palmyra's Reefs from the Benthic Team's Photo Album

Time to bid farewell to Palmyra and steam on to Kingman Reef. The researchers had enjoyed the luxury of the ample lab space at the PARC research station, but now all their gear and equipment is back on board the Hanse Explorer. For the rest of the expedition, their laboratories will be whatever unoccupied niches they can find scattered about the ship. Palmyra was indeed splendid. Can it really get even better?

Crystal Blue & Cotton Candy Pink

by Nichole Price, member of the Benthic Team

It's day five on Palmyra, one the most beautiful places on earth, and I couldn't be happier. Today we are diving at my favorite site here, the northwest fore-reef at about 35 ft depth. The water is crystal blue and gin clear, reef fish of every color and size swarm all around us, and the reef floor is covered in cotton candy pink. The source of the pink color has been the focus of my research program on Palmyra for the past two years and today I get to see the first results from my labors!

Palmyra has an extraordinary abundance of reef building species that includes not just the well-known corals but also an important and often underappreciated group—the crustose coralline algae. These pink, rock-like seaweeds are responsible for the vivid colors I see on the reef floor beneath me. This group is unique among the algae in that they make a hard calcareous skeleton, much like corals, yet they get all of their energy from photosynthesis, like kelp and other algae. Their function in the ecosystem is vital for coral reef resilience in times of natural disturbances. These encrusting algae cement the reef framework, thus strengthening it against storm damage. They also produce a chemical signal that encourages baby corals to settle —a first step in rebuilding a depleted coral population following a disturbance. Seeing so many of them here tells me that not only is this reef healthy today, but it will do better than many when challenged by climate change in the future.

Time Travel into Palmyra's Past

Environmental forensic detective Jessica Carilli and other members of the Paleo-Benthic Team have started probing into Palmyra Atoll to extract and decipher the record of its troubled past.

by Jessica Carilli, head researcher on the Paleo-Benthic Team

While Palmyra Atoll was occupied by the military during WW II, the lagoon was significantly altered (check out the earlier blog entry for more info). As a result, today many parts of the lagoon have little to no live coral cover whatsoever. What types of corals were living here in the past? To investigate that, the Paleo-Benthic team has begun collecting push-cores in the lagoon. Because both the living corals and the accumulating sediments build upwards over time, by collecting a core down into the sediments (which include fragments of dead corals, which were visible on the surface as well), we can essentially look back through time to see how things have changed. Our push-coring device consists of a thick aluminum pipe, a collar that fits snugly around the pipe, and a heavy steel sleeve that is manually hammered onto the collar. It's a lot of work, but using this tactic we can sample down through several meters of sediment and coral rubble—traveling back in time hundreds or thousands of years. We're also going to be very fit by the end of this trip!

In Sickness and in Health

While being dazzled by the corals, manta rays, and schools of fish at Palmyra, it is easy to forget that many coral reefs around the world are struggling. Numerous interacting factors have already led to widespread coral decline. Of particular concern is that all of these current impacts can reduce the resilience of the corals, thus making the reefs more vulnerable to the inevitable effects of climate change that lie ahead.


by Gareth J. Williams, member of the Benthic Team

Coral reefs are declining worldwide due to pollution, intense overfishing, and the global effects of climate change. Two other culprits—coral bleaching and disease—are also taking a toll on coral health. When corals die, the decreased coral cover on the reef has knock-on effects that can impact, and often change, reef-associated communities such as the fish.

The term coral bleaching refers to the loss of color from a coral colony, giving the colors a ghastly pale appearance. The normal vibrant coral colors are due to the pigments of the coral's resident algae, the zooxanthellae. Bleaching results when the breakdown of this symbiotic association leads to either the loss of photosynthetic pigments by the zooxanthellae or the loss of zooxanthellae from their coral hosts. Either way, the resulting decline in photosynthesis can mean death for the corals. Bleaching occurs in response to environmental stress, predominantly to elevated water temperatures. Much recent research has focused on understanding how local human impacts interact with global climatic stressors to influence the extent and location of coral bleaching (the bleaching pattern) on coral reefs.

Two Welcomes to Palymra

The first expedition hours are especially exhilarating when most everything is a first: first trip to the Line Islands, first visit to Palmyra Atoll, first dive on a spectacular healthy reef. It's all new for Jill Harris, a graduate student in the Smith Lab at Scripps Oceanography. She shares her thoughts upon arrival at Palmyra aboard the Hanse Explorer and her first underwater view of the reef.

by Jill Harris, member of the Benthic Team

As a first-time visitor to Palmyra, I hope that my first impressions of this place can help our blog readers understand just how phenomenal it is to be here. We are on a tiny speck of land in the middle—the middle!—of the vast Pacific ocean.

Day 1: We arrive at Palmyra mid-morning, and I marvel at how smoothly the captain of the Hanse Explorer maneuvers his ship up to the packed-earth dock at the field station. Gangway down, we quickly spring into action to unload our scientific equipment. For these few days, we can use the ample lab space at the research station here—a treat compared to onboard the ship, where everything needs to be packed up and secured to the deck each night.

In the afternoon, we are officially welcomed to the Palmyra Atoll National Wildlife Refuge. We learn about daily life on Palmyra (where to sleep and eat), important safety procedures, and, perhaps most importantly, we are reminded about the guiding mission of this place: wildlife first. We are, after all, but temporary visitors to a very remote, thriving wilderness.

Hitting Bottom at Palmyra

The expedition researchers wasted no time after arriving at Palmyra Atoll before getting to work. We follow the Benthic Team as they head out to the reefs with their gear to face the challenges of their first day of diving and deploying their experimental set-ups on site.

By Jen Smith, head researcher on the Benthic Team

Yesterday afternoon we arrived on Palmyra with a small group of scientists and some guests of Scripps Oceanography. The flight down was quite comfortable and quick—just under four hours from Honolulu. As we approached Palmyra Atoll, the excitement began to grow as the picturesque scene of a tropical wonderland came into view, and then we saw our ship, the Hanse Explorer, docked in the lagoon, waiting for us. We landed on the coral runway and were greeted by the Nature Conservancy staff that runs the Palmyra Atoll Research Consortium field station. One by one the scientists who had traveled over with the ship from Honolulu came out to greet us, as well. At this point we all began to feel that—finally!—the weeks and months of planning and coordinating were behind us. Finally it was time to start doing the science—the hard work, the exhausting days, and the research activities that we are all good at.

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