Palmyra Atoll

Entering East Lagoon

To get to the East Lagoon, we first had to cross the North-South Causeway built by the US Navy. While once a single lagoon, it is now compartmentalized into East, Central, and West. Fortunately, there is a cut in the causeway deep enough for the lagoon boats to pass through, allowing access to all parts of the lagoon. Driving through the cut just requires a bit of maneuvering, since there is a shallow reef directly on the other side. As we passed through the cut and boated parallel to the causeway for a couple of minutes to circumvent the reef, we were serenaded by the calls of red-footed boobies nesting in the Tournefortia trees and the murderous screams of frigatebird chicks in the distance. Upon reaching the buoys marking the end of the pathway through the cut, we angled toward the center of the lagoon. We were headed for a shallow sandy patch off of one of the original islets. GPS unit in hand, I navigated us to the site. Upon arriving, I donned my snorkel and hopped into the cerulean blue water to check out the benthos. Exactly as described in the substrate map that I had found of Palmyra’s lagoons, the sediment here was fine with a small amount of silt, making it ooze a bit between my fingers. I popped up with a smile on my face and instructed Hope, our captain for the day, to anchor the boat. Dana and I slipped into our SCUBA gear and split up the cloth sampling bags – five for each of us to fill. We were ready.

We descended to the bottom, which was only about 12-15 feet deep, and set up our bright yellow lift bag as a central marker around which we would sample. This prevented us from straying too far and getting lost in the murk. We then set off to fill our first bags. I perused the benthos, looking for a relatively flat, undisturbed patch of sediment between the algae-covered coral heads and avoiding areas that were obviously bioturbated. For example, some species of shrimp build burrows that look like tiny underwater volcanoes. They carry particles of sediment from deep within the substrate to the surface to construct these burrows. Therefore, we do not want to sample near them because the sediments there are very mixed.

This site was fairly close to the blue hole on Palmyra, which is apparently boiling with sharks from what I’ve been told. Thus, I suppose it was not a coincidence that a couple of blacktip reef sharks swam over while we were digging to see what we were up to. They were still juveniles and darted off once they had been spotted… what sleek creatures! It was certainly a change of pace from my experiences doing field work in the Caribbean to actually get to see my study organism!

 

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Into the deep, dark lagoon

Half of our proposed sampling sites were located in the lagoon. These words may strike fear in the hearts of some of the researchers who have dove in the lagoon before and seen large shadows lurking in the murky depths or fended off tiger sharks. At least these are the stories that people told me before my first lagoon dive. I wish they had told me after. You can throw rocks off the wharf into the lagoon and the sharks and giant trevally will come… and not just blacktip reef sharks, which I don’t mind hanging out with. There are tigers, lemons, grays, and potentially hammerheads that patrol the lagoon. The scariest part is that the visibility is so bad in some areas that you would barely be able to see them coming.

However, the sediment here is soft and silty (which further lowers the visibility when you dig into it and kick up a swirling cloud of silt). A mix of live and dead coral can be found where the lagoon flat slopes down into the lagoon proper, and there are some shallower patches toward the center of the lagoon. This is where we sampled.

Our first dive was in the West Lagoon, almost directly opposite the research station. We descended about 20ft along the slope before kneeling on the sandy bottom to start our work. Because of the incline, it was easier to kneel with my back to the lagoon. About halfway through each sample, I would nervously look back over my shoulder to make sure nothing big was there. And fortunately nothing ever was… at least on this dive.

 

 

A glimpse of the forereef

Dana and I were lucky enough to get to do two dives on the forereef to retrieve some sensors from a mid-water mooring. Two-spot red snapper (Lutjanus bohar) lurked behind us and gave us toothy sneers as we swam around the reef, but no sharks were spotted on our quick dives. Still, the scenery was breathtaking!

The first samples

Our story begins at a place called Penguin Spit, a reef located outside of the lagoon just south of the channel (lower left hand corner of the map). This is a commonly accessed reef on the atoll and the site of our first sediment collection. Situated safely behind the reef crest, this area is protected from much of the wave energy that batters the forereef. These waves and swell become abundantly obvious as you move offshore from the channel, and our tiny lagoon boats are only allowed with the boundary of the reef terrace for that very reason. The lower wave energy at Penguin Spit also means that there will be finer sediments that we can sample. Today, we were moored at Penguin Spit Middle, but later in the week we’ll head to Penguin Spit Inner as well, where the sediment is even siltier.

File:Palmyra Atoll Visitor Access Map.jpg

Palmyra Atoll Access Map. United States Fish and Wildlife Service.

Sliding into the water from the boat, I was surrounded by a colorful mosaic of corals. The diversity and density were astounding! There were thousands upon thousands of corals. The coral cover for much of the reef was 100% or close to it, leaving us a just few patches of sediment to sample. My dive buddy, Dana, and I perused our surroundings, keeping an eye our for suitable patches of sediment and marveling at the hustle and bustle of the underwater city that surrounded us. Coralline bommies towered overhead and highways of convict tang and juvenile parrotfish cruised by. We later accompanied the person who wrote the narration for March of the Penguins here, and his first impression was one of pure astonishment. This place can really take your breath away.

However, even on this remote reef, there is a pernicious intruder. Thought to have first been introduced by the shipwreck of a long line vessel on the reef terrace north of the channel in 1991, corallimorph (Rhodactis howesii) has crept across the reef, displacing other corals. Even after the removal of the wreck, it continues to spread, leaving scientists scratching their heads. Efforts are in the works to try to curb corallimorph growth, which otherwise could threaten the dominance of corals on these reefs. In the picture below, it is the anemone-like organism crowding out the sediment patch that we sampled.

Welcome to Palmyra Atoll

Palmyra Atoll is very much located in the middle of the Pacific. So how does one get there, you ask? There are two primary modes of transportation: by plane or by ship. We cut to the chase and flew. The flight from Honolulu was around 2.5 hours, and the plane (see below) was certainly an upgrade from my trip in 2011. After a bumpy landing – complete with food and coolers flying around the cabin – we disembarked and began preparing our field gear for the next day’s sampling. We had arrived in own scientific paradise.

 

 

Off to the Pacific

I just returned from a fruitful month-long expedition to Palmyra Atoll, a tiny atoll within the Northern Line Islands located approximately 1,000 miles southwest of Hawaii. While previously occupied by the US Navy during World War II, Palmyra is now protected as a National Wildlife Refuge by the United States. The Navy drastically altered Palmyra’s landscape by extending existing islands and building new ones, constructing causeways to connect these islands, and dredging a channel to allow access to the lagoon. Despite these terrestrial perturbations, the coral reefs surrounding the atoll have remained largely untouched, offering scientists a glimpse into the inner workings of a healthy coral reef ecosystem. Here, sharks abound, providing a stark contrast to the relatively depauperate reefs from which we collected sediment in the Caribbean. Palmyra Atoll is of particular relevance to our study because the shark populations there are both large and well-characterized, giving us the opportunity to validate and refine our use of dermal denticles preserved in sediments as a time-averaged proxy for living shark assemblages on reefs.

Palmyra Atoll is also where I first discovered my passion for coral reef ecology. In 2011, I assisted with field work on Palmyra’s lagoon flats as an undergraduate student at Stanford. While most of my time was spent in the sandy shallows, I went snorkeling on the reef terrace on several occasions. There, plunging into the aquamarine waves, I came face to face with a shark, then two, then three. Never before had I been in the company of a reef so full of predators. This was the first time I had directly observed the ecological splendor of a protected coral reef. It was as if I had been transported back in time to glimpse how reefs may have operated before humans. Three years later, when I began working on the dermal denticle project with Aaron, applying this technique to Palmyra was always in the back of my mind. It’s incredible to now make this idea a reality and share it here with you.

While WordPress was not working on our internet servers on the atoll, preventing me from posting live from the field, I will now be publishing my experiences collecting sediment on Palmyra in regular installments.