Blog

Reminiscing Klein Curaçao

28 February 2017, 0545HRS

It was still dark out when we departed the field station. Groggily, we loaded up the truck with our dive gear and SCUBA tanks while sipping coffee to try to wake up. The clock was already ticking. We had 30 minutes to get to the dock in Caracasbaai before the ferry was scheduled to leave.

This was a risky yet critical endeavor. Our aim: collecting sediments from the reefs of Klein Curaçao, a tiny, uninhabited island located approximately 15 miles off the southeast point of Curaçao. Less visited or fished than Curaçao, the reefs there would provide a more ‘pristine’ end member with which to compare our other Caribbean samples. The orientation of the island, which was nearly perpendicular to the trade winds, meant that the leeward side would be quite sheltered despite lacking any lagoonal environments. But would the sediments be fine enough to contain shark dermal denticles? This was the gamble.

We arrived at the dock just in time and confirmed that no recreational divers were joining the group. We would therefore have the flexibility to select our dive sites and use the tour group’s dingy to lift our heavy sediment samples to the surface. We decided to board the ferry.

After a rough 1.5-hour ferry ride, the island’s barren landscape came into view. A thin strip of white sand beach intersected the cerulean sea and stormy sky. A lighthouse, accompanied only by a rusting shipwreck, rose in the distance, breaking the otherwise flat horizon. ‘Paradise,’ thought the tourists. ‘Healthy reef,’ thought our team.

Descending along the reef slope, I was astonished by the vibrant reef and number and size of the fish. Large parrotfish swam by in a swirl of colors and movement, and I had a standoff with a toothy barracuda within minutes of entering the water. This reef was obviously full of life. While the staghorn coral (Acropora cervicornis) had likely died off in the 1980s like in many other places in the Caribbean, many other coral species abounded.

The fine sand on the beach was a good sign. Feeling the sediment along the reef substrate, we found that the gamble had paid off. There were patches of fine, silty carbonate sediments! I let out a sigh of relief through my regulator and signaled ‘okay’ to my dive buddy. We collected eight bulk samples in spots where sediments had accumulated on ledges or patches between corals. Here, the sand grains were often held in place by an interlocking matrix of dead staghorn coral, limiting mixing.

The day, however, was far from over. Upon arriving back at the dock on Curaçao, we loaded the samples and gear into the truck and began what should have been a 20-minute drive home. Except that it was Shrove Tuesday of Carnival and half of Willemstad was blocked off for the big parade. After desperately searching for a clear route, we stopped to get directions from a police officer, who gave us the disheartening news that we would have to drive around half of the island to get home. An hour and a half later, we finally reached the station, exhausted yet victorious. What a roller coaster of a day and a fitting end to the expedition.

Fetching the pallet

Today, I got a very good workout. Our 604kg (~1300 lbs) pallet could only be delivered as far as Los Angeles, so I had to go pick it up myself. After a 354km (220 mile) road trip, a fortunately uneventful visit to the US Customs Office, and nearly 1.5 hours of unloading the crates from the truck, the samples are finally safe and sound in the lab at UC Santa Barbara.

What’s in a sample?

Monday was a good day. We met our boat exactly where and when planned (a first!) and motered south to Caracasbaai, past the colorful buildings of Willemstad, a towering cruise ship, and a fleet of tiny sailboats that looked remarkably like the schools—flocks? — of flying fish that also skimmed the waves. Erin easily located a potential denticle site in a short snorkel foray, and the dive team quickly got to work filling the sample bags. While they worked, the boat captain tossed in a fishing line baited with what he’d caught on the trip down. By the time Felix and I were winching the samples up to the surface, more fresh fish sizzled on the boat’s tiny stove. It is immensely satisfying to snack on fresh fish and simultaneously admire a pile of fresh samples. Like I said, it was a good day. We traveled back to Piscadera with tired bodies, satisfied stomachs and 20 bags full of denticles.

…Well, not quite. The sample bags are filled with fine-grained reef sediment, which may or may not contain denticles. So, why are we collecting bags and bags of sand anyway? It may seem like a strange way to determine the relative health of a coral reef ecosystem, much less shark abundance. However, hidden within the reef sediment is a time-averaged sample of some components of the reef ecosystem. It’s similar to a school’s lost-and-found: over time, the accumulated detritus preserves a sampling of the year’s fashion trends and fads. Grabbing a sample of the lost-and-found might better represent the school’s generalized clothing choices than an hour’s observation during gym. Similarly, observing a reef during the day (when humans are most active) may not accurately represent the diversity of the reef’s inhabitants, or provide a good way to compare a declining reef to a “pristine” reef less impacted by, or familiar to, human presence. The reef sediment is analogous to the lost-and-found: the denticles, shells, teeth, bones, and other hard parts are the cumulative signal of the reef’s inhabitants. While not every part of the reef is preserved, what is preserved can be compared between sites and across time to assess key differences in reef diversity. The sediment is a way to look at several years’ worth of diversity rather than assessing the reef based on a couple days of highly-variable observation.

At present, it appears that sharks are uncommon in the waters surrounding Curacao. We haven’t seen any in our time here. In contrast, anecdotal evidence suggests that sharks were very common in the past. The samples collected on this trip will hopefully address this disparity. Furthermore, other members of the O’Dea lab will look at otoliths (fish ear bones that preserve growth history much like tree rings do), molluscs, bryozoans and other components of the sediments, trying to piece together a broader picture of the reef’s health. Hopefully, the sediment collected in this field trip will show how the reef we see today—the reef which supported the delicious, though small, fish we snacked on—compares to the reef’s recent years, and how that compares the reef before humans arrived. Just as the bulk sample bags preserve a time-averaged history of the reef’s inhabitants, they also preserve the time-averaged impacts of industry, tourism and fishing on the reef’s health. That’s pretty good for a bag of sand!

An unexpected trip to Curaçao

“How would you like to go to Curaçao?” These were not the words I expected to hear when I answered my phone after the third consecutive call from an “Unknown Number” on Monday night. Thirty-six hours later, I was dragging a heavy metal object through the airport on my way to join the search for shark dermal denticles. My surprise journey with the Grab Sampler is only part of what is becoming an epic battle against Murphy’s Law in the ongoing Denticle Quest of the Baseline Caribbean team. This post details some of the obstacles the team has already overcome. You can watch many of these events unfold in the live-science videos.

Obstacle 1: Small Denticles

Shark dermal denticles are small—smaller than a grain of salt—and you might think that collecting denticles would be harder than finding a needle in a haystack. However, their small size helps the Baseline Caribbean team narrow down potential denticle sites. In areas washed by waves or current, any denticles would likely be swept away. Consequently, denticles only accumulate in low-energy locations where they can settle undisturbed. These sheltered locations are what the team is seeking in “1: Looking for Sites.” Silty sediment is an indication that the water is quiet enough for the denticles to remain.

Obstacle 2: Deep Denticles

The team came prepared to scuba dive in and dig for denticles by hand. You can see them at work in “2: The Perfect Sediment.” However, it turns out that in Curaçao at least, much of the “perfect sediment” is deeper than the divers are prepared to go. So, how to collect these deep silty sediments without diving? The Grab Sampler provides a solution: it is a heavy metal scooper that can be lowered over the side of a boat to collect deep sediments. Problem solved, right? …except that the Grab Sampler remained in Panamá. Lucky for me, the easiest way to get it to Curaçao was for me to bring it. I got to travel to Curaçao, several customs officers got to learn about the mysterious metal object in my luggage, and the Baseline Caribbean team got back to work, digging denticles.

Obstacle 3: The Grab Sampler works! And then it doesn’t.

The Grab Sampler may look like a boring metal scoop, but it is actually an instrument of high drama and suspense. After it’s lowered over the side of the boat, it sinks into the blue depths and disappears. The line keeps feeding downward, down past the rising bubbles, down farther until suddenly it goes slack: the Grab has hit bottom. Quickly, all hands go to the rope, everyone sweating to pull it back up and wondering what it will bring. That first retrieval, we all crowded around, watching as it surfaced, watching as Felix swung it over the side, leaning in to see… a single algae-encrusted shell deposited on the tray. The second go brought nothing. We tried a slower descent, than a faster one. We moved shallower, then deeper. Finally, we started bringing up the silty material we were looking for. Success! We danced the Denticle Dance, and our collection of sample bags started growing.

Unfortunately, that was not the end of the Grab Sampler’s drama. As we sent it down again, the wind picked up, pushing the boat over the descending line. The Grab Sampler must have dragged along the bottom, because when we retrieved it the sturdy metal was bent out of shape, rendering the instrument useless. As we research options for fixing the Grab, the team is back to diving for sediment in the sites that are not too deep.

. . .

Beyond these obstacles, the team has struggled against 75 million-year-old radiolarians (the backbone of the island is silica-rich rock made of ancient plankton skeletons, and as it erodes into the bays it makes the denticle search more difficult), wary property owners, Carnival traffic, difficult-to-find docks, and even an issue with the coast guard. Yet even when it seems that everything that can go wrong does go wrong, the team finds a way around the problem and the search for denticles continues.  This is how science works—often it is the challenges that lead to creative problem solving, novel approaches, and interesting new questions. And sometimes when things go wrong, an intern gets to go on an unexpected trip to Curaçao.