Dominican Republic

Nicte-Ha’s farewell!

Earlier this year, the coral project was set. The research question was clear, the samples – the key to the question – were at hand, and I was making good progress. But the coral team had only one member: me. This was not great because I love working in teams and to learn new stuff. How best to learn if not by teaching?

Potential interns had shown interest in working in the lab. Not always, however, this works well for the intern or researchers. It is hard to find a good match. Then, a young woman emailed Aaron. Shortly after, she was standing in front of us. “Gosh! Nicte-Ha is very determined”, I initially thought. And she was.

On day one, Nicte-Ha said that she aimed to find a research job in Bocas del Toro. We were sitting hundreds of kilometers from Bocas, but for Nicte-Ha, we were pretty close. A few hours after she analyzed the last sample in our lab, she headed off to Bocas del Toro.

What do you think happened between day one and the last sample she analyzed? Success! That is what determined people consistently get. Just to name a few of her achievements, Nicte-Ha learned fast and taught others, analyzed hundreds of kilograms of coral samples, developed and presented a poster at a conference, and was actively engaged in the daily life and discussions of our scientific community. More than anything, she got a special place in everyone’s heart.

Thank you, Nicte-Ha. Today we see you leave, moving in the direction you chose. We are happy and proud.

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Nicte-Ha Muñoz presents a poster in APANAC.

Progress report

How much? We processed 61 large bags of sediment for dermal denticles, totaling 534kg (1177lbs). This is equal to 6 baby elephants at birth or a small mature great white shark.

How long? Processing this massive amount of sediment took about three months total, although we’re still picking out some of the denticles. Fortunately, many of the processing steps could be done simultaneously:

~2 months washing and sieving the samples

~3 months digesting the carbonate with acid, split into six rounds of digestions. This ate up nearly 265L (70 gallons) of acetic acid.

~1.5-2 months picking for denticles

Now how much does it weigh? The acid digestions reduced our load of sediment to around 6kg total. That’s about a 99% reduction in weight. Now that’s much easier to sort through!

How many denticles have we found so far? We’ve currently found about 150 denticles of various forms, but we still have more to pick!

 

Mission accomplished … phase one, at least

Two weeks after crisscrossing the Dominican Republic from one compass extreme to another, the Baseline Caribbean team delivered their collection of reef fossils and modern reef sediments — all 800kg of it — to Santo Domingo’s Las Américas International Airport for shipping to Panama.

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Erin and Félix carefully pack the crates at the Santo Domingo airport.

In all, the expedition logged about 1,500km on the road, three full field days exploring fossil reefs, 14 dives on modern reefs, two birthdays (Aaron had his b-day, too) — and only a couple of upset tummies from the mystery meat dishes and/or the choppy seas.

The 18 crates of samples include 65 large bulk bags and 130 small ones. “There are a lot of steps you have to go through to get them shipped,” said Erin. “Filling out papers with customs, checking the permits, waiting around, sending the samples through customs where some get randomly opened, and then packing them up nicely.”

If all goes as planned, the samples should arrive for analysis at the lab of STRI staff scientists Aaron O’Dea in the next few days. Then the “real” work begins — finding and identifying all the corals, dermal denticles and other traces of past and modern Caribbean reef in those bulk bags will take many months. But let’s not remind the team of that until everyone gets a much deserved rest after two nonstop weeks on the road!

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Phase two: 800 kilograms of lab work

 

Farewell, Samaná

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Samaná under the waves

After three days of sampling in Samaná Bay, it’s time to pack up and head back to Santo Domingo with another 90 sediment samples. It was neat to see the differences between the fossil reefs of the Enriquillo Valley and their modern counterparts in Samaná, a bay with a similar form and comparable sheltered fringing reef environment.

While one of our study sites was home to a large thicket of living staghorn coral (Acropora cervicornis), most of the reefs we visited were devoid of this IUCN critically endangered species. All that remained were eroded fragments of their branches covered in algae and encrusting organisms. Instead, algae, sponges, the occasional coral head, soft coral, or gorgonian (sea fan) populated the sandy bottom. Starfish and urchins patrolled the substrate, but we saw few fish.

In contrast, fish were much more abundant at the reef with healthy staghorn coral. We spotted small parrotfish, wrasses, surgeonfish, lizardfish, and territorial damselfish tending their algal gardens amongst the branches of the staghorn coral. We even saw an octopus crawling along a crevice between coral heads. In this shallow habitat, we collected sediment between the living staghorn colonies or in areas containing its rubble. While we encountered large waves and wind during our visit, the bay is normally more quiet. As such, we found the sediment to be fine and silty — exactly what we were looking for.

Deeper on the reefs, the corals were more densely distributed than I had originally expected them to be. As on the fossil reefs, we collected sediment samples between the thickets of coral heads, including brain coral (Diploria), star coral (Orbicella), lettuce coral (Agaricia), and starlet coral (Siderastrea). We even observed some of the same coral species that we had identified a week earlier on the fossil reefs.

While our qualitative observations suggest differences between the mid-Holocene and modern reef communities, the next step is processing the sediment we collected to characterize the microfossils left behind by the inhabitants of these reefs — both common and cryptic. Now we just need to get the samples back to Panama!

—Erin Dillon

 

The reefs at Samana – a modern comparison

We reached Samana, in the very northeast of the island of Hispañola. This natural bay was a 17th century pirate hangout. We are here because the site is very similar in geography to how the Enriquillo bay would have looked 7,000 years ago — open to the ocean to the east, very sheltered, flanked on either side by mountains, with high run-off and sedimentation. It is critical we make our fossil and modern samples as comparable as possible in order to measure changes over time. We are therefore sampling the sediments in the reef crests and the fore-reef of fringing reefs around the Bay — just as we did in the Enriquillo basin. We were very surprised to see healthy-looking staghorn coral (Acropora cervicornis) in this region. Four years ago it did not look like this.

A guide to collecting a bulk sample

A bulk sample simply means that there is as little bias as possible during collection. Instead of picking the most beautiful or well-preserved fossils from an outcrop, we take whole lumps of the sediment, which are then transported whole back to the lab in Panama for washing, picking and identification of the fossils. Only then will the bounty they yield be revealed.

This means we have to collect massive amounts of rock and sediment, but it’s the only way to provide a measure of the abundance of the many different organisms in an ecological way. This ecological approach to paleontology is critical for we want to know what the structure of the whole ecosystem was like.

Sped up from 15 minutes to a minute and a half, the video shows Erin and Aaron collecting a 10kg bulk sample of 7000 year old reef sediments in the Enriquillo basin. All the coral, mollusks, fish otoliths, sponge spicules and shark dermal denticles will be picked from these to help reconstruct the ecosystems of the past.

Beautiful forms and incredible functions

Dermal denticles are small scales that line the skin of sharks. Denticles have a similar composition to teeth, forming a strong and streamlined suit of armour. If you were to pet a shark, its skin would feel smooth in one direction and rough like sandpaper in the other direction. This is due to the serrated peaks of the layer of overlapping denticles that cover the shark’s body.

Denticles are continually shed by sharks and accumulate in marine sediments, where we can find them beautifully preserved – in both on modern and fossil reefs.

shark denticle family diagram (blog body)

Denticles display a diversity of forms and play a variety of functions. For example, fast predatory sharks – such as hammerhead and requiem sharks – are covered almost entirely by thin, highly ridged denticles that reduce drag and make the shark more hydrodynamic. This type of denticle served as inspiration for the controversial Speedo swimsuits in the 2008 Beijing Olympics.

In contrast, demersal (bottom-dwelling) sharks are have thicker, smooth denticles that resemble pebbles. These protect against abrasion, given that their owners live along rocky, sandy, or coralline substrates.

Other demersal or schooling sharks possess spiny, defensive denticles that are thought to discourage the settlement of parasites and epibionts on the skin.

To make sense of the different types of denticle we had to first build a reference collection of modern denticles from museum collections of sharks. That way, when we find a denticle in a fossil reef we have some idea of which type of shark it could have come from and the way the shark lived.

One big problem is that denticles are rare and that is why we have been collecting so many hundreds of kilograms of fossil and modern reef sediments. Once back in the lab, we will dissolve the calcium carbonate that forms much of the sediment in our bulk sample bags using a process pioneered in Richard Norris’ lab. Picking them is arduous for they are usually less than half a millimetre in size. We hope to find enough to be able to rigorously compare the assemblages of denticles across our sites.

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Erin and Félix carry off heavy bags of samples for analysis.

If we get lucky, the denticles from modern Caribbean reefs could tell us about the presence of sharks in areas where fish surveys have failed to report them because of their rarity, yet dive shops and fishermen confirm their presence.

Even more exciting is the possibility that we will uncover enough denticles from the fossil reefs to be able to reconstruct shark populations 7000 years ago, before major human impact.

It’s hard work but we hope that these massive bulk bags of reef sediment will uncover enough tiny denticles to help paint a picture of shark communities past and present.

DILLONE_320_Fig 1 (body)_Great hammerhead_body_275x, Erin Dillon & Jorge Ceballos