A new lab note has been posted for our crowdfunding campaign, which shares some preliminary observations from Curaçao made during our trip last year. You can check it out here!
We’re 25% funded with 19 days to go! Thanks to all of our backers so far. This field work will not be possible unless we reach our funding goal.
Denticle of the day: Scanning electron microscope image of a lemon shark (Negaprion brevirostris) denticle at 245x magnification. Scale = 100 micrometers.
Thanks to everybody who donated during the first week of our crowdfunding campaign! We really appreciate your support. Every little bit counts, and we’ll need to reach our goal of $4,000 in the next three weeks to receive the funds for our next field work mission. Again, please check out our project at experiment.com/sharkskin and share it with your friends and colleagues. This campaign will help us uncover the history of sharks on reefs in Curaçao and keep the ‘Baseline Caribbean’ blog posts rolling.
Yesterday evening, Aaron and I launched a crowdfunding campaign as part of Experiment.com’s Coral Reef Challenge. We are raising money to support our upcoming field work in Curaçao, which will supplement an award we received at the Association of Marine Laboratories of the Caribbean scientific meeting last year. You can check out our campaign’s page and learn more about what we’re planning to do at experiment.com/sharkskin. The campaign participating in this challenge with the most donors by September 13 will win an additional $1000, and our campaign will run for a total of 30 days. We must raise at least our goal of $4000 to receive the funds. We’ll need your support to reach this goal and keep the blog posts flowing as we collect more samples for the Baseline Caribbean project. Donors will receive a shoutout on our Baseline Caribbean blog as we report live from the field, so keep an eye out in February. Thank you in advance for your support!
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!
The first big experience I had as a marine biology student was being an intern as part of a scientific investigation at the Smithsonian Tropical Research Institute in Panama. I had the opportunity to help Erin Dillon with her project by processing sediment samples for dermal denticles. During the past three months, I learned a lot about shark dermal denticles’ morphology and physiology. I also practiced the methods to process marine sediment (washing, drying, digestion, peroxide, and picking) in order to collect the denticles from each sample. The skills I developed through this internship helped me comprehend what lab work is like, how long the procedure can be, and how patient a scientist has to be in order to collect data and get results. In the end, I gained priceless knowledge, and helping Erin was another experience that confirmed my passion for marine life.
What’s next for Yamilla?: Yamilla is now headed to Florida International University as a transfer student to continue pursuing her studies in marine biology. She’s very excited to take upper division classes, explore the multitude of topics within the field of marine science, and further refine her interests.
How do we move from the residue remaining after a round of acid digestions to an isolated denticle ready for measurement and identification? It’s not as easy as it sounds.
As I peered down through the ocular of my microscope at the diverse array of particles illuminated by the bright light above, I spotted countless sponge spicules (minuscule glassy spears that compose their porous skeletons), fish teeth, bone fragments, otoliths (fish ear bones), and the occasional strand of organic material or remnant chunk of calcium carbonate. These stood out against the black gridded background of my metal picking dish, recounting the history of the menagerie of creatures that left their mark on this particular patch of sediment before it was collected from the reef. Paintbrush in hand, I was ready to begin. However, I would be painting no masterpieces today.
I spread a small scoop – maybe equivalent to the size of a pinch of salt – of my sediment sample out over the area of the picking dish, trying to evenly distribute it and produce a single layer of particles. Now came the fun yet tedious part. I began to manually brush through the particles, visually scanning them with care in hopes that a denticle would catch my eye. Each time I found one, a little flurry of excitement would well up within me and I would suddenly feel like I had the endurance to pick for five more hours (as well as the inspiration to write a blog post). It’s a seemingly endless treasure hunt, but my tiny yet precious haul of denticles validates every minute of the search.
After working hard to collect and process the sediment, the first denticle has emerged! This is an ‘abrasion strength’ denticle extracted from the fossil reef at Cañón de Buho.
While sieving the bulk bags of sediment allows us to constrain the particle sizes that we eventually pick for denticles, we are still left with around 260kg of sediment to work with. This is an enormous task, perhaps impossible. However, with acetic acid, we can make it feasible. Our samples are largely composed of coral and shell (calcium carbonate). These react with acetic acid to produce water, CO2, and calcium acetate, therefore eliminating the carbonate. This reaction can remove up to 99% of the sample weight, leaving behind just pieces of rock and resistant microfossils such as bone, teeth, denticles, and sponge spicules that we are interested in studying.
Our samples are so large that we’ve built a processing ‘factory’ outside the lab, where the sediment can react with acid and bubble off CO2 without ventilation issues or space limitations. Each size fraction is placed in a five gallon bucket, and acid rinses (10% acetic acid) are added daily over the course of about a week and a half. A little over 300L of 100% acetic acid is required to complete the digestion of the 65 bulk bags we collected in the Dominican Republic. That’s a lot of acid! We can also process 39 size fractions, or 13 bulk bags, simultaneously, which is 11 bulk bags more than what I was able to digest in the past using just the fume hood in the lab. This has cut the total digestion time down by months.
While this step requires a large quantity of acid to complete, it is crucial, as it turns the task of finding a needle in a haystack into the task of finding a needle in a small sprinkling of hay. Denticles are sparse in the sediment samples, but digesting away the calcium carbonate makes it possible for us to find them and reveal their secrets.
Like a gold miner crouched on the bank of a stream, shoveling sediment into his pan and hoping for a golden glint to catch his eye, we stood at the edge of a washing table, placing scoops of reef sediment onto our stack of sieves. However, we’re interested in something far more minuscule. Our collection of five sieves, with mesh sizes ranging from 63µm to 2mm, helps narrow the search by partitioning the sediment by particle size. Large pieces of dead coral and shell remain on the top mesh screen, while the smaller particles fall through and are caught by the finer mesh. Denticles are approximately 100µm to a little over 1mm across, so we process the 106µm-2mm size fractions to find them, saving both time and acetic acid. The very largest (>2mm) and smallest (63-106µm) fractions are stored in the lab for future use.
With two people working simultaneously, each 8-10kg sediment sample takes around two hours to sieve. After sieving, each size fraction is placed on a separate tray and deposited in our ‘drying bubble’ for a day or two until completely dry. It is then either digested with acid or stored. With one to two samples sieved per day, our mountain of bulk bags is gradually dwindling.
After several days’ wait, our precious and much-anticipated delivery of calcium carbonate cargo arrived at the lab upon clearing customs in the Panama City airport. Months of work went into preparing the agreements for these samples to pass into the country, and they were completed just in the nick of time. Now we were off and running with phase two. We also welcomed two new lab members to the team: Yamilla Samara and Henbelk Hernandez.
First, we had to unpack all of the samples from the crates and remove the plastic bags that they had previously been packaged in, allowing them to dry completely. In particular, the sediments collected underwater were still a bit soggy. Left outside or in the lab, these large, damp bulk bags could take a couple of months to dry completely without extra help. To expedite the drying process, some were moved to the ‘drying bubble’ that we had constructed in advance before leaving for the field. The drying oven that we had previously used was not nearly big enough for all of these new samples, so we decided to make our own! The ‘drying bubble’ consists of two metal bookcases, two dehumidifiers, and a fan completely enclosed by plastic, creating a hot, dry, confined space to dry samples simultaneously in large batches. It’s essentially a walk-in closet for sediment, complete with a Velcro sealed door flap. And trust me, it gets hot working in there. Now, this first batch of wet bulk bags would be dry in a week.
After each bulk bag of sediment is completely dry, it is weighed and stored in preparation for the next step: sieving. Fortunately, most of our fossil sediments were already dry, so no time was lost.
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.
In this shark tale for Save our Seas Foundation, Erin Dillon explains the characteristics of some of the shark scales found on four well-known shark species. Erin is pioneering a new technique that uses these scales, known as dermal denticles, found in modern reefs and the fossil record to study changes in shark abundance and community composition over time.
Erin carries a bulk bag of a fossil reef sediment from Cañon del Buho in the Dominican Republic on March 17, 2016. The ten-kilogram bag may hold some 25 tiny shark scales known as dermal denticles.
Erin tells us more about her research here: