New expedition: Curaçao February 20th

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The Baseline Caribbean team is gearing up for another expedition, this time to the sparkling, cerulean seas of the Netherlands Antilles in the Southern Caribbean.

Reefs on these Dutch Islands are in relatively good shape when compared to the rest of the Caribbean. But what were they like in the past?

Anecdotal evidence suggests that sharks were once abundant around these islands, yet empirical data are desperately needed to guide management. Reef fish communities are overfished today, but by how much? When did coral communities begin to deteriorate, and did it depend on their proximity to historical settlements?

To get at these questions and more, we plan to collect nearly a ton of sediment from modern and fossil reefs along the southwest coast of Curaçao. We also hope to get the chance to explore Klein Curaçao — a 1.7-square-kilometer uninhabited island just southeast of its big sister and namesake.

Instead of reading about the results in a stale journal in two years’ time, experience science in action. Beginning February the 20th, join us with daily posts, photos, and short videos from the field on the Baseline Caribbean science blog.

This expedition builds on our previous exploits in Panama, Belize and the Dominican Republic. We see familiar faces return: Erin Dillon (who recently hightailed it to the McCauley Lab), faithful malacologist Felix Rodriguez and ring-leader Aaron O’Dea. We are also joined by some fresh blood in the form of fish ecologist and evolutionary biologist Michele Pierotti and STRI videographer extraordinaire  Ana Endara.

A huge Thank You to our supporters who will make it possible: The Caribbean Research and Management of Biodiversity field station (CARMABI) who kindly gave us a Research Prize, the Smithsonian Tropical Research Institute (STRI), and YOU! – the generous donors who contributed to our crowd-funding campaign. Stay tuned…!

 

 

 

 

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When parrotfish abound the reef grows faster

 

Several years ago Katie Cramer, Dick Norris and I hatched a plan. We knew that the sediments on coral reefs preserved the robust teeth of fish and we guessed that the branching corals of the reef would hold it all in place. We just needed a way to extract the layers of reef sediments to reconstruct the history of fish communities on the reef.

Katie led the project with support from MarineGEO and Dick built a pushcore/vibracore hybrid, with which we managed to extract a good number of 3-4 metre long cores from coral reefs in Bocas del Toro, Panama.

Back at Scripps Katie led the troops to split the cores, take samples along them and extract the teeth from the matrix by acid digestion of the carbonate sediments. Sounds easy?

Then she had to identify what all these teeth were. Along with the team in Norris’ lab, and help from our lab in Panama, she built a reference collection of coral reef fish teeth, which turn out to be variable in shape, but on the whole extremely well-preserved over millennia.

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We needed to date the cores, that’s where Jian-xin Zhao at University of Queensland came in. There we were able to date small pieces of coral using the U-Th dating technique which gave really high-resolution dates, and more importantly showed that the chronology of the cores were intact – i.e. there had been no mixing up and down which would have ruined any attempt to explore changes through time.

Our cores from Bocas stretched back 3000 years or so, and one of the most abundant teeth that Katie found was the various teeth produced by parrotfish.

Using the dates of the samples to calculate reef accretion rates we discovered that as the reef was growing it did so at a faster rate when there were more parrotfishes. This results shows that the benefit of parrotfishes for the health of the reef is always high, not only in the degraded habitats of today but also on “near-pristine” reefs which were much less fished.

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The fossil record is a powerful tool to reveal ecological processes that have direct implications for conservation. And parrotfish conservation must be made a priority for the recovery and persistence of coral reefs.

 

Denticle side view

Some of the denticles that we find in the sediments are exceptionally well-preserved. Here is an example of a denticle that still possesses the basal plate that once held it to the underlying skin. In many cases, though, we only find the crown (the top part). This side view taken via scanning electron microscopy (SEM) can give you an idea of the three-dimensionality of a fully intact denticle. It almost looks like some strange sort of hat (which perhaps I will 3D-print, patent, and sell online if our funding runs out prematurely or is frozen by the government… just kidding).

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Some things you may notice about this denticle:

  • It has a very thick crown proportional to the crown length. While many fast swimming shark species have denticles that are thin and light, this denticle means business. Its thickness lends durability, forming a protective ‘armor’ around the shark. This type of denticle is generally found on sharks that live in close-association with the benthos.
  • The crown is positioned at a slight angle relative to the base. This angle can alter the way in which water flows over the denticle, thereby changing the hydrodynamics of the shark on a micro level. Some of the fastest swimming species are thought to be able to vary this angle through adjustments to the basal plate and skin tension (Raschi & Tabit 1992).

 

Literature cited

Raschi W, Tabit C (1992) Functional aspects of placoid scales: a review and update. Aust J Mar Freshw Res 43:123–147

Evidence of a nighttime visitor

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Scanning electron microscope image of a denticle extracted from the fossil reef in Bocas del Toro, Panama. 283x magnification.

Here is a denticle that I was not expecting to find. It belongs to a shark that I only on second thought included in my denticle reference collection, one that ought not belong on a coral reef. This appears to be the denticle of a crocodile shark (Pseudocarcharias kamoharai). While denticles can normally only be identified at the family level, this one fails to resemble any other denticle in my reference collection… except one. It looks almost identical to those that I isolated from the skin of a verified crocodile shark at the Smithsonian National Museum of Natural History (image below), except that it is a little smaller and much more weathered.

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Scanning electron microscope image of a denticle isolated from the body of a crocodile shark for inclusion in our reference collection. 185x magnification.

Not only are crocodile sharks unassociated with coral reefs – in fact they generally only ascend from the depths at night to feed – but this shark has not been documented in the region in which this denticle was found. What’s more amazing is that this denticle is not even modern. It was extracted from our  6,600-year-old fossil reef!

While you may have never heard of a crocodile shark, they are listed as ‘Near Threatened’ on the the International Union for Conservation of Nature (IUCN) Red List. We obviously need to learn more about this species of shark in order to better protect it.

Our finding suggests that crocodile sharks did occasionally venture onto the lagoonal reefs of Bocas del Toro, Panama in the past (and perhaps even in the present day as well). More importantly, to me, this denticle epitomizes the beauty of the technique. Extracting and analyzing dermal denticle assemblages can reveal the rare, cryptic, or ephemeral elasmobranch visitors on reefs, an otherwise very challenging task to accomplish.

Crocodile shark. Source: PIRO-NOAA Observer Program. Wikimedia commons.

 

Time to ring in the New Year with some coral measurements

Sometimes we do a little more than just dig in the sand. Over the New Year, Mauro and I taught the coral reef ecology unit of an undergraduate field course from the University of Wisconsin–Green Bay and St. Norbert College at the STRI field station in Bocas del Toro, Panama. While we spent a portion of our time in the lab discussing the importance of the area and looking at creatures under microscopes, we also brought the class snorkeling on the reefs with us to do some field work and explore. For some of the students, this was their first time snorkeling and seeing a coral reef in person. For me, that moment was life-changing, so I’m delighted to be able to share this magic with them. We visited a diversity of reefs during the trip, some of which were clearly healthier than others, and we discussed the differences between them and the potential underlying anthropogenic and natural drivers. For example, instead of merely reading that runoff and eutrophication are harmful for coral reefs, the students were able to glimpse algae-covered corals off the coast of the Changuinola River floodplain, the site of extensive banana plantations.

The students also got some hands-on experience doing field work. With the help of the class, we’re investigating long-term bioerosion rates on branching corals, specifically staghorn (Acropora cervicornis) and finger (Porites sp.) corals, in Almirante Bay. This study will improve our understanding of the carbonate budget on reefs in the region and, in particular, which way the seesaw between reef accretion and dissolution is tilting. This question pertains directly to the future of reefs in Bocas del Toro as well as how resilient they may be to future perturbations such as storms. Furthermore, it helps us key into one of the processes contributing to the reef substrate, which is where our lab collects bulk samples and sediment cores to reconstruct historical reef communities. Understanding whether the reef is actively contributing to this substrate through coral growth and reef accretion or whether it is stagnant or even shrinking can provide context for interpreting patterns of microfossil abundance. This study may also shed light on dates we computed for corals extracted from cores at these sites, which suggest that some of the dead corals lying on the surface are far from modern.

We started this study in December 2015 by collecting, measuring, and redeploying recently-dead pieces of coral on mesh plots. We successfully relocated the plots this past December and took our first annual measurements. Some bioeroders were even see in action on the reef! Interesting trends are already starting to emerge in the data. One of the students will be conducting an independent study to try to unravel some of these patterns, so stay tuned for her findings.