Adios, Mexico!

Well, the blog proved a bit more difficult to maintain once we had to start running our experiments, and now everyone has gone home. But thanks for following along with us for a while. We will likely add a few more details and photos here in the future as time allows, so do check back in.


Night 3: (Minor) Spawning!

Sorry for the late update.  In a business like this, sometimes no news is indicative of very very good news.  We’ve been up all night processing larvae from a minor spawn tonight in Puerto Morelos!

One colony released about 10ml of gametes (not too shabby), while another two released smaller amounts.  It was enough to run some of our experiments.  Though tonight wasn’t a massive spawn, it’s indicative that tomorrow will probably be the big day.  We got some good practice in, so the process should go very smoothly.

Time for some sleep!

Why Are We Here? Part II: Karyotyping

When studying genetics, it’s important to know how DNA is organized in your species.  For the Elkhorn coral Acropora palmata, we’re still missing an important piece of data: just how many chromosomes are found in the cell nucleus?

A chromosome is a densely packed string of DNA–the genetic material that codes for life processes.  Humans have 23 pairs of them, cabbages have 9, and corals, well, it depends.  Across one lineage, the number of pairs is conserved at 14.  However, within the genus Acropora, the variation can be quite extreme.  The only way to find out for sure is to test your particular species, so that’s what we’re going to do with our larvae.

Chromosomes can be visualized and counted, but it’s not an easy process.  This type of analysis, called karyotyping, involves arresting cell development during replication, when the chromosomes are at their densest.  This requires the use of a nasty chemical called colchicine; over-exposure is similar to the effect of arsenic poisoning.  Don’t worry, we’ll be careful!  After the larvae are exposed, we stain their DNA and look at them under a powerful microscope.


Karyotype of a human female (Image:

Since the larvae lack symbionts just after fertilization, there’s no concern about cross-contamination; we won’t accidentally count algae chromosomes.  We’ll be able to detect if there’s anything strange going on, such as polyploidy.  And, importantly for genome sequencing, we’ll have the basis for physical mapping of genes onto different chromosomes.  This will be a valuable piece of information for further molecular studies.

To Create a Coral From Scratch…

…you must first invent the universe.  Fortunately, that’s already been taken care of.  Now we can make baby corals by forcing their parents to reproduce with each other.  If it sounds barbaric, don’t worry, we’re simply helping nature along.  Here’s the breakdown:

Corals are sedentary.  Once they find a good spot on the ocean floor, they tend to stay there forever.  This makes reproduction a real challenge.  How are two adults supposed to ‘get together?’  The answer is simple: use the currents to your advantage.  Release enough gametes into the water column so that your spawn is bound to meet up with someone else’s. 

This strategy requires two important steps.  First, corals need to invest their reproductive energies into creating vast quantities of gametes.  Second, all the corals in an area need to spawn at the same time.  How they manage to do this has yet to be completely figured out, but it depends on several environmental cues.  We can tell you that an Acropora palmata in the Caribbean will likely spawn approximately 2 hours after sunset, 3-7 days after the full moon in August.  In other words, possibly tonight!

Since we have the potential spawning time frame pinned down, we can anticipate the event, and intervene before gametes from different corals have a chance to mingle.  We do this by placing large nets over the colonies.  When eggs and sperm are released (Acropora palmata is hermaphroditic, so it releases both simultaneously in small bundles), they float up and get caught in an inverted cup at the tip of the net.  Back in the lab, we can separate sperm from egg, and make our own crosses between distinct parents.  That way, we have control over the genetic composition of the larvae that result from fertilization. 

Being able to conduct controlled crosses opens up a whole world of research into the genetic basis of a range of important characteristic for endangered corals.  Which genes are being targeted by natural selection?  How important is paternity in dictating dispersal potential?  How quickly can corals adapt? 

When we find that certain crosses perform better than others, we can prioritize which individual colonies in a given area should be targeted for conservation.  When possible, we even plant our coral babies back out onto the reef, and past experience has proven that at least some of them survive.  When you consider how many millions of larvae die naturally, having just one or two juveniles last for a year on the reef is a huge success. 

So, every evening, we don our diving gear and our nets and our flashlights and head back into the ocean, hoping that tonight will be the night.  Wish us luck!

No Spawn Tonight

The Caribbean was silent this evening.  So far we have reports from Belize, Florida, and Curacao that no spawning took place.  The same is true here in Puerto Morelos.  But that doesn’t mean the night was a waste.  We had a great chance to test the waters, as it were, and practice everything involved with spawning before it actually takes place.  It’s a complicated procedure, and I’ll get into the details tomorrow.

The other important story is that today our equipment finally cleared customs!  Let’s just say that if you ever plan to send something to Mexico as a temporary import, make sure you follow every instruction to the letter.  Otherwise it might take you over a month to get your gear.  At around 2:00PM a large truck arrived bearing our 16 boxes.  Diving was scheduled for 6:00PM, which gave us a four hour window to set up our mobile aquarium unit.



Here’s Nick plugging something in.  It’s always a struggle not to electrocute ourselves.  Under the safety of the roof we built yesterday, the aquariums were finished in 3 hours–a new record.  That gave Iliana plenty of time to prepare for her dive, but she hung around to help fill up some tanks.


But even after everything was filled, the unit had to be flushed and refilled and brought to temperature.  It was tough to get things done before the divers returned, but we finished with about ten minutes to spare.  So now we have three separate systems, each maintained at a different temperature, in which to raise our coral larvae when we get them.  Keep your fingers crossed for tomorrow night!


Why Are We Here? Part I–Temperature Experiment

Today began with a little reconnaissance. With the help of our captain, Amaury, and fellow students Sandra and Francisco, we snorkeled the reef to get our bearings. Since we’ll be diving at night and spending all of our energy trying to collect spawn, we need to be able to find the coral colonies blindfolded. Here’s just one example:


Hopefully the fin at the top of the picture gives you a sense of scale. Some of these formations are huge! It’s really encouraging to see that large stands of Acropora palmata, a threatened species, can still be found in the Caribbean.

Which brings us to the question of why we’re here in Mexico. What’s the point? What are we hoping to accomplish? We actually have a lot of experiments lined up for this summer, all designed to answer different questions. In the first installment of a multi-part series, we’ll first address the one that’s been going on the longest–close to five years!

Corals are very sensitive to high temperatures, and the oceans have been getting warmer and warmer. One life stage where this change might be really important is larval dispersal. When some corals reproduce, they release millions of gametes into the water, where they mingle and form larvae. These larvae are transported on the currents and eventually settle down and begin to grow into adult colonies. We want to know how temperature is affecting this process. Is it hurting the larvae? Do they travel shorter distances? Do they settler faster?

To get at these questions, we’ve been attending annual spawning events for years, raising collected larvae in special aquaria where we control the temperature, and seeing how the larvae develop in stressful conditions compared to normal ones. So far we’ve documented several differences in gene expression, including greater production of heat-shock proteins in stressed larvae, as well as atypical morphologies (strange shapes) that likely reduce larval duration (time spent traveling in the water).

To make things more interesting, we can control which corals reproduce with one another, giving us insight into genetic mechanisms for such characteristics. We’ve found that certain coral families perform better than others. These would make great targets for protection. Such natural differences provide hope that there is enough standing genetic variation in current populations for adaptation to climate change to be possible. Still, the corals are in a sorry state, and things will continue to get worse before they get better. With any luck, our research can help.

Ready, Set, Build!

Did we mention how great our accommodations are here in Puerto Morelos?  No really; check out the view from our balcony:


There are certainly worse sights to wake up to.  Though the day began peacefully enough, it wasn’t long before sandy vistas gave way to harsh concrete, and smooth cocktails to hammers and nails.   We’ll soon be caring for millions of coral larvae, and they need someplace to live.  Today, we had to build them a roof.


With most of our equipment stuck in limbo, it was quite a task to put together a venue for our experimental set up.  The units need to stay outside, but we can’t let the larvae bake in the sun.  We also can’t let rain mess with the salinity in the tanks.  So we drove up to Cancun and purchased some plastic tiles to serve as a ceiling and shade cloth to reduce UV exposure.  Then we put it all together with duct tape, zip ties, and a few odds and ends we scavenged from campus.  By the end of the day, the shelter was up and running.


As if that weren’t enough cause for celebration, today happens to be Nick’s birthday.  Note the cake.  Happy birthday, Nick!

Lunar Landing

We arrived in Mexico this morning without difficulty (surprising, given that we were traveling with a dry shipper primed with liquid nitrogen) and dropped our bags off in our home-away-from-home, an impressive condominium located right next door to the University of Mexico’s Institute of Marine Science and Limnology.  After meeting up with our local collaborators, we took a brief tour of the facility, which should accommodate our experiments quite nicely.  The students, faculty, and staff were more than happy to show us around and offer their assistance. 

Unfortunately, we hit a snag when we found out our previous shipment of lab equipment was still tied up in customs, but we are confident that it will be available to us before spawning takes place.  Even without our equipment, we had a lot of things to get done today, including coordinating chores and making shopping lists.  Believe it or not, we still have to eat!  The evening passed with a beautiful full moon–a clear signal to our corals that it’s almost time to reproduce.  Let’s hope they got the message.