Costa Rica

Marietta College Biology and Environmental Science Department Field Trip 2005/2007

Note: Lots of big, pretty pictures on this page - it may take a while to load, even over a high-speed connection!

Click on the image above to skip to the town (1), park(2) or reef (3).


Cahuita - Getting there

In 2007, we went to the small Caribbean beach town of Cahuita from the small beach town of Tortuguero.  Since Tortuguero is accessible only by boat and air, we traveled for several hours by boat to the small town of Moin, near the large port of Limón.  We stopped for lunch in Limón, then went on by van to Cahuita.

At first, we moved along the estuaries behind the barrier islands through wide waterways with lots of wildlife to see.  After a while, the natural waterways petered out and we entered the long canal dug to link the estuaries and create an inland waterway between Moin and Tortuguero.

The canal needs to be dredged in order to keep it open to traffic.  Sediment  flowing from the agricultural fields of Costa Rica would otherwise gradually fill in the canal.  We came across one such dredge working a canal.  Above, the front end of the dredge, which is basically  a pontoon boat with a huge diesel engine, a dredge up front, and jacks in the back.  Above right the front of the dredge.  The actual dredge head is underwater, suspended by winches and hydraulics.  It has an intake head that moves water and sediment into a pipe.

Above right is the back end of the dredge.  The tall poles are the jacks which can be lowered to hold the dredge in place.  Black rubber floats hold the discharge pipe off the bottom; the dredge engine, which drives a large pump is also visible.

To the right  the discharge pipe comes ashore, discharging water and sediment from the bottom.  The sediment is played out to form a high bank that can be seen at lower right.  Below, a typical scene along the canal.

At one point the canal emptied into one of several rivers that it crossed and linked.  Despite the dredging, the entrance to the canal was partially blocked by sediments and we got stuck.  Above, a small boat tries to pull us off, above right it eventually took two of the boat's crew getting out into the river to push us off.  Note how shallow the water is!


Finally, we got underway (right); one advantage of our stranding was that it enabled us to collectively reconstruct the entire lyrics to the Gilligan's Island theme song.    We were heavy on professors, light on movie stars and millionaires, but we did have two Gilligans (above right).

Among the wildlife we spotted were a number of crocodiles, some approaching 10 feet in length.  The American Crocodile, pictured here,  is endangered in the United States, and isn't really common anywhere.  On the other hand, we've seen them all over Costa Rica, usually in rivers near the coast, though they range at least as far upstream as La Selva and La Suerte.   In any event, these were bigger than the one we petted at Playa Nancite, and smaller than the ones in the picture below; we saw those monsters from a bridge near Manuel Antonio in 2005.



Remember the guys pushing the boat?  They were in the water with these guys!


Above:  Crocs from a bridge.  


Not all of the transport is very elegant...  This guy is paddling with the crocs, too.

We pulled into the dock at Moin and transferred to a van.  The boat dock was next to a large port facility with large container ships flying the colors of  various well-known fruit companies.

As you can see, the exhaust from the stacks of these ships is pretty obvious, and for someone living nearby it's probably not too healthy.  On the one hand, the ships load quickly, on the other hand, a new ship will come in to replace the one that has just loaded.

Below, the streets of Limón.  Limón is a somewhat gritty town; it is the main port for Costa Rica and the place where most of the bananas and pineapples are exported.  The city, like the rest of this part of Costa Rica, was settled by people of African descent recruited from across the Caribbean to work in the banana fields.  Thus, this part of Costa Rica is less "Spanish" then the rest of the country.  We ate lunch at Manolo's (below right).

Lunch in the little soda was very good, even if it was sweltering hot.  We were entertained by the antics of a little Tican who was trying out some new-found independence.

Above:  a satellite view of Cahuita, Costa Rica.  The town of Cahuita is shown at number 1; number 2 is the point at the National Park that we hiked out to, and 3 delineates the coral reef.


The town of Cahuita is small and has a wonderful ramshackle feel to it.  Streets alternate dirt and brick, with little restaurants and shops at every turn. Like Limón, it has a strong Caribbean influence.  The background music for this page comes from one of the town's most famous sons, the Calypsonian Walter Ferguson.
Our hotel was just across the street from the entrance to the national park.  Right, the group relaxes on the porch outside a couple of the rooms.  Below right, we had dinner at the National Park Hotel several nights, and took advantage of the big tables in the open patio to discuss readings from the book Breakfast of Biodiversity.  


Below, the beach at the entrance to the National Park.  The trail we followed paralleled the beach just in from the treeline on the right.

Our second day in Cahuita we went for a hike in the National Park.  Above, signing in at the entrance to the park.  To the left, Dr. Brown demonstrates the level-eye behavior of a crab caught along the beach.
Above, Bonnie and Mallory look for a shark we had spotted out on the reef.  Justin jumps over a small stream flowing across the beach.

We saw leafcutter ants here, too.  You can learn more about leafcutters on our leafcutter ant page.

This group of ants was crossing the trail behind the beach; we wondered how they could have underground nests with the water table so close to the surface.



Video of Leafcutter Ants at Cahuita National Park.


Don't Feed the Monkeys!!


At the point, we came across a group of Capuchin Monkeys.  This troop visits the point every day, timing their visit to coincide with snorkeling boats coming ashore.  Apparently the park was seeing a problem with people feeding the monkeys all kinds of junk - you know, the stuff we eat - and they were worried about the monkey's health.  So, they put up a sign.  Of course, this didn't work, so they posted two employees out there at a picnic table; their job seemed to be handing out fruit to the tourists to give to the monkeys.  They gave several of our students pieces of mangos and watermelon; these in turn were passed on to the monkeys as you can see here.


Video of the Capuchin Monkeys at Cahuita National Park.


I was concerned about the feeding for two reasons.  First, anytime humans step into the food chain of wild animals it's almost always to the detriment of those animals in the long run.  Even feeding the monkeys "good" food can cause problems, as it no doubt affects their overall diet - and you don't want to get fat if you are swinging around in trees.  On the other hand, I doubt the monkeys will become dependent on humans for their food.

The second concern was a simple one of safety.  These monkeys have sharp teeth, and they probably are scared stiff as they approach large people for food.  A scared animal is likely to bite, and who knows what diseases they might carry (as if the wound wouldn't be enough).  

In the end, I let the students have their fun, and the monkeys get their mangoes.  No one was hurt, and I passed out a few hand wipes to clean their hands.  It's hard to philosophize on the proper ecological etiquette when there are some cute animals and great pictures there in front of you. 

Snakes on a Tree!

Read the exciting account of the race for the Triple Photographic Crown of 2007 on the jungle trails of Cahuita!  This stuff used to sit right here, but IE explorer kept cutting off the bottom of the page below the video.  Stupid IE Explorer....

Click Here!!!


Above:  We also saw a 2-toed sloth up in the trees just behind the beach. Sloths feed on tree leaves and only descend to the ground about once a week to defecate.  Many have algae growing in their hair; this contributes to their camouflage, and there is a species of moth that lives in the fur and feeds on the algae. The area along the trail also had a number of interesting plants including the Dwarf French Kiss (it's not clear if the name implies a small kiss or a kiss bestowed by a diminutive Gaul).

The Noni is a fruit found growing along the beaches in a number of places.  Apparently the fruit isn't the tastiest thing, but it is edible and used medicinally.

4-lined whiptail lizards replace the Central American Whiptail lizards along the beaches and are a common sight darting into and out of the sun and shade.

The trail was also a good place to spot butterflies, although the one on the right had obviously seen better days.  It was quite striking, and had a habit of darting under leaves to perch, thus throwing off the pursuer.

Snorkeling on the Reef

We had planned to go snorkeling on our third day, after exploring the park and getting the lay of the land - not to mention getting everyone used to snorkeling gear.  I had brought along two masks, one purchased for $4.99 and another for $1.99 (at our local grocery store in Marietta).  The plan was to use them to make sure everyone was comfortable with a mask by taking a hike into the national park and snorkeling from shore.  Alas, soon after checking in we met our guide, José, and found out that because of the weather our best bet to snorkel was the next day.  So, we  met up with José and his son the next morning.  We walked across town with them to their landing and loaded into their two outboards to run down the coast to the reefs.

As it happened, everyone in the group except for one or two not only were comfortable in the water, but used to snorkeling as well - although few had ever had the opportunity to snorkel in waters as interesting as these.  We strapped the non-snorkelers into life jackets so they could float at the surface and everyone jumped in.  The water was pleasantly warm and reasonably clear.  

Although not the largest or most diverse reef in the world, the reef at Cahuita does have examples of many of the more common species in the Caribbean.   Above are two typical corals of the forms that grow upwards.  Remember that corals harbor endosymbionts, dinoflagellates (a type of photosynthetic protist) called zooxanthellae.  The zooxanthellae provide the coral polyp with sugars from photosynthesis while the coral provides the zooxanthellae with its waste products - CO2 and ammonia, primarily - which help the zooxanthellae make more sugars.  

In order to photosynthesize the coral needs to think like a tree.  It needs to get sun and keep the sediment off its "leaves", so many corals grow up towards the sun, and compete for light, even to the point of shading out other corals.  Two examples of this growth form are shown above, the Elkhorn and Staghorn coral, named because the growth-forms of these corals resemble the antlers of those two species.  If you don't think the Elkhorn coral looks very elk-like you are probably from North America; the animal we call a moose is called an elk in Europe, and the name was probably applied to the coral by a European.  Myself, I use the native American term Wapiti to refer to an elk, but I can't bring myself to call a moose an elk.  

The Staghorn coral pictured above doesn't look very antler like. It turns out this coral was destroyed in a storm.  That's the problem for the corals that grow upright, they get plenty of light but are likely to be toppled in a storm.  Other corals grow flat on the bottom; they get less light (and more sediment), but they can't be blown over.  Frequency of storms determines which strategy is "best".

The filefish (left) is typical of the maneuverable fish that populate a reef, looking for tidbits of food to bite off with a tiny mouth.

The boulder coral above is a lower-growing form of coral not likely to be uprooted in a storm.  We're not sure exactly what species we were dealing with here.  To the right is a coral with the polyps a bit more extended.  Each polyp is tiny - only a few millimeters across - and resembles a miniature sea anemone.  Thousands of them make up the large coral formations that cover the bottom.  Each coral polyp secretes a limestone shell around itself; it is these secretions that make up the coral rocks of the reef.  A reef formation may be composed of many feet of rock laid down over many years - even centuries.  Only the very outer layer is populated by living coral polyps, which build their shells on a foundation of previous  years' growth.  Sometimes other animals such as Christmas tree worms will burrow down into the coral rock to make a home in the dead rock.

Fire coral (below, left) has a distinctive growth form, which is a good thing.  Brushing up against it creates a burning rash (hence the name).  The mustard color and flat-topped blades are cues to warn the diver of the danger.  Of course, you don't want to brush against any coral as the contact is almost always deadly - for the coral. The green grape algae was one of many types of algae growing on the reef (note all the algae among the fire coral as well).  Algae are quick to respond to increases in nutrients and can outcompete and overgrow a reef quickly.  Nutrient increases are often tied to human activities such as deforestation and agriculture; both activities send nutrients into rivers which then empty into the oceans, putting additional stress on the corals.

The Bristle Brush - sometimes called a merman's shaving brush - is another type of algae.  The parrotfish are ubiquitous reef inhabitants.  They feed mostly on algae from the reef, but their parrot-like beaks are able to bite off chunks of coral rock as well. Later, when they defecate, a stream of fine white sand from the pulverized coral settles to the bottom.  The next time you lie down on the clean white sands of a Caribbean beach, remember that many of those sand grains started out as parrotfish feces....

One of the most fascinating things we saw were a number of cleaning stations.  One of the best examples of a mutualistic symbiosis, a cleaning station is some prominent local landmark (such as the large brain coral colony to the left) where cleaning fish and shrimps set up shop.  Approaching a cleaning station, a large fish such as the grouper at left will adopt a characteristic vertical position.  This signals the cleaners that the fish is there to be cleaned, not to eat.  With this sign, the cleaners dart out and swarm over the larger fish, picking off external parasites and eating them.  They will even swim into open mouths and through the gills removing parasites.  The big fish gets cleaned, the cleaner fish get fed, and the parasites.... Funny, the textbooks never mention the parasites.  They get screwed.

The photo to the left shows just a few cleaner fish; in the lower left picture a few more are present working over a parrotfish although not all the fish pictures are cleaners, which tend to be very small.

I should mention that after a good swim along one portion of the reef José picked us up and moved us to another part of the reef (well, most of us,  some of us just swam the distance).

In addition to the corals there were a lot of other invertebrates present on the reef.  One of the most spectacular were the long-spined urchins.  These urchins have long spines (up to 4" long) and crawl over the reef, mostly removing algae.  The spines protect them from most fish; although a few fish have figured out how to nip off the spines until they work their way down to the hard test, or shell, of the urchin, which they then punch through to eat the soft insides.  

The spines of the fireworm are much shorter but serve the same function - protection.  Easily shed, these tiny hairs are as irritating as a brush with fire coral.  With this protection, the fireworm, a polychaete relative of the earthworm, is able to roam about in daylight to search for food, which is seizes with hardened jaws.

There were a number of fish on the reef as well.  One of the more interesting was the Blue-headed wrasse (above).  The supermale, as it is known, sports a blue head and black and white stripes ahead of a yellow body.  The interesting thing is that this fish used to be a female.  These wrasses start out female, and swim in a school called a harem (sorry) escorted by a supermale, with whom they mate and produce young.  The supermale defends a territory and chases off other fish (and even attempts to chase off divers), thus assuring its harem a good food supply.  Inevitably, the male takes on something just a bit too big for it to handle (it is only about 6-8" long) and it gets killed.  At this point, the females in the harem no longer get the visual stimulus of seeing the male, and this changes the hormonal balance in their bodies.  They begin to grow and their ovaries turn to testes.  The largest of the females makes this transition first; she gets the blue head and black and white stripes, and takes over the harem.  The others settle back down into being females, until the new male gets killed...


The Ocean Surgeonfish (below, left) are algal grazers that can hover precisely while they expertly remove the algae with their small mouths.  They also have sharp spines at the base of their tail fins.


The Christmas Tree worm is another polychaete, a close cousin of the fireworm.  Rather than running around after its food, it lives in a burrow (usually into the hard coral rock) and extends only the front end of its body which bears two large tentacles which look like, well, Christmas Trees (and I'm writing this on December 20th, so I'd know).  These tentacles filter fool from the water, and also gather oxygen.  Eyes allow the worm to detect nearby fish (or divers) and pull the tentacles in very quickly, even faster than a nightcrawler in a bait-hunter's flashlight beam.


The sun anemone is an interesting story.  In Jamaica, I learned that these anemones with their short, squat tentacles did not sting, but clung to their prey.  In fact, we touched them and the feeling was like touching one of those sticky wall-crawling toys - even underwater.  There was no sting.

All of the books I've read since them state that these anemones feed like any others.  When brushed, tiny stinging cells (cnidocytes)  release tinier harpoons from little structures (nematocysts).  These impale the prey and inject a poison that paralyzes small prey and stings us.  Armed with book knowledge, I stayed away from the sun anemones this trip, but always wondered what happened in Jamaica.

Below right you can see a sun anemone growing out from under a stony coral.  Below left is a bright red sponge.  Sponges are another important constituent of the reef.  They filter the water, and at greater depths the calcium they acquire to build the spicules that support their bodies may contribute more to the rock of the reef (after their deaths) than corals (which grow in shallower waters where there is more light for the zooxanthellae).

For most of the group, the biggest "thrill" was getting to see an actual shark.  Granted, it was a nurse shark, one of the most docile of sharks, but a shark is a shark.  Nurse sharks spend most of their time basking on the bottom (where they feed) instead of cruising the waters hungry for human flesh.  Still, they (we saw 2) were really a sight.  Also, Nurse Sharks account for more bites than any other shark, probably because they are relatively common and because people, knowing that they are not killers, will approach them too closely and try to touch them, which ticks them off - and then they bite.

Snorkeling at Cahuita National Park 

Sorry for the jerky quality of the video; it's much more difficult to film with a digital camera (vs. a camcorder) and while snorkeling rather than diving.


For those keeping score, in 2007 by the time the group left Cahuita (our 3rd stop) we had seen 3 species of poisonous snakes, crocodiles, and, now, sharks (2 species, including the really dangerous bull shark, spotted from the beach).

Want to know more about coral reefs?  See the Marietta College Biomes of the World Coral Reef Pages.


Audio for this page mixed from:  Dr. Bombodee by Walter Ferguson.


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