Nature and Environment Education - SCHOOL PROGRAMS - CORAL REEF
Is it true that corals spawn on schedule?
Some coral species spawn once a year, synchronously and in accordance with a time schedule that seems to be linked to the lunar cycle. The Boulder star coral (Montastrea annularis) is perhaps the most spectacular example. Every year, between 6 and 8 days after the August and September full moons, between 9:00 and 10:30 p.m., this species releases millions of tiny pink-colored bundles of sperm and eggs. Most often all polyps in a colony release their sperm and egg bundles simultaneously, as if the entire colony bursts open. The little bundles then slowly float up to the surface where they fall apart and where fertilization takes place. It may require some patience to watch the coral spawning, but you will definitely not be disappointed when it happens!
What are the main threats to Bonaire’s reefs?
Coral bleaching. Reef-building (also called “hermatypic”) corals have a symbiotic relationship with one-celled algae, called zooxanthellae. The presence of zooxanthellae in the coral tissue explains the common tan or green color of coral colonies. It also explains why hermatypic corals need sunlight, because the algae (plants) need light for their photosynthesis. The symbiotic relationship between the coral polyps and the algae is a mutually beneficial one: both algae and polyps not only recycle some of each other’s waste products, the algae also create a chemical environment that promotes the deposition of calcium carbonate, the building material for the coral skeleton. The coral cannot survive without the algae.
Periodically coral colonies expel all or part their zooxanthellae; the coral animals, called polyps, become transparent, the color of their white skeleton shows through them and they appear white. This phenomenon is known as bleaching. Scientists have demonstrated that stressful conditions, such as increased turbidity or water temperature, may cause bleaching. Corals can recover from short periods of bleaching, but prolonged bleaching causes death. Coral bleaching is the subject of much research and scientific debate. There is great concern that global warming may be the primary agent responsible for increasing incidence of mass bleaching.
White band disease. During the early eighties, a disease manifested itself which decimated the stands of Staghorn coral in Bonaire. White, dead areas appeared on the coral that progressed along the branches like a band, hence the name white band disease. The disease, which occurred region-wide, affected both Elkhorn and Staghorn coral; in Bonaire, however, mostly Staghorn coral was affected. The dead branches were quickly overgrown by algae and many Staghorn thickets collapsed. The exact cause of the disease was never identified, but there were indications that it was associated with the presence of a bacterium. Although the disease has not disappeared entirely, the Staghorn coral is recovering quite well and healthy new growth can be found again at most locations.
Urchin die-off. In 1983 a mysterious epidemic raged through the Caribbean, killing locally almost 100% of the Long-spined urchins (Diadema antillarum). The mortality started somewhere along the coast of Central America and then swept across the Caribbean in a northerly as well as an easterly (upcurrent!) direction. At the time we watched the wave of death move eastward at the remarkable speed of 1 to 1.5 km per day. The disappearance of this urchin with its needle-sharp spines that penetrate your skin upon the slightest contact and easily pierce fins and wet suits, did not cause a great deal of regrets among swimmers and divers.
Coral reef scientists, though, were wondering what the effect of the disappearance of this grazing organism, that was considered to be essential in controlling algae on the reef, would be. There was definitely an increase in the amount of algae on the reef, but the ultimate effect seemed to depend largely on the status of the herbivorous grazing fish (primarily parrotfish and surgeonfish) population. Where the herbivorous fish population was healthy, fish were able to control the increase in algal abundance, but where overfishing had taken its toll, all available substrate was quickly colonized by algae, making recruitment and settlement of corals impossible. The impact was especially well-demonstrated in the north-eastern Caribbean, where Elkhorn coral had suffered seriously from white band disease: absence of herbivorous fish meant immediate smothering of the dead coral by algae and no coral recruitment, while even localized come-back of the urchins immediately resulted in clean substrate and subsequent recovery of hard corals.
By the early 2000’s, Bonaire’s Longspined urchins were making a noticeable comeback.
Finding popular creatures in the Bonaire National Marine Park (Where can big fish, turtles, and other popular creatures be found?)
Where can I see big fish? Encounters with big fish are difficult to predict. Occasional encounters with Tiger and Yellowmouth groupers are possible in the south and at most sites around Klein Bonaire. The chance of such encounters decreases as we go north from town, until we get to Rappel and La Dania where encounters become more frequent again.
Hot spots for large groupers are: Red Slave, the southwest point of Klein Bonaire (Forest to Sharon’s Serenity), and the very north (Playa Benge and Boca Bartol).
Tarpon can always be expected at 18th Palm, and are frequently seen between Small Wall and Something Special.
Sea horses. No, I’m not going to tell you where you can find sea horses. Sea horses have become so popular with divers that there would be an instant demand for this site, word would spread quickly around the dive shops, and the poor animal could literally be “loved to death”.
Of course, it’s exciting when you find a sea horse and you deserve to congratulate yourself. Look at your seahorse as much as you like, but the instant it moves or even leans at all away from you, back away; the leaning means your presence is disturbing the seahorse. Photographers should limit themselves to three shots with a flash, especially if the photos are being taken at night. Think about how disturbing the flash is to you, and remember that seahorses (and other fish) don’t have eyelids and can’t close their eyes against the flash. What’s also extremely – possibly fatally – stressful to seahorses is being handled, cuddled, petted or posed.
What’s the best place to see turtles? Thanks to the efforts of the Sea Turtle Club Bonaire, a non-profit, non-governmental organization established in 1991 with sea turtle conservation as its main goal, we now know much more about the distribution and nesting of sea turtles on Bonaire. The work of Van Eijck & Eckert (1994) and Valkering et al. (1996), conducted with the help of a volunteer network, indicates that about half of the turtles sighted are Hawksbills, 30% are Green turtles, 4% Loggerhead and 1% Leatherback (the remaining 15% could not be identified in the field).
Their studies further reveal that turtles are most frequently sighted along the north coast of Klein Bonaire (Ebo’s Reef to Leonora’s), the southwest point of Klein Bonaire, at Karpata, the Andrea’s, Pink Beach, and in the far south. Most nesting activity takes place between June and September, with by far the largest number of records from the north and west coast of Klein Bonaire.
Turtles are fully protected on Bonaire and the trade in turtles or turtle products is strictly controlled through the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Queen conch. This large sea snail, featured on the menu of many restaurants in the Caribbean, Florida and the Bahamas, has been heavily overfished and is now protected on Bonaire. Collecting requires a special permit. Although the reef is not a typical habitat for the Queen conch, you may come across a conch once in a while on the shallow terrace and in the sand channel of the Alice in Wonderland double reef complex in the south. The trade in conch and conch shells is also controlled through CITES.
Dolphins. When you hear the cry “Dolphins!”, excitement, running and a hurried fumble for cameras are guaranteed. Although the diver’s dream of swimming or snorkeling with dolphins may not be that easily fulfilled, sightings of dolphins are quite common on Bonaire. When you go out on a boat twice a day, your chances of seeing dolphins during a one-week stay may be as high as 50%. Do not harass the dolphins and do not go with high speed through a pod of dolphins.
Sea birds. Whether you are boat diving or shore diving, you will have a chance to observe several interesting sea birds. Magnificent frigatebirds soar high over the water or dive down to pick up fish guts thrown overboard by fishermen. Not really into fishing themselves, they also attack terns in an attempt to steal their catch. The Brown pelican is quite common and a concentration of these birds indicates the presence of a school of baitfish. Opportunistic seagulls sometimes land on the pelican’s head after its dive, hoping for scraps. You will also see Ospreys along the coast, and, from a boat, you may see a Brown booby making a shallow dive at great speed in pursuit of flying fish.
The reef creatures are all so busy! What are they doing?
Marine animal behaviors:
Cleaning stations. You are probably already familiar with cleaning stations. They are specific sites on the reef where small fish and shrimps rid larger fish of skin parasites. A typical cleaning ritual that you can see on almost any dive involves a conspicuous head of Boulder star coral near the drop-off, where juvenile Spanish hogfish and juvenile Bluehead wrasses provide their cleaning service to some Creole wrasses or a Bar jack. Another scene puts a Tiger grouper in uncharacteristic pale coloration, almost motionless and with its mouth wide open, near a Boulder brain coral. Upon closer inspection you see a tiny cleaning goby moving swiftly over the Grouper’s body and perhaps a cleaning shrimp working within the mouth of the fish. Cleaning is clearly a mutually beneficial relationship: the cleaner gets food and the larger fish gets rid of parasites. Cleaning is accompanied by strong body language: the cleaners are often brightly colored, while those wanting to be cleaned make this desire known by a specific posture (for example, a head stand for the Creole wrasse and a tailstand for Parrotfishes) or by color changes (Groupers).
Camouflage and mimicry. What’s that Trumpetfish doing, swimming closely aligned with the dorsal body curve of a Bar jack? This phenomenon, also referred to as “hitch hiking”, has to do with camouflage. You can also often see a Trumpetfish hanging vertically, head down, among the branches of soft coral. The Trumpetfish is not only using camouflage to hide itself from predators, it is trying to fool a potential prey fish. It can leave its disguise and suck in a prey fish by powerful suction of its mouth in a fraction of a second. The tiny Slender filefish mimics a soft coral by assuming the coloration of the coral’s branches. Champions of camouflage are obviously Scorpionfishes and Frogfishes.
Less obvious forms of camouflage are “hunting parties”. Once in a while you come across an odd party of seemingly excited, undistractible fish, busy exploring and feeding. The party may include such species as Bar jacks, Trumpetfish, Spanish hogfish, Graysbys, Coneys, and Yellow goatfish, hanging around a moray or snake eel. Some may be in it for scraps, other may use the cover of the mob to stealthily stalk a prey – but the reason they’re there is the eel, who can get into places none of the other fish can reach. If the eel invades the crevice of a damselfish or goby, for example, the little fish may be eaten by the eel. It may escape, though – and when it darts out of its den, each member of the hunting party is ready to gobble it down. It’s no coincidence that the participants in the event – other than the eel – are particularly opportunistic feeders.