Nature and Environment Education - SCHOOL PROGRAMS - CORAL REEF

The seagrass and mangrove ecosytems (Lac)

Lac, the large inner bay on the east coast of the island, well known for its excellent windsurfing conditions and its naturist hotel, is clearly not a dive destination. Yet it is extremely interesting and important in a number of ways. Lac is a lagoon, protected from the eastern trade winds and the resulting wave action by a long reef barrier. Only in the north, at Cai, does a small pass provide entrance into the bay.

The lagoon Lac is bordered by extensive mangrove forests and most of its bottom is covered with seagrass beds. This is significant not only because mangroves, seagrass beds and coral reefs are the three most important tropical marine ecosystems, also because these ecosystems are inter-dependent in many ways.

Mangrove forests are known to trap sediments and act as nurseries for many species of reef fish, including several commercially important species, such as grunts, snappers and barracuda. Snorkeling in the mangroves is like a trip into a terra incognita, where you encounter all these life forms that are reminiscent of those you have seen on the reef, yet different. They grow up and eventually find their way out to the reef and contribute to its restocking.

The seagrass beds provide food and shelter for a variety of organisms. Sea turtles feed on the seagrass and the beds are the main habitat for the Queen conch, which is now severely depleted. They are also important as nurseries for several species of reef fish and for the Spiny lobster.

The ecosystems of Lac continue to fulfill their important functions today, but utmost care must be taken that other interests do not affect these systems and reduce the value of their services to mankind.

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Who’s who on the reef? (How can I learn to identify reef creatures without feeling as if I’m back in school?)

So far, you may be satisfied with looking, enjoying or photographing while you are diving, but you invariably reach a point where you want to know the names of the critters you see. And for a good reason! Because, once you know the name, you can talk about the creature with others, look it up in books and learn more about it if you want. The question is where to begin. It’s all so overwhelming, and there are so many species!

This section gives some hints and suggestions for those of you who are hungry for more knowledge. First of all, get yourself some good field identification guides. Personally, I don't go anywhere without Paul Humann’s books (Reef Fish, Reef Creatures, and Reef Coral). There is no doubt in my mind that they are the best identification guides on the market. Secondly, assign yourself tasks, and start with easy tasks. You can also take a Fish ID course from your dive school.

For example, starting with fish, you should be able to identify in one dive the Yellowtail snapper, Trumpetfish, Brown and Blue Chromis, Creole wrasse, Sergeant major and Stoplight parrotfish. Look them up in the book before your dive, carry a slate and make notes, or even better a sketch if you’re not sure, and check the book again after your dive. You will do alright as long as you don’t try to tackle difficult groups as gobies or damselfish right away.

REEF ( he Reef Environmental Education Foundation) is a non-profit group that has been collecting information about fish sightings since the early 1990’s. Surveying fishes for REEF rewards us for learning fish identifications, and provides useful information to the scientific and diving communities. Find out more at www.REEF.org.

When you are ready to learn corals, begin with common and easily recognized types. Branched corals are easy: you should be able to identify Elkhorn coral, Staghorn coral, Yellow pencil coral and Finger coral without any trouble. Pillar coral, although not as abundant, shouldn’t give you any trouble either. You can then move to the most common star corals: Boulder star coral and Great star coral. Brain corals are next, and meanwhile you will have noticed the Mustard hill coral that occurs anywhere on the reef, but is mustard-colored only in shallow water. Smooth flower coral and Orange cup coral -on night dives - are easy ones. You definitely leave Sheet, Scroll, Lettuce and Cactus corals for last. Some of those are quite difficult to identify in the field. Memorize or note down important characteristics before your dive, make notes while you are diving (or take photos – digital photography simplifies this enormously), and then go back to your books after the dive. You’ll be amazed at how much you can learn in a short time and how much fun it is.

Ecological notes

These “notes” simply answer frequently asked questions (“Where can I see turtles?”), point out interesting features or phenomena that are specific for the reefs in Bonaire (expansion of colonial Tunicate), and point out features or phenomena of general interest that would otherwise be easily overlooked or not understood by the less experienced visitor (e.g. cleaning symbiosis).

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About the coral reef (What are van ‘t Hof’s personal and objective views on the last 25 years of reef growth?)

Has the reef changed? Part 1: The subjective view. Since I conducted extensive survey work for the first guidebook in 1981, many people wanted to know if I found that the reef had changed over a period of 15 years. In my subjective view, I do see a number of changes, some of which are probably natural, others man-induced:
In 1981 and following years, the so-called white band disease was causing serious mortality among the Staghorn coral; the Staghorn coral has clearly come back, albeit not as abundant as before the disease.
The region-wide mass mortality among the Long-spined urchin (Diadema antillarum) in 1983 triggered an increase in the number of herbivorous fish such as Parrotfish - the two compete for the same food source - and as a consequence the number of bite marks caused by feeding of herbivores on coral seems to be much higher than 15 years ago. Meanwhile, Diadema is clearly coming back.
In comparing my notes on groupers, I find that the chances to see the larger grouper species (Tiger, Yellowmouth, Yellowfin grouper) are much smaller now (restricted to fewer sites) and that the chances to see a Nassau grouper along the leeward coast are virtually zero.
The reefs in front of town and most of the hotels have suffered from serious degradation. This is the combined result of, sewage disposal, seepage of untreated sewage from cesspits and disposal of waste and junk.
On a more positive note, despite some of the phenomena described above, the major part of the reefs of Bonaire are in good shape and their ecological integrity is not threatened.

Has the reef changed? Part 2: The objective view. Scientists have this notion that, unless an observation is based on objective scientific research, it has no true value. Even though I did not hesitate to give you my subjective opinion above, as a scientist, I also attach value to the notion of objective observations.

My research conducted for The World Bank (Scura and Van’t Hof, 1992), geared towards answering the question: “Can marine protected areas sustain high levels of use?”, revealed that cover by hard coral had decreased significantly in heavily used dive sites as compared to control areas. At the same time, the data also indicated that the change was confined to the surrounding of the moorings. It rings a warning bell, but it does not overthrow my subjective observation that the ecological integrity of the reefs is not under threat.

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How fast do corals grow?

Coral growth is accomplished through budding off new polyps and deposition of calcium carbonate by the coral polyps that jointly form a coral colony. Growth rates differ significantly between coral species. As a general rule, the massive head corals have the lowest growth rate and the branched corals the highest. For example, Staghorn and Elkhorn coral branches can increase 10-12 cm (4-5 inches) in length per year, while a massive coral may increase 1-2 cm (less than 1/2-1 inch) in diameter annually.

The coral skeletons, together with the spicules (calcareous or siliceous skeletal elements) of soft coral and sponges and with crustose coralline algae, contribute to the formation of reefs. Coral skeletons also “lose” calcium carbonate as a result of bio-erosion. Bio-erosion is caused by the boring action of sponges and Molluscs and by the grazing of urchins and fish. Prof. Rolf Bak, PhD, who headed the coral reef research program at the Caribbean Marine Biological Institute in Curacao for over ten years, estimated that boring sponges remove 5-10 tons of calcium carbonate per ha per year (2-4 tons/acre/yr) and fish and urchins another 25 tons per ha per year (10 tons/acre/yr). At maximum cover, corals, along with crustose coralline algae, can produce 100 tons of calcium carbonate per ha per year (40 tons/acre/yr). Depending on coral cover, Bak estimated that the net production of calcium carbonate by reef building organisms of Bonaire and Curacao result in an upward growth of the reef of 1-4 mm per year (a little more than 1/32-1/8 of an inch).

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