Cape Tribulation's Fringing Reef EarthCache
Cape Tribulation's Fringing Reef
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Captain James Cook named Cape Tribulation on his journey to this area in 1770. After nearly running aground on a reef northeast of the shore, he travelled further out to sea in the hopes of finding deeper water, only to fetch up on Endeavour Reef (reference point W2). Cook named the headland Cape Tribulation “because here began all of our troubles.” [1]
Cape Tribulation is a significant area of Tropical North Queensland, for it is here that the rainforest meets the reef. The lush forests of the Daintree extend to the coast where reef can be seen at the shore.
There are three main kinds of coral reef: barrier reefs, coral atolls, and fringing reefs. The reef along the beaches at Cape Tribulation is an excellent example of a fringing reef. [2]
Most coral reefs are less than 10,000 years old, having started after the last Ice Age; Australia’s current Great Barrier Reef is approximately 6,000-8,000 years old and is built upon older reef underneath. [3] Fringing reefs can take up to 10,000 years to form and are comprised primarily of the coral skeletons from mostly intact coral colonies. [4] Fringing reefs differ from other reef forms in that they are directly attached to shore, or border the shore with a small lagoon or channel.
Sea level changes directly affect the growth of reefs. Coral tends to grow upwards to sea level before changing direction and growing seaward. For a large fringing reef to grow, the sea level needs to remain fairly constant. The coastal waters of Australia have remained at a fairly constant level and temperature, allowing for the development of its world-famous reef system. Of the 3,400 reefs in the Great Barrier Reef system, 760 of them are actually fringing reefs. [5]
Fringing reefs appear on sub-tidal rock, mostly along the coastline. The reef has living coral on its top, with an underlying structure of calcareous sand and remnants of previous coral and skeletal material. As the living coral lives inside of an aragonite shell (made of calcium carbonate), when the coral dies these shells become cemented together and covered with more calcium carbonate. In this manner, reefs can grow and form significant features in tropical marine environments. [6]
Over time, reefs may have grown from different kinds of organisms. For example, in the Ordovician period many reefs were formed from rugose corals, which had skeletons made of calcite instead of aragonite. Scientists can learn about Earth’s history by examining the structure of the geologic reef structure and analyzing the layering and structure of coral skeletons. [7]
Coral bleaching occurs when a change in environmental conditions causes an imbalance in the symbiotic relationship between the living coral on top of the reef and the photosynthetic protozoa that give the coral their colour. Extensive coral bleaching has occurred on the Great Barrier Reef at least seven times since 1980, causing much concern amongst environmentalists. [8.]
The beaches both north and south of Cape Tribulation have fringing reef. To log this Earthcache, walk along the beach north of Cape Tribulation until you reach fringing reef (waypoint W1) and conduct the following experiment.
EXPERIMENT
For this EarthCache, you will conduct a short experiment on a piece of coral found on the beach. This experiment should allow you to determine if the coral you have found is made from calcite or aragonite. You will be conducting an acid test to determine which kind of coral you have found. In a lab, you would use a fairly strong acid for this test, but in the field vinegar is an acceptable (and safer) substitute. Vinegar has the added benefit of reacting with calcite but not with aragonite. [9]
You will need to bring a few items with you to conduct this experiment:
- Paper towel
- Eye protection (sunglasses should be fine)
- Vinegar
Walk along the beach and find a small piece of coral. A dry piece of coral is preferable for this experiment, but it can also be done with wet coral if necessary. Please do not break any coral off of the reef itself.
Follow these instructions:
- Get the coral as dry as possible. If you have found a wet piece, dry it with your paper towel and let it sit in the sun for a few minutes to dry.
- Put on your protective eyewear.
- Put a liberal amount of vinegar on the dried piece of coral. Look and listen carefully for bubbles. It may take 1-2 minutes for the reaction to start, so be patient in your observations.
If the piece of coral you have selected is porous, it is possible that air bubbles will initially escape when you put the vinegar on it. This is not an indication of a reaction. If you are in doubt, you can always take your coral back to the carpark and scrape the coral onto the asphalt to produce a dust/grains and put some drops of vinegar onto the dust.
Once you have completed your experiment, please email the answers to the following questions to the cache owner:
- Did you notice any bubbling when you put the vinegar on the coral? Describe the reaction, if present.
- Based on your experiment, what kind of material is the coral likely made from?
- Based on the information from this cache listing, the experiment and your visual observations of the coral, how old do you think it is?
- (Optional) Take a photo of yourself in the water with the reef or Cape Tribulation visible.
You will only receive a response if your answers are incorrect. Enjoy your trip to Cape Trib!
References:
[1] http://en.wikipedia.org/wiki/Cape_Tribulation,_Queensland, accessed 12 November 2013.
[2] http://en.wikipedia.org/wiki/Reef#Biotic_reef, accessed 12 November 2013.
[3] CRC Reef Research Centre Ltd. "What is the Great Barrier Reef?", http://www.reef.crc.org.au/discover/coralreefs/coralgbr.html, accessed 12 November 2013.
[4] http://en.wikipedia.org/wiki/Formation_of_coral_reefs#Formation, accessed 12 November 2013.
[5] http://en.wikipedia.org/wiki/Fringing_reef#Location_of_fringing_reefs, accessed 12 November 2013.
[6] The Australian Museum, “Great Barrier Reef,” http://australianmuseum.net.au/Great-Barrier-Reef/, accessed 12 November 2013.
[7] http://en.wikipedia.org/wiki/Reef#Geologic_reef_structures, accessed 12 November 2013.
[8.] http://en.wikipedia.org/wiki/Coral_bleaching, accessed 12 November 2013.
[9] http://geology.com/minerals/acid-test.shtml, accessed 15 December 2013.
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