Ecology

Experiment

Corals face major threats as coastal development grows next to reef habitats. One of the problems related to this is sediments runoff from the coast, as sediments clouds the water making hard to corals to feed because they rely on the products from the photosynthesis of zooxanthelae that lives in their tissues.If they cannot reject the sediments in less than 48 hours, partial tissue necrosis starts to happen. To test this an experiment was set up in one of the tanks of the Advanced Aquarium Facilities at UQ. The sediments used were plastic Microbeads that had previously known sizes. The two sizes tested were one with really fine 10µm and another with 40µm. The tests were ran in two different days one week apart from each other so the coral could recover from the stress of the experiment. To run the test the coral was moved to another tank in the Aquarium system that had the same water running through. Despite it had the same water in the tanks, the coral was let acclimate in the new tank for a little over an hour. The circulation was shut off so it would not affect the sedimentation of the Microbeads and for them not to get to the aquarium system. In every test two grams of Microbeads were placed on top of the colony and a camera was placed in the tank to take pictures every ten seconds so the rate of rejection could be recorded.

Microbeads40 – The test was ran 14/05/14.

               
The first test showed a faster rejection rate at the first 5-10 minutes. After that the sediments that were still left on top of it took a lot more time to be removed, actually some were still sitting when the experiment was ended. But for larger sediments it may take up to two days to the coral reject them completely (Stafford-Smith 1993). The second test seemed to work a lot faster than the first one. In the first ten minutes the sediments was almost completely rejected by the coral. But there were still some spots were the sediment accumulated, especially in the more deep chalice-shaped polyps. This could be because the more chalice shaped polyps had steeper walls that are harder for the coral to reject the sediments that fall there. But overall the experiment showed similar results to Stafford-Smith, 1993, that noticed that corals have a better rejection rate for smaller sized sediments.