| 英文摘要 |
There are two parts in the investigation of this year. In the first, we tested if the number of algal species provided to herbivores affected the amount they ingested. We provided either 9 or 3 species of algae simultaneously to a sea urchin or a snail, then compared the amount each of them feed in the laboratory. In the second, we tested if present herbivores have any detectable effect on algae in Taiwanese coral reefs. We used cage experiment in five sites, among them two sites are supposed to be more protected from human activities.
The sea urchin, Tripneustis gratilla ate more algae in the 9-species than in the 3-species treatment in a total of 4 independents tests. Even for individual species of algae, the amount consumed was generally higher in the 9-species than in the 3-species treatment. It is possible that in natural reefs, where diversity of algae is high, the sea urchins are likely to consume more than that estimated from laboratory conditions. Similar results, however, were not found in the Turban snail we tested. For the comparison of herbivory, data from 3 sites were retrieved successfully. Marks of fish bite were higher outside than inside the cages. This indicates that cages we employed did have certain effect in preventing fish from entering and there are herbivores in all these sites. When comparing number of bite marks, we found that the protected “Inlet” had more than that in “Tiaoshe”. Whether the difference is due to abundance or species composition of herbivorous fishes remain to be studied. No such difference was found in the snail bite marks, they were equally abundant in or out of the cages. The small size of snails might have rendered the cage ineffective. |