Hiding space available for fish in a natural reef compared with an artificial reef
1998
Vogt, H.P. (Centre for the Establishment of Marine Reserves in Negros Oriental, 109 San Jose Extension, P.O. Box 187, 6200 Dumaguete City, Negros Oriental (Philippines))
In 1991, two clusters of discarded tires were placed close to a coral reef in the vicinity of Lutoban in Negros Oriental [Philippines]. Observations in both areas indicated that fish in the artificial habitat were considerably larger than in the coral reef. It is assumed that reef fish are attracted by the tire cluster because it provides more hiding space for larger fish. In order to test this assumption, the hiding space available for fish in both the reef and the tire clusters was calculated. To this end, 10 belt transects each 10 m long and about 0.5-1 m wide were deployed in the reef and in the tire habitat. Recordings were conducted by employing a video camera in an underwater housing. For image analysis a total of 400 video images were digitized using a video framegrabber card measurements of coral and tire outlines were used to represent space available for fish to hide in. For branched corals the distance between the ends of the branches was used. A comparison using Chi-square tests indicated significant differences between the two habitats. The coral reef provided abundant space for small fish to hide in, whilst the tire cluster provided more space for larger fish to seek shelter from predators. However, some massive corals in deeper areas seem to support a large number of fish although they provide only limited shelter. This suggests that fish may be attracted by other factors, such as the presence of corals or prey fish as food. The video recordings were also employed to obtain counts and cover estimates of corals, other organisms and dead substrate for both habitats. Five years after installation of the modules, a large number of corals was found growing on the tires covering 14% of the area of the artificial habitat
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