The structure, stability and the biological effectiveness of the coal ash artificial reefs installed at Wan-li, northern Taiwan were monitored and evaluated for more than four years. These 100 large cubic hollow blocks were casted in the depth of about 10 meters. Through 14 times of underwater observations, it was found that the effectiveness and durability of coal reefs were as good as that of concrete artificial reefs near-by. The coal ash reefs can also attract the fishes and the settlement of benthic organisms. Although only 27 species recorded belong to economical species, their biomass was higher than 85% of total biomass estimated for the entire 88 species in the reef. Additionally most economical species were truly attracted by the reefs since they were not usually found in surrounding natural reefs. The analytical results using numerical taxonomic technique based on binary or multistate also indicate that the reef fish community has stabilized. The seasonal or yearly difference is not obvious. The community stability index is about 0.5, which means that the similarity of species composition between any two monitorings is about one-half no matter what the time interval was.
