The Ecology of Juvenile Hawaiian Corals

Abstract

I studied coral recruitment, growth and community development in Kaneohe Bay, Oahu, Hawaii. In one experiment, I investigated coral recruitment at 7 sites, in 3 consecutive years. Coral community development was followed for up to 3 y. Hollow concrete blocks were used as experimental substrata. The smallest recruits which I detected were 1 mm in diameter. variability in recruitment was observed both between sites and between surfaces of the blocks. Temporal variability in recruitment patterns between years was also recorded. After 3 mo immersion, Pocillopora damicornis, a brooding species, was-the most abundant coral. Another brooding species, Cyphastrea ocellina, and the ahermatype, Culicia cf. tenella were also detected. Two spawning. species, Montipora verrucosa and Porites compressa were not detected until after 6 mo immersion. Over 3 y, the relative abundance of Pocillopora damicornis declined at most sites and the relative abundance of Porites compressa increased. Montipora verrucosa recruits remained uncommon. The distribution of hermatypic corals on the blocks also changed with time. Initially recruits were most abundant on interior top surfaces after 3 y, they were most common on outer surfaces of the blocks. Inter- and intraspecific differences in growth were recorded. pocillopora damicornis attained the largest colony sizes. Growth rates varied considerably between sites. Successful recruitment was highest after 3 y immersion, at sites where corals grew most rapidly. In the second set of experiments, I measured invisible recruitment sensu wallace (1983) and investigated the effects of urchin and fish grazing on coral recruitment. Montipora verrucosa was the most common recruit after 3 mo immersion. Fish and urchin grazing significantly affected the abundance of M. verrucosa but not that of Porites compressa or Pocillopora damicornis. After 3 mo immersion, the maximum size attained by P. damicornis was greater than P. compressa or M. verrucosa which had similar colony diameters and number of polyps. However, during the next 5 mo P. compressa grew more rapidly than M. verrucosa. The different growth rates of these species explains why P. compressa increased, and M. verrucosa decreased in relative abundance. Interspecific differences in larval size at settlement, the time taken to deposit a skeleton, and postsettlement growth strategies, all influence recruitment success.