Early maximum growth of stony corals (Scleractinia) after settlement on artificial substrata on a Caribbean reef

Abstract

ABSTRACT: This study reports maximum linear extension rates of several species of stony corals (Scleractinia) during formation of the colony base. Growth was determined during the first years after settlement of larvae on artificial substrata. Diameters of juveniles at the start of growth intervals ranged from 1.4 to 28.2 mm; in 66 % of measurements they were < 10mm. Substrata were deployed in different orientations between 5 and 30m depth and thus offered a large range of environmental circumstances to demonstrate potential growth. A total of 769 growth values 20.6 mm mo-' diameter extension rate was measured in juveniles of 13 species. In 8 species sufficient data were collected to estimate maximum growth rates. Maximum diameter extension rates of about 2.1 to 2.4 mm mo-' were found in 1 ahermatypic species and in 6 hermatypic species. Acropora sp. was one of the latter species, which is remarkable in view of its relatively high adult growth rate. A range of 2.1 to 2.4 mm mo-' points to much slower juvenile growth rates than previously assumed, but is not much different from the scarce growth data available in the literature. The ahermatypic species Madracis pharensis forma pharensis showed a maximum diameter extension rate of 11.6mm mo-'. This rate is comparable to the most rapid linear extension rates ever recorded in hermatypic corals. It demonstrates for the first time that such fast linear skeletal extension rates are possible in the absence of zooxanthellae, not only on the actual growth site, but also in other colony regions. This finding constitutes an enigma, considering contemporary knowledge of calcification mechanisms and coral growth.