Competence and longevity in planulae of several species of soft corals

Longevity and competence were studied in planulae of several species of Red Sea soft corals, including the zooxanthellate planulae of Litophyton arboreum, Nephthea sp, and Xenia umbellata, and the azooxanthellate planulae of Parerythropodium fulvum fulvum and Dendronephthya hemprichi. The relationship between presence of zooxanthellae in the planulae and their competence, longevity and caloric content was examined. Planulae of X. umbellata and D. hemprichi had the longest competency of 76 and 74 d, respectively, planulae of P. f, fulvum were competent for a maximal period of 64 d, and planulae of L, arboreum and Nephthea sp, showed a similar competency of 57 d. The highest longevity of 155 d was found in planulae of X. umbellata. Planulae of P. f. fulvum, D. hemprichi and L. arboreum had maximum longevities of 76, 81 and 92 d, respectively. No significant differences existed between the competence or longevity of the zooxanthellate and azooxanthellate planulae. The ratio of the maximum values of longevity to competency was significantly higher for the zooxanthellate compared to the azooxanthellate planulae. That zooxanthellate planulae survived beyond their competence period might be due to the ability of larvae to utilize photosynthates produced by the zooxanthellae. However, the presence of symbiotic algae in planulae does not necessarily increase competency. The caloric value of 3 d old planulae of P. f. fulvum was 0.096 +/- 0.002 cal planula(-1), and that of 4 d old planulae of X. umbellata was 0.012 +/- 0.001 cal planula(-1). The caloric content of the former decreased with development, but increased in the latter. These results support the assumption that the photosynthates of symbiotic algae contribute to the energetic content of the planulae throughout their life. Considering the competence and longevity of the planulae, it is concluded that they are able to disperse from the southern Red Sea reefs to the degraded reefs of Eilat (northern Red Sea).