The taxonomy, life cycle and seasonal growth of Codium and its effect on coral communities in Nanwan Bay, southern Taiwan

• Main Authors: Jui-Sheng Chang, 張睿昇
• Other Authors: Chang-Feng Dai
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/24837619771638578354

博士 === 國立臺灣大學 === 海洋研究所 === 90 === The taxonomy, life cycle and seasonal distribution of prostrat, dichotomously branching Codium species in Nanwan Bay and its effects on coral communities were studied. Morphological analysis distinguished four prostrate Codium species belonging to two groups, one is C. intricatum Okamura and another is C. geppiorum complex, including C. edule P.C. Silva, C. geppiorum O.C. Schmidt, and a new taxon, C. nanwanense. The utricle sizes of three species of C. geppiorum complex from big to small are C. edule, C. nanwanense, and C. geppiorum. Karyological study by microspectrophotometry with DAPI on the four Codium species also showed an obvious divergence on the nuclear area, long axis, width and relative fluorescent unit (rfu), especially in C. geppiorum complex. The ratio of nuclear long axis vs. width is about 3.01, 1.46, 1.13 and 1.00 for C. edule, C. geppiorum, C. intricatum, and C. nanwanense, respectively. C. edule has the largest nucleus and expectedly the highest relative fluorescent unit (rfu) among the four species. Codium edule is the most abundant species of four prostrate Codium species in Nanwan Bay. A specialized organ act as propagule was found on the side of utricles at the end of its growth season. The filaments were sprouted out the propagules and formed new utricles after culture of 10-14 days. The new utricle and filament were divided by a septum and the propagules showed the ability to develop a thallus. It is proposed that the seasonal growth of C. edule in Nanwan Bay, is possibly generated by the propagules rather than by fragmentation or parthenogenesis. It also showed that the life cycle of C. edule is different with Codium fragile. To investigate the influence of seasonal blooming of Codium edule on corals, an experiment was designed to monitor the changes of coral cover in different macroalgal clearance treatment groups from February 1997 to June 1999 in Nanwan Bay. Codium edule appeared December, reached its maximum biomass in next May, and disappeared rapidly in June. Algal cover was relating high occurred in 1997 (10.8 ± 9.1 %) and decreased in the following years. Coral cover remained relatively stable and ranged between 38.2 ± 7.1 % and 44.1 ± 7.8 %. There was no significant difference among the three groups (F=1.38, P>0.05). Both the Codium cover and the increment of coral cover in 1997 were higher than those in 1998 (C. edule, F = 11.88, P < 0.01; corals, F=4.58, P<0.05). Comparisons among years and algal clearance treatments showed that positive relationships between exist the increment of coral cover and Codium cover (1997 and 1998, F=17.44, P<0.001; algal clearance treatment, F=9.05, P<0.01). This suggests that the seasonal growth of C. edule on corals did not inhibit the growth of corals and hence the increasing of coral cover. This co-variation may be regarded as the result of similar requirements of environmental conditions for corals and C. edule rather than the interactions between them. Among the 495 coral colonies monitored between February 1997 and June 1999, 47.4 % died, disappeared or damaged seriously, and most of them were in branching and foliaceous forms. The massive, submassive and encrusting forms remained their cover during this study. The responses of different growth forms to environmental changes have resulted in coral community changes in Nanwan Bay.