Reproductive phenology of a dominant crustose coralline alga, Sporolithon sp., from Taoyuan algal reefs in Northwest Taiwan

ABSTRACT Sporolithon is a common genus of crustose coralline algae occurring at Taoyuan algal reefs in Northwest Taiwan. However, little is known of the reproductive cycles and growth pattern of the genus in relation to environmental changes. In this study, the asexual and sexual reproductive stages of a dominant species of Sporolithon (Sporolithon sp.) occurring in different seasons were documented in detail for the first time based on collections made from the reefs during 2020–2022. Sexual reproductive structures (spermatangial or carposporangial conceptacles) were found all year round, whereas asexual reproductive structures (tetrasporangial compartments) appeared only in the summer and autumn, when sea surface temperature rose above 25°C. These results suggest that the reproductive cycle of this dominant species of Sporolithon is largely affected by sea surface temperature, which ranged between 13.5 and 31.5°C. Furthermore, the high ratio of sterile thalli found in most seasons suggests that the dominant Sporolithon sp. can thrive in environments having variable temperature by vegetative growth. In addition, almost all old gametophytes of Sporolithon sp. have multiple bands of embedded spermatangial or carposporangial conceptacles (up to six layers), suggesting that Sporolithon sp. is a perennial species. Further investigation into the growth pattern and reproductive cycles for other reef-building crustose coralline species occurring in Taoyuan algal reefs is needed to establish a set of biological baseline data for future conservation plans and guidelines.