Reproductive ecology of Caulerpa taxifolia (Caulerpaceae, Bryopsidales) in subtropical eastern Australia

Abstract

This paper provides the first detailed account of sexual reproduction in Caulerpa taxifolia, describing gametogenesis, sex ratios, periodicity of reproductive episodes and breeding system in C. taxifolia from Caloundra on the subtropical east Australian coast. Gametogenesis is similar to published accounts of the process in 11 other Caulerpa spp. Gender is reliably determined late in gametogenesis: mature dark-green male portions of fronds that release gametes without eyespots are distinguished from brownish-green female portions of fronds that release gametes with eyespots. Twenty-one reproductive episodes were observed for C. taxifolia during the 3.5-month fertile period, with peak reproductive activity occurring in February/March when 13 reproductive episodes were observed over a 36-day period. Caulerpa taxifolia is monoecious, but the Caloundra population showed marked variation in phenotypic gender expression during the fertile season, when various proportions of male plants, thalli with bisexual fronds and thalli with bisexual, unisexual male and/or female fronds were observed. Sex allocation in the Caloundra population was markedly male-biased throughout the fertile season with only male plants present, or with male plants dominating the population, for 13 and three reproductive episodes respectively. The implications of these observations are discussed in relation to the reported lack of sexual reproduction in the invasive Mediterranean populations of the species.

Keywords:

• Caulerpa taxifolia
• invasive species
• sexual reproduction
• monoecy
• gender expression
• reproductive ecology

Acknowledgements

This research on reproduction of C. taxifolia was funded for one summer as part of a research grant from National Heritage Trust (Environment Australia) to B. Schaffelke, CSIRO Marine Research (Hobart), Centre for Research on Introduced Marine Pests, and J. A. Phillips. I thank R. Hancock for the preparation of the photographic plate and the valuable and helpful comments on the manuscript from two reviewers.