Ecological Studies of Floridian Eucheuma (Rhodophyta, Gigartinales). I. Seasonal Growth and Reproduction

The seasonal growth and reproduction of three species of Eucheuma (Rhodophyta, Gigartinales) are described. Eucheuma isiforme and a plant designated as the Bahia Honda form, because of its unclear taxonomic status, were studied (monthly) at two sites in the Florida Keys for a 2-year period. The third species, E. nudum, was collected monthly for a year offshore Anclote Key, on the west coast of Florida. The growth and reproduction of the three species were correlated with a variety of physical and chemical data. Each species exhibited peak spring and lower summer-fall growth rates. The period of maximum growth coincided with low temperatures, reduced light intensities and maximum nutrients. Up to 90 per cent of the E. nudum and Bahia Honda plants were reproductive during December and January, and the majority of their populations reacted as annuals. In contrast, E. isiforme exhibited a much lower level of reproduction and it was represented by perennial populations. Eucheuma nudum appears to have a typical triphasic life history, while E. isiforme and the Bahia Honda form seem to have modified (derived) life histories. Vegetative reproduction is a major means of reproduction for all three species. Transplantation experiments indicate that the life history of E. nudum may be modified by environmental factors.