Reproduction in Sphacelaria biradiata Askenasy (Sphacelariales, Phaeophyceae) in Southern Australia

Sphacelaria biradiata Askenasy is a little known but common brown alga of southern Australian coasts. This paper describes its reproduction. Populations of S. biradiata reproduced asexually by vegetative propagules in all localities examined. The propagules were produced throughout the year and did not appear to be affected by season, although, if sexual structures occurred, propagule numbers declined. Sexual reproduction can occur and involves an alternation of generations, but it is a rare event. Gametophytes may produce male gametangia, female gametangia or both. Male gametangia, however, are extremely rare and are described for the first time. Production of female gametangia was influenced by season and occurred at all areas studied. The sexual behaviour of the male and female gametes is described.

Variation in gametophyte dominance in populations of Chondrus verrucosus (Gigartinaceae, Rhodophyta)

We describe the abundance, including spatial and temporal variability, of phases of the isomorphic Chondrus verrucosus Mikami from Japan. Chondrus verrucosus occurred in a dense (∼90% cover) and temporally stable bed on a small, isolated rocky outcrop (Oyakoiwa) in Shizuoka Prefecture. Small vegetative fronds were always much more abundant than large vegetative and fertile fronds over the spring to late summer periods in 1999 and 2000. Over the same period, fertile carposporophytic fronds were generally more abundant than fertile tetrasporophytic fronds, and fertile male fronds appeared infrequently at low densities. Using the resorcinol-acetal test, we determined the proportion of gametophytes and tetrasporophytes in three populations of C. verrucosus: Oyakoiwa and Noroshi (Shizuoka) in the summers of 1999 and 2000 and Kamehana Point (Miyagi) in autumn 2000. All populations had a significantly higher proportion of gametophytes than tetrasporophytes in both years, although gametophytic proportions were lower at Noroshi (∼70%) than at Oyakoiwa (∼80%) and Kamehana Point (∼97%). However, examination of all isolated individuals sampled on Noroshi showed equal proportions of each phase in 1999, but gametophyte dominance (74%) in 2000. Differences in dispersal and spore production between phases are discussed as mechanisms potentially contributing to variation in gametophyte dominance.

Fourier transform infrared microspectroscopy as a tool to identify macroalgal propagules

Understanding of macroalgal dispersal has been hindered by the difficulty in identifying propagules. Different carrageenans typically occur in gametophytes and tetrasporophytes of the red algal family Gigartinaceae, and we may expect that carpospores and tetraspores also differ in composition of carrageenans. Using Fourier transform infrared (FT-IR) microspectroscopy, we tested the model that differences in carrageenans and other cellular constituents between nuclear phases should allow us to discriminate carpospores and tetraspores of Chondrus verrucosus Mikami. Spectral data suggest that carposporophytes isolated from the pericarp and female gametophytes contained κ-carrageenan, whereas tetrasporophytes contained λ-carrageenan. However, both carpospores and tetraspores exhibited absorbances in wave bands characteristic of κ-,ι-, and λ-carrageenans. Carpospores contained more proteins and may be more photosynthetically active than tetraspores, which contained more lipid reserves. We draw analogies to planktotrophic and lecithotrophic larvae. These differences in cellular chemistry allowed reliable discrimination of spores, but pretreatment of spectral data affected the accuracy of classification. The best classification of spores was achieved with extended multiplicative signal correction (EMSC) pretreatment using partial least squares discrimination analysis, with correct classification of 86% of carpospores and 83% of tetraspores. Classification may be further improved by using synchrotron FT-IR microspectroscopy because of its inherently higher signal-to-noise ratio compared with microspectroscopy using conventional sources of IR. This study demonstrates that FT-IR microspectroscopy and bioinformatics are useful tools to advance our understanding of algal dispersal ecology through discrimination of morphologically similar propagules both within and potentially between species.