ARAGONITE IN HALIMED A AND TYDEMANIA (ORDER SIPHON ALES)12

The mineral component of the marine green algal genus Halimeda is the orthorhombic calcium carbonate (aragonite); its presence appears to be a generic characteristic. Tydemania expeditionis also precipitates aragonite in contradistinction to species of the red alga Corallina wliich precipitate calcium carbonate of the hexagonal form (calcite). The analyses are based on x-ray diffraction methods. Although other inorganic substances arc present, the amounts are minor and probably represent contaminants. Specimens that are to be studied for mineral components should not be stored in formalin.     

NEW SPECIES OF HALIMEDA: A TAXONOMIC REAPPRAISAL12

A study of new Halimeda material available from the International Indian Ocean Expedition, and of type and other specimens not previously available to me, further indicated that Halimeda opuntia is a composite of species rather than a single species. The characteristics of some of its infraspecific taxa differ sufficiently from typical H. opuntia that I have elevated them to species. Extended diagnoses of three, H. hederacea, H. minima, and H. distorta, are given in this paper. Some characteristics new in Halimeda taxonomy are introduced, and distinguishing macroscopic and microscopic characteristics for the new species are discussed. Available ecological data are included.     

Halimeda growth and diversity on the deep fore-reef of Enewetak Atoll

The deep fore-reef at Enewetak has been examined from the submersible Makali'i. Green algae grow to about-150 m at photon flux densities of approximately 1 Em^-2s^-1. Halimeda cover is 50% at many sites down to-90 m. Halimeda populations are important within the zone of scleractinian corals down to about-65 m, while a Halimeda zone with low coral cover or lacking corals between-65 m and-150 m probably is an important source of reef carbonate. Halimedas of the deep fore-reef, like those of the lagoon, constitute an important structural component in reef building. Other calcareous green algae such as Tydemania are less important on the deep fore-reef, but growth of coralline red algae continues to over-200m. Halimeda diversity is high down to near the base of the euphotic zone.