Marine Biology

, Volume 93, Issue 1, pp 91–101 | Cite as

An electron microscope study on the mineralization of the skeleton of the staghorn coral Acropora hebes

Article

Abstract

The skeleton formation in the reef-building coral Acropora hebes (Dana) was ultrastructurally investigated by observing the skeletogenic tissue and the skeleton in the apical portion of the branches. The skeletogenic tissue was made of a layer of tall calicoblastic cells which displayed high exocytotic activities. A number of hollow spherules and tiny vesicles were found in the sub-epithelial space between the calicoblastic cell layer and the skeletal plate. These organic materials appeared to occur in the perinuclear Golgi vesicles in the cells. The energy-dispersive X-ray analysis revealed a calcium element in the osmiophilic granules of the calicoblastic cells, but not in any other cell organelles. As the granules showed no diffraction pattern, it was suggested that they could be a Ca-reservoir in the cells. Crystalline particles were found to deposit on the periphery of the sub-epithelial spherules. The spherules developed to spherular crystals by depositing granulated crystalline particles. Two of the spherules appeared to fuse with each other to form a spindle-shaped crystal. The spherular and spindle-shaped crystals accumulated on the thecal ridge and the lateral side surface of the thecal plate, and seemed to contribute to the elongation and thickening of the thecal plate. The thecal plate exhibited a porous structure which probably originated from an aggregation of the central cores of these crystals. On the surface of the thecal plate more than about 5 μm thick, scale-like structures composed of spherular crystal substructures were observed. These observations suggest that mineralization in A. hebes occurs in the extracellular space by elabolating the spherular and spindle-shaped precursor structures and that growth of the corallite is brought about by an aggregation and coalescence of these crystals.

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Literature cited

  1. Barnes, D. J.: Coral skeleton: an explanation of their growth and structure. Science, N.Y. 170, 1305–1308 (1970)Google Scholar
  2. Barnes, D. J.: The structure and formation of growth-ridges in scleractinian coral skeletons. Proc. R. Soc. Lond. B 182, 331–351 (1972)Google Scholar
  3. Chalker, B. E.: Daily variation in the calcification capacity of Acropora cervicornis. Proc. 3rd Int. Symp. Coral Reefs 2, 417–424 (1977)Google Scholar
  4. Chalker, B. E. and D. L. Taylor: Light-enhanced calcification and the role of oxidative phosphorylation in calcification of the coral Acropora cervicornis. Proc. R. Soc. Lond. B 190, 313–331 (1975)Google Scholar
  5. Gladfelter, E. H.: Skeletal development in Acropora cervicornis: I. Patterns of calcium carbonate accretion in the axial corallite. Coral Reefs 1, 45–51 (1982)Google Scholar
  6. Gladfelter, E. H.: Skeletal development in Acropora cervicornis: II. Diel patterns of calcium carbonate accretion. Coral Reefs 2, 91–100 (1983)Google Scholar
  7. Goreau, T. F.: Histochemistry of mucopolysaccharide-like substances and alkaline phosphatase in madreporarian. Nature, Lond. 177, 1030 (1956)Google Scholar
  8. Hayashi, K.: On the detection of calcium in the calicoblast of some reef corals. Palao Trop. Biol. St. Stud. 2, 169–172 (1937)Google Scholar
  9. Hayes, R. L. and N. I. Goreau: Intracellular crystal-bearing vesicles in the epidermis of scleractinian corals, Astrangi danae (Agassiz) and Porites porites (Pallas). Biol. Bull. mar. biol. lab., Woods Hole 152, 26–40 (1977)Google Scholar
  10. Isa, Y., N. Ikehara and K. Yamazato: Evidence for the occurrence of Ca++-dependent adenosine triphosphatase in a hermatypic coral, Acropora hebes (Dana). Sesoko mar. Sci. Lab. Tech. Rep. 2, 19–25 (1980)Google Scholar
  11. Isa, Y. and K. Yamazato: The ultrastructure of calicoblast and related tissues in Acropora hebes (Dana). Proc. 4th Int. Coral Reef Symp. 2, 99–105 (1981)Google Scholar
  12. Johnston, I. S.: The organization of a structural organic matrix within the skeleton of a reef-building coral. Scann. electron Microsc. 2, 421–431 (1979)Google Scholar
  13. Johnston, I. S.: The ultrastructure of skeletogenesis in hermatypic corals. In: International review of cytology, vol. 67, pp 71–214. Ed. by H. Bourne and J. F. Danielli. New York: Academic Press 1980Google Scholar
  14. Kawaguti, S. and K. Sato: Electron microscopy on the polyp of staghorn corals with special reference to its skeleton formation. Biol. J. Okayama Univ. 14, 87–98 (1968)Google Scholar
  15. Mitterer, R. M.: Amino acid composition and metal binding capability of the skeletal protein of corals. Bull. mar. Sci. 28, 173–180 (1978)Google Scholar
  16. Reed-Miller, C.: The initial calcification process in shell-regenerating Tegula (Archaeogastropoda). Biol. Bull. mar. biol. Lab., Woods Hole 165, 265–275 (1983)Google Scholar
  17. Sato, T.: Electron microscopic observation on the minute structure of the skeletons of some scleractinians (I). Chikyu-Kagaku 66, 9–14 (1963)Google Scholar
  18. Spiro, B. E.: Ultrastructure of Acropora. Bull. geol. Soc. Denmark 23, 72–78 (1974)Google Scholar
  19. Shimada, T., K. Ota, M. Yamamoto and M. Murakami: Eponfreeze cracking for scanning electron microscopy. Kurume med. J. 23, 139–143 (1976)Google Scholar
  20. Vandermeulen, J. H., N. Davis and L. Muscatine: The effect of inhibitors of photosynthesis on zooxanthellae in corals and other marine invertebrates. Mar. Biol. 16, 185–191 (1972)Google Scholar
  21. Vandermeulen, J. H. and N. Watabe: Studies on reef corals. II. Skeleton formation by newly settled planula larva of Pocillopora damicornis. Mar. Biol. 23, 47–57 (1973)Google Scholar
  22. Wainwright, S. A.: Skeletal organization in the coral, Pocillopora damicornis. Q. J. microsc. Sci. 104, 169–183 (1963)Google Scholar
  23. Young, S. D.: Organic material from scleractinian coral skeleton-I. Variation in composition between several species. Comp. Biochem. Physiol. 40B, 113–120 (1971)Google Scholar

Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Y. Isa
    • 1
  1. 1.Department of BiologyUniversity of the RyukyusNishihara, OkinawaJapan

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