Macrocystis

Macrocystis is a monospecific genus[1] of kelp (large brown algae). This genus contains the largest of all the phaeophyceae or brown algae. Macrocystis has pneumatocysts at the base of its blades. Sporophytes are perennial and the individual may live for up to three years;[2] stipes/fronds within a whole individual undergo senescence, where each frond may persist for approximately 100 days.[3] The genus is found widely in subtropical, temperate, and sub-Antarctic oceans of the Southern Hemisphere (e.g. Chile, New Zealand, Australia, Falkland Islands, Auckland Islands, etc.) and in the northeast Pacific from Baja California to Sitka, Alaska. Macrocystis is often a major component of temperate kelp forests.

For the genus of mushrooms, see Macrocystidia. For the condition of enlarged red blood cells, see Macrocytosis.

Macrocystis
Macrocystis pyrifera
Scientific classification
Clade: SAR
Phylum: Ochrophyta
Class: Phaeophyceae
Order: Laminariales
Family: Laminariaceae
Genus: Macrocystis
Synonyms
  • Macrocystis angustifolia
  • Macrocystis integrifolia
  • Macrocystis laevis

Description

Macrocystis is a monospecific genus, the sole species is M. pyrifera. Some individuals are so huge that the thallus may grow to up to 60 m (200 ft).[4] The stipes arise from a holdfast and branch three or four times from near the base. Blades develop at irregular intervals along the stipe.[5][6] M. pyrifera grows to over 45 m (150 ft) long.[6][7] The stipes are unbranched and each blade has a gas bladder at its base.[8]

  • M. pyrifera growing in the Channel Islands

Life cycle

The macroscopic sporophyte has many specialized blades growing near the holdfast. These blades bear various sori containing sporangia, which release haploid spores, which will grow into microscopic female and male gametophytes. These gametophytes, after reaching the appropriate substrata, grow mitotically to eventually produce gametes.[9]

Females release their eggs (oogonia) along with a pheromone, the lamoxirene.[10][11] This compound triggers sperm release by males. The Macrocystis sperm consists of biflagellate non-synthetic antherozoids, which find their way to the oogonia following the lamoxirene. The egg is then fertilized to form the zygote, which, through mitosis, begins growth.

Growth

Juvenile giant kelp grow directly on the parent female gametophyte, extending one or two primary blades, and beginning a rudimentary holdfast, which will eventually cover the gametophyte completely. Growth occurs with lengthening of the stipe, and splitting of the blades. This occurs by means of small tears where the blade meets the stipe, which splits the stipe into two. Pneumatocysts grow after the first few blade splittings.

Ecology
Main article: Kelp forest

Macrocystis typically grow forming extensive beds, large "floating canopies", on rocky substrata between the low intertidal.[6][9] It was harvested by barges which used large blades to harvest up to 300 tons a day along the coast of California.[12]

Species

Initially, 17 species were described within the genus Macrocystis.[13] In 1874, Hooker, following blade morphology, put them all under the same taxon, Macrocystis pyrifera.[14] In modern times, the large number of species were re-classified based on the holdfast morphology, which distinguished three species (M. angustifolia, M. integrifolia, and M. pyrifera) and on blade morphology, which added a fourth species (M. laevis) in 1986.[15] In 2009 and 2010, however, two studies that used both morphological[16] and molecular[17] assessments demonstrate that Macrocystis is monospecific (as M. pyrifera), which is currently accepted by the phycological community[18]

Distribution

Macrocystis is distributed along the eastern Pacific coast from Alaska to Mexico and from Peru and along the Argentinian coast as well as in Australia, New Zealand, South Africa and most sub-Antarctic islands to 60°S.[9]

Although Macrocystis is a monospecific genus, some split M. pyrifera into the four morphs, or sub-species, described below:

References
  1. E.C. Macaya and G.C. Zuccarello (2010) DNA barcoding and genetic divergence in the Giant Kelp Macrocystis (Laminariales). Journal of Phycology 46(4): 736–742.
  2. W.J. North (1971) The biology of giant kelp beds.
  3. G.E. Rodriguez, A. Rassweiler, D.C. Reed, & S.J. Holbrook (2013) The importance of progressive senescence in the biomass dynamics of giant kelp (Macrocystis pyrifera). Ecology, 94(8), 1848-1858.
  4. C. van den Hoek, D.G. Mann and H.M. Jahns (1995) Algae An Introduction to Phycology. Cambridge University Press, Cambridge. ISBN 0-521-30419-9
  5. Mondragon, Jennifer and Mondragon, Jeff (2003) Seaweeds of the Pacific Coast. Sea Challengers, Monterey, California. ISBN 0-930118-29-4
  6. I.A. Abbott and G.J. Hollenberg (1976) Marine Algae of California. Stanford University Press, California. ISBN 0-8047-0867-3
  7. A.B. Cribb (1953) Macrocystis pyrifera (L.) Ag. in Tasmanian waters Australian Journal of Marine and Freshwater Research, Vol 5, issue 1.
  8. Kain, J M (1991) Cultivation of attached seaweeds in Guiry, M D and Blunden, G (1991) Seaweed Resources in Europe: Uses and Potential. John Wiley and Sons.
  9. M.H. Graham, J.A. Vásquez and A.H. Buschmann (2007) Global ecology of the giant kelp Macrocystis: From ecotypes to ecosystems. Oceanography and Marine Biology: An Annual Review 45: 39-88.
  10. I. Maier, D.G. Müller, G. Gassman, W. Boland and L. Jaenicke (1987) Sexual pheromones and related egg secretions in Laminariales (Phaeophyta). Zeitschrift Naturforschung Section C Biosciences 42: 948–954.
  11. I. Maier, C. Hertweck and W. Boland (2001) Stereochemical specificity of lamoxirene the sperm-releasing pheromone in kelp (Laminariales, Phaeophyceae). Biological Bulletin (Woods Hole) 201: 121–125.
  12. Smith, G.M. 1955. Cryptogamic Botany. Volume 1. Algae and Fungi. McGraw-Hill Book Company, Inc.
  13. W.J. North (1971) Review of Macrocystis biology. In Biology of Economic Algae, I. Akatsuka (ed.). Hague: Academic Publishing, 447–527.
  14. J.D. Hooker (1874) The Botany of the Antarctic Voyage of H.M. Discovery Ships Erebus and Terror. I. Flora Antarctica. London: Reeve Brothers.
  15. C.H. Hay (1986) A new species of Macrocystis C. Ag. (Phaeophyta) from Marion Island, southern Indian Ocean. Phycologia 25: 241–252.
  16. K.W. Demes, M.H. Graham, T.S. Suskiewicz (2009) Phenotypic plasticity reconciles incongruous molecular and morphological taxonomies: the Giant Kelp, Macrocystis (Laminariales, Phaeophyceae), is a monospecific genus. Journal of Phycology 45(6): 1266–1269.
  17. E.C. Macaya and G.C. Zuccarello (2010) DNA barcoding and genetic divergence in the Giant Kelp Macrocystis (Laminariales). Journal of Phycology 46(4): 736–742.
  18. AlgaeBase: Genus: Macrocystis
  19. M. Neushul (1971) The biology of giant kelp beds (Macrocystis) in California: the species of Macrocystis. Nova Hedwigia 32: 211–22.
  20. AlgaeBase: Species: Macrocystis pyrifera
  21. AlgaeBase: Species: Macrocystis integrifolia
  22. J.M. Huisman (2000) Marine Plants of Australia. University of Western Australia Press. ISBN 1-876268-33-6

Further reading
  • Lopez, James. "Macrocystis pyrifera." Monterey Bay Aquarium Research Institute. 2001. Monterey Bay Aquarium Research Institute. 10 Jan 2007
  • M.H. Graham, J.A. Vásquez and A.H. Buschmann (2007) Global ecology of the giant kelp Macrocystis: From ecotypes to ecosystems. Oceanography and Marine Biology: An Annual Review 45: 39-88.
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