2.1 Basic Coral Biology

Cnidaria Characteristics

• Cnidarians have two tissue layers separated by mesoglea, a single hole that functions as the mouth and anus, leading to gastrovascular cavity (incomplete gut)

• The mouth is surrounded by tentacles capable of ingesting prey covered with nematocysts, produced by the specialized cells cnidocytes

• Medusa or polyp form

• Four classes: Hydrozoa (colonial hydroids & siphonophores), Scyphozoa (jellyfish), Anthozoa (corals, sea fans, anemones), Cubozoa (box jellies)

• Radial symmetry

Anatomy of Coral

Corals consist of three main parts, collectively referred to as the holobiont:

1. The host coral tissue; a ring of tentacles surrounding a single opening called the mouth which leads to the stomach.

   1. Mesoglea - The mesoglea is a gelatinous, noncellular connective tissue layer.

   2. Gastrodermis: has glandular and phagocytic cells that digest and incorporate the nutrients.

   3. Cenosarc: The cenosarc is a thin band of living tissue that connect individual polyps to one another and help make it a colonial organism.

   4. Mesentarial filaments - used to capture and kill prey, and sting competitors

   5. Mucus Ciliary system - traps and ingest organic particles

2. The host coral skeleton, made of calcium carbonate

   1. See Morphology Section

3. The symbiotic organisms living within the coral tissue

   1. See Symbiosis Section

Basic Taxonomy

• Phylum: Cnidaria

  • Subphylum: Anthozoa

    • Class: Hexacorallia (Anthozoans with 6-sided symmetry)

      • Order: Scleractinia (Stony Corals)

      • Order: Actiniaria (Sea Anemones)

    • Class: Octocorallia (Anthozoans with 8-sided symmetry)

      • Order: Pennatulacea (Sea pens)

      • Order: Alcyonacea (Soft Corals/Gorgonians)

  • Subphylum: Medusozoa (jellyfish & hydra)

Historical Study of Coral Reefs

• History of the study of marine biology

  • Early expeditions - James Cook (1720s-80s) & Charles Darwin (1800s-80s) focused on the discovery of new species, defining ecological concepts, plotting oceanographic features

  • Establishment of scientific institutions - oldest marine lab in France in 1859, woods hole established in 1888

  • Deep sea exploration - 1934 HMS challenger expedition: humans descending to depths, 1960 Mariana's trench expidition

  • Scuba - introduced by Cousteau in the 50s-70s

• Important Scientists

  • ICRS Darwin Medal Recipients

  • Darwin, Earle, Carson, Cousteau