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Cnidarians : Stingers and Reef Builders. Marine Science Mr. Bromwell February 2011. Q: What is a Cnidarian ?. Types of Cnidarians Phylum Cnidaria includes four classes of organisms: Hydrozoans – fire corals, lace corals, hydras, siphonophores Cubozoans – box jellyfish

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Stingers and Reef Builders

Marine Science

Mr. Bromwell

February 2011

q what is a cnidarian
Q: What is a Cnidarian?

Types of Cnidarians

Phylum Cnidaria includes four classes of organisms:

  • Hydrozoans – fire corals, lace corals, hydras, siphonophores
  • Cubozoans – box jellyfish
  • Scyphozoans – true jellyfish
  • Anthozoans – corals & anemones
characteristics of cnidarians
Characteristics of Cnidarians
  • All aquatic, mostly marine
  • Prefer warm, shallow waters
  • Few natural predators
  • Radially symmetrical
  • Life history is bimorphic
  • Diploblastic
  • Contain stinging nematocysts
radial symmetry
Radial Symmetry

Radially symmetrical animals have body structures arranged around a central axis in a repetitive pattern.

  • Divide animal through center in any direction and have two identical anatomical halves
  • Two morphs (body plans) are experienced during the life of a cnidarian.
    • A sessile, polyp (hydroid) stage
    • A free-swimming/floating (medusa) stage
  • Polyps are generally (but not always) colonial
  • Anthozoans (corals & anemones) lack a medusa stage
  • Cnidaria are diploblastic which means they have an ectoderm (outer tissue layer) and an endoderm (inner tissue layer) separated by an undifferentiated mesoglea and muscle fibers.
  • There is an interior cavity called the enteron which has a single opening that serves as both mouth and anus.
  • Nematocysts or (cnidae) are harpoon-like stinging structures in the cells of the tentacles.
  • Coiled barb discharges at 2m/s.
  • Barb contains a toxic venom.
  • Used to capture and kill prey or deter predatory organisms

Video of nematocysts firing

Intra-anemone competition

other characteristics of cnidarians
Other Characteristics of Cnidarians
  • Tissue level of organization
    • Few simple organs
    • Rudimentary ‘nerve net’
  • Tentacles vs. oral arms
  • Statocysts – cells which detect simple changes in the animal’s equilibrium.
  • Weak powers of locomotion usually by slow muscular contraction
introduction to coral reefs
Introduction to Coral Reefs


Consider the following questions silently for one minute. Then share your answers with a partner for one minute. Be prepared to share your answers with the class.

  • What is a reef?
  • What is a coral reef?
  • What is a “coral?”
q what is a reef
Q: What is a reef?


A ridge of sand, rock, or coral, that lies at or near the surface of a sea or other body of water.

q what is a coral reef
Q: What is a coral reef?


A reef composed of calcium carbonate (CaCO3), limestone, that is deposited by living organisms, mostly scleractinian corals.

scleractinian – ‘reef building’ corals, often referred to as stony or ‘true’ corals

types of reefs
Types of Reefs

Fringing Reefs

Barrier Reefs

Grow in a narrow band or fringe along the shores of tropical islands or mainland.

Occur on rocky bottoms or soft bottoms with rocky outcrops

Especially vulnerable to freshwater runoff, sediments, and human disturbance

Occur along coastlines but farther from shore than fringing reefs (up to 60 miles).

Separated from the shore by a relatively deep lagoon.

Extent and morphology of coral growth depends on the location on the reef.


Ring reef of islands or sand cays surrounding a central lagoon.

Occur when a fringing reef is left around a volcanic island that has subsided.

Often in open ocean away from harmful lithogenic effects and most human disturbance.

q what is a coral
Q: What is a “coral?”


A general term applied to many members of the Phylum Cnidaria and Class Anthozoa that produce some type of hard skeleton and which have lost a medusa generation.

world distribution of coral reefs
World Distribution of Coral Reefs

Major coral reef sites are seen as red dots on this world map. Most of the reefs, with a few exceptions are found in tropical and semitropical waters, between 30° north and 30° south latitudes.

coral symbiosis
Coral Symbiosis
  • symbiosis – a close relationship between two species

In this case, a mutualism (+/+)

  • Coral animal
  • Photosynthetic dinoflagellates living inside them called zooxanthellae

Only corals with zooxanthellae build reefs.

conditions for reef growth
Conditions for Reef Growth
  • Warm, shallow water
    • depths to 50m
    • prefer water temperatures > 20ºC (68ºF)
conditions for reef growth1
Conditions for Reef Growth
  • Temperature tolerances may vary among reefs.
  • Range of temperature tolerance of corals is usually linked to geographic temperature variations.
  • Can be affected by:
    • ElNiño-Southern Oscillation (ENSO)
    • Global climate change
kamikaze questions
Kamikaze Questions

You have 10 minutes to research the answer to these questions. Record your answer and the source.

What percentage of the world’s reefs are affected by bleaching?

Where in the world is

coral bleaching having the most dramatic impact?

greg stone pipa
Greg Stone – PIPA

First scientific researcher to dive in the Phoenix Islands in the nation of Kiribati.

Helped to establish the Phoenix Islands Protected Area in the central Pacific.

Used the principle of a “reverse fishing” license to convince the Kiribati government to forgo revenues from the sale of fishing licenses in PIPA.

Coral bleaching anecdote – 13:21 to 14:50

conditions for reef growth2
Conditions for Reef Growth
  • prefer higher salinities
    • avoid osmotic difficulties
    • seawater contains salts that corals need to precipitate their skeletons
  • prefer clear water
    • Low nutrients – avoids algal competition and eutrophication
    • Low sediment – avoids sunlight obscurity and sediment coverage
      • Some corals can remove sediments
      • Physical phenomenon distributes sediment – can cover or uncover corals
  • Organism that consumes corals solely or in part
  • Zooxanthellae may account for a significant portion of reef primary production
  • Read and review comparative dissection packet for tomorrow (packet posed on NetClassroom).
  • Answer pre-lab questions.

Goggles and apron are required!

work cited
Work Cited

Amit. Snorkelers exploring the coral reef at Green island. 207. Photograph. Cairns, Queensland, Australia. Flickr. Amit (Sydney), 1 Oct. 2007. Web. 28 Feb. 2010. <>.

Birdsnest.jpg. Photograph. Tank of the Month April 2004. Reefkeeping. Web. 14 Feb. 2011. <>.

Castro, Peter, and Michael E. Huber. Marine Biology. New York: McGraw-Hill Companies, 2005. Print.

Cnidarian. Digital image. Britannica. Web. 28 Feb. 2010. <>.

Coral reef cross section. Digital image. National Ocean Service Education. National Oceanic & Atmospheric Association, 25 Mar. 2008. Web. 28 Feb. 201. <>.

Diploblastic. Digital image. Ch 32: An Introduction to Animal Diversity. 21 Dec. 2008. Web. 28 Feb. 2010. <>.

Doubilet, David. Box jellyfish. Photograph. National Geographic. 2010. Web. 28 Feb. 2010. <>.

Hoegh-Guldberg, O., and G. J. Smith. "The Effect of Sudden Changes in Temperature, Light and Salinity on the Population-density and Export of Zooxanthellae from the Reef Corals StylophoraPistillata and SeriatoporaHystrix." Journal of Experimental Marine Biology and Ecology 129 (1989): 279-303. Coral Reef Ecosystems Lab. Centre for Marine Studies, University of Queensland. Web. 08 Mar. 2010. <>.

Jellyfish. Photograph. Wild Animals A to Z. Animal Planet, 2010. Web. 28 Feb. 2010. <>.

"NOAA's Coral Reef Information System (CoRIS) - What are Coral Reefs." NOAA Coral Reef Information System (CoRIS) Home Page. 23 Feb. 2010. Web. 28 Feb. 2010. <>.

Nollette, Elyce, Eric Florio, Stevie Lewis, and Brendan Gallagher. "Vulnerability of Southern African Coastline (vulnerability/adaptation)." Google Sites - Free Websites and Wikis. Dickinson College, 30 Apr. 2009. Web. 08 Mar. 2010. <>.

O.S.F./Animals Animals—Earth Scenes. Portugeuse man-o-war. Photograph. National Geographic. 2010. Web. 28 Feb. 2010. <>.

"Reef." Def. 1. MacMillian Dictionary for Students. 1984. Print.

Santos, Scott R. Zooxanthellae. Photograph. Ocean World. Jason Education Project of Texas A&M University, 2004. Web. 2 Mar. 2010. <>.

Sea anemone. Photograph. Fel2005 Conference Photos: Tours & Sightseeing. Web. 28 Feb. 2010. <>.

Stylophora.jpg. Photograph.

"Types of Coral Reefs: Atolls, Barrier Reefs, and Fringing Reefs." Coral Reef Facts and Information: Your Online Guide to Coral Reefs. 2010. Web. 28 Feb. 2010. <>.

University of Miami. "Andrew C. Baker | The Rosenstiel School of Marine and Atmospheric Science at the University of Miami." | The Rosenstiel School of Marine and Atmospheric Science at the University of Miami. 2010. Web. 14 Feb. 2011. <>.