Cnidarians : Stingers and Reef Builders

Cnidarians:Stingers and Reef Builders

Marine ScienceMr. BromwellFebruary 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• Scyphozoans – true jellyfish• Anthozoans – corals & anemones

Hydrozoa

Cubo

zoa

Scyphozoa

Anthozoa

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 SymmetryRadially 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

Bimorphism• 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

The Coral Polyp

Diploblastic

• 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.

Diploblastic

Nematocysts•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

• 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

Think-Pair-ShareConsider 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.

1.What is a reef?2.What is a coral reef?3.What is a “coral?”

Q: What is a reef?Answer: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?

Answer: 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

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

Fringing Reefs

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.

Barrier Reefs

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.

Atolls

Q: What is a “coral?”

Answer: 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

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

In this case, a mutualism (+/+)• Coral animal• Photosynthetic

dinoflagellates living inside them called zooxanthellae

Only corals with zooxanthellae build reefs.

• symbiosis – a close relationship between two species

Coral Life History

Conditions for Reef Growth• Warm, shallow water

– depths to 50m– prefer water temperatures > 20ºC (68ºF)

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:• El Niño-Southern

Oscillation (ENSO)• Global climate

change

Coral Bleaching

Coral Bleaching

Kamikaze QuestionsYou 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

Coral bleaching anecdote – 13:21 to 14:50

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.

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

Coral Nutrition

Corallivores• Organism that consumes corals solely or in part• Zooxanthellae may account for a significant portion of reef primary

production

Homework

• Read and review comparative dissection packet for tomorrow (packet posed on NetClassroom).

• Answer pre-lab questions.

Goggles and apron are required!

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<http://oceanservice.noaa.gov/education/kits/corals/media/supp_coral04b.html>.Diploblastic. Digital image. Ch 32: An Introduction to Animal Diversity. 21 Dec. 2008. Web. 28 Feb. 2010.

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<http://animals.nationalgeographic.com/animals/invertebrates/portuguese-man-of-war/>."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.

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