What’s Going on Down There?? Turf Wars on the Reef!
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Transcript of What’s Going on Down There?? Turf Wars on the Reef!
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What’s Going on Down There??
Turf Wars on the Reef!
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What are benthic reef creatures?
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Benthic creatures live on the bottom of the ocean
• Often the word benthic refers to the deep ocean but in the case of coral reefs….
• It means creatures that live on the bottom or “floor” of the ocean
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While not as flashy and fast moving as fish, these creatures are the “heart” of the reef
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How many creatures do you see in this photo?
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That last question was tricky….
• Benthic reef creatures consist primarily of corals, algae, sponge and…
• other invertebrates that shelter within reef they create
• In the last photo there were over a dozen species!
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When looking at pictures of a reef, the first thing noticed is the diversity of life. All space on the reef is filled with
different organisms suited to fill every niche
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The Benthic reef environment is a place of constant, slow motion, turf war!
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How do Benthic Reef Creatures Fight for
Survival?
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Survival in the benthic environment is not as easy as it appears!
• Diversity in the benthic reef environment is the result of the organisms evolving through competition.
• One factor underlying this competition is aggression, both subtle and more obvious.
• Aggression occurs in corals as a result of their constant battle for survival.
• Corals have to cope with currents, predation by fish and other invertebrates, as well as competition from neighboring corals for light, nutrients, and food.
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Corals battle algae for space
Coralline algae
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Healthy reefs in Hawaii are often algae-dominated
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However, alien algae species can smother corals!
Reef without alien algae species
Reef smothered by alien algae
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Algae release sugar, fueling bacterial growth on the corals
• These bacteria suffocate the coral by cutting off the supply of oxygen
• Once the corals die, this frees space for more algae to grow
• Over-fishing by humans can reduce the number of fish that graze on algae, thus increasing the amount of algae on the reef
• Nutrients from sewage and agricultural runoff fertilize the algae
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Bubble algae growing over coral
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The battle for a majority of the benthic reef “real estate” involves corals, which deploy both
offensive and defensive weapons in order to survive and reproduce
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Corals acquire and maintain space on a reef by:
• Reproducing and/or growing rapidly
• Competing for available food
• Having offensive and defensive weapons
• Having the ability to sustain damage and still continue to reproduce
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Corals can literally grow over each other
Overtopping: • Fast growing
corals can grow over slower growing corals, blocking their sunlight.
• Overtopping may not always cause death of the shadowed coral
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Living in the shade may limit growth!
• Unlike the terrestrial world, most things growing on the sea floor are animals of some sort.
• They don't move because they get most of their food from tiny algae growing under their skin. It is this algae which gives them their color.
• This animal-plant combination only works if there is enough light for the algae to grow, and feed its animal host.
• Benthic real estate is limited, and there is a slow-motion, but fierce competition for a place in the sun.
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Corals can grow right on top of another species!
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Some corals have the ability to extract nutrition from the overrun coral!
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To understand other coral weapons…..
• You should know a little anatomy of a coral polyp
• Make a labeled drawing of a polyp on your worksheet using the picture on this slide
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Corals have weapons!
• Some corals have sweeper tentacles
• Much longer than other ("normal") tentacles
• Capable of feeding, but used primarily as weapons
• The tips break off and stick to other corals when contacted
• After contact, they continue to discharge nematocysts, damaging the invader
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Nematocysts are “stinging cells”
• They exist in many corals and jellyfish
• They are tiny, coiled speargun-like structures that trigger at a touch
• They often deliver a toxic substance into any creature they contact
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Stinging Nematocysts:
• Are present on short tentacles for close range offense and defense.
• Can be fired long range, stinging any corals downstream but usually are triggered by close contact
• Normally result in the death of contacted tissue
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When a sweeper tentacle encounters a competing coral, it may attack the competing coral and literally "burn" the offending coral to the point of either killing it or severely damaging it.
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Another weapon corals use: Mesenterial filaments
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These filaments come from the stomach of a coral polyp
• They allow one polyp to kill or devour other coral polyps through a process similar to digestion
• Some corals even have the capacity to produce both sweeper tentacles and mesenterial filaments, enabling them to fight a battle on several fronts
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Corals can also “fight” with Extracoelenteric Digestion
• Corals expel digestive filaments which contain cnidocytes (digestive fluids)
• Cnidocytes can be expelled from the digestive track en masse (puking) onto a nearby coral, digesting it
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Yet another weapon of corals: mucus
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Mucus is an effective weapon!
It can:
• be toxic or contain nematocycts
• be carried long distances by water currents
• be quite damaging as it "sticks" to corals
.
.
.
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Corals may use chemical weapons!
• The production of toxic compounds is known as allelopathy
• Most commonly known producers of toxins are soft corals
• Effective in the aggressive competition for space on the reef – toxins can kill competitors
• They are also excellent defense against predation and parasitism.
Chemical Competition .
and gorgoneans. Toxins emitted by these corals can be lethal to fish.
.
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A few corals use movement to defend themselves and avoid the weapons of
other corals
• Some corals have the ability to move about on the reef.
• Some corals can detach from the bottom and settle in another location
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There is a price for doing battle on the reef: The energy spent on both offense and defense uses
precious resources that could otherwise be spent on growth and reproduction
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Try to explain the concept of benthic reef “turf wars”
Start by taking turns trying to explain it to a partner in class.
Next, write a paragraph explaining this concept as you would to someone who has not
seen this slide show.
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Acknowledgements
• Micheal Paletta, Author and Marine Biotechnology Consultant
• Scripps Institution of Oceanography, UC San Diego
• Photos by James Watt, Kevin Hahn, Dave Krupp and Sandy Webb