Transcript What`s going on down there?

What’s Going on Down There??
Turf Wars on the Reef!
What are benthic reef creatures?
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
While not as flashy and fast moving as
fish, these creatures are the “heart” of
the reef
How many creatures do you see in this
photo?
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!
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
The Benthic reef environment is a place
of constant, slow motion, turf war!
How do Benthic Reef
Creatures Fight for
Survival?
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.
Corals battle algae for space
Coralline algae
Healthy reefs in Hawaii are often
algae-dominated
However, alien algae
species can smother corals!
Reef without alien algae species
Reef smothered by alien algae
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
Bubble algae growing over coral
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
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
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
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.
Corals can grow right on top
of another species!
Some corals have the
ability to extract
nutrition from the
overrun coral!
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
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
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
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
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.
Another weapon corals use:
Mesenterial filaments
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
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
Yet another weapon of corals: mucus
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
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 le
.
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
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
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.
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