What we've been looking at is what role
do Sharks play on coral reef's and in order to
do that we've compared to reef in
northwestern Australia we have a reef
called the rolly shows where sharks are
really abundant it's a marine and then
we have the Scott Reefs  a couple of
hundred kilometers away from that and
there indonesian fishes have removed
sharks over the last few centuries and
as a result numbers of sharks have
substantially the declined and what we can
do here is compare in order to get a
really good understanding of the role
that sharks play on Coral reefs.
so the first thing we found is that
sharks are indeed far less abundant at
Scott Reef the fishers have removed and
the largest sharks have reduced the
diversity and even reduced the size of
the Sharks and this seems to have had
knock-on effects on the rest of fish
communities we found that small fish the
kind of fish shark might eat around 0-30
centimeters a far more abundant where sharks
are rare and we also finding is that
these fish are fish at the bottom of the
food chain so when you put it all together
what this suggests is that sharks do
indeed have an effect on coral reefs and
when you remove them you get increases
in the kind of fish which can really
substantially alter the coral reef
itself by eating algae algae is one of
the main threats to coral reefs  it can
grow on the reef it can block out the
Sun and it can prevent coral from
establishing itself so what parrotfish
another fish at the bottom of the food chain do
is they nibble away at the algae and they prevent
from over growing the reef far more interesting are the
implications that the study has globally
and in Australia throughout the world we
have marine reserves were sharks are
protected from fishing but we also have
large fractions of the ocean which are not
protected and where sharks are being
eradicated at a terrifying rate so what
these results suggest is that globally
we have a situation where by removing
sharks we're going to see changes in the
coral reefs changes in the fish
communities and we don't know where
that's gonna lead we don't know what
the knock-on effects are going to be on
the coral reef itself.
