Coral Reef Ecology - Herbivory
In looking at the health of the reef when we
were snorkeling, and then noticing what a destructive force a single parrotfish can be, I began to wonder about the
effects of the Parrotfish on the ecology of the reef itself. Herbivores
play a major role in the ecology of any system, and such a destructive
herbivore was sure to have mixed effects. Since I was not able to
conduct a long-term study on the health of the reefs in which I was
snorkeling, I turned to previous research on the subject to gain an
insight into the role of the Scaridae on
the reef ecology as a whole. In the Caribbean, herbivorous fishes are
necessary in maintaining healthy coral reefs, as they benefit corals by
removing the algae growing on top of the corals which compete with the
zooxanthelle symbiont in the corals themselves (Hughes 1994).
Observational data by researchers at the Bermuda Institute for Ocean
Sciences in the 1980s noticed a high level of algae growing on top of
the corals as the parrotfish population declined due to overfishing. As
Bermuda placed bans on the number of fish that could be caught and the
number of traps able to be set, the researchers noticed an increase in
the parrotfish population and a decrease in the algae covering the
corals (BBSR website). These results were not looked at numerically and
so could not be proven statistically, however the data suggests that
the parrotfish herbivory plays a large part in restricting the growth
of competitive algae on the coral reef in Bermuda.
On the other hand, the parrotfish often tear off large chunks of the
coral as they eat, digesting the biotic material (usually algae) and
then depositing the abiotic material as a fine, white sand (a trademark
of beautiful beaches). This blatant gnawing damages the coral by
allowing the top surface to be ripped away.
So are parrotfish a blessing or a curse?
Through reading past research, it seems like these beautiful parrotfish are both a blessing and
a curse. Like most other species, the parrotfish has its good and bad
effects on the environment around them. If it weren't for parrotfish,
reefs would most 
likely
be overrun by encrusting algae and the corals depending on the
zooxanthellae would die out as the zooxanthellae would not get any
light; but all good things must come in moderation - too much foraging
would cause massive breakdown of the coral structures.
Coral growing on a rocky substrate
where parrotfish would feed