[Coral-List] Parrots not needed?
gregorh at reefcheck.org
Sun Feb 19 08:11:16 EST 2017
Haiti is an interesting place to make observations regarding reef condition,
parrotfish, Diadema, etc because it has the most overfished reefs that I
have seen in the world. Several experiments have been created by different
levels of extreme overfishing. We recently completed a 4-year census of
almost the entire 1500 km coast of Haiti. The zone around Port Au Prince was
not surveyed due to heavy pollution of all kinds, but long stretches of
Haiti's coast have low human population levels and slightly less fishing
On shallow reefs (<15 m depth) about 95% of all fish are smaller than 15 cm..
The fish are so small and so few that it often appears that there are no
fish at all on long stretches of algae-dominated reef. On most reefs we did
not record a single parrot fish >20 cm. There are however, small groups of 5
to 10 juvenile parrots (<15 cm) on most reefs. On a couple of these reefs,
we found a few patches where Diadema are making a comeback, but where there
were no schools of Acanthurus spp. or adult scarids. These patch reefs had
almost zero macro-algae and a relatively "high" percentage of living coral
for Haiti (>30%).
Haiti's reefs extend to 30 m depth in many areas and rocky habitat continues
to 700 m in several. We have observed very small numbers of larger fish of
all types below 15 m depth in a few areas. Any adult fish visiting the
shallow reefs are caught by 100 m long, 2 cm mesh gill nets, traps or
About 80% of Haiti's reefs have been destabilized such that macro-algae
dominate (mean 30% cover vs 13% for the Carib) and hard corals struggle
(mean 15% cover vs 25% for Carib). We found two large reef complexes that
(before Hurricane Matthew) were still in relatively "good" condition with
relatively little macro-algae (<15%) and 30 to 60% live coral cover I.e.
well above the Caribbean mean. The major difference on these "good" reefs is
that they feature schools of several hundred Acanthurus bahianus of about 20
to 30 cm total length, but effectively zero adult parrotfish and low numbers
of Diadema ( <1 Diadema/100 sq m). While the juvenile parrots no doubt help
consume a bit of algae, their low numbers and tiny sizes suggest their
effect is small but this was not measured.
These unpublished observations of extremely overfished reefs tend to back up
the "multiple potential factors hypothesis" that various different
herbivores can maintain the stability of coral reefs and that parrot fish
are not necessary because other herbivores can do the same job. This
"ecological rule" is also a reminder of one reason why the taxonomic
complexity of the IndoPacific allows IP reefs to do so much better than
Caribbean reefs against multiple impacts.
Gregor Hodgson, PhD
Reef Check Foundation
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