AD 2016 Q3

LIFE AQUATIC
PARROTFISH
in some locations of the Caribbean for thousands of
years. 8,9 The largest species in the Caribbean, including
the rainbow parrotfish (Scarus guacamaia) and midnight
parrotfish (Scarus coelestinus), are rare or absent on most
Caribbean reefs. 9 Furthermore, these species are most
abundant in places with little or no fishing pressure.
The decline in parrotfish populations, particularly in
the Caribbean, is a loss not only for the ecosystem but
also for the economy. Caribbean coral reefs generate
more than $3 billion annually from tourism and fisheries, 6
benefitting 38 different countries. Many people who visit
these countries want to swim with large, colorful fish.
Although restoring healthy parrotfish populations will
make Caribbean reefs more colorful, it won’t solve every
problem they face. The good news, as far as parrotfish
are concerned, is that overfishing is not a universal
problem like ocean acidification or global climate
change. Parrotfish populations can be managed locally.
A variety of herbivores is needed to help control
algal growth. Herbivorous reef fishes are diverse with
specific dietary preferences and assorted feeding
techniques, which have different impacts on the reef.
For example, parrotfish in genus Sparisoma prefer
macroalgae, whereas those in genus Scarus target
turf algae. 9 Parrotfish tend to be “scrapers,” while
surgeonfish are “grazers.” Scrapers, which remove
portions of the underlying limestone as they feed,
are important in clearing new space for colonization
by coral or crustose coralline algae, but scrapers
also bioerode the reef. There are many important
invertebrate grazers as well, such as the famed
Diadema urchin. Maintaining a diverse herbivore
population is key for reef resilience.
Parrotfish predation may be a source of coral
mortality. 10 More research is necessary to determine if
the positive effects of herbivory outweigh the negative
effects of corallivory. A 2012 study revealed that
parrotfish coral predation intensity could increase
as coral density declines. 11 Another study found that
parrotfish eat polyps with the highest number of
gonads and concluded “chronic grazing by parrotfishes
has negative fitness consequences for reef-building
corals.” 12 A contradicting study from the same
year, however, stated, “Corallivory may constitute a
source of acute mortality in coral recruits, but the
available evidence implies that any negative impacts
are outweighed by positive effects in removing algal
competitors.” 3
Even the evidence that herbivorous fish can
promote coral recovery on Caribbean reefs has been
inconsistent. While the long-term GCRMN study
found a strong correlation between healthy reefs and
healthy parrotfish populations, not all studies have
come to the same conclusion. Paulina Guarderas
and colleagues at Oregon State University studied
herbivorous fish within a marine protected area
and found that protection of herbivorous fish was
not associated with increases in coral cover when
compared with a fished location. 13
The “herbivore/algae/healthy coral” paradigm has
many layers and is extremely context dependent. Reefs
are unique in structure, species and stressors, and
each factor influences a reef’s resilience. Coral reefs
are complex ecosystems, and the diversity that makes
them such exciting places to spend a few hours are also
important in keeping them healthy.
Each organism has a niche — a role it plays on the reef.
Many of these niches, like that of herbivorous parrotfish,
are not yet completely understood, and understanding
them better is perhaps more important than ever as we
place increasingly more stress on reef habitats.
Save a parrotfish, save a reef? Maybe, maybe not, but
these colorful fish certainly play a significant role in the
coral reef ecosystem. AD
References
1. Grutter AS, Rumney JG, Sinclair-Taylor T, Waldie P, Franklin CE. Fish
mucous cocoons: the ‘mosquito nets’ of the sea. Biol Lett. 2011; 7(2):292-4.
2. Bruggemann JH, Kuyper MWM, Breeman AM. Comparative analysis
of foraging and habitat use by the sympatric Caribbean parrotfish Scarus
vetula and Sparisoma viride (Scaridae). Mar Ecol Prog Ser. 1994; 112:51-66.
3. Mumby PJ. Herbivory versus corallivory: are parrotfish good or bad for
Caribbean coral reefs? Coral Reefs 2009; 28(3):683-90.
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controlled by herbivores. Proc Natl Acad Sci. 2010; 107(21):9683-88.
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10. Rotjan RD, Lewis SM. (2005) Selective predation by parrotfishes on the
reef coral Porites astreoides. Mar Ecol Prog Ser. 2005; 305:193-201.
11. Burkepile DE.(2012) Context-dependent corallivory by parrotfishes in a
Caribbean reef ecosystem. Coral Reefs 2012; 31(1):111-20.
12. Rotjan RD, Lewis SM. Predators selectively graze reproductive
structures in a clonal marine organism. Mar Biol. 2009; 156(4): 569-77.
13. Guarderas AP, Hacker SD, Lubchenco J. Ecological effects of marine
reserves in Latin America and the Caribbean. Mar Ecol Prog Ser. 2011;
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