cover (only reported for La Azufrada reef) was

Rev. Biol.
Trop., 39 (2): 203-206, 1991
Diet of tbe corallivorous pufferfisb Arothron meleagris (Pisces: Tetraodontidae)
at Gorgona Island, Colombia.
Héctor M. Guzmán and Juan D. López
Smithsonian TropicalResearch Institute, Apartado 2W2, Balboa, Panama
.
(Rec.13-IX-1990, Acep. 2O-II-1991)
Abstrad: The density and diet of Arothro1'l meleagris and lhe abundance of corals are compared between Playa
Blanca and La Azufrada reefs at Gorgona lsland,.Colombia. Corals, an important food resource for A. meleagris, are
abundant after lhe widespread coral mortality caused by lhe El Niño event in 1982-83. Bolh puffee density and percent
live coral cover were similar between reefs. The diet of A. meleagris showed strong preferences foc lhe abundant
Pocillopora spp. Arothro1'l may affect lhe recovety of some eastem Pacific reefs, where lhe fish has been reported fee­
ding on rare or less abundant corals. In contrast, lhe effect of A meleagris on Gorgona reefs may be non significant; in
fact, the fish may help lhe process of recovery, by fragmenting and dispersing colonies while feeding on pocilloporid
coral!, but not feeding on raee coral species.
Key words: Corallivory, Colombia, coral reefs,eastem PacifiCo
Arothron meleagris (Bloch & Schneider) is
an Indo-Pacific pufferfish (Tetraodontidae)that
is widely distributed throughout the eastern
Pacific Ocean. It lives on rocky shores, bom on
me mainland andoffshore islands (Thomson et
'al. 1979). Almough its diet consists largely of
live corals (Glynn et al. '1972, Guzmán and
Robertson 1989),"ü also feeds on tunicates
(Hobson 1974), crus10se coralline algae, spon­
ges, echinoids, and other i nvertebrates
(Guzmán and Robertson 1989). Guzmán and
Robertson (1989) found that A. meleagris has
me ability 10 switch its diet when changes on
!he coral composition occur. They also found
mat ilS feeding preference on several eastem
Pacific reefs is not related in a consistent way
10 the abundance or availability of different co­
ral species .
The c oral reef community structure al
Gorgona Island in Colombia, and me influence
of corallivoreshave been examined byPrahl el
',al. (1979), Cantera (1983) and Glynn el aL
(1982). The reef-building coraIs at Gorgona are
similar 10Panamanian reefs, where pocillopo­
rid corals are me· dominant species. Glynn el
al. (l982) reported that A. meleagris was one
of me corallivores that consumed the greatest
amount of live coral, and fed mainly on poci­
lloporids. This inference was based on its abun­
dance and feeding habits, and not on stomach
contents. Prahl (1983) reported87% coral mor­
tality at sorne reefs at Gorgona during the
1982-83 El Niño warming event, when most of
the coral species, except Pocillopora eydouxi
were affected. By December 1987, Uve coral
cover (only reported for La Azufrada reef) was
43% (prahl et al. 1988), wim pocilloporid co­
rals (P. capitata?) c omprising 69 % and
Psammocora 30.5%. That unprecedented and
catastrophic disturbance. produced large chan­
ges in community structure al me level of spe­
cies composition, abundance, and zonation.
Therefore. changes in corallivoresdistributions
and feeding habits might also be expected.
We present data from November 1989 con­
ceming the diet and abundance of A. me lea­
gris that complements previous studies at
Gorgona and elsewhere in meeastem Pacific
(e.g., Glyn n et.al. 1972, Guzmán and
Robertson 1989). The puffer's diet, and coral
cover composition of two fringing reefs were
compared. We also examined me relation bet,
204
REVISTA DE BIOLOGIA 1ROPICAL
ween puffer distribution in different habitats on
a reef and habitat-related variation on its dieL
This paper is the ftrst of a series on the ecology
of eastern Paciftc coral reefs.
MATERIAL AND METHODS
Gorgona Island (44 km2) is located 56 km
off the S.W. Col ombian coast (2058'N,
78011'W). General descriptions of the flora,
fauna and physical oceanography can be foqnd
in Prahl et al. (1979), Glynn el m. (1982) and
Rubio (1986). In the present study, coral distri­
bution and coverage, and the pufferfish abun­
dance and diet were determined at Playa
Blanca and La Azufrada reefs, both located on
the eastern side of the island, about 1 km apart
from each other. The áreas of those two reefs
are approximately 15 Ha and 8 Ha respectively
(Glynn el al. 1982).
Diet composition was studied in 10 speared
f ish at Playa Blanca reef, and 13 at La
Azufrada reef. Stomach contents were extrac­
ted within 1h of collection and stored in ethanol
(70%). AH contents were oven-dried (6510 80
oC) 10 a constant weight, then sorted under a
dissecting microscope (se nsu G uzmán and
Robertson 1989). The percentage by weight of
dry material in each identiftable group was re­
corded. At La Azufrada reefs, ftsh were collec­
ted at two different coral zones (Pocillopora
and Psammocora).
At each reef, A . meleagris was censused
along 5 belt transects (5-10 m wide depending
on visibility) and the percent of substratum ca­
vered by live corals was estimated from 5 line
transects. For both surveys, transects were ron
perpendicular to the shore, about 25 m apart,
and extended along the depth gradient (110 10
m). Line transects totalIy covered 730 m and
766 m at Playa Blanca and La Azufrada reefs,
respectively.
AH data were arcsine transformed for statis­
tical anaIyses.
RESULTS
In 1989, densities ofA. meleagris. which did
not differ between reefs (t= .11, P> 0.05), were
2L9 ± 6.2 ind./Ha and 25.8 ± 4.9 ind./Ha at
Playa Blanca and La Azufrada reefs, respecti­
vely. Though densities at La Azufradá had de­
clined from 34 ind./Ha in 1987 to 25 ind./Ha in
1989 (Guzmán and Robertson 1989), the diffe­
rence was not signiftcant (t= .91, P> 0.05).
As expected, the proportion of ca:als in tl;te
ftsh's diet was similar10 the percent of coral
cover found at each reef (Fig. 1). Pocillopora
was more consumed than Psammocora ati>laya
Blanca (t= 24.69, P< 0.01), w here
P sammocora coverage was less than at La
Azufrada (t= 2.55, P< 0.01). However. al La
Azufrada A .. meleagris consumed (regardless of
reef habitat) similar proportions oí both corals
(t= L39, P> 0.05), in relation to their similar
availability (Fig. 2). Pocillopora and Pavona
cover were similar between localities (t= .26.
P> 0.05 and t= .69, P> 0.05, respectively).
Dead coral cover was not signiftcant among re­
ef SileS (t= L25, P> 0.05) but il was 17% grea­
ter at Playa Blanca reef (Fig.·1).
.
Playa Blanca Reef
DIET
FIELD
La Azufrada Reel
Fig. 1. ReJative abundance of live and dead c:ora1s in tite
fieId. and diel compositiOll of Arothrtm meleagris al Playa
Blanca and La Azufrada reefa . Colombia. "Others" cate-'
gory in di el consista mainIy of un:bins and gaatropodl.
"Other" coral. were mainIy pavonids. Valuel are meana
(standard error).
Furthermore, variation in Arothron's diel
was related with the availability oí coraIs wit­
hin differenl ree í zones at La Azufrada, where
Psammocora is abundanl and forms large den�
patches in the upper slope and al the base oíthe
reeí.(Fig. 2 ) . Fish captured within the
Psammocora zone contained in their stomachs
75% of that coral species. significaDtly more
than Pocillopora (t= 3.56, P< 0.01). In the
Pocillopora zone. A. meleagris consumed more
Pocillopora than Psammocora (t= 4.71, P<
0.01).
GUZMAN & LOPEZ: Diet of Arothron Colombia
100
�
80
o
o
60
§
40
o
""
20
H,
30
45
60
DistS0ce
75
(rn)
90.
120
105.
3eaward
Fig. 2. Otanges in me percentage cover of live and dead
corals along a 120 m transect perpendicular 10 the shore,
from the lagoon to me reef base (layer graph); and puffer's
diet at each reef zone within me reef profile (pie diagrams),
La Azufrada reef, Colombia. Diet values are means (stan­
dard error).
DISCUSSION
At Gorgona Island the 1982-83 El Niño event
caused a reduction in coral cover in excess of
50% (Prahl 1983). Six years after coral morta­
lity, me Playa Blanca and La Azufrada reefs ha­
ve about half of their total areas covered with li­
ving corals. and pocilloporids are still abundant
and widely distributed within each reef.
Both puffer density and percent Uve coral
cover did nol differ between reefs, in spite of
La Azufrada reef being twice me size. Guzmán
and Robertson (1989) reportOO no relationship
between puffer and coral densities, and· sugges­
too that puffer densíty on eastem Pacific reefs
is not set by coral availabilíty. Similar or higher
population densities are known from reefs in
Panama, where me total area of Uve coral is
less than 2% (Guzmán and Robertson 1989).
The pattems of both variation in density of puf­
ferfish and resource abundanee may suggest
that populations are recruitment-limited ramer
than resource-limited.
A. meleagris feeding preferenees have been
shown to be eomplex and variable. In sorne
plaees it behaves as a passive generalist, consu­
ming corals in relation te meir availability. In
others it is an active generalist, broadening its
diet by selecting the rarer corals (Guzmán and
Robertson 1989). At Gorgona Island. the fish
showed strong preferences for what was availa­
ble, both within reef zones and me whole reef
area.
205
A. meJeagris may affect the recovery of so­
rne eastem Pacific reefs, on one hand, by fee­
ding on rare corals (e.g., Psammocora at Caño
Island, Costa Rica), but on ihe oiher band. the
puffer's apparent ability te change the diet, may
favor the re-establishment of sorne coral spe�
cies, as is the case for Pocillopora at Cafto
Island (Guzmán and Robertson 1989). Rare co­
ral species observed at Gorgona Island (e.g.,
Pavona varians, P. clavus. Porites spp.) were
not eaten by ihe puffer. This may be explained
by the sOOentary nature of the fish, which con­
centrates its feeding movements to certain areas
of the reef, where mere are large monospecific
coral stands.Therefore, !he effect of A. me/ea­
gris on Gorgona reefs may be remote; in fact,
the fish may help the process of recovery by
fragmenting and dispersing colonies while fee­
ding upon Pocillopora and Psammocora. as
observOO at !he lower reef slope and reef base.
Coral dispersion and fragmentation have been
found 10 be an important aspect of the recovery
of Panamanian and Costa Rican reefs (Guzmán
and Cortés 1989, Glynn 1990).
ACKNOWLEDGEMENTS
We mank me personnel al Parque Nacional
Natural Islas Gorgona y Gorgonilla, and INDE­
RENA, Colombia for facilitating and supporting
our study. Special manks to L. Fl6rez-González
and W. Henao for their help during the field
work, and to D.R. Robertson, and H. Sweatman
for their comments 10 the manuscrlpt
RESUMEN
Se comparan la abundancia de coral, y la
densidad y la dieta del pez timboril_�!gthr()n­
meleagris de los arrecifes de Playa Blanca y La
Azufrada, Isla Gorgona, Colombia. Ciertas es­
pecies de coral, recurso alimenticio principal de
A. meleagris, continuan siendo abundantes des­
pués de 6 años de la mortandad masiva ocurri�
da a causa del fenómeno de El Niño 1982-83.
La densidad del pez y el porcentaje de coral vi­
vo fue similar para ambos arrecifes estudiados.
A. meleagris demostró una marcada preferencia
por el coral más abundante o disponible del
arrecife (pocillopora). Arothron posiblemente
irifluye en la recuperación de ciertos arrecifes
coralinos del Pacífico Oriental. debido a que
puede consumir ciertas especies de coral raras
RBVISTA DB BIOLOGIA TR.OPICAL
o poco abundante s. Por el contrario. e n
Gotgoila el efecto posibleme nte sea poco evi­
dente. ya que el pez posiblemente ayude en el
proceso de recuperación. debido a que. durante
su alimentación. fragme nta y dispersa los cora­
les.
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