Nasoata Mangrove Island, the PABITRA Coastal Study Site for
Viti Levu, Fiji Islands
Thaman, Randolph R.
Keppel, Gunnar.
Whatling, Dick.
Thaman, Batiri.
More
Pacific Science, Volume 59, Number 2, April 2005, pp. 193-204 (Article)
Published by University of Hawai'i Press
DOI: 10.1353/psc.2005.0027
For additional information about this article
http://muse.jhu.edu/journals/psc/summary/v059/59.2thaman.html
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Nasoata Mangrove Island, the PABITRA Coastal Study Site for
Viti Levu, Fiji Islands1
R. R. Thaman,2 Gunnar Keppel,3 Dick Watling,4 Batiri Thaman,5 Timoci Gaunavinaka,6
Alifereti Naikatini,7 Baravi Thaman,8 Nemani Bolaqace,9 Etika Sekinoco,9 and Manasa Masere 9
Abstract: Nasoata Island is a predominantly mangrove island located near the
outflow and delta of the Rewa River, Fiji’s largest and longest river. The river
originates on the eastern slopes of Mt. Tomaniivi in the Central Highlands
of Viti Levu. The island has been selected as an integral coastal site for Fiji’s
PABITRA Gateway Transect. Information is provided on: (1) the reasons it
was selected as a PABITRA site; (2) geographical, geological, climatic, and edaphic setting; (3) the vegetation; and (4) brief notes on the fauna, with particular
focus on the avifauna. Because of its rich flora and fauna, Nasoata Island is an
excellent ‘‘prototype’’ coastal and mangrove site for enhancing our understanding of the complexities of island biodiversity, both within Fiji and in relation to
other small offshore islands within the broader PABITRA network.
Nasoata is a small, predominantly mangrove island located in the Rewa River Delta,
near the outflow of the Nasoata River, one of
the main subsidiary channels of the Rewa
River, Fiji’s largest and longest river, which
empties into the Pacific Ocean in southeastern Viti Levu (Figure 1). Because of its
relatively pristine condition, its relatively rich
flora, avifauna, and marine biodiversity, particularly its migratory birds, seabirds, and
waterfowl, and its rich mangrove-associated
crustacean fauna, the island has been selected
1
Manuscript accepted 27 April 2004.
Professor of Pacific Islands biogeography, University of the South Pacific, Suva, Fiji Islands.
3 Assistant lecturer in biology, University of the South
Pacific, Suva, Fiji Islands.
4 Environmental consultant and ornithologist, Environmental Consultants Fiji, Ltd., Suva, Fiji Islands.
5 Scientific officer, Institute of Applied Science, University of the South Pacific, Suva, Fiji Islands.
6 Coordinator, Fiji National Ramsar and Wetlands
Working Group, Suva, Fiji Islands.
7 Technical assistant, South Pacific Regional Herbarium, University of the South Pacific, Suva, Fiji Islands.
8 Tutor in geography, University of the South Pacific,
Suva, Fiji Islands.
9 Community leader, Nakorovou Village, Rewa Province, Viti Levu, Fiji Islands.
2
Pacific Science (2005), vol. 59, no. 2:193–204
: 2005 by University of Hawai‘i Press
All rights reserved
as a prototype coastal mangrove site in the
PABITRA mountain-to-sea landscape transect originating at Mt. Tomaniivi and the
Central Highlands of Viti Levu and extending along the Rewa River system to the coral
reefs and nearshore marine ecosystems of
southeastern Viti Levu.
The information presented here is based
on five reconnaissance visits to Nasoata between April 2001 and August 2002, during
which time preliminary assessments were
made of the flora and fauna of the island and
the surrounding nearshore environment.
Based on these preliminary assessments the
island was first selected as one of Fiji’s priority mangrove wetland sites under the Ramsar
Wetland Convention and subsequently for
designation as the coastal and mangrove site
within the proposed Fiji PABITRA Gateway
Transect. The main reasons for its selection
include (1) it is an uninhabited offshore island, which makes it an excellent site for the
study of processes within a discrete smallisland ecosystem surrounded by more diverse
ecosystems of main-island Viti Levu; (2) it is
a relatively undisturbed and extensive mangrove ecosystem with a diversity of associated
flora and fauna; (3) limited areas of other
representative coastal and nearshore marine
ecosystems exist, which support beach and littoral forest, disturbed coastal forest, a coconut plantation, intertidal sea-grass beds, and
193
194
PACIFIC SCIENCE . April 2005
Figure 1. Annotated aerial photograph of a portion of southeastern Viti Levu centered on Nasoata Island and the
lower reaches of the Nasoata River showing the main mangrove islands of Nasoata, Valolo, and Sagasaga; portions of
the Rewa River Delta; fringing reefs; mudflats and associated intertidal sea-grass beds; offshore barrier reefs; reef
passes; and the locations of Nakorovou Village (the custodians of Nasoata) and other Fijian villages that use the area
as an important fishing ground and the islands as sources of food and other products.
mudflats; (4) its pivotal location on the windward side of Viti Levu at the mouth of the
Rewa River and just off the main delta, about
1 km inside the main barrier reef, makes it a
prime target for potential colonization by terrestrial and aquatic organisms from both the
sea and the mainland; (5) the rich shorebird
and seabird avifauna; (6) the rich mangrove
invertebrate and vertebrate fauna of considerable economic and cultural importance; (7)
the designation of the island as a reserve and
a scientific study site has been strongly endorsed by the local Fijian community respon-
sible for the stewardship of the island and by
the Fiji Government.
geography, climate, soils, and tenure
changes
The area of Nasoata is about 76 ha (0.76
km 2 ). Its maximum elevation above mean sea
level is about 1.2 m in the higher southcentral portion of the island. It is located at
about 18 8 0 S latitude and 178 36 0 E longitude. The main mouth of the Rewa River
is located about 3 km to the west. There are
Nasoata Island, PABITRA Coastal Study Site in Fiji . Thaman et al.
coral reefs, including Nasilai Reef, located a
further 1 km to the south and extending to
the southeast of the island. Sagasaga and Valolo are two smaller mangrove islands located
about 1 km to the east of the island.
Nasoata lies just off the windward southeastern portion of Viti Levu and has a wet,
tropical oceanic climate. The area receives
about 3,000 mm mean annual rainfall, with
some rainfall being experienced on an average
of about 250 days per year. The average annual mean temperature is 25 C (77 F) with
an average monthly range of about 6 C. The
temperature seldom rises above 32 or falls
below 16 C (Smith 1979). The southeast
tradewinds, which affect the southern coast
of the island, are relatively consistent during
the cooler, drier season between April and
October. They shift more to the northeast
later in the year. During the warm, wet season between mid-November and mid-April
the entire Fiji group experiences gale-force
winds. Destructive tropical cyclones, storm
waves, and associated heavy rainfall are common during that period. This leads to flooding and accelerated runoff in the Rewa River
system and accelerated erosion on the southeastern windward side of the island. This
increased river flow brings with it increased
sediment loads that affect not only the central
low-lying portions of Nasoata, but also the
surrounding sea-grass beds and nearby coral
reefs. The increased river flow with its high
sediment load also substantially reduces the
biogenic proportion of beach sand on the
more upraised southern portions of the island. The high river flows and storm waves
also bring flotsam and propagules of many
inland plants to the island. The presence of
some of the noncoastal plant and animal species found on the island, including some reptiles (e.g., geckos and skinks) and countless
insects, is probably due to these storm-related
events. During one visit to the island in August 2001, just after heavy flooding in the
Rewa Delta, a juvenile Pacific boa, gata (Candoia bibroni), was found in a tree just behind
the beach on the southeastern corner of the
island. High seas, reinforced by the predominant tradewinds, have also led to extensive
deposits of pumice (soata in Fijian) through-
195
out the low-lying areas of the southeastern
portion of the island. This is the origin of
the island’s name, Nasoata (literally ‘‘the pumice’’ or place of the pumice).
The island was formerly a freehold property run as a copra plantation, first as the
Hedstrom Estate, and subsequently by a Mr.
B. Garnett and most recently by Ram Singh
from the 1950s until the late 1970s when the
title to the island was transferred from freehold to native land under the high chief of
Rewa, Ro Lady Lala Mara, the Rokotui Dreketi. At the time the people of nearby Nakorovou Village were designated as the owners,
custodians, and main users. Although the island was a source of construction materials
for traditional Fijian houses (bure) in the
past, the island is now used almost exclusively
as a fishing ground (iqoliqoli) or ‘‘breadbasket’’ (ikanakana) and for the production of copra from the existing coconut palms on and
around the old copra estate in the southeast
of the island. The island was used during
World War II by New Zealand and American
troops as a training ground for jungle combat
and, more recently, during the 1970s and
early 1980s by the O Kei Viti group of Nakorovou as a tourist destination, where Fijian
cultural displays and meals were provided as a
source of income to the village. It remains a
favorite picnic site for schools in the area.
flora
The flora of Nasoata is composed of some
123 species of vascular plants from 54 families. Of these species, 15 are ferns or fern
allies and the balance consists of 108 angiosperms, of which 32 are monocotyledons and
76 dicotyledons (Table 1) (see Appendix for a
listing of the flora). Four of the monocotyledon species are sea grasses, from two exclusively aquatic families. All of the ferns are
assumed to be indigenous, whereas 36 of 106
angiosperms are probably introduced species,
half of which (18) are assumed to be either
accidental introductions by humans or recent
natural arrivals to the island carried from
mainland Viti Levu by the river, waves, birds,
or fruit bats (see Appendix). There are no
gymnosperms on the island.
196
PACIFIC SCIENCE . April 2005
TABLE 1
Summary of the Composition of the Flora of Nasoata Island Based on Studies Conducted from 2001 through 2003
(a Detailed Listing of Species Is Included in the Appendix)
Flora
Pteridophyta (ferns and fern allies)
Monocotyledonae (monocots)
Dicotyledonae (dicots)
Total vascular plants
Families
Indigenous
Introduced
Total
9
13
32
54
15
22
50
87
—
10
26
36
15
32
76
123
Vegetation Types
The main vegetation types on Nasoata include Rhizophora- and Bruguiera-dominated
mangrove forest, mixed tidal forest, episodic
swamp forest, inland coastal forest or coconut
woodland, littoral forest and strand vegetation, ruderal vegetation, and sea-grass beds.
Figure 2 is a general vegetation map showing
these vegetation types.
rhizophora forest (vei tiri or vei
kaka). The eastern and northern coastal
zone of the island is dominated by Rhizophora
stylosa (tiri solo) and Rhizophora mangle (tiri or
tiri wai), with the former generally occupying
the outer fringes and the latter the inner,
more protected areas of this mangrove forest
system. There are also areas of dense thickets
dominated almost exclusively by Rhizophora
spp. along the outer edges of the central
Bruguiera-dominated Bolavou Swamp in the
south-central part of the island. These impenetrable thickets are known in Fijian as veikakaka. A sterile hybrid, Rhizophora stylosa
mangle, known in Fijian as selala, which is
occasional in other parts of Fiji, is also found,
but uncommon, on the island. At least one
selala, approximately 15 m in height, was
seen, which is similar in height to the uppercanopy Rhizophora spp. in the area.
bruguiera gymnorrhiza swamp forest. Most of the poorly drained central
swampy portion of the island is covered by
an extensive mangrove swamp forest. This
vegetation type is dominated almost entirely
by large Bruguiera gymnorrhiza as the uppercanopy species, with the occasional presence
of individuals of Xylocarpus granatum in more
well-drained sites. The largest trees in the up-
per canopy are up to 16 m high. Scattered
throughout this community is the mangrove
or swamp fern (Acrosticum aureum). Also common in this plant community is a range of
epiphytic ferns, including Davallia fijiensis,
Davallia solida, Pyrrosia lanceolata, and Nephrolepis sp. Less common ferns include the
climbing fern, Stenchlaena palustris, and the
epiphytic ferns Vittaria elongata, Vaginularia
angustifolia, and Drynaria rigidula. The latter
was seen as a single, large fern growing on
a Bruguiera tree in the center of Bolavou
Swamp. The other ferns are mainly found
growing on Bruguiera and Xylocarpus trees,
often on older, often broken branches. The
epiphytic orchid Grammatophyllum elegans
was also seen on a number of dead trunks
and branches of B. gymnorrhiza. Lumnitzera
littorea was reportedly a common component
of this forest in the past but was logged out
because of its value as one of the most durable
and desirable woods for houseposts for Fijian
houses.
mixed tidal forest. There are also
small areas of mixed tidal forest, usually on
the southern edges of the Bruguiera gymnorrhiza forests or in slightly raised, more
well-drained sites on the southern and northeastern sides of the island. These mixed
forests are mostly dominated by either Xylocarpus granatum or Excoecaria agallocha,
although scattered Rhizophora spp. and Bruguiera gymnorrhiza are also found. Heritiera
littoralis and Intsia bijuga are occasional trees
in this mixed tidal forest. The introduced invasive species known as pond apple, Annona
glabra, is also present. Occasional throughout
this community are the large sedges Scirpodendron ghaeri and Mariscus javanicus. Other
Nasoata Island, PABITRA Coastal Study Site in Fiji . Thaman et al.
197
Figure 2. Generalized vegetation map of Nasoata Island, Rewa Delta, Viti Levu, Fiji Islands (prepared by Baravi Thaman from a 1994 aerial photograph).
common species include the climbing vines
Derris trifoliata, Dalbergia canadatensis, and
Entada phasioloides; the mangrove fern, Acrostichum aureum; and the epiphytic ferns Davallia fijiensis, Davallia solida, and Pyrrosia
lanceolata. Uncommon to occasional are the
climbing swamp fern, Stenochlaena palustris,
and the epiphytic orchids Taeniophyllum
fasciola and Oberonia halophila (the latter two
were seen on a Morinda citrifolia tree, the
same species that hosts orchids in the
Veisari mangrove forest on southeastern
Viti Levu). In one area in the southern
portion of the island, in a back-beach basin,
the introduced invasive species pond apple
(Annona glabra) has established itself in limited areas in almost monospecific stands,
probably in areas formerly covered with
Rhizophora.
episodic swamp forest. There are
limited areas of relatively open forest that are
episodically subjected to swampy conditions.
These are found in a number of sites that are
frequently waterlogged or submerged with
brackish water, due to a rising water table,
during exceptionally high spring tides associated with heavy rains. This intermediate vegetation type is restricted to a narrow belt,
which is found mainly on the southeastern
part of the island slightly inland from the
beach forest and on the southeastern windward border of the central Bolavou Swamp.
The substrate is intermediate between the
muddy mangroves and sandy beaches but
also includes a large proportion of highly
acidic pumice, in various stages of breakdown. Common trees of this community include the mangrove associates Excoecaria
198
agallocha, Heritiera littoralis, and Barringtonia
asiatica on the outer edges, with Inocarpus fagifer, Cocos nucifera, and Hibiscus tiliaceus dominating the more well-drained sites that are
less subject to saline overflow from the tidal
areas. Other scattered shrubs or small trees
include Morinda citrifolia and Barringtonia
racemosa. The latter is found occasionally in
low-lying spots that are periodically swampy.
Also common in these sites are the climbers
Smythea lanceolata, Derris trifoliata, and Entada
phasioloides. In more expansive areas of this
type, there are aggregations of Xylocarpus
granatum and a few individuals of Intsia bijuga
(others probably have been logged out in the
past, because the wood is useful for construction purposes). Climbers and epiphytes are
absent or similar to those in the mixed swamp
forest.
inland coastal forest or coconut
woodland. There are substantial areas of
inland coconut-dominated coastal forest or
woodland on better-drained sites on the
southeastern and southern parts of the island,
just inland from the raised beach ridge. These
areas are rarely, if ever, inundated. Much of
the original vegetation in these areas was
undoubtedly cleared during the establishment
of copra plantations during the middle of
the last century, but there are remnants of
the original native vegetation. Recent natural
recolonization by pioneer species has also
occurred as coconut plantations were abandoned or not maintained. Native tree
species are found scattered throughout this
community. Some may have been planted as
multipurpose trees when permanent residents
were on the island. These trees include Cerbera manghas, Pongamia pinnata, Xylocarpus
granatum, Barringtonia asiatica, Inocarpus fagifer, Tarenna sambucina, Dysoxylum richii, Ficus
vitiensis, Erythrina variegata var. orientalis, and
the introduced Annona glabra. Shrubby species include Morinda citrifolia, Ficus barclayana,
Geniostoma sp., and the introduced Lantana
camara. Occasional naturally occurring climbing vines or lianas include Derris trifoliata,
Smythea lanceolata, Entada phaseoloides, the adventive Passiflora laurifolia, the terrestrial fern
Phymatosorus grossus, and the mainly epiphytic
PACIFIC SCIENCE . April 2005
ferns Davallia fijiensis, Davallia solida, Pyrrosia
lanceolata, Vittaria elongata, Vaginularia angustifolia, and Nephrolepis spp., the latter of which
are both epiphytic and terrestrial. The grass
Centotheca lappacea; the sedge Scleria polycarpa;
the adventive herbs Polygala paniculata, Clidemia hirta, Vernonia cinerea, and Spermacoce sp.;
and the epiphytic orchids Appendicula reflexa,
Taeniophyllum fasicola, and Oberonia halophila
are also present. There are rare remnants of
cultivation: the air yam (Dioscorea bulbifera)
and derris root (Derris malaccensis), which is a
source of rotenone used by Fijians to poison
fish.
littoral forest and strand vegetation. There are relatively extensive areas of
littoral forest and strand vegetation along the
south coast of the island. These fall into two
relatively distinct types. The first occurs on
the more windward southeastern and southcentral coast of the island, which has been
strongly and continually eroded. The second
occurs on the southwestern coast of the island, which is eroded to a much lesser extent.
The beaches of Nasoata differ from other
comparable ones in having terrestrial sand
brought in with the river outflow mixed with
sand from coral reef and oceanic sources.
These mixed sands are, therefore, likely to
be richer in nutrients than the sands of
most coastal littoral beaches. The accelerated
coastal erosion reportedly was most pronounced during Tropical Cyclone Bebe in
1972. Many coconut palms and other large
coastal trees were uprooted and serious erosion of topsoil along the inner margins of the
coastal vegetation occurred at that time. This
initial major erosion has been reinforced by
more recent storms and associated high seas.
In the outpost or frontal zone of the littoral beach forest on the southern side of the
island are the trees Cocos nucifera, Hibiscus
tiliaceus, Excoecaria agallocha, Hernandia nymphaeifolia, Thespesia populnea, Calophyllum inophyllum, Cerbera manghas, Pandanus tectorius,
Terminalia catappa, Premna serratifolia, and a
few young individuals of Rhizophora samoensis;
the shrub Clerodendrum inerme; the grasses
Paspalum vaginatum and Lepturus repens; the
sedge Cyperus stoloniferus; and the spreading
Nasoata Island, PABITRA Coastal Study Site in Fiji . Thaman et al.
or climbing vines, Canavalia rosea, Ipomoea pescaprae, Ipomoea macrantha, and Vigna marina.
The southwestern coast vegetation has a similar composition but also includes some isolated individuals or relicts of the original
coastal littoral forest. These include Tournefortia argentea and Xylocarpus moluccensis and
the shrub Scaevola taccada. The only remaining individual of red-flowered mangrove,
Lumnitzera littorea, is also found in the outer
coastal zone along the beach on the southwestern coast of the island. This tree species
was reportedly abundant on the coastal margins of the mangroves in the past, but was
harvested for houseposts. In a number of places the aliens trailing daisy (Wedelia trilobata)
and Para grass (Brachiaria mutica) are successfully outcompeting the indigenous herbaceous
species (e.g., Ipomoea pes-caprae, Canavalia
rosea, and Vigna marina). These introduced
plants constitute a threat to this vegetation
type.
ruderal vegetation. There are
limited areas of ruderal vegetation found
mainly in and around the former Hedstrom
settlement, in well-drained areas formerly
utilized as copra plantations, and in a limited
number of open sites in more well-drained
parts of the island. The former site is dominated by Cocos nucifera in the tree layer with
undergrowth dominated by the grasses Ischaemum indicum and Brachiaria mutica. Occasional weedy species include Mimosa pudica,
Vernonia cinerea, Polygala paniculata, and
Clidemia hirta. In less-open areas, the undergrowth may consist of Annona glabra, Lantana
camara, and other introduced plants, as well
as some members of the inland coastal forest
vegetation. Along the southern front of the
former Hedstrom Estate, the introduced
groundcover Wedelia trilobata has become established. It is now found in about five sites
along the southern coast and constitutes a
threat to the indigenous coastal littoral vegetation and the plants that border the mangrove swamp. Its eradication from the island
is suggested as an immediate priority.
sea-grass beds. There are relatively extensive areas of sea-grass beds located on the
intertidal sand-mud flats and subtidal areas
199
along the oceanside southern coast of the island. The dominant species include Halophila
ovalis, Halodule pinifolia, and Halodule uninervis. The dominant species in the deeper,
sandier subtidal areas off the intertidal flats is
Syringodium isoetifolium, which is also a dominant component of the flotsam and drift deposits along the beaches and in back-beach
basins.
fauna
The fauna of the island and surrounding mud
flats is very rich given the small size of the
island. Particularly important is the rich
avifauna, a number of other vertebrates, arthropods, and other terrestrial invertebrates.
The culturally important crustacean fauna,
shellfish, and many other intertidal marine
invertebrates are present. In-depth studies
have not yet been conducted on the marine
fauna and flora. The subtidal and riverine
areas around the island contain a rich finfish
fauna. Studies focusing on the diverse arthropod fauna are lacking.
Avifauna
Preliminary estimates indicate that there are
at the very least 14 species of land, freshwater,
shore-, and seabirds resident on or visiting
the island (Table 2). Further studies conducted during different times of the year and
at night will undoubtedly add to this list.
Of particular interest is the abundance of
the Pacific black duck, which is commonly
seen in flocks feeding or resting on mudflats,
including about 60 in three flocks counted
from one spot during a lunch break in April
2001. This was the largest number ever seen
at one time in Fiji by resident bird expert
Dick Watling, who has studied birds in Fiji
for over 35 yrs. Also common to occasional
are the collared kingfisher, the wattled honeyeater, and the Vanikoro broadbill. A rather
surprising, perhaps disturbing, observation
was the presence of six individuals of the introduced jungle mynah in the mangroves,
which has been shown to outcompete indigenous birds, especially in disturbed habitats
(Watling 1982).
200
PACIFIC SCIENCE . April 2005
TABLE 2
Land, freshwater, shore-, and seabirds reported present on Nasoata Island and on surrounding mudflats, based on a
survey by D. Watling in April 2001
Fijian Name
Land and freshwater birds
Belō
visakō
gā ni Viti
sōsō
kikau
matayalo, solesole waqa, tina ni uto
mainā
Sea- and shorebirds
kasaga
icō
turı̄
dilio
batibalavu, teitei kai dawa
dilio seasea
juli
Common Name
Scientific Name
Reef heron
Mangrove heron
Pacific black duck
Collared kingfisher
Wattled honeyeater
Vanikoro broadbill
Jungle mynah
Egretta sacra
Butorides striatus
Anas superciliosa
Todiramphus chloris
Foulehaio carunculata
Myiagra vanikorensis
Acridotheres fuscus
Lesser frigatebird
Crested tern
Whimbrel
Pacific golden plover
Bar-tailed godwit
Turnstone
Wandering tattler
Fregata ariel
Sterna bergii
Numenius phaeopus
Pluvialis fulva
Limosa lapponica
Arenaria interpres
Heteroscelus incanus
In terms of Fiji’s shore- and seabird fauna,
the extensive mudflats adjoining the island are
of major interest with respect to Nasoata’s
possible nomination as a conservation area
under the Ramsar Wetlands Convention.
Over 300 waders were observed on these
mudflats in April 2001. Most were wandering
tattlers, which are the last waders to leave
on their northern migration (they leave in
late April or early May). Fiji’s other common
waders, the golden plovers, bar-tailed godwits, and turnstones, already would have
commenced their northern migration, which
accounts for their low numbers at that time.
Also relatively abundant were whimbrels,
seen off the southern beach. If these waders
occur around Nasoata in the same proportion
as they do at Suva Point, where the numbers
are regularly monitored, then peak numbers
in February to March at Nasoata are estimated to be approximately 900–1,000, a very
impressive number by Fijian standards. The
other bird seen in substantial numbers was
the crested tern, of which some 50 were seen
resting on flats adjacent to the island. Two
of these mudflats are quite elevated and concentrate the waders as the tide rises, allowing
them to rest and feed when much of the surrounding flat is submerged.
Other Vertebrates
Reptiles seen on the island include blue-tailed
and copper skinks (Emoia cyanura and Emoia
impar), which were common; the moth skink
(Lipinia noctua); the oceanic gecko (Gehyra
oceanica); and the mourning gecko (Lepidodactylus lugubris). Neither the snake-eyed skink
(Cryptoblepharus eximius) or the green tree
skink (Emoia concolor) were observed but
may well occur. As mentioned above, a juvenile Pacific boa, one of Fiji’s two native land
snakes, was also seen in a coastal tree after a
major flood that swept past the island in August 2001. It has not been seen since.
The only indigenous terrestrial mammals
are nonresident fruit bats (Pteropus tonganus),
which fly from the mainland to feed on the
island. Of concern is the presence of the introduced mongoose (Herpestes auropunctatus),
which is common on the island and is a
major threat to ground-nesting birds and
crabs. Rats (Rattus spp.) may also occur on
the island.
Nasoata Island, PABITRA Coastal Study Site in Fiji . Thaman et al.
Terrestrial Invertebrates
Although formal studies have not been conducted, preliminary studies conducted by a
PABITRA team in November 2002 indicate
that there is a relatively diverse terrestrial
invertebrate fauna. This includes a range of
centipedes and millipedes, spiders, butterflies,
moths, stick insects, grasshoppers, beetles,
flies, bees, wasps, ants, and other insects, most
of which have important ecological roles
on the island. The wide range of specimens
collected in 2002 still awaits identification.
Marine Fauna
The most immediately obvious components
of the marine fauna are the economically and
culturally important crustaceans that abound
on the island. Most notable is the mangrove
or mud lobster or manā (Thalassoma anomala),
which is caught using an ingenious traditional
snaring system. It is in season between December and April and sold at local urban markets as an important source of income. There
are two species of mangrove crabs, the redclawed mangrove crab or kuka damu (Sesarma
erythrodactyla) and the black mangrove crab,
kuka vulu or uka loa (Metapograpsus messor).
There is also the larger mud crab, qari (Scylla
serrata). These three crab species are common in the mangrove habitats. In addition,
the land crab, lairo or tubā (Cardisoma carniflex), is found in more well-drained sites. All
of these species are hunted in season and
sold at local markets as an important source
of cash income. Commonly caught prawns
or shrimp include ura (Penaeus spp.), kadikadi
(Macrobrachium equidens), and moci (Palaemon
concinnus). These species are also sold. The
rock crab, taqara (Grapsus albolineatus); the
box crab, cugavotu (Calappa hepatica); and a
number of species of fiddler crabs, toto (Uca
spp.), and hermit crabs, uga (Ceonobita spp.)
occur along the coastline or on the mudflats.
The latter is considered a preferred bait
species for line fishing. Penaeid prawns or
shrimps (Penaeus spp.) are common on the
reef flat and are seasonally caught for local
consumption and sale.
201
Commonly collected mangrove-associated
shellfish include mangrove oysters, dio (Crassostrea mordax); nerite snails, sisici or telei
(Nerita spp.); periwinkles, sisi ni veidogo (Littorina scabra); sponge-finger oysters, drivi
(Vulsella vulsella); mangrove mussels, kuku
(Modiolus agripetus); and saddle tree oysters,
civaciva (Isognomon ephippium). These are not
commonly sold and are used mainly for subsistence. Other edible shellfish found on the
mudflats include ark shells, kaikoso (Anadara
antiquata) and kaibakoko (Codakia spp.); venus
clams, qeqe or qaqa (Gafarium tumidum); and
moon snails, drevula (Polynices spp.). Also
common on the mudflats are lamp shells, ivoce
(Lingula unguis); peanut worms, ibo (Siphonosoma australe); and the sandfish or dairo, a species of bêche-de-mer (Metriatyla scabra).
Commonly caught finfish include qitawa
(Terapon jarbua); ki (Upeneus vittatus); kaikai
(Gazza minuta and Leiognathus equulus); kake
(Lutjanus fulviflamma); matu (Gerres spp.);
damu (Lutjanus bohor); kurukoto (Eleotris melanosoma); kawakawa (Epinephelus spp.); nuqa
(Siganus spp.); kabatia (Lethrinus harak); kanace (Crenimugil crenilabi, Valamugil saheli);
molisā (Liza melinoptera or small mullet); and
freshwater eels, duna (Anguilla marmorata)
(Thaman 1998). Some of these fish are sold,
although most are consumed in the local
communities. The mudskipper, tidrai (Periophthalmus argentimaculatus), is also common
but not eaten.
conclusions
The observations made during seven trips to
Nasoata Island in 2001 and 2002 have confirmed Nasoata as a prime mangrove study
site, which offers a wide range of opportunities to conduct controlled studies of the
mangrove ecosystem and other associated terrestrial, riverine, and marine ecosystems surrounding the island. The island constitutes
a good example of a ‘‘classical’’ Rewa Delta
mangrove ecosystem with fringing tiri (Rhizophora spp.) and extensive mature stands of
dogo intertidal swamp forest (Bruguiera gymnorrhiza), known as Bolavou Swamp. Scattered throughout the island, mostly on the
202
southern margins of Bolavou Swamp, are
slightly raised areas with impressive stands of
dabi (Xylocarpus granatum) and Heritiera littoralis. This mangrove swamp forest is as impressive as any seen anywhere in Fiji. With
the exception of reported widespread removal
of Lumnitzera littorea (now a critically threatened species on the island), the current use
of the island seems to be on the whole nondestructive. Overall the mangroves look almost untouched, whereas many similar areas
on mainland Viti Levu have had some logging. However, Nasoata was never included
in the Forestry Department’s plan for the exploitation of timber and firewood in the Rewa
mangroves.
There are a number of introduced plant
species that have been shown to have been
highly invasive in other areas of Fiji. These
include the trailing daisy (Wedelia trilobata),
which was seen in five locations on the
southern coast of the island. This plant has
invaded mangroves, river courses, and coastlines on mainland Fiji and other areas in the
Pacific Islands and could become one of the
most invasive weeds in the Pacific Islands. It
could lead to serious ecological disturbance,
particularly on small offshore islands and in
mangrove ecosystems. The pond apple (Annona glabra) is naturalized in limited areas
of back-beach swamps on the southeastern
portion of the island, where it now forms almost monospecific stands of large trees. Also
of concern is a member of the pepper family,
the hooked pepper bush, Piper aduncum. It
is currently uncommon but has become a serious weedy large shrub in coastal areas elsewhere in Fiji. Para grass (Brachiaria mutica) is
dominant on a couple of beach terraces on
the south-central and southwestern portions
of the island and is outcompeting the herbaceous outpost vegetation along beaches. Also
of concern are the introduced mongoose
and the jungle mynah bird, which could lead
to the collapse of populations of some native
vertebrate and invertebrate animals. Concerted attempts should be made to eradicate
or control these pest species so that they do
not become ecologically dominant or destructive on the island.
PACIFIC SCIENCE . April 2005
In short, Nasoata Island is an accessible,
complex mangrove ecosystem with associated
terrestrial, freshwater, and marine ecosystems. It is ideally located at the extreme
southeastern end of the PABITRA Gateway
Transect, which extends from cloud forest
to mangrove and coral reef ecosystems. The
PABITRA Gateway Transect includes Fiji’s
largest river system, the Rewa River and its
upstream catchments and lower delta, as an
integrated system. The high level of terrestrial, freshwater, and marine biodiversity,
including the presence of some introduced,
potentially invasive species, also adds to the
value of the PABITRA landscape for the
study of interacting ecosystems. The fact
that the island is seen by the local user communities as their ‘‘breadbasket’’ (ikanakana)
and is currently being used in what appears
to be a sustainable manner, adds an important
human dimension, so central to the PABITRA philosophy. Finally, the strong support
from the local communities, who are responsible for caring for and using the island, for
the designation of the area as a conservation
site and scientific study area further adds
to the importance of Nasoata Island as an
integral component of the Fiji PABITRA
Gateway Transect. This also underlines its
suitability for designation as a priority site
for protection under the Ramsar Wetlands
Convention.
Literature Cited
Smith, A. C. 1979. Flora Vitiensis nova: A
new flora of Fiji (spermatophytes only).
Vol. 1. Pacific Tropical Botanical Garden,
Lāwa‘i, Kaua‘i, Hawai‘i.
Thaman, B. 1998. Community utilisation and
valuation of mangrove resources in Fiji:
Case studies of Sawa, Daku and Nadoria
Villages and Kinoya and Tamavua-i-wai
urban settlements, Viti Levu, Fiji. M.S.
thesis, James Cook University of North
Queensland, Townsville, Australia.
Watling, D. 1982. Birds of Fiji, Tonga and
Samoa. Millwood Press, Wellington, New
Zealand.
Nasoata Island, PABITRA Coastal Study Site in Fiji . Thaman et al.
203
Appendix
Field Checklist of the Flora of Nasoata Island, Rewa Delta, Rewa Province, Viti Levu, Fiji Islands
Pteridophyta (Ferns and Fern Allies)
Aspleniaceae (Spleenwort Fern family)
Asplenium nidus L., bird’s-nest fern
Blechnaceae (Water Fern family)
Stenochlaena palustris (Burm.) Beddome, swamp or
mangrove fern
Davalliaceae (Hare’s-Foot Fern family)
Davallia fejeensis Hooker, Fiji hare’s-foot fern
Davallia solida (Forst. f.) Swartz, hare’s-foot fern
Nephrolepidaceae (Sword Fern family)
Nephrolepis biserrata (Sw.) Schott, fishtail fern
Nephrolepis hirsutula (Forst.) Presl., sword fern,
fishtail fern
Polypodiaceae (Polypody Fern family)
Drynaria rigidula (Sw.) Bedd., basket fern
Phymatosorus grossus (Langsd. & Fisch.) Brownlie,
scented fern
Pyrrosia lanceolata (L.) Farwell, lanceolate felt fern
Psilotaceae (Psilotum family)
Psilotum nudum (L.) Beauv., psilotum, reed fern,
whisk fern
Pteridaceae (Brake Fern family)
Acrosticum aureum L., swamp fern, mangrove fern
Pteris tripartita Sw., lacy fern, sword brake
Vittariaceae (Tape Fern family)
Vaginularia angustissima (Brack.) Mett., grass fern
Vittaria elongata Swartz, tape fern
Schizaeaceae
Schizaea dichotoma (L.) Sm., branched comb ferm
Angiospermae (Angiosperms)
Monocotyledonae (Monocots)
Agavaceae (Century Plant family)
*Cordyline fruticosa (L.) A Chev., cordyline, ti
(Hawai‘i)
Araceae (Arum family)
Epipremnum pinnatum (L.) Engl., taro vine
Arecaceae or Palmae (Palm family)
Cocos nucifera L., coconut palm
Commelinaceae (Spiderwort family)
**Commelina diffusa Burm. f., day flower
Cymodoceaceae (Cymodocea family)
Halodule uninervis (Forssk.) Aschers, sea grass
Halodule pinifolia (Miki) den Hartog, sea grass
Syringodium isoetifolium (Aschers.) Dandy, turtle
grass
Cyperaceae (Sedge family)
**Cyperus rotundus L., nut sedge, nut grass
Cyperus stoloniferus Retz., beach sedge
Mariscus javanicus (Houtt.) Merr., marsh sedge
Scirpodendron ghaeri (Gaertn.) Merr.
Scleria polycarpa Boeck.
Dioscoreaceae (Yam family)
*Dioscorea bulbifera L., bitter yam, air yam, aerial
yam, air potato
Hydrocharitaceae
Halophila ovalis (R. Br.) Hook f., salt-loving sea
grass
Orchidaceae (Orchid family)
Appendicula reflexa Bl.
Grammatophyllum elegans Reichenb. f.
Oberonia heliophila Reichenb. f.
Taeniophyllum fasciola (Forst. f.) Seem.
Pandanaceae (Pandanus family)
Pandanus tectorius Warb., pandanus, screw pine
Poaceae or Graminae (Grass family)
*Arundo donax L., reed
*Brachiaria mutica (Forsk.) Stapf, para grass,
Mauritius grass
Centotheca lappacea (L.) Desv.
*Ischaemum indicum (Houtt.) Merr., Batiki blue
grass
Lepturus repens (G. Forst.) R. Brown, beach
bunch grass
**Oplismenus compositus (L.) Beauv., basket grass
Miscanthus floridulus (Labill.) Warb., sword grass
Paspalum vaginatum Sw., knot grass, salt grass,
swamp couch grass
Sporobolus cf. elongatus (Retz.) Beauv.?, wiregrass
Stenotaphrum micranthum (Desv.) Hubb.
Thuarea involuta (Forst. f.) R. Br. ex R. & S.
Taccaceae (Polynesian Arrowroot family)
*Tacca leontopetaloides (L.) O. Kuntze, Polynesian
arrowroot
Zingiberaceae (Ginger family)
*Zingiber zerumbet (L.) Sm., wild ginger
Dicotyledonae (Dicots)
Anacardiaceae (Cashew or Rhus family)
*Mangifera indica L., mango
Annonnaceae (Custard Apple Family)
**Annona glabra L., pond apple
Apiaceae (Parsley family)
*Centella asiatica (L.) Urban, Asiatic pennywort
Apocynaceae (Dog-bane family)
Cerbera manghas L., cerbera
*Plumeria rubra L., frangipani, plumeria
Asclepiadaceae (Milkweed family)
Hoya australis R. Br. ex Traill, wax vine
Asteraceae (Sunflower family)
**Mikania micrantha Kunth, mile-a-minute, milea-minute vine
**Vernonia cinerea (L.) Less., iron weed
*Wedelia trilobata (L.) Hitchc., wedelia, trailing
daisy
Wollastonia biflora (L.) DC., beach sunflower
Barringtoniaceae (Barringtonia family)
Barringtonia asiatica (L.) Kurz., fish-poison tree,
barringtonia
Barringtonia racemosa (L.) Spreng.
Boraginaceae (Borage family)
Cordia subcordata Lam., sea trumpet, kou (Hawai‘i)
Tournefortia argentea L. f., beach heliotrope
Caricaceae (Papaya family)
*Carica papaya L., papaya, papaw
Clusiaceae or Guttiferae (Mangosteen family)
Calophyllum inophyllum L., Alexandrian laurel,
beach mahogany
204
PACIFIC SCIENCE . April 2005
Appendix (continued)
Combretaceae (Terminalia family)
Lumnitzera littorea ( Jack) Voigt, red-flowered
black mangrove
Terminalia catappa L., tropical almond, Malabar
almond
Terminalia littoralis Seem., beach or coastal
almond
Convolvulaceae (Morning-Glory family)
Ipomoea littoralis Bl., littoral morning-glory
Ipomoea macrantha R. & S., wild moon flower;
white morning-glory
Ipomoea pes-caprae (L.) Sweet subsp. brasiliense (L.)
v. Ooststr., beach morning-glory
Euphorbiaceae (Spurge family)
*Codiaeum variegatum (L.) Bl., croton
Excoecaria agallocha L., blinding tree, poison
mangrove tree
Glochidion concolor Muell. Arg.
Macaranga seemannii (Muell.-Arg.) Muell.-Arg.,
macaranga
*Manihot esculenta Crantz, cassava, manioc,
tapioca
Fabaceae (Pea family)
Caesalpinia bonduc Roxb., beach nicker, gray
nicker, nicker bean
Canavalia cathartica Thou., Mauna Loa bean
(Hawai‘i)
Canavalia sericea A. Gray
Canavalia rosea (Sw.) DC., sea bean
Dalbergia candenatensis (Dennst.) Prain
*Derris malaccensis (Benth.) Prain, root, New
Guinea creeper
Derris trifoliata Lour., derris vine, derris root
**Desmodium heterophyllum (Willd.) DC.
Entada phaseoloides (L.) Merr., vine, St. Thomas
bean
Erythrina variegata var. orientalis (L.) Merr., coral
tree, dadap
Inocarpus fagifer (Parkinson) Fosb., Polynesian
chestnut, Tahitian chestnut
Intsia bijuga (Colebr.) O. Ktze., ipil tree
*Leucaena leucocephala (Lam.) de Wit, leucaena,
lead tree, jumbie tree
**Mimosa pudica L, sensitive plant, sensitive grass
Pongamia pinnata (L.) Merr.
*Samanea saman ( Jacq.) Merr., raintree,
monkeypod
Vigna marina (Burm.) Merr., beach pea, beach
bean, vigna
Goodeniaceae (Naupaka family)
Scaevola taccada (Gaertn.) Roxb, beach saltbush,
half-flower
Hernandiaceae (Hernandia family)
Hernandia nymphaeifolia (Presl.) Kubr., lantern
tree, hernandia
Lamiaceae or Labiatae (Mint family)
**Hyptis pectinata (L.) Poit., mint weed, wild mint,
purple top
Lauraceae (Laurel family)
Cassytha filiformis L., beach dodder, devil’s twine
Malvaceae (Mallow family)
Hibiscus tiliaceus L., beach hibiscus, hibiscus tree
**Sida rhombifolia L., broomweed, broom plant,
Cuba jute
Thespesia populnea (L.) Sol. ex Correa, Thespians
tree, milo (Hawai‘i and Polynesia)
Melastomataceae (Melastoma family)
**Clidemia hirta (L.) Don, Koster’s curse
Meliaceae (Mahogany family)
Dysoxylum richii (A. Gray) C. DC., stinkwood
Xylocarpus granatum Koenig, puzzlenut
Xylocarpus moluccensis (Lam.) M. Roemer,
puzzlenut
Moraceae (Mulberry family)
Ficus barclayana (Miq.) Summerhayes, Barclay’s
fig
Ficus vitiensis Seem., Fiji fig
Loganiaceae (Strychnine family)
Geniostoma vitiense Gilg & Benedict
Passifloraceae (Passion Flower family)
*Passiflora laurifolia L., bell apple, laurel-leaved
passionfruit
**Passiflora maliformis L., hard-shelled
passionfruit
Piperaceae (Pepper family)
**Piper aduncum L., hooked pepper bush
Polygalaceae (Polygala family)
**Polygala paniculata L.
Rhamnaceae (Buckthorn family)
Colubrina asiatica (L.) Brongn., soapbush, hoop
withe
Smythea lanceata (Tul.) Summerhayes
Rhizophoraceae (Mangrove family)
Bruguiera gymnorrhiza (L.) Lam. f., black
mangrove, oriental mangrove
Rhizophora samoensis (Hochr.) Salvoza, mangrove
Rhizophora stylosa Griff., mangrove
Rubiaceae (Coffee family)
Morinda citrifolia L., beach mulberry, Indian
mulberry
**Mitracarpus hirtus (L.) DC.?
Tarenna sambucina (Forst. f.) Dur. ex Drake
Sterculiaceae (Cocoa family)
Heritiera littoralis Ait., looking-glass tree
Tiliaceae (Linden family)
**Triumfetta rhomboidea Jacq., Chinese burr
Verbenaceae (Verbena family)
Clerodendrum inerme L., beach privet
**Lantana camara L. var. aculeata (L.) Mold.,
lantana
Premna serratifolia L., premna
**Stachytarpheta urticaefolia Sims, blue rat tail,
false verbena
Vitex trifolia L. var. trifolia, blue vitex, beach
vitex
*, Species that are considered to be nonindigenous but of deliberate introduction by humans. **, Species that are assumed to be
either accidental introductions or nonindigenous species that made it to the island naturally through either river or animal dispersal
(e.g., bird or fruit bat).