Plant strategies, dispersal and origins of flora at the northern
Coral Sea Islands Territory, Australia
George N. Batianoff1, Gillian C. Naylor, Hans A. Dillewaard and V. John Neldner
Queensland Herbarium, Department of Environment and Resource Management, Mt Coot-tha Botanic Gardens, Mt Coot-tha Road,
Toowong, QLD 4066. Correspondence to: john.neldner@derm.qld.gov.au 1Deceased, see page 121
Abstract: A checklist of vascular plants of Coringa-Herald National Nature Reserve (CHNNR) (17º 11’S, 149º 00’
E to 16º 23’S, 150º 30’E and Willis Island (16º 24’S, 149º 58’E) at the northern Coral Sea Islands Territory of Australia
compiled during 2006/07 surveys, recorded 30 species including 18 species indigenous to the Coral Sea Islands
(60%), 10 exotic species (33%) and two that were planted (7%). Plant life-forms included: 5 species of trees and tall
shrubs (17%), 2 species of low shrubs (6.5%), 21 herbs (70%), and 2 vine/creepers (6.5%). Plant dispersal for the 30
species is predominantly by human activities (40%), ocean currents (33%) and seabirds (27%). The garden species
and dispersal modes at Willis Island indicate that non-residential casual human visitation at CHNNR has at present
had little effect on establishment of exotic weeds.
Resilience of leverage lora, loristic diversity and species origins of CHNNR are discussed in relation to its connectivity
with the Melanesian region due to the South Equatorial Current operating in the region. Colubrina asiatica was
recorded as a new record for oceanic islands in Australian territories. Previously recorded Ximenia americana and
Digitaria ctenantha are considered locally extinct. Pattern analyses indicate that cays of similar size and vegetation
structure are the most similar in loristic composition. Willis Island lora is relatively dissimilar to the CHNNR cays,
due to the inluence of anthropogenic activities associated with a staffed weather station.
Key words: coral cay, leverage lora, loristic diversity, species origins, naturalised species and similarity indices.
Cunninghamia (2009) 11(1): 97–106
Introduction
Relative to their isolated offshore location, Coringa-Herald
National Nature Reserve (CHNNR)) and Willis Island are
‘hot spots’ of terrestrial and marine wildlife within the
northern Coral Sea Islands Territory (Jaensch et al. 2002).
These islands are considered some of the most signiicant
nesting sites in Australia for 14 species of seabirds (Hicks
1985; Jaensch et al. 2002). These islands also provide critical
breeding habitat for colonies of the green turtle (Chelonia
mydas). The study area is an important stepping stone
between the Great Barrier Reef and the broader Melanesian
and Western Paciic regions. The drift seed lora of CHNNR
and Willis Island is linked to the Melanesian region by the
prevailing east–to–west South Equatorial Current and the
predominant east to south-easterly trade winds (Farrow,
1984; Bureau of Meteorology, 2008).
The terrestrial vegetation of coral cays provides signiicant
services for the physical and ecological balances of
the islands. Plants trap moving sand particles and form
relatively stable elevated surfaces, which are important for
the development of coral cay landscapes (Batianoff 2001a).
Cunninghamia: a journal of plant ecology for eastern Australia
www.rbgsyd.nsw.gov.au/science/Scientific_publications/cunninghamia
Plants also provide shade, shelter and breeding habitats for a
variety of wildlife (Batianoff 2000). Hicks (1985) observed
that cays with complex vegetation have a greater diversity
of breeding seabirds and invertebrate fauna. At CHNNR,
70% of the seabird species may utilise forest vegetation for
breeding (Batianoff et al. 2009).
The main objectives of this paper are to analyse the lora of
the northern Coral Sea Islands, list leverage lora and discuss
plant species strategies that assist resilience and survival.
The loras of the CHNNR and Willis Island are compared
with previous surveys to assess changes over time and
implications for future management.
Methods
The Study Area
Coringa-Herald National Nature Reserve (CHNNR) and
Willis Island are situated approximately 440km east of
Cairns within the Queensland Plateau subregion of the Coral
© 2009 Botanic Gardens Trust
98
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Fig. 1. Coringa-Herald National Nature Reserve and Willis Island in the northern Coral Sea Islands Territory.
Sea (Figure 1). The cays are considered ‘low islands’ with
a maximum elevation of 5–6 m for the CHNNR islands
(Heatwole 1979; ANPWS 1989), and 8–9 m for Willis
Island (Farrow 1984). The CHNNR was proclaimed by
the Commonwealth of Australia as part of the Coral Sea
National Nature Reserves in 1982. The ive permanently
vegetated islands within the CHNNR are located between
17º 11’S, 149º 00’E to 16º 23’S, 150º 30’E. Willis Island
(16º 24’S, 149º 58’E) to the north of the CHNNR islands
is a relatively small cay and has had a manned Australian
Bureau of Meteorology weather station since 1921. The
total terrestrial island area is estimated at about 150ha, with
North East Herald Cay the largest cay studied (52 ha), and
Willis Island the smallest (7.7 ha). Area estimates for the
other islands surveyed are: South West Herald Cay (18.8ha),
Chilcott Islet (16.3 ha), South West Coringa Islet (17.3 ha)
and South East Magdelaine Cay (37.0 ha).
Fig. 2. Percentage of flora dispersed by each agent type, northern Coral Sea Islands (All species total 30, Willis total 21, CHNNR 17).
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Table 1. Terrestrial plants species recorded (2006/07) at
Coringa-Herald National Nature Reserve and Willis Island
Species: * naturalised species considered not native to Australia; #
planted/not naturalised.
Life forms (LF): Ha annual herbs; Hp perennial herbs; V vines; ST
tall shrubs/small trees (2–5m); T trees (>2m).
Dispersal DM): A human activity/anthropochory; O ocean currents/
hydrochory; V vegetative; W wind/anemochory; Z animal/
zoochory.
Islands: 1 NE Herald Cay; 2 SW Herald Cay; 3 Chilcott Islet; 4
SW Coringa Islet; 5 SE Magdelaine Cay; 6 Willis Island
Occurrence: a abundant (>30% cover/sites); f frequent (15–30%
over/sites); i infrequent (<15% cover/sites); r rare (<1% cover/
sites); ? possibly present; – not recorded during surveys.
The northern Coral Sea Islands Territory experiences a
tropical, maritime climate with distinctly seasonal rainfall,
stable annual temperatures and high evaporation rates (Farrow
1984; Neil & Jell 2001; Batianoff et al. 2009). Annual rainfall
at Willis Island (1115 mm) occurs predominantly during the
four ‘wet’ months of January to April with a ‘dry’ period
lasting from May to November. Drought periods lasting
between 1 and 5 years have also been recognised (Batianoff
et al. 2009). The mean monthly ambient temperature ranges
from a minimum of 21.9ºC in July to a maximum of 30.7ºC
in January with little diurnal variation between day and night
(Bureau of Meteorology 2008).
Data collection
Nineteen ield days were undertaken over two ‘dry seasons’
on three separate trips. (November–December 2006, May
2007, October 2007). North East Herald Cay was the most
comprehensively studied, with Willis Island receiving only
two hours for sampling.
A list of plant species were compiled for each island together
with loristic attributes such as genus, family, life-form and
dispersal modes and abundance. Plants that provide major
ecosystem services and determine island vegetation structure
were listed under the terminology of coral cay ‘leverage’
species. Previous botanical reports for the Coral Sea Islands
Territory (Heatwole 1979; Hicks & Hinchey 1984; Hicks
1985; Telford 1993a; Batianoff 2001a) were compared to
assess loristic changes over time and to identify erroneous
and anomalous recordings. Plant voucher specimens
collected during surveys were incorporated into the
Queensland Herbarium (BRI) collection. The BRI specimen
database (HERBRECS 2008) was utilised extensively to
verify dates and locations of previous botanical collections.
PATN analysis was used to determine dissimilarity between
island loras based on the frequency of species found on each
cay. The frequency data were classiied using a hierarchical
agglomerative polythetic clustering method based on lexible
unweighted pair-group averages method (Belbin 2004).
99
CHNNR Islands Willis
Family/Species
LformDisp 1
2
3
4
5
6
AIZOACEAE
*Trianthema
portulacastrum
Ha
AZ
–
–
–
–
–
r
AMARANTHACEAE
Achyranthes aspera
Ha/p
*Alternanthera pungens Ha
*Amaranthus viridis
Ha
Z
AZ
AZ
a
–
–
a
–
–
a
–
–
a
–
–
a
–
–
i
?
i
ARECACEAE
@#
Cocos nucifera
T
AO
–
–
–
–
–
r/i
ASTERACEAE
*Tridax procumbens
Ha
AW
–
–
–
–
–
r
ST
ST
O
OV
f
f
f
–
f
r
f
i
f
i
f
–
O
i
i
i
i
i
?
AOW –
–
–
–
–
r
CONVOLVULACEAE
Ipomoea macrantha
Vp
Ipomoea pes–caprae Hp
subsp. brasiliensis
OZ
O
f
–
f
–
a
–
a
–
f
–
–
i
EUPHORBIACEAE
*Chamaesyce prostrata Ha
#
*Euphorbia
Ha/p
cyathophora
AZ
AZ
–
–
–
–
–
–
–
–
–
–
i
f
–
–
–
–
i/f
–
BORAGINACEAE
Argusia argentea
Cordia subcordata
BRASSICACEAE
Lepidium englerianum Ha
CASUARINACEAE
#
Casuarina equisetifolia T
subsp. equisetifolia
FABACEAE
Canavalia rosea
V/Hp O
MALVACEAE
Abutilon albescens
S
ZWO a
f
f
f
f
i
NYCTAGINACEAE
Boerhavia albilora
Boerhavia mutabilis
Pisonia grandis
Hp
Hp
T
f
i
a
a
–
–
f
–
–
f
i/f
–
f
i
f
PLUMBAGINACEAE
Plumbago zeylanica
Z
Z
ZV
a
–
–
Hp
Z
–
i/f
i/f
f
i/f
–
Ha
Hp
Ha/p
AZ
AVZ
AV
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
i
i
f
Ha
Ha/p
Hp
Ha/p
AZ
OZV
OZV
OV
–
i/f
f
i
–
i
f
i
–
f
i
i/f
–
f
–
–
–
f
f
i
i
f
f
?
Ha/p
ZO
i/f
i/f
i
i
i
i
S
O
–
–
–
–
r
–
ZO
f
f
f
f
f
14
12
13
12
17
i/f
POACEAE
*Cenchrus echinatus
#
*Cynodon dactylon
*Dactyloctenium
aegyptium
*Eleusine indica
Lepturus repens
Sporobolus virginicus
Stenotaphrum
micranthum
PORTULACACEAE
Portulaca oleracea
RHAMNACEAE
Colubrina asiatica
ZYGOPHYLLACEAE
Tribulus cistoides
Ha/p
TOTAL
17 families, 28 genera,
30 species
–
–
21
*10
100
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Results
Floristic appraisal
The regional lora for CHNNR and Willis Island lora
including exotic species comprises 30 species in 17
families and 28 genera (Table 1). The dominant group are
the dicotyledons (72%), represented by 15 families, 20
genera and 22 species. The monocotyledons (28%) were
represented by two families (8 genera and 8 species). The
family Poaceae was represented by seven species (23%)
including four exotics. Poaceae and Nyctaginaceae have the
highest proportion of indigenous species with 3 species each.
Naturalised populations of exotic species were found only
on Willis Island. There were 10 species (table 1), two of
which (Cynodon dactylon and Euphorbia cyathophora) have
been deliberately introduced and planted on Willis Island.
Alternanthera pungens was recorded as a common weed at
Willis Island in March 1995 (Donaldson 1995) and though it
was not recorded during the October/November 2007 survey,
it is a persistent annual herb and is most likely still present
on this island. With the exception of Cynodon dactylon
and Dactyloctenium aegyptium, which are perennial grass
species, the remaining eight exotic species are all short-lived
herbs that produce large amounts of viable seed.
Cocos nucifera and Casuarina equisetifolia subsp.
equisetifolia are Australian tree species that have also been
planted on Willis Island as part of a landscaping program but
are not considered to be naturalised. During our October–
November 2007 visit, three young individuals of Cocos
nucifera were recorded establishing outside the landscape
compounds of the meteorological station. No naturalised
individuals of Casuarina equisetifolia were recorded away
from the two patches of planted trees.
Apart from naturalisations, there is considerable evidence
of turnover among the islands’ loras. During the 2007
survey, Colubrina asiatica, a seashore shrub species widely
distributed along Western Paciic seashores including
Australia (Ridley 1930), was recorded for the irst time in
the northern Coral Sea Islands Territory (on SE Magdelaine
Cay). Other new records for individual islands within
CHNNR were Cordia subcordata (recorded on SW Coringa
Islet), Stenotaphrum micranthum (at SW Herald Cay and
Chilcott Islet), Boerhavia mutabilis (at Chilcott Islet and
SE Magdelaine Cay), and Sporobolus virginicus (at SE
Magdelaine Cay).
Two previously recorded plant species now considered
locally extinct from CHNNR are.
•
Digitaria ctenantha, a tropical annual grass has been
previously collected at SE Magdelaine Cay (S. Hogg –
May 1984, T. Scotney – October 1987, and I. Telford
– 1989), Willis Island (S. Donaldson – March 1994) and
NE Herald Cay (G. Batianoff – June 1997). It was not
found on any island during the 2006 and 2007
surveys.
•
Ximenia americana irst recorded at NE Herald Cay by
J. Hicks (December 1983) as a small tree (Du Puy
& Telford, 1993c). In December 1991, I. Telford
recorded Ximenia americana at the same location,
describing one large shrub and several small shrubs. In
June 1997, G. Batianoff recorded 10 individuals of
different ages (Batianoff, 2001b). By the time the
2006 and 2007 surveys were undertaken, the entire
Ximenia americana population had died, with only the
dry stems remaining.
Recordings of species from previous surveys now considered
erroneous are given in Table 2. For example the saltmarsh
species Suaeda australis has been listed for Chilcott Island
in the two Management Plans (ANPWS 1989; Environment
Australia 2001), but is not recorded on any other Australian
Oceanic Islands, and according to Telford (1993b) is
erroneous.
Plant life-forms include trees, shrubs, vine/creepers
and prostrate herbs. 21 species (70%) are herbaceous
groundcover species, including 15 (50%) annuals and 12
(40%) with leshy foliage. Five species (17%) are tall shrubs
and/or trees, including the large Pisonia grandis tree; two are
low shrubs, and two are creeper/vine species.
Table 1 lists the regional dispersal modes of the 30
species. Overall 40% are dispersed by human activities
(anthropochory), 33% by ocean currents (hydrochory) and
27% by seabirds (zoochory). 21 species (70%) are adapted
for more than one mode of dispersal (Figure 2). Of the 17
indigenous species found at CHNNR (Table 1), 9 species
(53%) are primarily dispersed by ocean currents, and 8
(47%) by seabirds; no species are primarily dispersed by
humans. Most of the Willis Island lora is dispersed by
human activities (57%). Seabirds and ocean currents account
for 24% and 19% respectively.
Individual island species composition and similarity
Indigenous plant species richness for CHNNR individual
cays ranges from 12 species at SW Herald Cay and SW
Coringa Islet, to 17 at SE Magdelaine Cay (Table 1). With
the exception of Ipomoea pes-caprae subsp. brasiliensis
(which occurs only on Willis Island), SE Magdelaine Cay
has all of the native species currently recorded at CHNNR.
SW Coringa Islet has the lowest species richness relative to
its size. Although indigenous species richness compared to
Australian mainland islands is low (Batianoff & Dillewaard
1997), the biodiversity at the generic and family levels is
high, as indicated by the low species per genus and family
ratios (1.1 spp./genus and 1.7 spp./family).
The loras on these cays constitute distinctive assemblages
that share a close similarity (Figure 3). Chilcott Island and
SW Herald Cay have the closest association with almost
identical species compositions and abundances. Cordia
subcordata, found on Chilcott Island is the only species
that differentiates the species composition of Chilcott Island
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
101
Table 2. Erroneous recordings in previous reports of flora of Coringa-Herald National Nature Reserve
Species
Comments
Caesalpinia bonduc (Caesalpiniaceae)
Seedlings recorded at NE Herald (Telford, 1993a). Transient drift seed species, seedlings at NE
Herald were removed by nesting green turtles.
Suaeda australis (Chenopodiaceae)
Listed for CHNNR – Chilcott?! (Environment Australia, 2001). According to Telford (1993a), the
record is erroneous.
Calophyllum inophyllum (Clusiaceae)
Terminalia spp. (Combretaceae)
Ipomoea pes-caprae (Convolvulaceae)
Collected by Heatwole at the Herald Cays in September, 1967. Listed by Telford (1993a). Not
reported in subsequent botanical surveys at NE Herald or SW Herald Cays. This transient drift seed
species is now presumed locally extinct.
Seedlings of drift seed plants recorded by Batianoff (2001a) on the shores of NE Herald. The
seedlings were removed by nesting green turtles.
Listed by Telford (1993a) for Turtle I., Lihou Reef. Listed by Environment Australia (2001) for
CHNNR. Recorded as seedlings at NE Herald by Batianoff (2001a). Not recorded in subsequent
surveys at NE Herald. I. pes-caprae is well established at Willis Island.
Erythrina spp. (Fabaceae)
Seedlings of drift seed plants were recorded by Batianoff (2001a) at NE Herald. However, seedlings
were removed by nesting Green Turtles.
Scaevola taccada (Goodeniaceae)
Transient seashore shrub (Telford, 1993a). According to M. Hallam (1997, pers. comm.),
Scaevola taccada had established at NE Herald in the mid-1990s but died out three years after its
establishment.
Hibiscus tiliaceus (Malvaceae)
Boerhavia diffusa (Nyctaginaceae)
Boerhavia glabrata (Nyctaginaceae)
Boerhavia tetrandra (Nyctaginaceae)
Commicarpus chinensis (Nyctaginaceae)
Commicarpus insularum (Nyctaginaceae)
Thuarea involuta (Poaceae)
Listed by Batianoff (2001a) at NE Herald as a drift seed only.
Listed by Heatwole (1979). Misapplied name for Boerhavia mutabilis.
Listed by Telford (1993a). Misapplied name for Boerhavia mutabilis.
Listed by ANPWS (1989) and Environment Australia (2001). Misapplied name for B. albilora var.
albilora.
Listed by Heatwole (1979). This species not found in Queensland, its pink lowers are similar to
Boerhavia mutabilis.
Listed by Heatwole (1979) and Telford (1993a). Not reported in subsequent botanical surveys.
Listed in Environment Australia (2001) at CHNNR. Listed by Telford (1993a) as a doubtful record.
Fig. 3. Fusion dendrogram of Coringa-Herald National Nature Reserve and Willis Island flora associations based on PATN analysis (Belbin
2004). Notes: NEH, NE Herald Cay; SWH, SW Herald Cay; CI, Chilcott Islet; SWC, SW Coringa Islet; SEM, SE Magdelaine Cay; WI,
Willis Island.
102
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Table 3. Ecological notes on leverage coral cay species at Coringa-Herald National Nature Reserve and Willis Island
Species
Colonisation patterns
Ground layer
Lepturus repens (beach lepturus)
Ocean dispersed tropical beach grass; widespread annual and/or short-lived grass; major component
of littoral herbfields (Telford 1993b; Batianoff 2001b); persists in the interior with in Abutilon
shrublands and herblands.
Boerhavia albiflora var. albiflora
Bird dispersed; widespread prostrate perennial herb; persists under cover of Abutilon and Argusia
(white flowered tar vine)
communities; occurs mainly in the interior herbfields (Telford 1993b; Batianoff 2001a).
Sporobolus virginicus (sand couch)
Ocean dispersed; widespread perennial grass of littoral margins and seepage areas, including brackish
water; persists within interior communities (Telford 1993b; Batianoff 2001a).
Shrub layer
Possibly bird, wind and ocean dispersal; widespread shrub, 0.5– 2m tall; mainly in the interior of
Abutilon albescens (coastal lantern flower) Argusia fringe; dominant heathlands/shrublands (Batianoff 2001a) common within Pisonia glades
(Batianoff et al. 2009).
Tree layer
Ocean dispersed; widespread tree 2–6m; halophyte, tolerant of 80–90 % canopy inundation by beach
sand; predominant as fringing scrub on seaward margins; prone to dieback along landward margins;
Argusia argentea (octopus bush)
rare in the interior beach ridges (Batianoff et al. 2009).
Cordia subcordata (sea trumpet)
Ocean dispersed common tree, 3–8m; forms closed-scrubs to low closed-forests from beach ridge
to the Pisonia rainforest margins. Prone to dieback due to insect damage at CHNNR (moth larvae:
Armactica columbina and Ethmia sp).; resistant to scale insect damage (Freebairn 2007). In mid
to late 1800s, C. subcordata was almost exterminated by moth herbivory on the Hawaiian islands
(Guppy 1906).
Pisonia grandis (grand Pisonia tree)
Vines/twiners
Ipomoea macrantha (coast moon flower)
Bird dispersed; multi-stemmed; larges tree at the Reserve, up to 14m; soft spongy wood, able to hold
reserves of water and nutrients (Du Puy & Telford 1993e); dormant during dry periods by shedding
its leaves (Batianoff 1999); forms coral cay rainforests in the interior; persists along exposed shores
as wind-shorn closed-scrubs.
Ocean dispersed; widespread perennial climber/vine; common species in the interior herbfields or
canopy gap-filling role within woody vegetation (Telford 1993b; Batianoff 2001a).
from SW Herald Cay. NE Herald Cay and SE Magdelaine
Cay also have similar loras. It is only the presence of a few
distinct species, such as Canavalia rosea and Colubrina
asiatica on SE Magdelaine Cay which provide any sort
of dissimilarity between them. Willis Island tends to form
a loristic entity unto itself. It does not have widespread
species such as Ipomoea macrantha, Lepidium englerianum,
Plumbago zeylanica and Stenotaphrum micranthum that
tend to characterise the smaller CHNNR cays and has the
only record of Ipomoea pes-caprae subsp. brasiliensis. The
dissimilarity with other islands is evident when considering
either the loristic composition based on natives only or,
more predictably, when the occurrence of naturalised exotic
species are included. When exotics are included in the
analysis, the islands’ dissimilarity index rises from 0.41 to
0.61 (Figure 3).
Leverage coral cay flora
‘Leverage’ or ‘foundation’ species are abundant and/or
dominant plant taxa forming the main habitats that provide
vegetative cover and reduce temperature, wind and moisture
stress for other species (Krebs 2008). In CHNNR the key
leverage species are Abutilon albescens, Argusia argentea,
Boerhavia albilora var. albilora, Cordia subcordata,
Ipomoea macrantha, Lepturus repens, Pisonia grandis
and Sporobolus virginicus (Table 3). This leverage coral
cay lora includes species that are easily integrated into
Grime’s classiication of plant function (Grime 1979),
Ruderals, adapted for high disturbance environments, e.g.,
Lepturus repens, Sporobolus virginicus; Stress tolerator
species adapted to low moisture conditions, e.g., Boerhavia
albilora var. albilora; and Competitors forming dominant
populations under low-stress and low-disturbance conditions,
e.g., Abutilon albescens and Pisonia grandis. Some species
functions overlap. For example Sporobolus virginicus may
function as ruderal on the seashore but inshore in salt affected
areas it is a stress tolerant competitor.
Indigenous species that are common and widespread
within CHNNR, but which were not included as coral cay
key leverage lora include Achyranthes aspera, Plumbago
zeylanica, Portulaca oleracea and Tribulus cistoides (Table
1). These herb/shrub species are widespread in disturbed
areas of the Indian and West Paciic Islands due to human
activities rather than natural processes (Guppy 1906; Ridley
1930; Barker & Telford 1993).
Discussion
The lora of the northern Coral Sea Islands Territory is a
subset of the widely distributed Western Paciic low coral
island lora (Heatwole 1979; ANPWS 1989; Batianoff et al.
2009). A high percentage of low-lying coral island loras are
predominantly oceanic or seabird-dispersed littoral species,
with life-forms ranging from grasses to trees (Whistler 1992).
Plant dispersal and establishment
Dispersal modes play an important role in species’
geographic ranges and limits (Krebs 2008). Due to the strong
inluence of eastward winds (Bureau of Meteorology 2008)
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
and the South Equatorial Current (Farrow 1984), the origins
of ocean-dispersed species at CHNNR and Willis Island are
most likely derived from Paciic Melanesian islands (Smith
1992; Smith 1994; Heyligers 2007). The indigenous coral
cay species recorded from the northern Coral Sea Islands
(Table 1) are all littoral seashore plants. The ubiquitous seadispersed Australian/Paciic Colubrina asiatica most likely
established at CHNNR from seeds released from parent
plants growing outside of Australian territorial waters.
Littoral plants are well-adapted for long distance oceanic
dispersal, also referred to as ‘island hopping’ and/or ‘jump’
dispersal (Heatwole 1984; Hacker 1990; Batianoff 1999a;
Batianoff 2001a; Krebs 2008). During high wave conditions,
propagules of littoral and other ocean-dispersed species are
deposited along seashores (Guppy, 1906; Smith et al., 1990;
Smith, 1992; Batianoff et al., 1993; Smith, 1994; Heyligers,
2007). These species have buoyant propagules adapted
for transport by ocean currents, or seeds that are ‘sticky’
or easily swallowed and adapted for dispersal by avifauna
(Guppy 1906; Hacker 1990; Walker 1991; Batianoff 1999b;
Card 2001; Turner & Batianoff 2007). Plants with ‘sticky’
seeds or hooking devices, are also often dispersed by human
activities (Ridley 1930; Pijl 1972).
The modes of dispersal of some coral cay plants are dificult
to categorize. The widespread coral cay shrub Abutilon
albescens has dry seeds that are not buoyant or sticky and
according to Card (2001), is dispersed by seabirds. Dry
Abutilon albescens stems are used for nest-building and
thereby many seeds are dispersed around individual islands.
The ’green fruit’ casings containing dry seeds are capable
of loating for several hours (Batianoff, unpublished data).
Furthermore, the individual seeds are enclosed in lat
winged envelopes, capable of wind-dispersal (anemochory).
The wind-dispersal syndrome is uncommon for coral cay
plants (Batianoff 2001a). The poor representation of winddispersed lora is most likely a consequence of the vast areas
of ocean separating these small islands.
Species’ natural dispersal mechanisms together with humanassisted dispersal (anthropochory) frequently provide
problems for understanding of species origins and/or their
status. At Willis Island, most of the naturalised exotic weeds
including garden plants were established after deliberate and/
or accidental introduction associated with human activities.
The absence of exotic species at CHNNR indicate that their
low levels of human visitation have currently had little or no
effect on establishment of exotic weeds.
Plant origins
Bean (2007) used the terms ‘indigenous’ and ‘native’
synonymously in his system of determining the origins of
Australian plant species. However certain species may be
indigenous to some eastern Australian islands due to their
oceanic connectivity with the Melanesian region (Smith
1992; Smith 1994), though they may not be native to mainland
103
Australia. In this study, plants with ‘unknown’ origins that
are widely distributed in the Indo-Paciic region are assumed
to be indigenous to the northern Coral Sea Islands. Compilers
of lists of naturalised species need to recognise the role of
‘natural’ systems in continuing the incremental dispersal
of plants around the world. This dispersal has occurred for
millennia and is unlikely to have ceased in the current age.
Lepidium englerianum and Portulaca oleracea are
ubiquitous in the study area and are considered as ‘native’
in the study although they are listed as naturalised exotics
in mainland Queensland (Bostock & Holland 2007). Ridley
(1930) considered the cosmopolitan Portulaca oleracea
may have arrived relatively recently to the South Western
Paciic region. Even if Lepidium englerianum and Portulaca
oleracea are not indigenous as strictly considered by some
botanists, our observations indicate that they do not pose a
threat to any indigenous coral cay lora or fauna, and do not
require active management.
The case of the coconut Cocos nucifera is particularly
contentious. Bostock & Holland (2007) recognise Cocos
nucifera as an introduced exotic to Queensland, but many
botanists and biogeographers believe that it is indigenous
to the Indo-Paciic Region, including Australia (Du Puy
& Telford 1993a). (The questions and confusion about the
geographical antiquity of Cocos nucifera can be followed
through Corner (1966), Dennis & Gunn (1971), Buckley &
Harries (1984) and Harries (1992)). Whilst this species has
been cultivated at Willis Island, it is likely to be indigenous
to coral cays in the region.
Plumbago zeylanica is recognised as native to Australia
(Bostock & Holland 2007; Du Puy & Telford 1993d), has
been in cultivation from ancient times by Chinese and Indian
people for traditional medicine (Batianoff et al. 2009) and
is currently widespread across subtropical Africa, southern
Asia to northern Australia and some Paciic Islands (Du Puy
& Telford 1993d). It is common in the study area. According
to Ridley (1930), Plumbago zeylanica has an African/Asian
origin and was introduced into Australia during the early
1800s in contaminated imports.
Species richness and island species composition
The indigenous plant species richness at CHNNR is
comparable with the average of 18 indigenous species for
atolls ranging in size from 4–70 ha within the Caroline Atoll
Group (Kepler & Kepler 1994). The indigenous loras of
‘younger’ and/or less developed smaller cays such as SW
Herald (12 spp.) and Willis Island (11 spp.) comprise a few
herb species that are predominately ocean-dispersed (Table
1). These smaller cays frequently support only one or two
woody plant species such as Argusia argentea and Abutilon
albescens.
On more developed and/or larger cays, vegetation may
include some trees and/or shrubby plant species, but the
majority of species are herbaceous plants (Heatwole 1984;
104
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Kepler & Kepler 1994). The number of indigenous woody
species on atoll islands in the Caroline Islands remains
relatively low and constant, as interior forests rapidly
mature (Kepler & Kepler 1994). These forests form dense
canopy layers of the predominant tree species, mainly from
vegetative growth, and limit the establishment of other plant
species. Similar growth patterns have been observed in
forests in the interior of coral cays in Australia. For example,
Elsol (1985) reported that after the removal of feral goats,
most of the interior Pisonia grandis forest at Lady Musgrave
Island re-established by means of rapid vegetative growth,
thus excluding the establishment of other forest species.
Likewise, at NE Herald Cay, virtually no plant species are
found under the well-developed Pisonia littoral rainforest
(Batianoff 2001a).
Plant survival and resilience
The long-term survival of a plant species on a coral cay
island depends on its resilience to hostile conditions, and its
ability to successfully reproduce under continually changing
environmental conditions (Heatwole 1976; Batianoff
2001a). Newly dispersed plants that may initially germinate
on the seashores of coral cays often fail to establish and/or
reproduce due to desiccation, predation by foraging hermit
crabs and/or removal through excavation by sea turtles
during egg laying activities (Hacker 1990; Batianoff 2001a).
Some transient species frequently survive for short periods
of time (Heatwole 1984; Batianoff 2001a) but this shortlived establishment should not be interpreted as full-scale
naturalisation.
Excessive insect predation on successfully established plant
populations may result in mortality of individuals or localised
extinction of the entire population. According to Smith et
al. (2004), the entire Pisonia grandis littoral rainforest died
out on SW Coringa Islet between 1993 and 2002 as a result
of Pulvinaria urbicola (scale insect) outbreaks. Pulvinaria
urbicola has also been responsible for signiicant declines
of Pisonia grandis populations at Tryon Island (CapricornBunker Region) and on Palmyra Atoll in the Line Islands of
the northern equatorial Paciic (Kay et al. 2003; Handler et
al. 2007). This decline of Pisonia grandis presents a potential
long term conservation problem.
Regional vulnerability to naturalised flora
Most littoral and island loras including cays and atolls are
prone to invasion by weedy exotic plant species (Heatwole
1984; Chaloupka & Domm 1986; Heatwole & Walker 1989;
Kepler & Kepler 1994; Batianoff & Franks 1997). Humans
and the types of activities they undertake are important factors
inluencing all island loras. On Willis Island 57% of the
species are exotics, established as a result of human activities
(Figure 2). Given the high levels of human disturbance
and bird trafic (especially burrowing shearwaters), most
naturalised weeds have established soil seed banks, meaning
that weed control and/or eradication will be dificult and
require long-term weed control management strategies.
The susceptibility of most coral cays to invasion by exotic
plants is an important consideration for wildlife management
of islands in the CHNNR and on other Australian Oceanic
Islands. Signiicantly, on some ‘weedy’ islands, zonation and
succession patterns have been observed to change due to the
displacement of indigenous plants by exotic species (Kay &
Crocetti, 2004).
Unless strict quarantine and hygiene safeguards are in place,
it will only be a matter of time before some of the exotic
invasive lora from Willis Island spreads to other islands.
According to Telford (1993b), all the exotic species on Willis
Island (with the exception of *Trianthema portulacastrum)
are widespread weedy species of oceanic islands within
Australian territories. Euphorbia cyathophora and Tridax
procumbens were collected on Willis Island as early as
December 1981 (by A. Skeat and J. Henry). The invasive
weedy species that are widespread and/or highly competitive
with the indigenous plants on the island are Cenchrus
echinatus, Dactyloctenium aegyptium, Eleusine indica and
Euphorbia cyathophora (Batianoff unpublished data).
Leverage coral cay species and management implications
The recognition of ‘leverage coral cay species’ within
vegetation communities is considered important for plant
conservation management (Given 1994; Krebs 2008). All
coral cay key leverage species listed in Table 3 provide
plant materials for seabirds in nest building and/or nesting
and roosting habitats within plant canopies (Batianoff
2000; Batianoff 2001b; Batianoff & Cornelius 2005).
For instance, the Pisonia grandis and Argusia argentea
communities provide nesting sites for seven species (64%)
of seabirds breeding at the Reserve (Batianoff et. al. 2009).
The custodians of CHNNR have the potential to enhance
resilience of coral cays ecosystem and/or vegetation recovery
by encouraging the replanting of targeted species listed in
the group of leverage coral cay lora (Table 3). The ability to
repair habitats for wildlife communities after cyclone and/
or exotic pest damage is an important consideration under
current conditions of climate change (Batianoff et al. 2009).
Projected sea level rise may drown some current cay and reef
areas by inundation, and result in the erosion of shorelines,
and saltwater seeping into freshwater lenses (Burns 2000).
The CHNNR cays are likely to undergo some decline in
island area, with those of smaller size and without protective
beach rock likely to be the most affected (Smithers et al.
2007; Batianoff 2009a). As shorelines erode and saltwater
intrudes into freshwater lenses, it is likely that herbaceous
plants will be favoured over deeper rooted woody species.
This will impact on the ecology of the islands as it will
decrease foraging, roosting and breeding opportunities for
turtles and seabird species.
Cunninghamia 11(1): 2009
Batianoff, Naylor, Dillewaard & Neldner, Plant strategies, Coral Sea Islands
Conclusions
•
•
•
•
The species found on the cays of the northern Coral
Sea Islands Territory are a subset of the broader
ubiquitous tropical Western Paciic oceanic lora, with
a higher proportion of ocean and seabird-dispersed
species.
The CHNNR lora is subject to changes, particularly
through the introduction of exotic (pest) species.
However, the lora is resilient due to its plant strategies
and ongoing adaptations to climatic conditions.
A higher number of exotic species occur on Willis
Island due to residential human activities; however,
none of these exotics are currently in CHNNR.
Exotic pest species such as invasive weeds are capable
of establishment at CHNNR during favourable seasons.
As a result, strict quarantine and biosecurity measures
are recommended.
Acknowledgements
Coringa-Herald National Nature Reserve studies were
organised and inanced by the Australian Department of the
Environment, Water Resources and the Arts (DEWHA). All
survey participants are acknowledged. In particular, Neil
Gemmell, Astrida Mednis and Mark Hallam (DEWHA) for
organizing transportation and assistance during ieldwork
and for supplying old reports prior survey reports.
Queensland Herbarium management in particular Dr Gordon
Guymer is acknowledged for his support. Dr Paul Forster,
David Halford and Nigel Fechner are acknowledged for their
critique of this document. We are grateful to the anonymous
referees and the editor for contributing valuable comments.
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Manuscript accepted 22 December 2008