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FLORA AND VEGETATION OF CLIPPERTON (LA PASSION)
ATOLL, NORTH-EASTERN PACIFIC OCEAN: THREE CENTURIES
OF CHANGES AND RECENT PLANT DYNAMICS
Xenia Jost, Christian H. Jost,
and Jean-Yves Meyer
Atoll Research Bulletin No. 623 ⬧ 6 June 2019
Washington, D.C.
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ISSN: 0077-5630 (online)
CONTENTS
ABSTRACT .................................................................................................................................................. 1
INTRODUCTION ........................................................................................................................................ 1
A Brief History of Past Visits and Scientific Surveys ............................................................................. 4
Historical Documentation of The Vegetation .......................................................................................... 4
METHOD ..................................................................................................................................................... 5
Field-Work Constraints ............................................................................................................................. 5
Plant Collection and Identification ........................................................................................................... 5
Coconut Counting ..................................................................................................................................... 5
Vegetation Mapping .................................................................................................................................. 6
RESULTS ..................................................................................................................................................... 6
Plant Diversity .......................................................................................................................................... 6
List of Species ....................................................................................................................................... 6
Biogeographic Status ............................................................................................................................ 6
Newly recorded Plant Species .............................................................................................................. 7
Species Not Found ................................................................................................................................ 7
Drift Propagules .................................................................................................................................... 7
Coconut Palms .......................................................................................................................................... 8
Mapping and Implementing Data Into GPS .............................................................................................. 9
Description of the Vegetation in the Different Areas ........................................................................... 9
RESULTS ................................................................................................................................................... 21
A Very Depauperate Flora and Important Species Turn Over ................................................................ 21
Dramatic Changes in Vegetation Cover .................................................................................................. 21
CONCLUSION ........................................................................................................................................... 22
ACKNOWLEDGMENTS .......................................................................................................................... 23
REFERENCES ........................................................................................................................................... 23
APPENDIX ................................................................................................................................................. 30
1
FLORA AND VEGETATION OF CLIPPERTON (LA PASSION) ATOLL, NORTH-EASTERN
PACIFIC OCEAN: THREE CENTURIES OF CHANGES AND RECENT PLANT DYNAMICS
XENIA JOST1, CHRISTIAN H. JOST2,3 and JEAN-YVES MEYER4
ABSTRACT
The terrestrial flora and vegetation of Clipperton (La Passion) atoll, a very remote and small (170 ha
of land) French island located in the North-Eastern Pacific Ocean, at ca. 1,000 km west of the Mexican
coast, have dramatically changed during the past three centuries. This paper, based on historical
testimonies, previously published floristic studies, and an extensive plant inventory conducted during the
“International Scientific Expedition PASSION 2015”, show that the atoll has experienced particularly
active and rapid vegetation dynamics with alternating plant cover expansion and regression phases. Our
results provide the first comprehensive assessment of vegetation cover and vascular plant species
distribution based on georeferenced data and mapped with GIS software, as well as the first record of two
newly established non-native weeds. The current composition and abundance of native and alien vascular
plant communities (15 species including only 4 native taxa) appear to depend not only on abiotic factors
(e.g. substrate and climatic events) but also on biotic interactions with animal communities (e.g. native
seabirds and crabs). Anthropogenic activities and disturbances (e.g. coconut palm, pig, rat and weed
introductions) that have occurred in the past 100 years have also played an important role in explaining the
past and current floristic changes.
INTRODUCTION
The atoll of Clipperton, a French territory also called La Passion5, is located in the Tropical North-
Eastern Pacific Ocean at 109°12' W and 10°17' N (Figure 1), 1,080 km West of the nearest continental
land (Mexican coast), 3,980 km from the Marquesas Islands (French Polynesia), the nearest land being
Soccoro Island in the Revillagigedo Archipelago (Mexico) 945 km away. The total surface of the atoll
with its lagoon is 9 sq. km, with 170 ha of emergent coral ring, including six tiny inner lagoon islets.
Clipperton is unique because of the presence of a volcanic rock (called “Le Rocher” or “The Rock”) rising
at 29 m, and a completely closed lagoon (Figure 2). It is the smallest of the 11 French Overseas tropical
island territories (comprising French Polynesia, New Caledonia and Wallis et Futuna in the Pacific Ocean)
and is considered one of the most isolated uninhabited islands in the world. Despite its small land area,
Clipperton affords France sovereignty over 435 600 sq. km of ocean (Economic Exclusive Zone).
1 ENSAM Montpellier SupAgro, 2 place Pierre Viala, 34060 Montpellier, France
2 Université de la Polynésie française, B.P. 6570, 98702 Faaa, Tahiti, French Polynesia
3 PSL Université Paris, EPHE-UPVD-CNRS, USR 3278 CRIOBE, B.P. 1013, 98729 Papetoai, Moorea,
French Polynesia
4 Délégation à la Recherche, Gouvernement de la Polynésie française, B.P. 20981, 98713 Papeete, Tahiti,
French Polynesia
5 A text adopted by the French Assembly in November 24th, 2016 indicates that the names of La Passion
or La Passion- Clipperton can also be used.
2
Figure 1. Location of Clipperton (La Passion) atoll in the Tropical North-Eastern Pacific Ocean
3
Figure 2. Description of the atoll with the main area toponyms including the location of “Le Rocher” and the six inner lagoon islets
4
A Brief History of Past Visits and Scientific Surveys
Clipperton was first discovered and named “La Passion” in 1711 by the French Captain Michel
Dubocage en route to China on his vessel “La Découverte” (Briot and Briot, 2010). During the past three
centuries, the island went through periods of strong interest, alternating with long periods of forgetfulness.
In 1858, Lieutenant Le Coat de Kerveguen took official possession of Clipperton for France, but in 1892,
a US citizen, Frédéric Permien, reclaim the island on behalf of the USA, relying on the “Guano Islands
Act”. He created the Oceanic Phosphate Company to exploit the guano. In 1897 the Mexicans landed a
military garrison and guano workers stayed on the island until 1917.
Although the next visits on this very remote island were sparse, the number of scientific and report
papers are numerous, exceeding 500 (Jost, 2005a), allowing comparative studies of the natural
environmental of the atoll, both in the lagoon and on land. The French Army and the Oceanographic and
Hydrographic Service (SHOM) established the first map of reference in 1935. One of the first and most
important scientific surveys was conducted in 1958 by the Scripps Institution of Oceanography based in
California, with 13 scientists including the French botanist Marie-Hélène Sachet. The French Army
occupied the island through continuous trips called “Missions Bougainville” from 1966 to 1969 (Ehrhardt
and Niaussat, 1970). The famous French oceanographer, researcher, filmmaker, and undersea explorer,
Jacques-Yves Cousteau visited the atoll in 1980 with a small French-Canadian-American scientific team.
A Mexican-French scientific expedition “SURPACLIP” was organized in November 1997 directed by Dra
Solis-Weiss (Universidad Nacional Autónoma de México) with the participation of the second author
(then based at the University of New Caledonia) who later organized the “PASSION 2001” expedition
with scientists from IRD (Institut de Recherche pour le Développement) and the help of the French Navy.
A large scientific expedition was organized by the French explorer Jean-Louis Etienne between December
2004 and April 2005 with 30 French scientists rotating every two weeks (Charpy, 2009). The “PASSION
2013” expedition was again organized by the second author (then based at the University of French
Polynesia). Throughout these expeditions, detailed observations and data were gathered on plant and
animal communities in the lagoon and on land (Jost and Andréfouët, 2006).
The “International Scientific Expedition PASSION 2015”, organized and directed by the second
author and involving 14 scientists, took place in April 2015. It was held under the high patronage of M.
François Hollande, former president of France, sponsored by several French Ministries and Agencies, and
with the logistical assistance of the French Navy and Army. Its main goals were to continue the
inventories of coral reef biota and land fauna and flora, as well as an assessment of coastal dynamics and
erosion.
Historical Documentation of The Vegetation
The description of the natural environment of Clipperton (La Passion) and more specifically of its
vegetation and flora, come from episodic short-term visits and stays since the 18th century (Table 1).
Visitors (sailors then scientists) described drastic changes in the vegetation from almost no plant cover (in
1871 and 1897) to dense vegetation cover (in 1934 and 1958), followed by a decline in the 1980-1990s,
then a new increase of plant cover starting in 2005.
The most detailed description of the vegetation and flora was provided by French botanist M.-H.
Sachet during her two and a half weeks spent on the island in 1958 (Sachet, 1959). The low vegetation
was then covering almost 80% of the land (Sachet, 1962). Noticing the presence of 58 feral pigs with
dramatic impacts on seabirds and their eggs, decision was taken to eradicate them by shooting. The
number of land crabs Johngarthia planata Stimpson 1860 (syn. Gecarcinus planata, Gecarcinidae) then
increased up to 11 million in 1968 (Ehrhardt and Niaussat, 1970), suggesting that pigs were regulating the
crab population. As a result, the vegetation cover declined to become totally absent on the coral rim as
5
described by Jost in 1997 and 2001, except for coconut trees, and six plant species found on five inner
lagoon islets not reachable by crabs (Jost, 2003).
The black rat Rattus rattus was accidentally introduced between 1997 and 2001, probably by a ship
stranding (Lorvelec and Pascal, 2009). In 2005 a new census of the crab population showed that they
decreased significantly to 1.25 million, suggesting high predation by rats (Bouchard and Poupin, 2009).
C.H. Jost suggested that, despite the observation of remains of up to 20 crabs in each rat’s nest, the rodent
population, estimated at less than a 1000 in 2013, appeared insufficient to explain the strong decline of
crabs (Jost, 2013). The crab population might have reached its demographic optimum, and possibly the
island’s carrying capacity, then declined because of the scarcity of food resources. During the 2005
expedition, only a few patches of vegetation, mainly composed of the vine Ipomoea pes-caprae
(Convolvulaceae), were observed (Couté and Garrouste, 2009), while in 2013, vegetation was covering
one third of the atoll land surface (Jost, 2013).
The main purpose of this paper is to give a precise assessment of the current terrestrial vascular flora
and vegetation of the atoll. It updates the last plant inventory conducted 10 years earlier, and provides the
first georeferenced inventory of the vegetation cover, using the Quantum GIS software.
METHOD
Field-Work Constraints
Scientific surveys and field work on Clipperton (La Passion) are constrained by the strong geographic
isolation and remoteness of the island, the difficulty in accessing the closed atoll by boat, and by the lack
of housing infrastructure. Indeed, three to four days navigation are necessary to reach the island from the
closest land, i.e., the east coast of Mexico, and seven to eight days from the Marquesas islands (French
Polynesia) to the Southwest. The landing, and above all the re-boarding are always dangerous due to the
lack of channel to reach the lagoon. Moreover, the atoll is located in the tropical Northeastern Pacific zone
of cyclone formation which lasts from mid-May till the end of November.
During the “PASSION 2015” expedition conducted around and on the atoll, weather conditions were
fairly good during most of the 16 days spent on land except for two severely stormy days with heavy
rains.
Plant Collection and Identification
Two fertile (i.e., with fruits and/or flowers) samples of each plant species observed during the 16 days
of field-survey were collected by the first author. Plant specimens were labelled (with the date of
collection, the location, and a collection number), pressed in newspapers, and dried in full sun. The plant
collection was preserved in plastic bags with a small amount of 90% alcohol during the boat trip back to
Tahiti, and species identification was confirmed or completed by the third author.
This plant collection is temporarily stored at the “Délégation à la Recherche” in Tahiti (French
Polynesia) and will be permanently deposited in the main herbaria of Paris ([P]) and the Musée de Tahiti
et des Îles in Tahiti [PAP]).
A few samples of plant material were also dried in silica gel for further genetic analysis and
phylogeographic studies. Some seeds and fruits found on the ground in the intertidal zone (“drift
propagules”) were also collected.
Coconut Counting
Coconut palms (Cocos nucifera, Arecaceae) were counted, following a method used during past
surveys (2001 and 2013) on 10 m × 10 m squared plots in all coconut groves found on the atoll, with the
6
assistance of the French Navy and Army. Their height was visually assessed from the ground to the top of
the stipe (or trunk). Dead coconut trees (i.e., without leaves) were counted in 2001 and 2013, and
distinguished from those cut by people, often at a man’s height.
Vegetation Mapping
The different vegetation zones were identified, characterized and located by repeated and cross-
observations made by two observers and using two indexes: the relative plant cover rate of each species in
a specific area and the level of aggregation of each species (aggregated or scattered).
Areas which appeared to be homogeneous (either mono-specific, i.e., dominated by one species, or by
an association of two species and up to six) were delimited and called hereafter “vegetation zones.”
In order to survey the whole land area of the atoll in a relative short period of time, quadrats and
transects were not set up. The cover rate of each species and of the bare soil (uncovered land) of the
different vegetation zones were evaluated in relation to the surface of the study area, using the Braun-
Blanquet method (Braun-Blanquet, 1928). This approach consists of using a constancy class that is the
percentage of occurrences within the sampled zone: 0-5% (rare constancy), 5.1-25% (low constancy),
25.1%-50% (intermediate constancy), 50.1-75% (moderately high constancy), and 75.1-100% (high
constancy).
The delimitation of these zones was realised with a GPS (Garmin Etrex 10 GPS) in the WGS84-
coordinate system. These data collected in the field were imported into the Geographic Information
System (GIS) software Quantum (2.2.0 version Valmiera). The base map used was from a Worldview
geo-referenced satellite image dated 18 Sept. 2014.
In addition to the plant cover index, we used the specific richness, which is the number of species
occurring in a vegetation zone. For each zone, each species has been identified, and a map of the species
density was realised. When only one species was present, vegetation zone is considered as mono-specific.
Maps of the different vegetation zones, including plant cover rates, species number, vegetation types
(according to species life forms), dominant species in each zone, were produced. These geo-referenced
maps represent also a zero-reference state that will ensure a temporal and spatial comparability between
the different indicators (plant cover percentage, abundance/dominance, and expansion/recession
dynamics).
RESULTS
Plant Diversity
List of Species
Fifteen species of terrestrial vascular plants, all phanerogams and angiosperms (no pteridophyte nor
gymnosperm was observed), belonging to 11 different families were recorded in April 2015 (Table 2), as
well as three aquatic plant species.
By comparison, a total of 27 terrestrial plant species were reported in 1958 (Sachet, 1962), 11 species
in 2005 (Couté and Garrouste, 2009) and only nine in 2013 (Jost, 2013). Four aquatic plant species were
recorded in 1958 (Sachet, 1962) but only two in 2005 (Couté and Garrouste, 2009) (Table 3).
Biogeographic Status
The geographic origin of some of the species is sometimes difficult to assess, especially for plants
with a current pantropical distribution. Species of uncertain status (sometimes classified as “cryptogenic”,
Carlton, 1996) on Clipperton, known as “weeds” in the Pacific Ocean but considered native in the
Caribbean islands and tropical America, were considered as accidental or intentional introductions. They
include for instance Cenchrus echinatus (Asteraceae), Corchorus aestuans (Malvaceae), Ipomoea triloba
(Convolvulaceae), Phyllanthus amarus (Phyllanthaceae), Portulaca oleracea (Portulacaceae) and Sida
7
rhombifolia (Malvaceae), all recorded since 1958 (Sachet, 1962). The tree tobacco Nicotiana glauca was
also probably intentionally introduced as a useful plant (Sachet, op. cit.).
We considered four species as native or indigenous: two of American/Caribbean origin (Heliotropium
curassavicum and Eleocharis mutata), and two from an American or Asian origin (Ipomoea pes-caprae
subsp. brasiliensis and Eleocharis geniculata). It is noteworthy that Eleocharis geniculata, E. mutata, and
Ipomoea pes-caprae subsp. brasiliensis are considered as introduced taxa on Clipperton by the “Inventaire
National du Patrimoine Naturel” (INPN) taxonomic database6. We have considered Achyranthes aspera
var. aspera (Amaranthaceae) and Salvia occidentalis (Lamiaceae) as human introductions as they were
noted only recently.
Among the 15 recorded species, 11 are considered as “introduced” species, i.e., 74% of the total, and
four are considered “native”, i.e., 26% (Table 4). No endemic species are recorded on the atoll.
Newly recorded Plant Species
Two introduced and naturalized species were newly discovered: Achyranthes aspera var. aspera
(Amaranthaceae), an erect or shrubby herb with a pantropical distribution, and Salvia occidentalis
(Lamiaceae), an annual herb or sub-shrub native to Mexico, South America and the Caribbean islands.
Achyranthes aspera var. aspera, is considered as a “weed” in the Pacific islands and was probably
introduced to Clipperton by visitors because of its seeds with spiny bracts that adhere to animals and
clothing. In 2015, this species was seen in almost all vegetated areas, demonstrating a relatively high rate
of dispersal (probably by seabirds) and high colonizing capacities. Salvia occidentalis was only found at
one location, southwest of the airstrip forming a relatively dense mat (Photo A, cf. Appendix).
Species Not Found
Between 1958 and 2005, 17 species of terrestrial phanerogams have disappeared from the atoll (Table
3). Most of the missing species appear to be introduced weedy plants, and more than 70% of them are
herbaceous. Between 2005 and 2013 two additional species were missing, including the small tree
Hibiscus tiliaceus (Malvaceae) only recorded in 2005 as a single individual (Couté and Garrouste, 2009),
and the creeping vine Canavalia rosea (Fabaceae).
Four species observed in 1958, and not mentioned in 2005 and 2013, were observed again in 2015:
Phyllanthus amarus, Eragrostis ciliaris (Poaceae), Cenchrus echinatus and Nicotiana glauca. They were
either dormant (as seeds in the soil seed bank), or too rare to be noticed, or accidentally reintroduced
between 2013 and 2015. We also found drift seeds of the vine Mucuna sp. (Fabaceae) which was only
recorded in 1958 as living plants.
It is interesting to note that the number of introduced “weedy” species is higher during the periods of
relatively important plant cover (in 1958 and 2015), compared to the periods of sparse plant cover (in
1997, 2001 and 2005), suggesting that native species appear to be better adapted or more resilient to
harsher ecological conditions.
Drift Propagules
Seeds and fruits were searched and collected on the entire shoreline in the intertidal zone. They belong
to several different taxa, but only four could be identified: Mucuna sp. (Fabaceae), Entada gigas
(Fabaceae) and Dioclea sp. (Fabaceae) which were already reported in previous studies (Sachet, 1962),
and a newly recorded species, Lagenaria sp. (Cucurbitaceae), with several large fruits, some of them
containing seeds.
6 https://inpn.mnhn.fr/accueil/index
8
Coconut Palms
Coconut palms expansion started in 1897 with the introduction of the two first individuals by the
guano workers. In 1958, M.-H. Sachet noticed that “there appear to be two main varieties of coconut
palms on the island: some have more oval, green nuts, and the rachis of the young frond leaf is also
green; others have a bright orange young rachis, and rounder large orange nuts” (Sachet, 1962). These
two varieties were observed in 2015, but their distribution could not be precisely mapped due to lack of
time. However, 847 coconut trees over 1 m were counted in 2015 (Table 5). The orange nut variety is
much less common than the green one, and more abundant on the Eastern coast. There is a regular
increase (r²=0.9259) of the number of coconut palms during the past 120 years (Figure 3) which does not
distinguish the two varieties.
We noticed that the number of dead, headed and cut coconut trees was less than during previous visits.
The combined total was 85 in 2015 (of which 62 were topped and 23 cut), compared with 91 topped or cut
in 2013 and 168 in 2001 ( no distinction between topped and cut palms). In 2015, the trunks without
leaves were numerous (53) on the South coast in the old palm grove of Bougainville which seems to be
reaching the end of its life. The topping seems to be related to age and weather events. Cut stems,
obviously with a machete or an axe (presence of cutting lines at human height), are, on the other hand, a
large majority on the North-East coast (21 out of 23), which is more frequented by humans, where
landings are reported more numerous, but also where helicopter drops (purse seiners in operation) have
been recorded.
Despite an increase in the total population of palms, living trunks (above 1 m in height) have
diminished in the “Bois de Bougainville” from 479 in 2001, to only 305 in 2013. We also noticed in 2013
and in 2015 a total lack of undergrowth in this dense coconut grove (Photo B, cf. Appendix). This could
be explained by the age of the grove, which corresponds to the first two specimens planted in 1897 (a
coconut tree gives fruits for ca. 70 years and can live around 100 years) but also partly by the cleaning of
the undergrowth for the installation of the camp of the “Jean-Louis Etienne expedition” in 2005. The other
(younger) groves, located mainly on East and North coast, are rapidly expanding and have dense
undergrowths of young palms.
Figure 3. Increase of coconut trees between 1897 and 2015
240
353
557
674
581
806
847
R² = 0.925
0
100
200
300
400
500
600
700
800
900
1880 1900 1920 1940 1960 1980 2000 2020
Number
Years
9
Mapping and Implementing Data Into GPS
After processing the GPS data, various maps were developed using Quantum GIS. Figure 4 provides
information on the percentage of plant cover over the entire atoll ring, that is, the cover of all plant species
by vegetation zone. A total of 68 vegetation zones were identified. As described in the methodology, the
percentage of cover of each species is given as well as the percentage of bare soil. As an example, the
vegetation zone named "3C" located near the “Bois de Bougainville” is composed of Heliotropium
curassavicum (30%), Achyranthes aspera (5%), Portulaca oleracea (15%), and the bare soil represents
50% of the surface of the zone.
The entire cover extension of vegetation delimitated represents a total of 79 ha (46.5%). Most of the
vegetation zones (68 in total) are dense, comprising between 50 and 100% of plant cover. Zones with a
cover above 75.1% and up to 100% represent 46.7 ha, those with a cover between 50.1-75% represent
27.3 ha, and only one zone has a plant cover between 5.1-25%, representing 0.11 ha. Figure 5 illustrates
the different vegetation zones (in hectares) related to the percentage of bare soil within a zone.
The zones whose coverage is 75.1% to 100% are located along the West and East parts of the atoll.
Those with a 100% cover are mainly composed of Ipomoea spp. native and introduced vines and the
native tufted sedge Eleocharis geniculata located near the lagoon, on the East coast and on the West coast
beside the airfield, and at the Southern side of the “Bois de Bougainville”.
Figure 6 presents the specific richness for each zone. An average of three to four species are found in
closed association. Several zones have six associated plant species, two of which are very extensive: one
located in the North-West and the second in the South, both with a vegetation zone of more than 11
hectares. Monospecific zones are mainly represented by Ipomoea spp. vines, but also by species such as
Heliotropium curassavicum and E. geniculata mainly at the edge of the lagoon.
The three species are present in the largest number of zones: the native erect herb Heliotropium
curassavicum with 29 out of 68 zones (43%), the introduced erect herb Corchorus aestuans (22 zones or
32%) and the native sedge Eleocharis geniculata (22 zones, 32%). These three species are present on
almost the entire ring. In contrast, species such as Nicotiana glauca and Salvia occidentalis are only found
at one location, e.g., on the ring at the Southern tip of the island for the tree tobacco with 16 stems of more
than a meter high (Photo C, cf. Appendix).
Four main vegetation types can be distinguished on the atoll, namely sub-shrub stands, herbaceous
stands (erect or prostate herbs), creeping vines stands, and coconut groves, but with different plant
composition and abundance according to geographic areas (Figure 7).
Description of the Vegetation in the Different Areas
“Le Rocher” Area – Heliotropium curassavicum is particularly abundant, associated with small areas
of Corchorus, Portulaca oleracea and Sida rhombifolia. On the East side of “Le Rocher” two groups of
Ipomoea spp. vines are competing with each other (Photo D, cf. Appendix), I. pes-caprae in the South
and I. triloba in the North (Photo E, cf. Appendix). Some patches of both species of Eleocharis (E.
geniculata and E. mutata) are also found in contact with the lagoon at the base of “Le Rocher”.
Southern End Of The Atoll – A large stand of Eleocharis mutata surrounded by Eleocharis geniculata
(Photo F, cf. Appendix) is found at the Southern end of the atoll, near “Le Crochet”. Going Westward
from this tip, vegetation consists mostly of erect and tufted herbaceous plants dominated by Heliotropium
curassavicum, Corchorus aestuans, Portulaca oleracea, and Eleocharis geniculata. The latter forms a
monospecific stand bordering the shoreline of the lagoon side up to “Le Crochet” peninsula. In the
immediate vicinity of Eleocharis another monospecific stand of Ipomoea triloba is found. Shrub stands
with Sida rhombifolia and Achyranthes aspera are observed in the Western part of this area, parallel to the
shoreline and located in depressions of probably former phosphate mining areas (Figure 8).
10
Figure 4. Spatial distribution of vegetation zones according to plant cover
11
Figure 5. Areas (ha) of all vegetation zones (N=68) according to plant cover (in %) and species status (native or introduced)
12
Figure 6. Spatial distribution of plant species richness
13
Figure 7. Spatial distribution of the four main vegetation types
14
Figure 8. Spatial distribution of the dominant species on the Southern end part of the atoll
15
“Bois De Bougainville” Area Including “Pince Sud” And “Pince Nord” – The “Pince Sud” is entirely
covered by Ipomoea vines (80% of Ipomoea triloba and 20% of Ipomoea pes-caprae) (Photo G, cf.
Appendix). Couté and Garrouste (2009) have noted in 2005 that Ipomoea pes-caprae forms "an almost
continuous cover [...] along the Pince Sud [...]". On the small peninsula facing the “Pince Sud” on its West
side, a continuous and dense stand of Eleocharis mutata is found growing in the water Southeast of the
“Pince Sud”, two other patches of Ipomoea triloba are found beside the lagoon while Ipomoea is replaced
Southward by a cover of Achyranthes aspera in the middle part of the ring (Figure 9). In 2005 only two
patches of Ipomoea were present nearby the lagoon. A strip of Ipomoea is found in association with the
shrub Sida rhombifolia. Heliotropium curassavicum is abundant in the vicinity of the lagoon but much
more widely spread all along the shore, associated with other plants such as Portulaca oleracea and
Corchorus aestuans. In the Northern area of the “Bois de Bougainville” (Figure 10), the “Pince Nord” is
covered with Ipomoea pes-caprae vines, largely predominant and covering some Ipomoea triloba (Photo
H, cf. Appendix). The presence of Ipomoea was not recorded in 2005 but instead “a herbaceous
vegetation with Heliotropium and Portulaca, along with some spots of Corchorus aestuans" (Couté and
Garrouste, 2009).
On the edge of the “Pince Nord”, up to the French monument (called “Stèle” on the map) a shrubby
strip of Achyranthes aspera and Sida rhombifolia 50 to 70 cm in height, associated with other erect
herbaceous plants, totally covers the ground.
West And North-Western Area – On the West and largest part of the atoll (300 –400 m wide), the
most abundant plants are Sida rhombifolia, Cenchrus echinatus and Corchorus aestuans, a plant formation
also highlighted in 1958 by M.-H. Sachet. They make up a shrub cover of 30 –50 cm high. Low vegetation
formed by Heliotropium curassavicum is found on the edge of this vast and homogenous bushy area on
the upper part of the ring and more exposed to salt spray, while patches of Ipomoea triloba are found close
to the lagoon (Figure 11). The most extensive Ipomoea triloba stand is mixed with the Ipomoea pes-
caprae. To the North, at the edge of the lagoon, other small patches of Ipomoea spp. are observed,
including a monospecific patch of Ipomoea pes-caprae. The herbaceous Heliotropium associated with
Corchorus are forming a low and sparse cover.
North-Eastern Area – On the West side of the base camp of the “PASSION 2015” expedition. The
vine stands are mostly composed of Ipomoea triloba, but in association with Ipomoea pes-caprae on the
side of the lagoon.
Around the camp, the vegetation is very low and sparse (Figure 12), dominated by Heliotropium
curassavicum with Portulaca oleracea and also Corchorus aestuans stretched on a long strip from West to
East of the middle low part of the ring. A dense herbaceous cover hardly exceeding 15 cm high mainly
composed of Phyllanthus amarus is found down the camp site towards the lagoon. It is the largest and
almost only patch of this species on the island. At the time of Sachet’s expedition, this small herb was
found at the Northwest of the island and also on the East coast. A monospecific stand of Eleocharis
geniculata develops along the shoreline of the lagoon.
From the camp towards “Le Rocher” three groves of coconut trees (C. nucifera) are found, surrounded
by large stretches of Ipomoea spp. (Figure 13). The first and second stands of Ipomoea, up to the first
grove, are mostly I. triloba, while I. pes-caprae is in the background at the edge of the lagoon (Photo I,
cf. Appendix). From the second grove of coconut palms we find again a mixture of the two Ipomoea
species but dominated by I. pes-caprae (Photo J, cf. Appendix). The Southernmost Ipomoea stand is the
herbaceous tuft Eleocharis geniculata that grows around the lagoon. The Heliotropium curassavicum
cover that grows in the center of the ring from North to South is associated with Portulaca oleracea which
forms patches within the zone.
16
Figure 9. Spatial distribution of the dominant species on the Southern area of « Bois de Bougainville »
17
Figure 10. Spatial distribution of the dominant species on the Northern area of « Bois de Bougainville »
18
Figure 11. Spatial distribution of the dominant species on the West and Northern area
19
Figure 12. Spatial distribution of the dominant species on the Northeastern area
20
Figure 13. Spatial distribution of the dominant species on the Eastern area with three main coconut groves
21
DISCUSSION
A Very Depauperate Flora and Important Species Turn Over
Due to its extreme isolation, ca. 1,000 km from the nearest continent (Central America) and 945 km
from the first land, Soccoro island Northward (Mexico), and because of its very small land surface (170
ha) with harsh ecological conditions, Clipperton (La Passion) atoll shows a very low plant diversity. The
vascular flora, which comprised 27 species including 9 native taxa in 1958 (Sachet 1962), is currently
composed of 15 species including only five native taxa. These last species are particularly well adapted to
the dry tropical environments of atolls characterized by nutrient poor calcareous soils with a small amount
of organic matter and high salt concentrations, low rainfall, high temperatures, and periodic strong winds
and heavy tropical rains during cyclones. Some of them have developed succulent and/or small leaves to
reduce respiration and water loss, including the newly recorded alien subshrubs Achyranthes aspera var.
aspera and Sida rhombifolia. Some introduced species, on the other hand, are more sensitive to these
harsh ecological conditions and do not survive, such as the weed Erigeron bonariensis only recorded in
1958 or Hibiscus tiliaceus present in 2005 but not in 2015.
In 1958, according to M.-H. Sachet, the most common plants found in the atoll were the weeds
Cenchrus echinatus, Sida rhombifolia, Corchorus aestuans and Solanum americanum, and "other less
abundant plants locally mixed with this vegetation" (Sachet 1962) including Heliotropium curassavicum
and the weed Erigeron bonariensis. In 2015, the shrub Sida rhombifolia, was among the most abundant
plants, with Heliotropium and Ipomoea triloba, whereas Cochorus aestuans was one of the least common
plants. In 60 years, the plant composition has dramatically changed, and some community trends have
almost been reversed.
The plant density ranges between 8.8 (15 species) and 15.9 (27 species) per sq. km. In comparison, the
flora of other atolls in French Polynesia varies between 11.5 for the small (4 sq. km) uninhabited atoll of
Taiaro in the Tuamotu (Niva and Taputuarai, 2013) and 22.7 species per sq. km for the very isolated and
uninhabited atoll of Maria (150 ha) in the Austral Islands (Meyer, 2013) but with 25 and 24 native species
respectively. The floristic diversity of Clipperton is similar to the small (100 ha) island of Tromelin (Iles
Eparses, South-West Indian Ocean), an upraised atoll, with 20 plant species including seven native species
(Boullet et al., 2018).
No tree species is found on the atoll, except for the introduced coconut palms (which are not trees
botanically speaking). The absence of the small tree Heliotropium foertherianum (syn. Tournefortia
argentea, Boraginaceae) and Sophora tomentosa (Fabaceae) or the shrubs Suriana maritima (Surianaceae)
and Pemphis acidula (Lythraceae) is noteworthy, as these coastal woody species are commonly found on
almost all the atolls and low sandy islands in the Pacific Ocean (Mueller-Dombois and Fosberg 1998). S.
tomentosa is also known from the Revillagigedo Islands (Johnston, 1931), the nearest land at 945 km East
of Clipperton.
Dramatic Changes in Vegetation Cover
The vegetation cover of Clipperton (La Passion) atoll has dramatically changed during the past three
centuries. The atoll was described as almost a desert between 1858 and 1897, and densely covered by
vegetation in the 1960’s. A minimum cover was again reached between 1997 and 2001 with not a single
species observed on the main land, and only six plant species found in five inner lagoon islets.
It was previously noted that expansion and diversification of the flora were correlative to the
demographic growth of pigs from 1897 to 1958 (when pig population was eradicated during the Scripps
Institution expedition). However, a few pigs, said to be less than six, escaped the slaughter and were
finally killed in 1966 by the French Army during the “Missions Bougainville”. Despite the fact that land
crabs (Johngarthia planata, syn. Gecarcinus planatus), were already described as an “extremely dense
22
population” by Sachet (1962), it seems than their number kept increasing, reaching the spectacular
number of more than 11 million in 1967 (Niaussat and Ehrhardt, 1970).
All the studies and observations following the 1958 plant inventory by M.-H. Sachet (Ehrhardt, 1968;
Taxit and Ehrhardt, 1981; Jost, 1997, 2001) show a drastic reduction of the plant cover until the
disappearance of the grass layer noted for the first time in 1997 (Jost, 1997). Considering this as a process
of a rhexistasic period, one can assume that a species introduced by man, the pig, had for once a positive
impact at least on the vegetation cover by allowing diversity and extension to develop. Indeed, pigs were
observed eating not only bird eggs but also Gecarcinidae crabs whose shells were found in pig feces
(Ehrhardt, 1972). The elimination of pigs allowed the multiplication of crabs which consume not only
eggs and coconuts, but also the grass cover. The elimination of pigs had a very positive effect on the bird
population which exploded between the 1960s and the 2000s from 150 masked boobies (Sula dactylatra)
(Sachet 1962) to ca. 100,000 in 2001 and 2005 (Jost, 2003; Jost and Andréfoüët, 2006; Weimerskirch,
2009) becoming the world’s most important colony.
However, in 2005 the reappearance and extension of few patches of the herbs, vines and subshrubs
was observed (Couté and Garrouste, 2009). This evolution, in correlation with the reduction of the number
of crabs, was confirmed in 2013, then in 2015 (Jost, 2013, 2015).
The situations in 2001 and 2005 are difficult to compare since in 1997 and 2001 the only living plants,
beside coconut trees, were located in the five inner lagoon islets (Jost 1997, 2005b), unreachable by the
land crabs which were confined on main land.
If the factors which can explain these changes were still hypothetical 20 years ago, the recent and
more frequent visits and studies confirm that the extension and reduction of the vegetation cover in
Clipperton, mostly like on other atolls, are closely linked to two groups of factors. One group is related to
weather and sea conditions, while the other is dependant from the fauna dynamics to be linked, positively
or negatively, to human impacts.
The first and main factor, i.e., which has the fastest and strongest impact by being capable of
destroying or burying in few hours the whole or part of the plant cover, is submerging waves loaded with
sediments. In certain circumstances, they can cover the entire atoll ring. High waves of more than two
meters are produced either by major hurricanes or by tsunamis. Since hurricanes are frequent in the region
and may have a diameter of 500-1,000 kilometres, the fauna and flora are often directly impacted. For
example, during a storm with strong swell and waves in April 2015, we observed fresh sand and gravel
deposited by submerging waves in a strip several tens of meters long on the Eastern and Northern ring.
Another cause of vegetation changes is introduced plant or animal species and a demographic
explosion of one or another community. Introduction of pigs was followed by the recovery of vegetation
until their elimination in 1958 after which plant cover and diversity declined for forty years, followed by a
new period of expansion until today. This last period is marked by the decline of the crab population but
also the appearance of a new predator, the black rat Rattus rattus, accidently introduced with one of the
two boat wreckages between 1997 and 2001. If the crab demographic decline can be explained by the lack
of food after having eaten most of the plant cover, it is also partly linked to the rats which consume crabs
and occupy their burrows.
The 2015 inventory has demonstrated that the atoll can be quickly recolonized by vegetation, from a
few patches to almost half of the island in only 10 years. However, it will be important to monitor plant
dynamics with the increasing presence of rats, known for their deleterious impacts on island native biota
(Shiels et al., 2014), and more specifically to plant diversity and composition (Wolf et al. 2018).
CONCLUSION
Because of its geographical location, at the crossroad between the Pacific and American
biogeographic regions, its extreme isolation, small size, particular geomorphology (with a closed lagoon),
23
climate (on cyclone paths) and human history, the atoll of Clipperton (La Passion) is a unique natural
laboratory of global scientific interest.
The observed changes in native and alien plant cover and species composition for the past three
centuries are probably due to abiotic factors and natural disturbances (substrate, climate including
cyclonic events) but also to biotic factors (native seabirds and crabs) and anthropogenic impacts, including
the past introduction of pigs, rats and weeds. The vegetation dynamics seem to follow more or less 50-
year cycles tightly linked to human presence and activities. Thus, the alternating phases of plant
abundance could be divided into a “pig phase” between 1897 and the 1950’s with a high plant cover,
followed by a “crab and seabird phase” between the 1960’s and 2000 with a low plant cover, almost
absent in 2001 and 2005, and the “rat phase” since 2005 with a new increase of the vegetation (Jost et al.
2015). These ecological cycles also demonstrate the resilience of the atoll ecosystem with the rapid
recruitment of most of the vascular plants after natural and anthropogenic disturbances. However, the
regular increase of coconut palms and the recent (accidental) introductions of alien species (e.g. the weeds
Achyranthes aspera var. aspera and Salvia occidentalis) may profoundly alter the ecological balance of
this small island ecosystem. Strict biosecurity measures should be set up during the future visits on the
atoll, including scientific expeditions, to avoid new accidental plant and animal introductions.
Further research studies will include molecular analyses conducted on the native and alien plants and
drift propagules, in order to construct phylogenies and assess the origin of all plant taxa found in the atoll
(Pacific Islands versus Tropical America), as well as the assessment of the potential impacts of sea-level
rise on the island biota. Long-term surveys will be necessary to confirm these ecological cycles, including
plant dynamics, especially in the context of global changes.
ACKNOWLEDGMENTS
The “PASSION 2015” Expedition was made possible thanks to the French Navy, especially the crew
of the Prairial Frigate, and the French Army (RIMaP-P), to the “Haut-commissariat de la République en
Polynésie française”, the “Agence française de développement (AFD)”, the “Ministère des Outre-mer”,
the “Ministère des Affaires étrangères”, the “Délégation française auprès de la Communauté du
Pacifique”, the University of French Polynesia, the “Institut du Droit économique de la Mer“ in Monaco,
and the NGO “Clipperton – Projets d’Outre-Mer (CPOM)”.
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26
Table 1. Past description of the vegetation of Clipperton (La Passion) atoll and its evolution between
the 18th and 20th centuries.
Period or
year of
observation
Author
Description
Documents
(Reference)
1711
French discoverer
Michel Dubocage
“Some brushwood and one dry tree on the
Northeast point […] The Western side
appeared to us with few small bushes "
Sketch of the
island
(Dubocage,
1711)
1825
American Captain
Benjamin Morrell
“Little shrubbery and some coarse grass,
among which, I think, fresh water might be
found by digging. Among the few plant
productions of this island, we found a plant
resembling sarsaparilla7, which badly poisoned
several of the crew who handled it”
(Morell, 1832)
1839
British Admiral Sir
Edward Belcher
“Very-dangerous low lagoon island, destitute
of trees; North: appears to be clothed with
something like grass”
Map (Belcher
1843)
1858
French Lieutenant
Le Coat de
Kerveguen
« The land is only covered with guano. The
lagoon is totally closed and its water is salted »
Map (Le Coat
de Kerveguen,
1858)
1861
American
Lieutenant
Griswold
“I did not find the least sign of plant life upon
the island. The only plant seen grew in
considerable quantities in the lagoon”
(cited in Pease,
1868)
1897
French Lieutenant
Terrier
“There is no vegetation on the island apart
from two young coconut trees grown in crates”
(Terrier, 1897)
1934
French Navy vessel
“Jeanne d’Arc”
Vegetation was described as “covering a big
part of the land”
Map, pictures
and aerial
photos (Report,
1935)
1938
“US President
Roosevelt” cruise
Important vegetation cover on photographs
Aerial photos
(Taylor, 1939)
1958
French botanist M.-
H. Sachet
Abundant low vegetation covering almost 80%
of the land
Map (Sachet,
1962)
1968
French « Missions
Bougainville »
Vegetation cover decrease on map
Map (Ehrhardt
and Niaussat,
1970)
1980
French Cdt J.-Y.
Cousteau
Vegetation continues to decline to scarce
patches
Map and movie
1997
French geographer
C. Jost
Vegetation totally absent of the coral rim,
except 674 coconut trees
Map (Jost,
1997)
2005
French explorer J.-
L. Etienne
Patches of herbaceous and subshrub vegetation
in a few restricted zones
Map (Couté and
Garrouste
2009)
7 Refers to a creeping vine of the genus Smilax (Smilacaceae), more probably Ipomoea pes-caprae
27
Table 2. List of the 15 terrestrial vascular plant species observed in 2015 on Clipperton (La
Passion) atoll with their biological characteristics and proposed biogeographical and naturalization
status.
Family
Scientific name
Life
form
Dispersal
mode
Native
range
First
obs.
Biogeogra-
phical status
Naturalization
status
MONOCOTYLEDONS
Arecaceae
(Palmae)
Cocos nucifera L.
tree
(palm)
hydrochory
1897
introduced
(intentional)
cultivated,
naturalized
Cyperaceae
Eleocharis
geniculata (L.)
Roem. & Schult.
erect herb
(sedge)
epizoochory or
endozoochory
Caribbean,
South
America,
Western
Polynesia
1897
native
naturalized
Eleocharis mutata
(L.) Roem. &
Schult.
erect herb
(sedge)
epizoochory or
endozoochory
Caribbean,
South
America
1897
native
naturalized
Poaceae
(Graminae)
Cenchrus
echinatus L.
erect herb
(grass)
epizoochory
Caribbean,
South
America
1958
introduced
(accidental)
« weed »
Eragrostis ciliaris
(L.) R.Br.
erect herb
(grass)
endozoochory
Caribbean
1958
introduced
(accidental)
« weed »
DICOTYLEDONS
Amaranthaceae
Achyranthes
aspera var. aspera
L.
erect
(woody)
herb
epizoochory
Asia
2015
introduced
(accidental)
« weed »
Boraginaceae
Heliotropium
curassavicum L.
erect
(woody)
herb
hydrochory,
endozoochory
Caribbean,
South
America,
Australia,
Hawaii
1958
native
naturalized
Convolvulaceae
Ipomoea pes-
caprae subsp.
brasiliensis (L.)
Ooststr.
creeping
vine
hydrochory
Pantropical
1897
native
naturalized
Ipomoea triloba L.
creeping
vine
hydrochory
Caribbean,
South
America
1897
introduced
(accidental)?
naturalized
Lamiaceae
Salvia occidentalis
Sw.
sub-shrub
epizoochory
Caribbean
2015
introduced
(accidental)
« weed »
Malvaceae
Corchorus
aestuans L.
erect herb
anemochory
Caribbean
1958
introduced
(accidental)?
« weed »
Sida rhombifolia
L.
sub-shrub
epizoochory
Caribbean,
South
America
1958
introduced
(accidental)?
« weed »
Phyllanthaceae
Phyllanthus
amarus
Schumach. &
Tonn.
erect herb
endozoochory
Caribbean
1958
introduced
(accidental)?
« weed »
Portulacaceae
Portulaca
oleracea L.
prostrate
herb
anemochory,
epizoochory
Caribbean
1958
introduced
(accidental)?
« weed »
Solanaceae
Nicotiana glauca
Graham
sub-shrub
endozoochory,
epizoochory
South
America
1905
introduced
(intentional)
« weed »
28
Table 3. Changes in plant species composition on Clipperton (La Passion) atoll.
Family
Scientific name
Life form
Status
1958
2005
2015
Amaranthaceae
Achyranthes aspera var. aspera L.
herb
introduced
X
Arecaceae
(Palmae)
Cocos nucifera L.
tree
introduced
X
X
X
Asteraceae
(Compositae)
Erigeron bonariensis L. (syn. Conyza
bonariensis)
herb
introduced
X
Eclipta prostata (L.) L.
(syn. Eclipta alba)
herb
introduced
X
Boraginaceae
Heliotropium curassavicum L.
erect herb
native
X
X
X
Brassicaceae
Brassica juncea (L.) Czern.
herb
introduced
X
Convolvulaceae
Ipomoea pes-caprae subsp. brasiliensis (L.)
Ooststr.
creeping
vine
native
X
X
X
Ipomoea triloba L.
creeping
vine
introduced
X
X
X
Cyperaceae
Eleocharis geniculata (L.) Roem. & Schult.
sedge
native
X
X
X
Eleocharis mutata (L.) Roem. & Schult.
sedge
native
X
X
X
Cyperus subsquarrosus (Muhl.) Bauters
(syn. Hemicarpha micrantha)
sedge
native
X
Schoenoplectus acutus var. occidentalis
(Muhl. Ex Bigelow) A.Löve & D.Löve (syn.
Scirpus rubiginosus)
sedge
native
X
Fabaceae
(Leguminosae)
Caesalpinia sp.
shrub
native
X
Canavalia cf. rosea (Sw.) DC.
vine
native
X
X
Mucuna sloanei Fawc. & Rendle
liana
native
X
(drift
seed)
Leptospron adenanthum (G.Mey.)
A.Delgado (syn. Phaseolus adenanthus)
creeper
introduced
X
Lamiaceae
Salvia occidentalis Sw.
shrub
introduced
X
Malvaceae
Corchorus aestuans L.
erect herb
introduced
X
X
X
Hibiscus tiliaceus L.
tree
introduced
X
Sida rhombifolia L.
shrub
introduced
X
X
X
Waltheria indica L.
erect herb
introduced
X
Phyllanthaceae
Phyllanthus amarus Schumach. & Thonn.
herb
introduced
X
X
Poaceae
(Gramineae)
Cenchrus echinatus L.
grass
introduced
X
X
Dactyloctenium aegyptium (L.) Willd.
grass
introduced
X
Eragrostis amabilis (L.) Wight & Arn. ex
Nees
grass
introduced
X
Eragrostis ciliaris (L.) R.Br.
grass
introduced
X
X ?
Portulacaceae
Portulaca oleracea L.
prostrate
herb
introduced
X
X
X
Sapindaceae
Sapindus saponaria L.
tree
native
X
Solanaceae
Nicotiana glauca Graham
shrub
introduced
X
X
Solanum americanum Mill.
(syn. Solanum nigrum var. americanum)
herb
introduced
X
TOTAL
27
11
15
29
Table 4. Evolution in species richness on Clipperton (La Passion) atoll.
Year
1958
2005
2015
Total number of species
27
11
15
Number of introduced species
20
6
11
Number of native species
7
5
4
Newly discovered species since 1958
-
1
2
Number of species not found in-between each scientific expedition
-
17
0
Number of species not found since 1958
-
17
14
Table 5. Evolution in the number of living coconut palms on Clipperton (La Passion) atoll.
Year
1897
1934
1958
1997
2001
2005
2013
2015
Size
>1 m
>1 m
>1.50 m
>1 m
>1 m
Number
2
40
353
557
674
581
806
847
Size
<1.50 m
<1 m
Number
3083
1395
30
APPENDIX
Photographs of some particular plant species and vegetation zones (credit: Xénia JOST).
Photo A. Small patch of the recently introduced weed Salvia occidentalis (inside the red circle) within a
dense stand of Sida rhombifolia
Photo B. Dense coconut palms grove in “Bois de Bougainville” with almost no plant undergrowth
Photo C. Tree tobacco Nicotiana glauca, a subshrub first observed in 1958 and rediscovered in 2015
Photo D. A view of dense stands of the creeping vine Ipomoea pes-caprae (on the right: South side) and
the introduced I. triloba (on the left: North side) from "Le Rocher"
Photo E. Dense stand of Ipomoea triloba with the lagoon visible on the right side
Photo F. Dense stand of the native tufted sedge Eleocharis mutata near “Le Crochet”
Photo G. A view of the "Bois de Bougainville" area with a dense stand of Ipomoea triloba in the
foreground and coconut groves in the background
Photo H. A view of the "Pince Nord" area with the "Stèle" on a tumulus in the right background, and
dense stand of Ipomoea triloba with a patch of Eleocharis mutata on the foreground
Photo I. A view of the Eastern coast with an expanding pure stand of Ipomoea triloba surounding boobies
nesting sites
Photo J. A view between the 3rd coconut grove and “Le Rocher” in the background (southward):
Ipomoea pes-caprae on the left foreground and patches of Eleocharis geniculata elsewhere
31
