Marine Phytogeography of the Juan Fernandez Archipelago

15 Pages·2008·6 MB·English

PacificScience(1992), vol. 46, no. 4:438-452
© 1992byUniversityofHawaiiPress. AlI rightsreserved
Marine Phytogeography ofthe Juan Fernandez Archipelago:
A New Assessment!
B. SANTELICES2
ABSTRACT: Anewassessmentofthegeographicaffinitiesofthe marinealgae
of the Juan Fernandez Archipelago indicates a flora with a small number of
species and very high endemism (about 30%) as compared to other oceanic
islandsofsimilarage,size,origin,andabioticconditions.Thefloraalsocontains
many widely distributed species (45%) and a small group of species with
circumpolar-subantarctic affinities (about 13.5% of the flora). The potential
algal species sources for this flora seem to be distant localities in the southern
Pacific, including the southern tip ofSouth America, southern Australia, New
Zealand, and several subantarctic islands. Considering effective dispersal dis
tancesofmarinebenthicalgae,theJuanFernandezArchipelagoappearsasmore
isolated than Easter Island, which previously was supposed to be the most
isolated point in the Pacific basin. An analysis of the endemic components
suggests that there has been speciation but no radiation in these islands. Some
species originatingin thearchipelago might have migrated across the Pacificto
continentalSouthAmerica, perhapsvia EINino/SouthernOscillation (ENSO).
BASED ON THE SEAWEEDS collected by the by the abundance of subtropical elements,
Swedish expedition to Juan Fernandez and which were common in Peru and northern
Easter Island, Levring (1941) and Skottsberg Chile. Therefore, Skottsberg (l943a) con
(1943a,b) made what amounts to be the only cludedthattheislandflorawasmorelikethat
phytogeographic characterization ofthe ma ofPeru and northern Chile than that ofthe
rine algae of the Juan Fernandez Archipel continental flora farther south.
ago. They distinguished eightfloristic groups EventhoughSkottsberg(1943a)recognized
among the nearly 100 seaweed species re that the West Wind Drift and the Chile-Peru
ported from the islands. Endemic elements Current (Humboldt Current) was the route
weremostabundantlyrepresentedintheflora probably followed by a large number of
(32%), followed by subcosmopolitan (20%), species, he considered that the abundance
and subtropical species widely distributed in of subtropical elements in this insular flora
warm waters (14%). They also noticed the was greater than what could be attributed to
presence of a small (10%) Australasian temperatureconditionsalone. He(Skottsberg
Neozelandian element that did not belong to 1943a)furthersuggestedthathistoricalcauses
the circumpolar group known also from had been influential. Considering that the
southern Chile and Magellania, and a few fossillandfloraofsouthernChileandAntarc
(about 5% ofthe flora) subantarctic species. tica showed that during the Tertiary the cli
Both Levringand Skottsbergwere impressed mate was considerably warmer than now,
with the absence in the islands of the large Skottsberg supported the idea that Juan
kelpsandbullkelpsthataresocommoninthe Fernandez was formerly connected with
southern part ofPacific South America and South America. He disregarded a neovo1ca
nic, oceanic origin of the Juan Fernandez
Islands because seemingly it did not allow
1Manuscriptaccepted 18January 1992. enough time for the evolution of strongly
2Departamento de Ecologia, Faculated de Ciencias
marked endemic forms and because a major
Biol6gicas, P. Universidad Cat61ica de Chile, Casilla
114-D,Santiago,Chile. ity of the endemic species belong to genera
438
MarinePhytogeographyoftheJuan FernandezArchipelago-SANTELICES 439
regarded by Skottsberg (1943a) as having 1973).AccordingtoArana(1987)thismodifi
tropical and subtropical affinities. cationcouldhavebeenrelatedtotheaperiodic
In the 50 yr following Skottsberg's pro ElNino/SouthernOscillation(ENSO), which
posal, several expeditions have visited the wasexceptionally strongthat year.
islands, increasing the geological, oceano Marine floristic studies have added new
graphic, and floristic knowledge ofthe archi perspectives to the biogeographic affinities
pelago. It is now accepted that the Juan of the flora. Even though new collections
Fernandez Islands are entirely volcanic in (Etcheverry 1960, Earle 1969, Hawkes and
origin and apparently have never been con Johnson 1981)haveadded few records to the
nected to the mainland (Stuessy et al. 1984, islands, floristicstudieselsewhere have modi
Gonzalez-Ferran 1987). The Nazca Plate is fied the known geographic distribution of
movingfrom westto eastand apparentlynew several of the species found in the Juan
islands are produced as the plate moves east Fernandez Archipelago. Several of the sub
wardovera"hotspot."Theabsoluteagesare tropical elements considered as most impor
estimated at 3.8 to 4.2 million years (My) tant by Skottsberg(1943a) are now regarded
for Masatierra Island and I to 2.4 My for as widespread bothin temperateand tropical
MasafueraIsland.Theknownspreadingrates waters. Some of these taxa also have been
forthemarginoftheNazcaPlate(8.8cmyr-1 found in southern South America (see re
)
agree well with the observed distance sepa view by Ramirez and Santelices 1991), in
rating Masatierra and Masafuera (150 km) creasing the floristic affinities between the
and their known ages. Therefore, present Juan FernandezArchipelagoand localitiesin
geological data do not support Skottsberg's southern South America, New Zealand, and
(1943a) proposal ofa land connection ofthe Australia.
Juan FernandezIslands with SouthAmerica, Ontheotherhand, newdataonthefloraof
and the argument cannot be used to explain EasterIsland, anotheroceanicisland ofsimi
thegeographicaffinitiesofthemarineflora of lar age, size, origin, and approximately simi
the islandswith that ofthe continent. lar abiotic conditions as those in the Juan
Oceanographicstudieshaveconcludedthat FernandezArchipelago, areinconsistentwith
the surface waters surrounding the Juan ourpresentunderstandingoftherelationship
FernandezIslandsaremainlyofsubantarctic among isolation, species richness, and en
origin. The most superficial layer, and down demism,butareusefulforcomparison.Easter
to 200 m depth, corresponds to the subant Islandhasbeenfound tohaveabout 1/3more
arctic water mass, with temperature ranges species but only about halfthe percentage of
from 10to 19°Candsalinitiesbetween34.00/00 endemic elements as the flora of the Juan
and 34.2%0. Furthermore, the ocean circula Fernandez Archipelago (Santelices and Ab
tion around the islands, between 75° Wand bott1987).Alloftheseislandarevolcanicand
78° W, is under the influence of the strong ofabout thesameage(3.0 My, EasterIsland,
northward flow of the Humboldt Oceanic Newman and Foster 1983) and the same size
Branch, also called the Chile-Peru Current (Masatierra = 93 km2, Masafuera = 60km2,
(Figure I). Between 78° Wand 80° W, there Easter Island = 93 km2 All are hilly and
).
is a strong southward flow that may corre relatively barren, with coastlines character
spond to the Peru Oceanic Countercurrent; ized by cliffs; few, small beaches; and few
beyond 81°W, acurrentflowing to the north sheltered bays(Stuessyetal. 1984, Gonzalez
withlowvelocityandsmallvolume transport Ferran 1987). Winds are strong and change
has been identified (Arana 1987). directions seasonally and daily (Hajek and
Onatleastoneoccasionthisgeneralsubant Espinoza 1987). Thus, there seem to be no
arctic influence was found to be altered: the obviousdifferencesin theabovedeterminants
most superficial 50 m around the islands was ofspeciesrichnessandendemismbetweenthe
found in April 1973 to beoccupied bywaters islands in the Juan Fernandez Archipelago
of the subtropical water mass, with higher and EasterIsland.
temperaturesand salinities (Silvaand Sievers The most important difference between
440 PACIFICSCIENCE, Volume46, October 1992
110 100 90 80 70
0..(.'....0..".". •,,-. "\A'\ \ i\
~1~ "0.~('~ " \0;1
'~ ~O, :'\ C~" f'
20 (~' o,. ~.~ ~;':)\ 0 20
~ 1t ~ ;
~ '\0/\~ ~\ ~~lJ!
t
0
q
Easter Island
30 ~ '~J 30
t
FernanCf(.7./~
! /
J.
/1.
--.::,
/
40 • " ~ 40
West Wind Drift
50 50
110 100 90
FIGURE I. Pattern ofoceanographiccirculation around the Juan Fernandez Archipelago (redrawn from Arana
1987).
Easter Island and the islands in the Juan (Briggs1974)tobeconsiderablylessthanthat
FernandezArchipelagoseemstobethedegree ofEasterIsland.However,thehighendemism
ofisolation.EasterIslandisrecognizedasone and the small number ofspecies exhibited by
ofthemostisolatedpointsinthePacific,lying the flora ofthe Juan Fernandez Archipelago
3250kmawayfromtheSouthAmericancoast as compared to Easter Island are not consis
and 2315 km away from the nearest land to tentwith their respectivedegrees ofisolation.
the west (Ducie Atoll). The Juan Fernandez Thedegree ofendemismand the speciesrich
Archipelago is only 600 km away from the nessofJuan Fernandezmightbeexplainedby
South American continent. Therefore, the dispersion distances and biological isolation
degree of isolation of the Juan Fernandez severalordersofmagnitudegreaterthanthose
Archipelagohastraditionallybeenconsidered in effect on Easter Island. This assumption is
TABLE I
EXAMPLESOFPATTERNSOFGEOGRAPHICDISTRIBUTIONSOFBENTHICALGAEREpORTEDFROMTHEJUANFERNANDEZARCHIPELAGOANDEASTERISLAND
JUANFERNANDEZ EASTERISLAND REPRESENTATIVELOCALITIESELSEWHERE
Indo-PacificDistribution
Cladophorasocialis + Tahiti,Polynesia,Malaysia
Cladophoropsisherpestica + Vietnam,Japan,southernAustralia
Ectocarpusarabicus + + IndianOcean,India,Malaysia
Feldmanniaindica + Indo-Pacific,Indonesia,Philippines,HawaiianIslands
Sphacelariatailensis + Tahiti
Dictyotacrenulata + CentralPacific,Philippines,HawaiianIslands
Dictyopterisrepens + WesternPacific,Japan,Philippines,MarianaIslands
Lilhophyl/umsamoense + Tahiti,Samoa,Hawaii
Ceramiumcruciatum + Indo-Pacific
Polysiphoniasavatieri + TropicalPacific,Hawaii,Malaysia,Japan
Circumpolar-SubantarcticDistribution
Scytothamnusaustralis + CentralsouthernChile,Australia,Tasmania,NewZealand
Splachnidiumrugulosum + Tasmania,NewZealand,SouthAfrica
Glossophorakunthii + SouthernPerutoCapeHorn,ChathamIslands,NewZealand
Acrochaetiumcatenulatum + + CentraltosouthernChile,CampbellIslands,NewZealand
Gymnogongrusfurcel/atus + CentralPerutosouthernChile,NewZealand,Australia
Rhodymeniaaustralis + Australia
Rhodymeniacuneifolia + ChiloetoMagellanStraitinsouthernChile,FalklandIslands,
southernArgentina
Phycodrisguercifolia + CentraltosouthernChile,FalklandIslands,KerguelenIslands,
SouthGeorgiaIslands,andCampbellIslands
Schizoserisgriffithsia + ConcepciontoMagellanStrait,FalklandIslands,NewZealand,
AucklandIslands,ChathamIslands,CampbellIslands
Polysiphoniaabscissa + CoquimbotoMagellanStrait,severalsubantarcticislands
EndemicSpecies
Phaeophilapacifica Ectocarpuschnoosporae
Phaeophilaramosa Sargassumskottsbergii
Codiumfernandezianum Erythrocladialaurenciae
Codiumcerebriformis Erythrocladiarepans
Ectocarpusminutissimus Acrochaetiumdiscoideum
Distromiumskollsbergii Acrochaetiumralfsiae
Padinafernandeziana Galaxaurapaschalis
Leptophyl/umfernandezianum Botryocladiaskollsbergii
Chondriel/apusilla Ceramiumskollsbergii
Hypoglossumparvulum Laurenciaclavata
442 PACIFICSCIENCE,Volume46,October 1992
consistent with the notion that the majority
of the floristic elements present in the is
lands ofthe archipelago originate in Fuegia
MagellaniaandtheAustralasianarea,involv
ing dispersal distances of 3000 (Fuegia) to
12,000 km (Australia-New Zealand). This
relation was perceived by Skottsberg (1943a)
but was overlooked by him because he
supported a land connection between Juan
Fernimdezandthecontinent.Theabundance
oftropicalelementsinthearchipelago,andits
generalfloristic affinity with Peru and north
ern Chile, can be explained in two ways: (1)
Some species ofwidedistributioncould have
arrived independently in the islands and the
continent; (2) Species restricted to Peru
northern Chile and Juan Fernandez could
have been transported across the eastern
Pacificby aperiodicENSOevents.
Inthisstudytheseideasweretestedandthe
geographic affinities of the marine flora of
JuanFernandezwerereassessed. Forcompar
ative purposes, the marine flora of Easter
Island has beenincludedin the analysis.
!
+ I + I I I
~ .~ METHODS
This study is restricted to the benthic
~
Chlorophyta, Phaeophyta, and Rhodophyta
recorded in the Juan Fernandez Archipelago
andonEasterIsland. Dataonthegeographic
distribution of the species were taken from
the literature, most of which has been sum
marized by Santelices (1987), Santelices and
Abbott (1987), and Ramirez and Santelices
(1991) for the areas in question. Data were
initially recorded for 110 taxa in Juan
Fernandez and 165 taxa on Easter Island.
Taxonomic uncertainties or lack ofinforma
tion on geographic distribution elsewhere re
duced thenumberofspeciesconsidered to 89
inJuan Fernandez and 105 on Easter Island.
Our samples represent 80% and 65% ofthe
respective total number oftaxa reported for
theseislands, and theproportionofendemics
to total number of species is only slightly
differentfrom thevaluescorrespondingtothe
totalflora.
Thespeciesweregroupedaccordingtotheir
patterns of geographic distribution in the
MarinePhytogeographyoftheJuan FernandezArchipelago-SANTELICES 443
Pacific basin and elsewhere. Table I shows a ure2).Thenumericallymostimportantgroup
few outstanding examples of each group of includesspecieswithwidedistribution, which
speciesdistinguished in each location. Abun compose 45-50% of the flora of these is
dance of algae groups among locations was lands. Endemic elements are important in
compared bychi-squaretests. bothplaces,buttheyareproportionallymore
important in the Juan Fernandez Archipel
ago. A small group ofspecies that extends to
the Pacific coast of South America is also
RESULTS
moreimportantintheJuan FernandezArchi
Fivegroupsofspeciescan bedistinguished pelago. The two remaininggroups, taxa with
when the bulk ofalgal taxa reported for the Indo-Pacificaffinitiesandspecieswithcircum
Juan Fernandez Archipelago and Easter Is polar-subantarctic affinities, also are pres
land is grouped by geographic affinities (Fig- ent in both areas but their representation in
EASTER ISLAND J. FERNANDEZ
60 40 20 0 20 4.0 60
WIDELY
49.5 44.9
DISTRIBUTED
INDO- PACIFIC 28.6 2.2
J13'
CIRCUMPOLAR
3.8
SUBANTARTIC
ENDEMIC 13.3 29.2
0
ISLES- PACIFIC
1.9 67
SOUTH AMERICA .
OTHER 2.9 3.5
FIGURE2. Relativeimportanceofseveralfloristicgroupswithdifferentpatternsofdistributioninthemarineflora
ofEasterIslandandtheJuanFernandezArchipelago.
100 160 180 160 140 80
\1
100 120 140 160 180 160 140 120 100 80
CURRENT SySTEM ~
FIGURE3. Distributionof30speciesofbenthicalgaewithaffinitiesintheIndo-Pacific.Numberincirclesrepresents
themeannumberofspeciespresent.
100 120 140 160 180 160 140 120 100 80 60
~
~o : ! .' '.~,\\'"
;'~.. ..... ~.
~., ~::.sa~~~·J., :..,:~. ":~":~;':i"~ "'.""- .
o
.. ,.(.
'. ••
~ ~ '.
'. ~:.!).•.-....;".. , ":I/e"'.P.'• 1 ••:, ...t.. ...\ ....3,../..
20 '. ,'. ":0<.~~ ,.;,:'.-...:.: ..'.-"::...",... ~ '..:", t....:~""...~~:;1'..•....•. 13\ "',\""\...\3'.-,-/
'•••O'
(. '. ~ I \\
.~
EASTER ISLAND: 112\6
/ Q
-" ~~.
_ A\ J FE~NAN~E7'
I _
'--....."--"-" .. \ / 6 \.~) -_ .. ,,/ I 8
~. -"-...e.- " ,CH~THAM / / :\~
___.. _".-." -'.1
.................""........... 5· (<- -._..__.•- ...../.",,... .",.. _.._...._.-..._..._ .::..-::--/,' /
KERGU_E0L'E-N""__.o. '"'-- ....... ....... ";_'C.A.M -BE"L-L' .. _00 /.~"_"_.. _... . /'.'. '8..........".........._"'..
\J-J ....... .'--'" -" --...- .. -_.. _..,../' ~
-.~
-......."-"-" .-.'".'- -..'.".,/... /'./:";..
'.-.. ............. _ ... - __.. _.. --e.--... _._/' ~../' I 2 f.'
,,~ /'
';':.
_ ,,-?/' / .'
- ... ...
100 120 160 140 120 100 80 60
_._.._.._ ...... Current system
FIGURE4. Patternofdistributionof12speciesofbenthicalgaewithsubantarctic-circumpolardistribution.Number
incirclesrepresentsthemeannumberofspeciespresent.
446 PACIFICSCIENCE,Volume46,October 1992
each place is very different. The Indo-Pacific in distant places in the southern hemisphere,
elementsare very abundanton EasterIsland; a pattern ofdistribution that is closely asso
those withcircumpolar-subantarcticaffinities ciated with the West Wind Drift and the
are more abundant in Juan Fernandez. Al Chile-Peru Current systems (Figure 4). Eight
though the endemic elements usually are re ofthesespeciesarefound bothat localitiesin
gardedashighlycharacteristicofagivenarea, southernmost Chile and in distant places in
these last two groups, with differential repre the southern Pacific Ocean, including south
sentation and strong asymmetry among the ern Australia, New Zealand, Campbell Is
islands, may better reflect the geographic lands, and ChathamIslands. Four other spe
affinitiesofthelocalfloras. Theywilltherefore cies occur in these distant localities in the
beconsidered first. Pacific, but have not been found in southern
South America. Because all of these species
seem to have a similar dispersal route and
Species with Indo-Pacific Affinities
only a few are restricted to localities in Aus
This group of species is the second most tralasia or the subantarctic, it is unnecessary
numerousonEasterIsland(Figure2),amount to distinguishsubgroupssuchassubantarctic
ing to 28.6% of the flora in the sample andAustralasian-NeozelandianasSkottsberg
considered for this study. This group com (1943a) did. Moreover, only two or three of
bines species previously characterized by thesespeciesarealso found in northern Chile
Santelices and Abbott (1987) as having a andPeru,showingahighersimilaritybetween
western Pacific pattern ofdistribution and a JuanFernandezandsouthernChilethanwith
few taxa previously included among those morenorthernlocalities. Infact, thepresence
widely distributed in warm waters. Some of of these species in northern Chile and Peru
the species in the group (Figure 3) are re doesnotrequireacirculationsystembetween
stricted to a few islands in Polynesia; others the islands and the continent because they
are present also in Malaysia, northeastern couldhavereachedtherefromsouthernlocal
Australia, Vietnam, Japan, and the Philip itiesbymeansofcurrentsalongthecontinen
pines,andafewreachnorthernNewZealand. tal margins.
Thirty of these species are found on Easter Threespecieswithcircumpolar-subantarctic
Island, butonlytwo ofthem arefound in the affinitiesoccuronEasterIsland.Interestingly,
Juan Fernandez Archipelago. Furthermore, two of them (Codium pocockiae and Dasya
one of these two taxa (Laurencia clavata) villosa) are absent from the Juan Fernandez
couldhavearrivedinthearchipelago through Archipelago, illustrating the very limited ex
the West Wind Drift and the Chile-Peru change between Easter Island and this archi
Current system, because it is also found in pelago.
southernAustralia.Thedifferenceinthenum
ber of species of this group represented on
Species with Wide Distribution
Easter Island and in the Juan Fernandez
Archipelago emphasizes the influence of the In both insular floras discussed here the
Humboldt system on Juan Fernandez, which numerically most important group ofspecies
with its cold temperature and northern flow are taxa with wide geographic distribution
acts as a powerful barrier to dispersal for a (Figure 5A). About 17 of these species are
majority ofspeciesfrom EasterIsland. subcosmopolitan, including Juan Fernandez
andEasterIsland,andtheirgeographicdistri
butions do not provide additional clues on
Species with a Circumpolar-Subantarctic
their geographic origins and dispersal. An
Pattern ofDistribution
other 33 species are found on Easter Island
TheJuan Fernandez Archipelago contains butnot inJuan Fernandez (Figure 5B). They
agroupof12specieswithgeographicaffinities exhibit wide distribution, in tropical and
FIGURE5. Regional affinitiesofinsularspeciesofbenthicalgaewidelydistributed inwarmand temperatewaters
inthePacificbasinandelsewhere.Numberincirclesrepresentsthemeannumberofspeciespresent.
120 140 160 180 160 140 120
20 WIDELY DISTRIBUTED IN . 20
".
WARM AND TEMPERATE WATERS
..
0
....:.. :·E>:·
I
3
.. . '\
~ , ....... '0·:\};.i.. 5,
t'·-'.:":,.. ~t~. .' " ..' ® 6J 20
I
i Easterisland ~
~
Fernan at
J1, I
6
I
,
60
12il 140 160 180 160 140 120 100 80 60
DISTRIBUTED IN
',.
'"
SUBTROPICAL
i:.
1.:,-. ... ··e······
.•...
\:, ~\,'.,; " ..... .;.(.~~j:(.:'. ,
Ilio::-.. '" ..... ® 2I 20
~I
Easter island
., 2
.~ J Ferna ez
t'
i
40 ti rjJ.
I,
120 140 160 1 0 160 140 120 100 80
DISTRIBUTED IN
....'. 20
TEMPERATE WATERS
0
,. ......: ~"
':" ...~:
.~ '. ;.:'1:·:;;~.~"
:.'";:... ~1..: .. ..... ., ® 20
;.'
Easter island
(
.~p
.~
...
68
120 140 160 180 160 140 120 100 80 60