MARINE ECOLOGY PROGRESS SERIES
Ma Ecol P og Se Published Decembe
5
E ec s o en i onmen al s ess on ascidian
popula ions in Algeci as Bay (sou he n Spain).
Possible ma ine bioindica o s?
S.
A.
Na anjo*,
J.
L.
Ca ballo,
J.
C.
Ga cia-Gomez
Labo a o io de Biologia Ma ina, Dp o.
de
Fisiologia y Biologia Animal, Facul ad de Biologia, Apdo 1095, E-41080 Se illa, Spain
ABSTRACT: The dis ibu ion and abundance o li o al ascidians we e analyzed wi h espec o hel
possible ela ionships wi h en i onmen al s ess. As pa o a mul idisciplina y esea ch p ojec on he
ben h~c communi ies in Algeci as Bay, sou he n Spain, a sui e o en i onmen al a iables was mea-
su ed (hyd odynamism, sil ing, suspended solids and o ganic ma e ). A e displaying he similali ies
o auna h ough clus e ing and o dina ion o sampling si es, he ela ionships be ween communi y
di e ences and changes in he abio ic componen we e es ablished based on he
BIO-ENV
p ocedu e
and Canonical Co espondence Analysis. Hyd odynamism and he pe cen age o o ganic ma e in he
sil is he a iable combina ion ha bes explains (Spea man co ela ion o
0.82)
he bio ic s uc u e.
While all ascidians show a ce ain ole ance o di e se en i onmen al ac o s, some species such as
Ciona in es inalis. Diplosoma spongi o me, Phallusia mammilla a, Mic ocosmus squamige , S yela pli-
ca a
and
Synoicum a gus
could be conside ed
as
indica o s o a eas which ha e been subjec o in ense
s ess (subs a e ans o ma ion, wa e s agna ion and sedimen a ion excess) o e long pe iods o ime,
whe eas o he s such as
Aplidium conicu n, Aplidium punc um. Cla elina della allei, Halocyn hia
papillosa
and
S olonica socialis,
which li e only in na u al and non-pe u bed ock a eas, could be ca -
ego ized as species e y sensi i e o s ess, as well as ind~ca o s o good condi ions.
KEY
WORDS: Ascidian communi ies
.
En i onmen al s ess
.
hdul i a ia e communi y measu emen s
B~oindica o s
INTRODUCTION
The e is now widesp ead ecogni ion ha chemical
moni o ing o pollu ion alone is no enough, and ha
pollu ion is essen ially a biological phenomenon be-
cause o i s impac on li ing o ganisms (W igh e al.
1994). The analysis o changes in ben hic communi y
s uc u e has now become one o he mains ays in
de ec ing and moni o ing he biological e ec s o
ma ine pollu ion (Wa wick
&
Cla ke
1993).
Ne e -
heless, knowledge o he dis ibu ion pa e ns o ben-
hic o ganisms along na u al en i onmen al g adien s
(e.g. om u bulen o calm condi. ions) is necessa y
be o e a possible an h opogenic dis u bance can be
p o ed.
Algeci as Bay ea u es impo an indus ial de elop-
men s (wi h chemical indus ies, e ine ies, he mal
powe plan s, i onwo ks and pape mills) as well as in-
ense ha bou ac i i y. All o his esul s in a highly
ans o med coas line (mainly in he cen al zone)
whe e shipya ds, pie s and b eakwa e s, among o he
po cons uc ions, a ec he no mal wa e low. Some
a eas ha a e be e conse ed and ha e na u al ocks
exis in he ou e zone. Recen s udies show he
amoun o di ec was e in his a ea o be close o
2800
m"',
wi h much mo e u ban sewage han in-
dus ial was e-wa e s (Wai e al. 1990). consequen ly,
Algeci as Bay can be conside ed o
be
a pa chwo k o
small a eas unde di e en le els o s ess due o he
in luence o en i onmen al and an h opogenic ac o s.
Thus, a mul i ude o small en i onmen s can be iden i-
ied and, co espondingly, a simila le el o he e o-
genei y can be expec ed in he s uc u e
o
he ben hic
communi ies wi hin hese en i onmen s.
Algeci as Bay is conside ed o be an especially sui -
able a ea o biomoni o ing s udies (Nai-anjo
&
Ga cia-
O
In e -Resea ch
1996
Resale o ull a icle no pe mi ed
Ma Ecol P og Se
144: 119-131,
1996
Gomez 1993, Ca ballo e al. 1994, Con adi
&
Ce e a
1995, Ca ballo e al. 1996). In his sense, a mul idiscipli-
na y esea ch p og am was conduc ed om 1991 o
1995 in o de o gain knowledge o he mac oben hic
auna and i s ela ion o majo en i onmen al a iables
in his a ea. Among all sessile o ganisms s udied, he
ascidians a e a pa icula ly in e es ing g oup in his
espec , since hey display bo h o he main ecological
s a egies-soli a y and colonial-and
a
a ie y o
mo phological ypes which a e o adap i e signi icance
(Jackson 1977a, 1979) and which co ela e wi h dis inc
abili ies o colonizing new su aces. Acco dingly, i is a
good diagnos ic g oup whose d~s ibu ion may e lec
some o he p e ailing s uc u ing ac o s a ec ing ben-
hic assemblages (Tu on 1990)
Ascidians a e ound on all subme ged ha d su aces,
including conc e e, i on, ope and plas ics. Some
species a e mos abundan in highly ans o med and
pnll~~ e i ~n i nn nen q 5~1 -h as po s, ha ho s and
in-
dus nal a eas, whe e he excess o pa icula e o ganic
ma e and he p oli e a ion o bac e ia a e a sou ce
o ood o il e - eeding in e eb a es, pa icula ly
ascidia.ns (Monnio e al. 1991).
Ascidians can also ake up a ious me als om he
wa e ( anadium is one o he mos common) and
some oxic subs ances (hea y me als and hyd oca -
bons). The e o e, ascidians con ibu e o he cleaning
and pu i ica ion o was e-wa e s. Fo his eason,
nume ous s udies ha e ou lined
he
impo ance o his
g oup as pollu ion bioindica o s (Papadopoulou e al.
1972. Papadopoulou
&
Kanias 1977, Monnio 1978,
Bell e al. 1982). In spi e o his, li le is known abou
he in luence o local en i onmen al ac o s (such as
wa e mo emen , suspended solids o sil ing) on he
p esence o absence o he species in a gi en habi a .
In his sense, we ha e s udied he composi ion and
abundance o he ascidian communi ies in Algeci as
Bay, as well as hei le el o adap a ion o abio ic com-
ponen s.
MATERIAL
AND
METHODS
Ascidians we e sampled a 11 coas al s a ions dis-
ibu ed a ound Algeci as Bay, a dep hs om 3 o
15 m. Thei loca ions a e shown in
Fig
1. Due o
h.e he e ogenei y o he ha d-bo om habi a s (na u al
ock
o ma ions, po cons uc ions, shipya ds and
o he a i icial subs a es), he s a ions we e selec ed
on he basis o en i onmen al a iabili y.
In en o ies o species pe s a ion we e aken o he
specimens collec ed by SCUBA-di e s along con inuous
ansec s (app oxima ely
50
m
long). These in en o ies
we e comple ed by isual and pho og aphic sampling
along he same ansec s, wi h a simila imme sion ime a
Fig.
1
Loca ion o he sampling s a ions
in
Algeci as Bay,
sou he n Spain
all s a ions ( he e we e no eplica es on any occasion). All
ascidians sigh ed a a dis ance o 1 m on ei he side o he
ansec s we e collec ed and/o pho og aphed. Su eys
we e aken om Sep embe 1992 o No embe 1993.
Table 1 sho s he species abundance in e ms o
semi-quan i a i e abundance codes. Coding can be
use ul when di e en sampling me hods a e u ilized,
and in his s udy i pe mi ed mo e objec i e compa -
isons o he aunis ic composi ion a di e en s a ions
(Ca ballo e al. 1996). Fu he mo e, his p ocedu e is
p esumed o ha e an e ec sim~la o s anda diza ion
by columns, which minimizes da a a iabili y a ising
om sampling he e ogenei y (Maldonado
S1
U iz
1995).
The es abl~shmen o en i onmen al a iabili y among
s a ions was based on he analysis o
5
abio ic a iables
ha could be ela ed o en i onmen al s ess. These
we e hyd odynamism, sil ing, suspended solids, sus-
pended o ganic ma e and o ganic ma e in he sil
(SOM) ga he ed in collec ing bo les. The me hods
used o es ima e hese pa ame e s a e de ailed in Ca -
ballo e al. (1996); measu emen was made as in Gambi
e al. (1989) o hyd odynamism, Moo e (1972) o sill-
ing and S ickland
&
Pd sons (1960) o he o he h ee.
As a p epa a o y s ep o he s a is ical analysis, hese
abio ic a iables we e log- ans o med.
Na anjo e al. E ec s o en i onmen al s ess on ascidlans
121
-
Compa isons among sampling s a ions (on he basis
o species abundance) we e conduc ed acco ding o
he s a egy ou lined by Field e al. (1982) o he
analysis o da a on communi y s uc u e: (a) The bio ic
ela ionship be ween any
2
samples (sampling s a ions
in ou case) was dis illed in o a coe icien measu ing
simila i y (o dissimila i y) in species composi ion. The
B ay-Cu is lndex (B ay
&
Cu is 1957), which is no a
unc ion o join absence, was chosen o his pu pose.
I is ecognized as an e icien measu e o he e a-
lua ion o a ini ies on semi-quan i a i e da a om
la ge aunis ic assemblages (Gami o
&
Ra aelli 1992).
(b) S a ions we e classi ied in o g oups (using he i-
angula ma ix o simila i y ob ained be ween e e y
pai o s a ions) ei he by hie a chical agglome a i e
clus e ing, wl h g oup-a e age linking (e.g. Snea h
&
Sokal 1973), o by mapping he s a ion in e -
ela ionships in o o dina ion using non-me ic mul i-
dimensional scaling (MDS) (K uskal
&
Wish 1978).
(c) Rela ionships be ween species we e analyzed by
ansposing he da a ma ix and epea ing he classi i-
ca ion and o dina ion me hods on he new simila i y
ma ix be ween e e y pai o species. Species which
we e indica i e o he dissimila i y be ween g oups o
s a ions we e de e mined as in Cla ke (1993), using he
SIMPER compu e p og am.
In o de o link he mul i a ia e communi y s uc u e
( e lec ed in he aunis ic he e ogenei y o he di e en
sampling s a ions) o en i onmen al a iables (which
also change wi h each s a ion), we used
2
di e en , bu
complemen a y, s a is ical echniques:
(1) BIO-ENV p ocedu e (Cla ke
&
Ains~ o h 1993). In
summa y, his consis s o a sepa a e compa ~son o he
among-s a ion simila i y ma nx o he bio a wi h equi-
alen iangula ma ices o all combina ions o abio ic
a iables, and he consequen choice o he subse o
en i onmen al a iables which p o ides a good ma ch
be ween he 2 con igu a ions. A ma ch was measu ed by
he Spea man ank co ela ion coe icien
(p,),
which
was compu ed o he dissimila i y ma ices o he bio ic
and abio ic da a. Al hough no speci ic plo is p o ided
showing he esul , a diag am displaying he bio ic
MDS
(based on he B ay-Cu is dissimila i y index) in con-
junc ion wi h he abio ic MDSs (compu ed om
Euclidean dis ances) o he subse o en l onnlen al
a iables selec ed by he BIO-ENV p ocedu e as op imal
would be app opia e, especially when high alues o
p,
a e ob ained (e.g.
p,
%
0.8) (Cla ke
&
Ainswo h 1993).
(2) Canonical Co espondence Analysis (CCA). This is
a di ec g adien echnique, and ep esen s a special
case o mul i a ia e eg ession (Palme 1993). In he e-
sul ing o dina ion diag am, en i onmen al a iables can
be ep esen ed by a ows along wi h he species and/o
s a ion sco es. De ails o how o in e p e CCA diag ams
a e gi en in e B aak (1986) and Palme (1993).
The so wa e used was: PRIMER e sion 3.1 om
Plymou h Ma ine Labo a o y,
UK,
ol- clus e , MDS,
SIMPER and BIO-ENV analysis; STATGRAPHICS
6.0
o eg ession analysis; and CANOCO 3.12 o Co e-
spondence Analysis, CCA and Mon eca lo pe mu a-
ion es s.
RESULTS
S a ion g oupings based on species composi ion
Table 1 indica es la ge a iabili y in he na u e, ype
and a ailabili y o ha d subs a es cha ac e izing he
sampling s a ions. A p elimina y s udy o he local dis-
ibu ion o he mos common ascidians indica ed
3
basic g oups: (a) species exclusi ely dis ibu ed in he
ou e zone o he bay which se le mainly on na u al
ock subs a es; (b) species mo e abundan in he inne
zone o he bay which se le mainly on a i icial sub-
s a es; (c) species ound h oughou he bay.
Analysis o he dend og am in Fig.
2
shows he dl -
e ences among he s a ions as s a ed abo e. This clas-
si ica ion echnique sepa a es he s a ions in o 3 majo
g oups
(A,
B,
C) which a e ela ed, in pa , o he
na u e o he subs a e. In g oup
A,
he s a ions a e
cha ac e ized by he p esence o ex ensi e na u al
ock o ma ions (in he ex emes o he bay). G oups
B
and C include he es o he s a ions (In he inne pa s
o he bay), whe e a i icial subs a es a e dominan
(walls and columns in po s, b eakwa e s, shipya ds,
e c.).
The a e age dissimila i y be ween g oups A and
B
1s
59.74%. As is shown in Table
2,
17 o he 38 specles
explain he dissimila i y o 70% be ween g oups A
and
B.
Pseudodis o na obscu u n, Polyci o ad ia icu n,
Fig
2.
Dend ogl-am o s a ions using g oup-a e age clus e -
lng om B ay-Cu ~s simila i y on specles abundances The
3
g oups o s a ions
[A
o
C)
sepa a ed a a
50%
simila i y
h eshold (do ed line) a e indica ed
122 Ma Ecol P og Se 144 119-131,
1996
Table
1.
Asc d~an
species
abundance In Algec~ as Bay
and
subs a e cha ac e ~s ~cs a sampl~ng s a lons Sem~quan ~ a ~ e
abundance codes,
0
=
species abhen , 1
=
a e
(1
o 2 speclmens eco ded), 2
=
equen ( om 3 o 10 specimens pe ~ nme s~on)
3
=
e y common
(an
a e age o
mo e
han
10
speclmens pe imme sion) Subsi a e onen a ion
H
=
ho izon al
su aces,
V
=
e ical su aces,
0
=
o e hangs
U
=
unde
boulde s;
Cc
=
c e lces
and
can les.
E
=
ep~b~on
Na u al
ock ypes
a
=
la ge
sub-
me ged
boulde s,
b
=
s nall s ones
on
sandy bo oms;
c
=
ock slabs,
d
=
biode ~ ~c bo oms,
e
=
Caule pa p ol e a
weeds A l-
ic~al subs a e ypes a
=
piling
o
conc e e
blocks
in
b eakwa e s,
b
=
e lcal su aces In po walls, c
=
ple s in sh~pya cis,
d
=
o he s a l ic~al s uc u es sca e ed on bo om
Dep h
(m):
3
o
7
8
o
15
3 o
5
3
o 10
0
o
4
2 o
6
10 o 18
3
o
9
2 o
5
l
o
6
4
o 10 Subs a e
A ~ lc~al subs a e:
-
-
-
b,c a,c a,c,d b,c.d a,d d a,c,d b,d onen a lon
Na u al ock a,b a,b a,b,c c c c,d c,d c c,e c,d a,c
S n 1 S n 2 S n
3
S n
4
S n
5
S n
6
S n
7
S n
8
S n
9
S n 10 S n 11
Apli d~ um conicum
Aplidiu n elegans
Apl~diu n pallidum
Apl~d~um punc um
Ascldia men ~lla
Asadiella aspe sa
Ascidjella sca b a
Bo nllus leach1
Ro yllus schlossen
Qon<~ edwa ds~
Ciona ~n es lnalis
Cla elina de!Ja allej
Cla el~na lepadi o mis
Cla el~na nana
Dide nn
u n conaceu n
Didemnum maculosun~
D~plosoma lis enanun~
Diplosoma spong~io me
Dls om~ls a iolosus
Halocyn h~a pap~llosa
Mic~ ocosm us squamige
Molgula bleize!
Molgula occlden al s
Phallus~a umiga a
Phallusla inge ia
Phallusla mammilla a
Polyu o ad ial~cum
Polyci o c ~s aljn Llm
Polysync a on lacazei
Pseudodls oma obscu um
Pyu a nlc ocos n us
Rhopalaea neapol~ ana
S oloiuca soclal~s
S yela canopus
S yela phca a
Synoicum a]-gus
Syno~cu n blochmann~
T ld~demnu n cei-eum
A4ic ocosmus squamige and Synoicum a gus can be
conside ed as good disc ~.mina o s because hey con-
nbu e he highes alues o he a e age disslmilan y
(6)
and because hey ha e easonably high alues o
he
S,/SD(~,)
a io (Cla ke 1993) The s a ions whlch
make up g oup C
(5
and 9) show he lowes le els
o speci ic ichness in he bay and ha e a aunis ical
composi ion ypical o ha bou a eas (h/lic ocosmus
squamige , S yela plica a, Synoicum a gus, e c.); hus,
hey a e mo e closely ela ed o he s a ions in g oup
B
(40
%,
simila i y).
MDS
o dina ion
was pe olmed using he smla i les
be ween species In he esul ing
2-dimensional
con lg-
u a lon a de ~ni e species agg ega ion can be obse ed,
bu a di ec in ep e a ion could be inaccu a e Molgula
bleizel and Ascidiella aspe sa a e abundan bu exclu-
si e o S n 9, so hei
simila i y
wl h he o he species is
e y low The emo al o hese ou lie specles 1s ecom-
mended (Gauch 1982, Cla ke
&
G een 1988) in o de o
ob ain a mo e eliable pic u e o he
emaining
species
Al hough s ess ends o dec ease as dlmenslonal~ ~ is
inc eased (Field e a1 1982), when MDS was pe o med
Na anjo e al.: E ec s o en i onmen al s ess on ascidlans
123
in
3
dimensions IFia.
3).
he swecies' ela-
Table
2.
A e aqe abundance
(7)
o impo an ascidian species In q oups
A
[l
,
.,
.
ionships became
mo e
e idei ,
n
F,~, 3
i
o
3,
I
l)
and
B
(4, 6
o
8,
10)
a .kllgeci as Bay s a ions. species a eiis ed in
0;-
de o hei con ibu ion
(8,)
o a e age dissimila i y
(8)
(=
59.74)
be ween
is
o
iden i y
o
he
2
g oups (only pa ly gi en) Species names gi en In ull in Table
1
species based on he maio ends o dis i-
which li e on na u al ock a e on he igh
S.
a gus
2.8 0.25 4.15 1.38 3.01
side o he diaa am
IA~lidium ~allidum,
l?
ad ia icum
0.6 3.0 4.13 2.41 1.71 13.86
695
1
bu ion in he bay: species mainly dis ib-
u ed a he ou e pa o bay (S ns
1
o 3)
-
-
Species
Ys
YA
6,
SD(6,)
8,
,'SD(6,)
E$,(%8)
ga a, Rhopalaea neapoli ana, Synoicum
I
A.
eleqans
2.0 1.25 2 14 1.73 123 39.41
1
d
.
.
S olonica socialis, Cla eljna della allei,
Tn-
didenlnum ce eu n, Pseudodis oma c is al-
linum, Aplidium punc um, Phallusia u nl-
M.
s4Uamige
2.6
0.25
4.02
2.18 20.58
P
obscu u n
0.0 2.5 3 97 0.64 6.25
c is allnus
0,0
63
,73
27.24
1 52 31.63
A,
1.2 2.5 251 1.90 132 35.84
conjcum. Ciona edwa dsi, A~lidium ele-
I
D.
sponqi o me
1.8 1.0 186 1.10 170 59.48
1
blochmanhi, ~seudodis oma obscu um).
Species which a e conside ed o ha e a
medium le el o ole ance in ela ion o he
subs a e
(Polyci o ad ia icum, Aplidium
S.
b~~i ~mannj
0.4 1.5 2.13 1.20 1.78 42.98
A.
punc "m
0.2
2.06 1.95 1.06 46.44
C.della allei
0.0 1.5 2.02 2.11 0.96 49.82
C,
lepadi o m,s
2,2
1.99 1.46 1.37 53.15
P
mammilla a
1.4 0.5
1
92 1.52 1.26 56.36
na u al ock, bu hey can also colonize
,
.
gans, Didemnum n~aculosum, Cla elina
nana, Bo iyllus leachi,
e c.) a e g ouped in
he middle; hey a e mo e abundan o e
a i icial subs a es. These species a e dis-
.
-
ce eum
0.2 1.25 173 1.61
1
08 62.38
D.
a iolosus
1.6 1.0 1.71 1.18 1.45
D,
maculosum
65.24
1.58 1.17 1.35 67.90
D,
l;s e janum
1.4 0.75 1.55 1.11 1.40 70.49
ibu ed h oughou p ac ically all o he bay, excep o in luence o hyd ological ac o s along i s ma gins is un-
he mos in e nal a eas (pie s and shipya ds). Finally, e en. The
5
en i onmen al a iables eco ded showed a
species g ouped on he le
(Ciona in es inalis, Mic o-
no able a iabili y a bo h spa ial and empo al le els
cosmus squamige , Synoicum a gus, S yela plica a,
( he la e is no aken in o accoun in his wo k). Fig.
4
Phallusia mammilla a
and
Cla elina lepadi o mis)
a e
(b
o g) shows a mul iple box and whiske plo o each
ypical species o ha bou a eas and colonize e e y ype a iable analyzed. In spi e o some sampling s a ions be-
o a i icial su ace ing placed di e en ly, he ela ionships among s a ions
we e simila o he ones in Ca ballo e al.
(1996).
Due o he p oximi y o he S ai s o Gib al a , he
Rela ionship be ween species and en i onmen al hyd odynamic condi ions depend on majo coas al
a iables cu en s and, in consequence, on idal lows and p e-
ailing winds. Ex eme alues o hyd odynamism we e
Abio ic cha ac e is ics o he s a ions egis e ed a ou e (and mo e exposed) s a ions
(1
o 3
and
11).
The high hyd odynamism eco ded a S n
8
Because o he many coas al ans o ma ions in Alge- can be explained by he in luence o
2
li o al cu en s
ci as Bay (due mainly o indus ial de elopmen ), he which appea du ing low- ide pe iods (Camiiias
1987).
Fig.
3.
Th ee-dimensional MDS
con igu a ion o species slmi-
lan y ma nx (s ess
=
0.09).
Values o Asc~diella aspe sa
and Molgula ble~zei we e e-
mo ed p e ious o analyses.
Species names a e
abb e ia ed
om Table
1

124 Ma Ecol P og Se 144: 119-131, 1996
l
D,,
=
4
S a ~on S a ion
Fig
4
(a) Speci ~c nchness
(D,,,)
o ascidians a he
sampl~ng s a ions; (b o g) mul ~ple box and wh~ske
'O
plo o each abio ic ac o egis e ed a he 11 sam-
pling s a ions. (d) as (c] bu wi hou S n
5
S a ~on S a ion
In gene al, hyd odynamism is in e sely ela ed o
sil ing, bu a S n 5 hese pa ame e s seem occasionally
pa allel (e.g. du ing he ainy season). The unusual
condi ions o his a ea a e due o he in luence o he
Palmones Ri e (sedimen a ion is inc eased by he
i e 's low) Thus, bo h he ex eme and he highes
a e age annual alues o sil ing (195.6 and 74.04 g
m-2 mo-', espec i ely) and o SOM (13.2 and
7
g m-2
mo-', espec i ely) we e egis e ed he e. On he o he
hand, suspended solids and suspended o ganic ma e
eached he highes alues a S n 9, whe e wa e
enewal is limi ed by a pa ially enclosed ha bou zone.
Hyd odynamism seems o in luence he o he ac-
o s. Se e al en i onmen al
ela ionships
can be es ab-
lished among he se o anables measu ed (and log-
ans o med) by using co ela ion analysis. Whe eas
hyd odynamism and suspended solids show a nega i e
co ela ion (
=
-0.72; p
=
0.018), a posi i e linea ela-
ionship exis s be ween sil ing and suspended solids
(
=
0.54;
p
<
0.1), as well as be ween bo h a iables
and hei o ganic ma e con en s (absolu e alues
only, see Fig.
5).
Uni a ia e and mul i a ia e communi y measu es
A e he a ia ion le els o majo hyd ological ac o s
we e eco ded, di e en s a is ical me hods we e ca -
ied ou in o de o es ablish a ela ionship be ween
abio ic he e ogenei y and auna1 dis ibu ion ( om as-
cidian species abundance) h oughou he su ey a ea.
As a i s app oxima ion, he bio ic in o ma ion ela-
i e o each sampling s a ion was summanzed by sim-
ple uni a ia e measu es such as he numbe o species
ound
(S)
o he speci ic ichness. Fo his pu pose,
speci ic ichness has been es ablished om he Ma -
gale index:
D*,,
=
S
-
l/ln(N), whe e N is he o al
numbe o specimens collec ed (e.g. Bakus 1990). Al-
hough
S
and
DM,
a e usually co ela ed ( o his case:
=
0.67; p
<
0.05), speci ic ichness gi es a quan i a i e
measu e o di e si y a oiding some p oblems inhe -
en o o he indexes such as Shannon's o Simpson's
(Magu an 1989).
Fig
5
Llnea co ela ions be ween he o ganic ma e
(0
M
)
con en ( o al and pe cen age) wi h sil ing and suspended
solids
+
posi i e, and
-
nega l e co ela ions 'p
<
0 1,
'"p
<
0 001
Na anjo e al.: E ec s o en i onmen al s ess on ascidians
125
-
Fig. 4a shows he speci ic ichness h oughou he
bay. The low alues o his pa ame e
(DblEI
<
3.1)
ob ained a S ns
5,
6
and 9 a e ema kable, as well as
he highes speci ic ichness
(Db1,
>
7)
a S n 2. This
bio ic in o ma ion p o ided no signi ican ela ionship
wi h he se o en i onmen al a iables conside ed
he e; howe e , a de ini e posi i e ela ionship be ween
speci ic ichness and hyd odynamism and an in e se
one wi h espec o suspended solids is sugges ed
(
=
0.53 and
=
-0.51, espec i ely; p
<
0.1).
The biological da a a e bes ep esen ed using a
mul i a ia e summa y, such as an
MDS
o dina ion
(Cla ke
&
Wa wick 1994). Fig.
6
shows he spa ial
o dina ion o s a ions based on species abundances o
he se o abio ic a iables. In hese plo s, especially in
he i s one, he o dina ion o s a ions wi h ega d o
he ho izon al axis can be explained on he basis o a
hypo he ical hyd odynamism g adien , so ha he si es
mos exposed o cu en s a e clus e ed o he le and
hose in calm condi ions o he igh . Howe e , S n
5
modi ies his gene al pa e n and, especially wi h sil -
ing, i s ex eme alues can lead o a misin e p e a ion
o he plo s (Gami o
&
Ra aelli 1992). The ep esen a-
ions o he es o he abio ic a iables do no explain
he s a ion g oupings in a consis en manne ei he .
The limi a ions o he MDS echnique a e e iden ,
bu i can be used p e ious o mo e de ailed analyses.
The BIO-ENV p ocedu e is conside ed o be a be e
app oach o he p oblem. Table
3
shows he combina-
ions o en i onmen al a iables which gi e ise o he
la ges ank co ela ion (p,) be ween bio ic and abio lc
sample dissimila i ies. The combina ion o a iables
which bes g ouped he s a ions, in a manne consis-
en w~ h he ascidian composi ion, in ol es hyd ody-
namism oge he wi h SOM (ps
=
0.82),
and he com-
bina ion o hese wi h suspended solids (p,
=
0.78).
Hyd odynamism is he single ac o which eaches he
maximum ma ching coe icien (p,
=
0.64),
and when
u he explana o y a iables a e added p, inc eases.
Howe e , i sil ing o suspended o ganic ma e a e
included he coe icien dec eases, p obably due o
hei mino e ec s on communi y s uc u e (Cla ke
&
Ainswo h 1993).
I he mos impo an en i onmen al ac o s o
s uc u ing he communi y we e known, he locali ies
ha ing a he simila alues o hese ac o s would be
expec ed o p esen a he simila ascidian composi-
ion, and an o dina ion based on his en i onmen al
da a would g oup s a ions in he same way as o he
bio ic plo (Cla ke
&
Wa wick 1994). Fig. ?a shows
he MDS o species abundance a 10 s a ions (S n
5
emo ed). The emaining plo s in his igu e a e hose
o he bes 2- and 3- a iable combina ions selec ed by
BIO-ENV
and ha o he comple e se o a iables
measu ed. As Cla ke
&
Ainswo h (1993) s a ed, o
consis ency o p esen a ion, hese plo s a e also MDS
o dina ions, ye based on he Euclidean dis ance o
no malised abio ic a iables. This app oach would
he e o e be accep able, since he small numbe o
a iables lead o only mino di e ences be ween MDS
and he co esponding P incipal Componen s Analy-
sis, which is expec ed when he highe -dimensional
s uc u e is well- ep esen ed in 2 dimensions (no e he
low alues o s ess ob ained).
Fig.
6.
Two-dimensional
MDS o dina ion o s a-
ions. Supe imposed ci -
cles ep esen he annual
a e ages o each o he
abio ic a iables (s ess
=
0.05)
hyd odynamism
b
b..
36
c,
b
?
s~ll ng
am
o
0
SOM
suspended
sol~ds
'
0
00
0
'0
0
0
suspended
o ganlc
malle
-0
"63
O
@
0
126
Ma Ecol P og Se 144: 119-131, 1996
Table 3. Resul s o BIO-ENV analysis combina ions o en i onmen al a iables, aken
k
a a ime, y~elding he 'bes ma ches' o
bio ic and abio ic simila i y ma nxes o each
k,
as measu ed by s anda d Spea man coe icien
p,.
Bold ype indica es he combi-
na ion w~ h maxlmum
p,
o e all. En i onmen al ac o s hyd
-
hyd odynamism; susOM
=
suspended o ganic ma e (pe cen age),
SOM
=
o ganlc ma e in he sil (pe cen age); sus
=
suspended solids; sil
=
s~l ~ng
k
1
hyd
(0.64)
2
hyd,
SOM
(0.82)
3
hyd,
sus,
SOM
(0.78)
4
hyd, susOM, SOM, sus
(0.67)
5
hyd, susOM, SOM, sus, sil
(0.62)
Bes a iable comb~na ~ons
(p,)
SOM
SUS
susOM sil
(0.50)
(0.21)
(0.17) (-0.07)
SOM, sus SOM, susOM hyd. sus
. .
.
(0.66)
(0.56)
(0
491
hyd, SOM, susOM hyd,
SOM,
sll
(0.74) (0.64)
hyd, susOM, SOM, sil hyd, susOM, SOM, sil
(0.65) (0.61)
The high deg ee o conco dance be ween bio ic
and
abic ic
plo s in Fig.
7
is e ?a kab!e, pa icula ly
o dina ions (a) and
(b),
which g oup he si es in a
e y simila ashion. The clus e o med by S ns
1
o
3
and
11,
which a e loca ed in he ou e zone o he
bay, a e bo h consis en in he i s 3 plo s as is he
poo ela ionship o S n 9 o he o he s. Table 3 shows
how
p,
declines sligh ly when u he a iables, apa
om hose mos ele an , a e added; his is also
e lec ed in he co esponding MDS. In ac , he BIO-
ENV
p ocedu e has a na u al s opping ule o he
cases whe e
p,
dec eases wi h inclusion o unimpo -
an
a iables
(Cla ke
&
Ainswo h 1993). This is
shown in he MDS based on comple e abio ic da a
(Fig.
?d),
whe e he lack o conco dance wi h he
bio ic MDS is ob ious.
hyd odynamlsm
+
SOM
77
hyd odynamism
+
SOM
+
sus~ended solids all en l onmenlal a iables
10
On he o he hand, he highes
p,
ob ained (close o 1)
shows a s ong in luence o he abio ic a iables on he
ascidian popula ions, bu i is di icul o see i hey a e
ue en i onmen al g adien s, since hei le el o in lu-
ence on each species emains c yp ic. A CCA could be
use ul o sol ing his p oblem, gi en ha in he esul -
ing biplo s he species o dina ion is di ec ly ela ed o
he
a ia ion
o abio ic ac o s ( e B aak 1986).
In
o de o a oid dis o ions which can be caused by
a e da a (bo h bio ic and abio ic a iables), all da a om
S n
9
and o
AscidieUa aspe sa
and
Molgula bleizei
we e
emo ed. Fu he mo e, as suspended solids and he e-
spec i e o ganic ma e p opo ions we e s ongly co -
ela ed (
=
-0.92; p
c
0.051, he o me a iable was omi -
ed so ha mul i-colinea i y p oblems would no occu .
In his manne , CCA was conduc ed on a e ised se o
da a om
4
en i onmen al a iables
eco ded a
10
s a ions wi h a o al o 36
species ound. The biplo o species and hy-
d ological ac o s p o ided by CCA is
shown in Fig. 8. Axes
I
and
I1
expla.in
73.4
O/n
o o al a iance in he da a, wi h eigen al-
ues o 0.32 and 0.11, espec i ely. The abi-
o ic ac o s mos ela ed o axis
I
a e hyd o-
dynamism and SOM, whe eas sil ing is
close o axis
I1
(see Table
4).
The obus ness
o he analysis was de e mined using
he Mon e-Ca lo pe mu a ion es (Hope
1968, in e B aak 1988). The esul s we e
as ollows: F- a io
=
2.1;
p
c
0.01. The
ou come o CCA was also checked by
compa ing he species- ac o co ela ions
wi h hose ob ained by Co espondence
Analysis (CA) and De ended Co espon-
dence analysis
(DCA),
whe e no e iden
Fig.
7.
MDS plo s o 10 sampling s a lons based on: (a) abundance da a o
38 ascidian specles; (h) and
(c)
he bes
2-
and 3- a iable combina ions o
di e ences we e ound.
ans o med en i onmen al a iables: and Id1 all en i onmen al a ~ables
In he biplo , specles a e exp essed as
~,
(see ex ). S ess alues a e: 0.04; 0; 0.01; and 0.03, espec i ely
poin s and en i onmen al ac o s as
Na anjo e al.: E ec s o en i onmen al s ess on ascidians
SOM
1
0
C ~n
0
I
A.palo
suspended o ganic
Fig.
8.
Species- ac o biplo based on Canonical Co -
ma e
espondence Analysis o a
36
species da a se wi h e-
spec o he abio ic a iables ( ep esen ed by a ows).
Each a ow poin s in he
di ec ion
o maximum
change o he espec i e
en i onmen al
a iable
sil ing
ac oss he diag am, and ~ s leng h
IS
p opo ional
o
he a e
o
change in his di ec ~on. Specles names a e
abb e ia ed om Table
1
a ows. The leng h o an a ow indica es he impo -
ance o his ac o . Each a ow de e mines a di ec ion
o axis in he diag am, ob ained by ex ending he
a ow in bo h di ec ions. The p ojec ions o a species
on his axis shows i s p e e ence o high o low alues
o his en i onmen al g adien ( e B aak 1986). We
hus in e ha
Pseudodis oma obscu um, Polyci o
c is alinus, Polyci oi- ad ia icu n, Synoicum bloch-
manni, Halocyn hia papillosa
and
Rhopalaea neapoli-
ana
p e e a eas highly exposed o cu en s and high
le els o
SOM;
species such as
Aplidium punc um, T j-
didemnum ce eum, Cla elina della allei
and
S olonica
socialis
ha e he highes weigh ed a e age wi h
espec o suspended o ganic ma e ; while
Ciona
in es inalis, Ascidiella scab a, S yela plica a, Synoicum
a gus, Mic ocosmus squamige , Ascidia men ula
and
Phallusia mam nilla a
a e mos abundan in calm si es
whe e highes con en s o
SOM
(absolu e alues) a e
eached. The emaining specles p e e a e age alues
o show no clea p e e ences.
Table
4.
Canonical coe ~cien s o and in ase co ela ions
o
DISCUSSION
Rela ion o abio ic a iables
In ben hic communi ies, physical dis u bance, p e-
da ion and compe i ion a e conside ed o be he mos
impo an ac o s a ec ing he abundance and dis i-
bu ion o species al hough, in ela ion o ascidians, he
signi icance o la al beha iou mus also be aken in o
conside a ion (Buss 1979, S ane
&
Lundal 1982, Da is
1987, S ane
&
Young 1989). Along wi h hese ac o s,
he subs a e ea u es (na u e, size and a ailabili y)
de e mine he composi ion o ben hic sys ems (Jackson
197713).
In
Algeci as Bay, we ind ha he he e ogenei y o
he en i onmen s in es iga ed was condi ioned by he
ha bou wo ks and u ban de elopmen s exis ing along
i s li o al. This physical a iabili y, along wi h he di -
e en ypes o u ban and indus ial was es, clea ly
a ec s he numbe and composi ion o species p esen ,
which ha e di e en le els o adap a ion and ole -
ance. The e o e, he dis inc in luence ha he maio
1
.
P
1
and loca ion o subs a es in he bay. Those species
en ~ onn~en al a iables wi h he i s
2
axes o CCA. susOM:
en i onmen al
ac o s ha e along he coas line should
suspended o ganic ma e (pe cen age); SOM: o ganic ma e
in he sil (pe cen age)
be conside ed be o e he p incipal ends in he spa ial
dis ibu ion o ascidians can be es ablished.
Va iables Canonical coe icien s In ase co ela ions
Axis
1
Axis
2
Axis
1
Axis
2
and
Cla elina lepadi o mis)
we e mo e abundan in
The simila i y analyses show a clea co espondence
be ween he le els o species g ouping and he ype
Sil ing
-O
039
-0. 13 -0.041
-O
770
SUSOM
-0 223 -0.298 -0.236
-0
322
Hyd odynamlsm
-O
695
0,144
-0,737
0,156
SOM
-0 779 0.260 -0.827 0.281
which p e e ligh , shallow en i onmen s and which
colonize a i icial su aces
(Mic ocosmus squamige ,
S yela plica a, Phallusia mam nilla a, Synoicum a gus