INTRODUCTION
Ma ine coas al eu ophica ion has been ecog-
nised as an eme ging p oblem (Nixon, 1990, 1995;
Sme acek e al., 1991; Goldbe g, 1995; Wu, 1999),
on a wo ldwide scale (Mo and and B iand, 1996). I
is mainly caused by an inc ease in ni ogen and
phospho us a ailabili y in li o al ecosys ems
(Ca pen e e al., 1998). This en ichmen o nu i-
en s causes p oli e a ion o phy oplank on and
oppo unis ic mac oalgae such as Ul a,
En e omo pha, Chae omo pha and Cladopho a
(Ra en and Taylo , 2003; Cu iel e al., 2004), which
leads o he disappea ance o pe ennial mac oalgae
(Dua e, 1995; Pede sen, 1995), and seag asses
(Dua e, 1995; Ha lin, 1995; Sho and Bu dick,
TROPHIC CATEGORIZATION IN THE RÍAS BAIXAS 89
SCI. MAR., 70 (1): 89-97 SCIENTIA MARINA 2006
T ophic ca ego iza ion in he Rías Baixas (NW Spain):
nu ien s in wa e and in mac oalgae*
RUBÉN VILLARES1 and ALEJO CARBALLEIRA2
1 Ecología, Escuela Poli écnica Supe io , Uni e sidad de San iago de Compos ela, 27002 Lugo, Spain.
E-mail: [email p o ec ed]
2 Ecología, Facul ad de Biología, Uni e sidad de San iago de Compos ela, 15706 San iago de Compos ela, Spain.
SUMMARY: Ma ine eu ophica ion caused by an excess supply o nu ien s is a se ious p oblem in many coas al a eas
h oughou he wo ld. In he p esen s udy we used he capaci y o mac oalgae (Ul a and En e omo pha) o in eg a e he
nu ien egime o a wa e body in o de o examine he ophic ca ego iza ion in he embaymen s s udied. We ound ha he
ophic ca ego iza ion es ablished based on nu ien le els in mac oalgae di e ed om ha es ablished based on concen a-
ions in he wa e . The wa e s o he inne mos a eas o he inle s we e he mos nu ien en iched; he algae appea ed o be
mo e a ec ed by speci ic local condi ions and did no display he g adien o dec easing nu ien concen a ions om inne
o ou e a eas ha was obse ed in he wa e samples. The lack o co espondence be ween nu ien s in he wa e and in he
algae in he p esen s udy may ha e been due o he he e ogeneous nu ien condi ions ound in coas al a eas, so ha he in e -
idal algae did no adequa ely e lec he nu ien le els o he inne zones o he embaymen s unde s udy.
Key wo ds: En e omo pha,Ul a, eu ophica ion, nu ien s, Rias Baixas, Spain.
RESUMEN: SECTORIZACIÓN TRÓFICA EN LAS RÍAS BAIXAS (NW ESPAÑA): NUTRIENTES EN AGUA Y EN MACROALGAS. – La eu o-
ización ma ina, o iginada po un excesi o apo e de nu ien es, es á conside ada ac ualmen e como un g a e p oblema en
nume osas á eas cos e as de odo el mundo. En es e es udio empleamos la capacidad de las mac oalgas (Ul a y
En e omo pha) de in eg a el égimen nu i i o de un cue po de agua pa a ealiza una sec o ización ó ica de las bahías
es udiadas. Los esul ados de la sec o ización ó ica en unción de las mac oalgas ue on di e en es a la es ablecida en un-
ción de las concen aciones de nu ien es en agua. Las zonas más in e nas de las ías ue on las más en iquecidas en cuan o
a nu ien es en agua, pa eciendo es a las algas más a ec adas po condiciones locales especí icas, és as no siguen el g adien e
de concen ación del in e io al ex e io que se obse aba en el agua. La al a de co espondencia en e los nu ien es en agua
y algas en es e es udio puede se debido a la g an he e ogeneidad en las condiciones nu i i as que encon amos en á eas cos-
e as, de o ma que las mues as de algas in e ma eales no hayan e lejado adecuadamen e los ni eles de nu ien es del in e-
io de las masas de agua es udiadas.
Palab as cla e: En e omo pha, Ul a, eu o ización, nu ien es, Rías Baixas, España.
*Recei ed Janua y 1, 2005. Accep ed June 6, 2005.
sm70n1089-2041 1/3/06 16:28 Página 89
1996; Sho and Wyllie-Eche e ia, 1996), he eby
a ec ing associa ed animal communi ies. The disap-
pea ance o seag asses o en causes emobiliza ion
o unde lying sedimen s p e iously ixed by he
plan s’ oo s, p oducing g ea e u bidi y in he
wa e (Walke and McComb, 1992). Eu ophica ion
leads o changes in mac ozooben hic communi ies
(E e e , 1994; Pihl e al., 1995; P ena, 1995; Nei a
and Rackemann, 1996; No kko and Bonsdo ,
1996; Ryba czyk e al., 1996), and ish communi ies
(Rosenbe g, 1985; Hansson and Ruds am, 1990;
Pihl e al., 1995). In ce ain coas al a eas, eu ophi-
ca ion is also a se ious p oblem o he ou is sec o
(Rosenbe g, 1985; Pi iou and Ménesguen, 1992;
Mo and and B iand, 1996).
Se e al au ho s ha e pos ula ed he idea o using
he concen a ions o nu ien s in mac oalgae as
indica o s o hei a ailabili y in he en i onmen ,
ins ead o adi ional wa e analyses (Ho, 1987;
Wheele and Bjö nsa e , 1992; Fong e al., 1994,
1998; Lyngby and Mo ensen, 1994; Ho ocks e al.,
1995; Lyngby e al., 1999). The le els o nu ien s in
coas al wa e s a e highly a iable. T ansien peaks
o nu ien s caused by sewage e luen s, ainwa e ,
e c., a e common in hese a eas, and a e di icul o
de ec by pe iodic wa e analysis; e en i hey a e
iden i ied, i is di icul o de e mine hei e ec on
p ima y p oduc ion. Mac oalgae in eg a e he nu i-
en egime o e a ce ain ime pe iod and he e o e
may be sui able o e alua ing he ophic condi ions
o he a eas om which hey a e collec ed wi h less
sampling e o han wi h o he adi ionally used
me hods.
The main aim o he p esen s udy was o use he
capaci y o mac oalgae o in eg a e he nu ien
egime o a wa e body in o de o ca y ou ophic
ca ego iza ion o he s udy a ea, based on he nu i-
en le els in in e idal samples o wo gene a o
mac oalgae (Ul a and En e omo pha) which p oli -
e a e in eu ophic a eas. We also compa ed he
esul s o his me hod o ca ego iza ion wi h hose o
ca ego iza ion based on he nu ien le els in wa e
ound in a mo e in ensi e su ey ca ied ou in inne
a eas o he embaymen s unde s udy.
MATERIALS AND METHODS
Sampling
The s udy was ca ied ou in ou coas al embay-
men s known collec i ely as he Rías Baixas
(Galicia, NW Spain). The posi i e es ua ine ci cula-
ion, which concen a es nu ien s (F aga and
Ma gale , 1979), along wi h he pe iodic upwelling
e en s ha ake place in sp ing and summe
(Ál a ez-Salgado e al., 1993), combine o make
hese embaymen s e y p oduc i e sys ems (Teno e
e al., 1982; P ego, 2002).
Samples o mac oalgae we e collec ed om
in e idal a eas a low ide. Mos o he onds we e
en a i ely iden i ied as Ul a igida and
En e omo pha in es inalis. Howe e , we decided
no o iden i y he algae o species le el because o
he complica ions in ol ed in he axonomy o hese
gene a, in which polymo phism is common
(P o asoli and Pin ne , 1980). Mal a e al. (1999)
ha e shown ha Ul a specimens a e o en assigned
o di e en species when hey a e in ac di e en
mo pho ypes o one species. Recen ly, Hayden e al.
(2003) sugges ed ha Ul a and En e omo pha
should no be ecognized as sepa a e gene a (see
also www.algaebase.o g).
Algal samples we e collec ed mon hly om 22
sampling si es (Fig. 1) be ween Ma ch 1994 and
Feb ua y 1995. Sampling o En e omo pha was
in e up ed in Sep embe 1994 because he alga had
s opped g owing a many si es. A each sampling
si e we collec ed a leas 75 onds o Ul a and sam-
ples om a leas 30 ma s o En e omo pha along a
ansec o 100m pa allel o he coas . A i e selec -
ed si es (A2, A8, P2, P5 and V4) o nigh ly sam-
pling was ca ied ou be ween Ap il and No embe
1994. Algae we e s o ed in mesh bags and ans-
po ed a 4ºC o he labo a o y.
The da a on nu ien concen a ions in wa e
we e p o ided by he ‘Cen o de Con ol da
Calidade do Medio Ma iño’, un unde he auspices
o he Galician au onomous go e nmen (Xun a de
Galicia). The wa e sampling si es a e shown in
Figu e 1. Sampling was ca ied ou weekly a 3
dep hs (0-5, 5-10, 10-15m). The da a used he e a e
means o hese 3 alues, and can be conside ed as
ep esen a i e o he su ace wa e laye o he ías
(Ál a ez-Salgado e al., 1996).
Chemical analyses
In he labo a o y, algae we e washed ca e ully
wi h dis illed wa e , d ied a 50±1ºC un il cons an
weigh , c ushed using a mo a and pes le and s o ed
in plas ic bags.
The alues o he le els o issue ni ogen we e
measu ed wi h a LECO CHN 1000 elemen al
90 R. VILLARES and A. CARBALLEIRA
sm70n1089-2041 1/3/06 16:28 Página 90
analyse , using EDTA as a s anda d. Fo phospho us
analysis, samples we e combus ed in a mu le u -
nace a 550±5ºC o 3 hou s and hen diges ed in 2.5
ml o 2N HCl on a ho pla e a 200±2ºC o 15 min-
u es. The ex ac s we e il e ed using acid washed
il e s and he samples hen made up o 50 ml wi h
dis illed wa e (Chapman and P a , 1981).
Phospha e in he ex ac s was de e mined using he
anadomolybdophospho ic acid colo ime ic
me hod, which is he mos sui able o he ange o
concen a ions in ol ed he e (APHA, AWWA,
WEF, 1995). Ce i ied e e ence plan ma e ial,
BCR (Communi y Bu eau o Re e ence) nº 129 (hay
powde ), was analysed along wi h he samples o
es he e iciency o he me hod.
S a is ical analysis
P io o analysis o a iance (ANOVA), wa e
samples we e balanced (by making n equal in he
di e en g oups) o make he es mo e obus .
When he e was a missing alue o a compound, all
o he alues co esponding o ha compound we e
omi ed o ha week o sampling and o all sam-
pling poin s in he same embaymen . The loss o
in o ma ion caused by his p ocedu e was negligible
as he e we e e y ew missing alues ela i e o he
o al numbe o da a co esponding o nu ien s in
he wa e . The no mali y o he dis ibu ion was es -
ed o each g oup by he Kolmogo o -Smi no es ,
Lillie o s es and by examining equency his-
og ams. The homogenei y o he a iances was e -
i ied using Le ene’s es . Ma hema ical ans o ma-
ion o da a was ca ied ou whe e necessa y o
ob ain a no mal dis ibu ion and homogeneous a i-
ances. Samples we e conside ed signi ican ly di e -
en a p <0.05. Whe e signi ican di e ences we e
de ec ed by ANOVA, he Tukey-HSD (hones ly sig-
ni ican di e ence) es was applied o es ablish
homogeneous g oups (Za , 1984; Day and Quinn,
1989; Sokal and Rohl , 1995).
Clus e analyses we e ca ied ou by he a e age
linkage be ween g oups me hod, which uses he
in o ma ion om all pai s o dis ances by applying
he squa ed Euclidean dis ance, he mos commonly
used measu e o dis ance. To a oid a iables wi h
high igu es ha ing g ea e emphasis in he inal
esul , da a we e s anda dized by ans o ming hem
o z sco es by sub ac ing he mean alue om each
indi idual alue and di iding i by he s anda d
de ia ion co esponding o he en i e se o alues.
RESULTS AND DISCUSSION
Tempo al a ia ions in nu ien s
The changes in mon hly mean concen a ions o
nu ien s in he wa e and in he algae a e shown in
Fig. 2. Compa ison o he con ibu ion o each o he
N compounds o he o al dissol ed ino ganic N,
e eals ha ni a es comp ised he main o m o ino -
ganic ni ogen, pa icula ly in win e . The e we e wo
peaks in ammonium le els, one in June, when he
mean le els we e almos equal o hose o ni a es,
and ano he highe one in No embe . The wo maxi-
mal alues we e p obably associa ed wi h he ini ial
s age o decomposi ion o he o ganic ni ogen; in he
s udy a ea he e a e usually wo peaks in p ima y p o-
duc ion, a he end o sp ing and a he end o summe
(Noguei a e al., 1997; Villa es and Ca ballei a,
2003). Ni i es and ni a es ollowed simila pa e ns
wi h minimum alues in summe and maximum al-
TROPHIC CATEGORIZATION IN THE RÍAS BAIXAS 91
FIG. 1. – Loca ion o sampling si es. Mac oalgal sampling si es a e
indica ed by capi al le e s. Wa e sampling si es (o he “Cen o de
Con ol da Calidade do Medio Ma iño”-Xun a de Galicia) a e
indica ed wi h lowe case le e s.
sm70n1089-2041 1/3/06 16:28 Página 91
ues in win e , al hough he highes concen a ion o
ni i e was ound in Decembe and ni a e le els con-
inued o ise un il Feb ua y. In gene al, phospha e
le els did no show as clea a seasonal end as he N
compounds; lowes mean alues we e ound in sp ing
and summe , and highes alues in au umn and win-
e . The N:P a io was lowe han he Red ield a io
(N:P = 16) om Ma ch o Oc obe , and highe in
au umn and win e .
The inc ease in nu ien s in he wa e in win e
may ha e been due o an inc ease in lu ial inpu s and
a dec ease in p ima y p oduc ion, al hough he peaks
in N compounds appea ed o co espond o he deg a-
da ion o o ganic ma e syn hesized in summe , wi h
an ammonium peak in No embe , ollowed by peaks
o ni i e and ni a e in Decembe and Feb ua y
espec i ely. Simila esul s we e ob ained by
Noguei a e al. (1997) o he Ría de Vigo.
Tissue le els o N ollowed a simila pa e n in
bo h algae: hey we e lowes in summe , sligh ly
highe in sp ing and highes in win e . Tissue P also
ollowed a simila pa e n in bo h Ul a and
En e omo pha, he lowes issue le els o his nu i-
en we e ound in sp ing and summe hen inc eased
g adually h oughou au umn and win e . The e
we e wo peaks in he N:P a io in algae, in May and
in Oc obe -No embe , and minimum alues we e
obse ed in summe . Tempo al changes in issue
nu ien s we e simila o hose epo ed in mos
o he s udies o his ype, wi h high concen a ions
in win e and low concen a ions in summe
(Pede sen and Bo um, 1996; Mal a and Ve schuu e,
1997; De Casabianca and Posada, 1998; Lyngby e
al., 1999).
The e was a pa allel a ia ion in ino ganic nu i-
en s in he wa e and issue nu ien s in Ul a, which
was e lec ed in he good co ela ions be ween hem
(Table 1). Fo En e omo pha he co ela ions we e
no as high, and we e only signi ican wi h ni a es
and dissol ed ino ganic ni ogen (DIN). The nu i-
92 R. VILLARES and A. CARBALLEIRA
FIG. 2. – Tempo al changes in he nu ien concen a ions in he wa e and in mac oalgae. Values a e mon hly means om all he sampling
si es. E o ba s ep esen he s anda d e o , hese a e no shown o nu ien s in he wa e because in mos cases hey we e no la ge enough
o be dis inguished om he symbol ( iangle).
TABLE 1. – Spea man’s co ela ion coe icien s and le els o signi icance be ween mon hly a i hme ic means o nu ien s in wa e and in
mac oalgae. n = 12 o Ul a, n = 7 o En e omo pha. * Signi ican a p<0.05, ** Signi ican a p<0.01, *** Signi ican a p<0.001, n.s. = no
signi ican .
Ammonium Ni i e Ni a e DIN Phospha e N:P
N Ul a 0.587* 0.811** 0.888*** 0.916***
N En e omo pha 0.536 n.s. 0.607 n.s. 0.786* 0.821*
P Ul a 0.713**
P En e omo pha 0.536 n.s.
N:P Ul a 0.231 n.s.
N:P En e omo pha 0.607 n.s.
sm70n1089-2041 1/3/06 16:28 Página 92
en le els in he wa e we e hus appa en ly be e
e lec ed by Ul a han by En e omo pha, wi h he
addi ional ad an age ha he o me is p esen
h oughou he en i e yea .
T ophic ca ego iza ion in he ías
The da a on nu ien s in he wa e was analysed
using a one-way ANOVA o ind i he e we e sig-
ni ican di e ences be ween he sampling si es wi h-
in each ía (Table 2). Whe e his occu ed homoge-
neous g oups we e es ablished using he Tukey-
HSD mul iple compa isons es (Table 3). The e
we e no signi ican di e ences o ni a e o N:P in
any o he ías, in con as o he indings o ammo-
nium and phospha e. The g oups es ablished o he
inne mos pa o he ías always ep esen ed he
mos nu ien en iched a eas (Table 3). In he o he
TROPHIC CATEGORIZATION IN THE RÍAS BAIXAS 93
TABLE 2. – One way ANOVA o he concen a ions o nu ien s in he wa e o each ía. The deg ees o eedom a e shown in b acke s.
P epa ed using da a p o ided by he ‘Cen o de Con ol da Calidade do Medio Ma iño’ (Xun a de Galicia). * - Signi ican a p<0.05,
** - Signi ican a p<0.01, *** - Signi ican a p<0.001, n.s. = no signi ican .
Mu os A ousa Pon e ed a Vigo
Ammonium F 2.701* (5, 270) 5.940*** (9, 430) 6.326*** (5, 264) 19.47*** (5, 300)
Ni i e F 0.500 n.s. (5, 276) 0.903 n.s. (9, 460) 2.193 n.s. (5, 264) 6.776*** (5, 300)
Ni a e F 1.944 n.s. (5, 270) 0.546 n.s. (9, 450) 0.536 n.s. (5, 246) 1.688 n.s. (5, 294)
DIN F 2.315* (5, 264) 1.359 n.s. (9, 430) 2.275* (5, 228) 7.249*** (5, 294)
Phospha e F 3.538** (5, 276) 8.649*** (9, 460) 10.64*** (5, 282) 41.30*** (5, 300)
N:P F 0.606 n.s. (5, 264) 0.298 n.s. (9, 430) 0.339 n.s. (5, 228) 0.923 n.s. (5.294)
TABLE 3. – G oups es ablished using he Tukey-HSD mul iple compa isons es o nu ien s in he wa e in each ía. The si es a e o de ed by
inc easing he mean concen a ion o he co esponding nu ien . Sampling si es wi h he same g ouping numbe we e no signi ican ly di -
e en . In cases whe e no g oups appea , no signi ican di e ences we e ound. P epa ed using da a p o ided by he ‘Cen o de Con ol da
Calidade do Medio Ma iño’ (Xun a de Galicia).
MUROS
Ammonium DIN Phospha e
m5 1 - - - m5 1 - - - m5 1 - - -
m4 1 2 - - m1 1 2 - - m4 1 2 - -
m1 1 2 - - m4 1 2 - - m1 1 2 - -
m2 1 2 - - m2 1 2 - - m6 1 2 - -
m6 1 2 - - m6 1 2 - - m2 1 2 - -
m3 - 2 - - m3 - 2 - - m3 - 2 - -
AROUSA
Ammonium Phospha e
a0 1 - - - a0 1 - - -
a8 1 2 - - a9 1 2 - -
a9 1 2 3 a8 1 2 3 -
a4 1 2 3 4 a2 1 2 3 4
a7 1 2 3 4 a4 1 2 3 4
a1 1 2 3 4 a1 - 2 3 4
a5 - 2 3 4 a7 - - 3 4
a2 - - 3 4 a5 - - - 4
a6 - - - 4 a3 - - - 4
a3 - - - 4 a6 - - - 4
PONTEVEDRA
Ammonium Phospha e
p4 1 - - p5 1 -
p5 1 - - p2 1 -
p2 1 - - p4 1 -
p1 1 2 - p1 1 -
p3 - 2 3 p6 - 2
p6 - - 3 p3 - 2
VIGO
Ammonium Ni i e DIN Phospha e
6 1 - - 6 1 - - 6 1 - - - 6 1 -
5 1 - - 5 1 2 - 5 1 2 - - 5 1 -
1 1 - 1 1 2 - 1 1 2 3 - 1 1 -
2 - 2 - 2 - 2 3 2 - 2 3 4 2 - 2
3 - 2 - 3 - - 3 3 - - 3 4 3 - 2
4 - 2 - 4 - - 3 4 - - - 4 4 - 2
sm70n1089-2041 1/3/06 16:28 Página 93

g oups, he nu ien concen a ion in he wa e
dec eased owa ds he mou h o he ía. This was o
be expec ed as he inne mos pa o he ía is he
mos hea ily in luenced by nu ien inpu s due o he
upwelling e en s which gene ally occu in he cen-
al and inne zones o he ías (O o, 1975; Teno e
and González, 1975; P ego and F aga, 1992), and
also because o lu ial inpu s.
Clus e analysis was used o examine he mean
le els o ni i e, ni a e, ammonium and phospha e a
each sampling si e wi h he aim o de ec ing homo-
geneous g oups. The dend og am (Fig. 3) shows a
clea dis inc ion be ween wo g oups in he ías o
Mu os, Pon e ed a and Vigo, wi h he inne g oup
always being he mos nu ien -en iched. In he
ou e g oup in he Ría de A ousa ano he wo sub-
g oups can be dis inguished, wi h he g oup co e-
sponding o he si es closes o he open sea being
he poo es in nu ien s. Clus e analysis was also
ca ied ou conside ing phospha e and DIN, i.e.
ni i e+ni a e+ammonium, hus a oiding N com-
pounds ha ing g ea e emphasis. The esul s we e
almos iden ical o he p e ious ones.
T ophic ca ego iza ion in he ías was also ca -
ied ou wi h algal da a, using he same p ocedu e
as be o e. Fo Ul a, signi ican di e ences in le -
els o N and P in he Ría de A ousa and in he N:P
a io in he ías o Pon e ed a and Vigo we e
de ec ed by one-way ANOVA (Table 4); he g oups
sepa a ed using he Tukey-HSD es a e shown in
Table 5. Fo En e omo pha, signi ican di e ences
in concen a ions o N and P a di e en si es in he
Ría de A ousa, in he le els o P in he Ría de Vigo
and N:P in he Ría de Mu os we e de ec ed by one
way ANOVA. Clus e analysis was also used o
g oup he si es acco ding o he le els o N and P
in Ul a and En e omo pha (Fig. 4). The ca ego-
iza ion based on algal da a di e ed om ha
based on wa e da a. The g oups es ablished o
algae did no ollow a g adien om he inne o he
94 R. VILLARES and A. CARBALLEIRA
FIG. 3. – Dend og am o he ía by ía clus e analysis o he mean
concen a ions o each si e, o ni i e, ni a e, ammonium and phos-
pha e. The a e age linkage be ween g oups me hod was used wi h
he squa ed Euclidean dis ance. Scale in ela i e uni s.
TABLE 4. – One way ANOVA o he concen a ions o N, P and N:P in Ul a and En e omo pha o each ía. The deg ees o eedom a e
shown in b acke s. * - Signi ican a p<0.05, ** - Signi ican a p<0.01, *** - Signi ican a p<0.001, n.s. = no signi ican .
Mu os A ousa Pon e ed a Vigo
Ul a N F 0.451 n.s. (3, 28) 2.746* (7, 72) 0.401 n.s. (4, 40) 0.742 n.s. (4, 50)
Ul a P F 0.178 n.s. (3, 28) 2.477* (7, 72) 1.873 n.s. (4, 40) 1.892 n.s. (4, 50)
Ul a N:P F 0.537 n.s. (3, 28) 1.232 n.s. (7, 72) 3.599* (4, 40) 4.275** (4, 50)
En e omo pha N F 1.624 n.s. (3, 20) 3.984** (7, 24) 1.098 n.s. (4, 25) 1.412 n.s. (4, 20)
En e omo pha P F 2.463 n.s. (3, 20) 6.847*** (7, 24) 0.715 n.s. (4, 25) 4.246* (4, 20)
En e omo pha N:P F 3.332* (3, 20) 0.221 n.s. (7, 24) 1.544 n.s. (4, 25) 1.051 n.s. (4, 20)
TABLE 5. – G oups es ablished o nu ien s in Ul a and
En e omo pha o each ía, using he Tukey-HSD mul iple compa -
isons es . The si es a e o de ed by inc easing mean concen a ion
o he co esponding nu ien . Sampling si es wi h he same g oup-
ing numbe we e no signi ican ly di e en . In cases whe e no
g oups appea , no signi ican di e ences we e ound.
Ul a AROUSA VIGO
N P N:P
A8 1 A8 1 V1 1
A6 1 2 A6 1 2 V4 1 2
A4 1 2 A5 1 2 V2 1 2
A5 1 2 A4 1 2 V5 1 2
A2 1 2 A2 1 2 V3 2
A3 2 A3 1 2
A1 2 A1 1 2
A7 2 A7 2
En e omo pha
MUROS AROUSA VIGO
N:P N P P
M1 1 A5 1 A5 1 V4 1
M3 1 2 A6 1 A6 1 2 V3 1 2
M2 1 2 A7 1 2 A7 1 2 3 V2 1 2
M4 2 A4 1 2 A3 1 2 3 V1 1 2
A3 1 2 A4 1 2 3 V5 2
A2 1 2 A2 2 3
A1 2 A1 3
A8 2 A8 3
sm70n1089-2041 1/3/06 16:28 Página 94
ou e a eas o he ías as did he g adien s es ab-
lished using he wa e samples.
One possible explana ion o his misma ch
be ween nu ien s in he wa e and in mac oalgae
may be ha he di e en physiological condi ions o
he algae h oughou he yea may a ec hei use as
indica o s o he nu ien s a us o wa e . A ce ain
imes o yea , mac oalgae may ake up nu ien s
om he wa e and use hem di ec ly o g ow h
wi hou accumula ing hem. Acco ding o Fong e
al. (1994), a ela ionship be ween nu ien s in he
wa e and in mac oalgae will only be ound when
nu ien s a e no limi ing, and can hus be accumu-
la ed. Fong e al. (1998) poin ed ou he use ulness
o En e omo pha in es inalis as an indica o o
nu ien en ichmen in coas al wa e s, al hough hey
sugges ed ha his indica o would possibly only be
accu a e when nu ien supplies we e high.
The mean concen a ions o nu ien s in he
wa e canno be conside ed low in ela ion o hose
epo ed in o he s udies ha demons a e he use-
ulness o mac oalgae as indica o s o he nu ien
s a us o he wa e in which hey a e ound (Ho,
1987; Lyngby and Mo ensen, 1994; Ho ocks e al.,
1995; Lyngby e al., 1999). Despi e his, he p e i-
ous app oach in ol ing using ANOVA, pos -hoc
analysis and clus e analysis was epea ed o Ul a,
al hough only conside ing hose mon hs in which
he concen a ions in he samples we e highe han
he c i ical issue concen a ions o N and P. The
c i ical concen a ion ep esen s he minimum con-
cen a ion o a nu ien in plan issue ha is needed
o suppo maximum g ow h a es. Villa es and
Ca ballei a (2004) calcula ed he c i ical concen a-
ions o issue N and P o Ul a in he s udy egion
(24.5 mg g-1 and 0.810 mg g-1 espec i ely); he c i -
ical concen a ions o En e omo pha in he ci ed
s udy could no be calcula ed. Only hose algae in
which he nu ien le els al eady allow maximal
g ow h we e he e o e aken in o accoun , which
acco ding o Fong e al. (1994) a e he mos sui able
o e lec ing he nu ien s a us o he wa e . The
elimina ed samples co esponded abo e all o he
summe mon hs, and o a lesse ex en , o sp ing.
The samples co esponding o he same pe iods o
ime o each nu ien in he wa e in each ía we e
also omi ed. The new classi ica ion in e ms o
nu ien s in he wa e was simila o he o iginal
classi ica ion, i.e. wi h dec easing concen a ions
always om he inne o he ou e a ea o each ía.
The classi ica ion based on he nu ien s in Ul a did
no a y much om ha obse ed p e iously wi h
he annual da a, and hus di e ed om ha o he
wa e . In conclusion, he di e en physiological
condi ions ha may be ound in Ul a h oughou he
yea do no appea o explain, a leas o ally, he di -
e en esul s o wa e and algae; pe haps using
annual a e age alues minimized any in e e ence
associa ed wi h he seasonal changes in algal physi-
ology. Ho (1987) ound highly signi ican co ela-
ions be ween he mean annual concen a ions (cal-
cula ed om mon hly da a) o nu ien s in he wa e
and in Ul a lac uca.
In gene al, he sampling poin s wi h he highes
le els o nu ien s in algae we e hose si ua ed close
o small illages ( he a eas close o la ge ci ies we e
TROPHIC CATEGORIZATION IN THE RÍAS BAIXAS 95
FIG. 4. – Dend og am o ía by ía clus e analysis o he mean con-
cen a ions o N and P in Ul a and in En e omo pha. The a e age
linkage be ween g oups me hod was used wi h he squa ed
Euclidean dis ance. Scale in ela i e uni s.
sm70n1089-2041 1/3/06 16:28 Página 95
discoun ed when he sampling poin s whe e selec -
ed). The nu ien s o igina ing om hese illages
may ha e caused an inc ease in he nu ien le els in
he wa e , al hough only locally, he eby a ec ing
he nu ien le els in ou algal samples bu no he
mean le els in he wa e in he ias.
The N:P a io in he algae s udied may be con-
side ed high (median alues o 65:1 o Ul a and
68:1 o En e omo pha, bo h a omic a ios) in com-
pa ison wi h he alues co esponding o he wa e
(median 12:1). Mac oalgae usually show alues
highe han he Red ield a io (Dua e, 1992),
al hough he p esen alues a e highe han he a e -
age alue epo ed by his au ho o seaweeds
(49:1). Villa es and Ca ballei a (2003) sugges ed he
e en ion o P by sedimen as a possible explana ion
o he low le els o his nu ien in in e idal algae
in he s udy a ea. I is hus possible ha in he in e -
idal zone, whe e sedimen s may ha e g ea e
impo ance in he nu ien cycles due o he high
a io be ween he su ace a ea o sedimen and he
olume o wa e , he seques a ion o phospha es
om he wa e by sedimen s would make he local
le els o P in he wa e ela i ely low.
In conclusion, i is possible ha he local le els
o nu ien s in he wa e a he algal sampling poin s
we e di e en om hose ound a he wa e sam-
pling poin s. I appea s ha because o he high he -
e ogenei y in he le els o nu ien s in coas al
wa e s, in e idal mac oalgae may no be sui able o
indica ing he nu ien s a us o la ge wa e bodies.
CONCLUSIONS
In gene al, he highes alues o bo h issue nu i-
en concen a ions and dissol ed ino ganic nu ien s
we e ound in win e and he lowes alues ound in
summe ; a si ua ion ha may be conside ed no mal
a in e media e la i udes. The mon hly mean le els
o nu ien s in Ul a ollowed a seasonal pa e n ha
appa en ly e lec ed he nu ien le els in he wa e
be e han he pa e n co esponding o
En e omo pha.
The ca ego iza ion based on he nu ien le els in
he wa e always showed ha he inne a eas o he
ías we e he mos nu ien en iched; his can be
explained by lu ial inpu s and upwelling e en s,
which a e pa icula ly ele an in his zone. The ca -
ego iza ion based on algal da a di e ed om ha
based on wa e da a. The mos en iched sec o s,
based on algal issue nu ien s, we e gene ally hose
close o small illages. E en small supplies o nu i-
en s o e es ial o igin may cause, on a local scale,
la ge a iabili y in he ophic condi ions in he a ea
immedia ely adjacen o he coas , which oge he
wi h he impo ance o sedimen in he nu ien
cycles in he shallowes zones may imply g ea he -
e ogenei y in he nu ien condi ions in he s udy
a ea. In e idal algae may pe haps adequa ely e lec
local nu ien condi ions, bu hey may no be ep e-
sen a i e o he nu ien s a us o la ge wa e bodies,
as in he case o he embaymen s unde s udy.
ACKNOWLEDGEMENTS
We hank he “Cen o de Con ol da Calidade do
Medio Ma iño” (Xun a de Galicia), in pa icula
Joaquín Ma iño and Juan Manei o, o supplying us
wi h da a on nu ien s in wa e . We also hank Xoán
Puen e o his help wi h he ieldwo k. The au ho s
a e g a e ul o he cons uc i e c i icisms o wo
anonymous e e ees, which helped o imp o e he
o iginal e sion o he manusc ip .
This s udy was pa ly inanced by he “Banco de
Especímenes Ambien ales de Galicia (BEAG)”
(Conselle ía de Medio Ambien e, Xun a de Galicia).
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