OLABARRiA&a/
Bivalves and relationships With environmental parameters
APEX 13(3) 81-93,20 juil 1998
The influence of physicochemical parameters on the distribution
of dominant bivalve species in the ensenada do BaAo
(Ria de Ferrol) in Northwest of Spain
c O L A B A R R I A \ V URGORRI^ & J S TRONCOSO^
' Fac Ciencas del Mar, Univ Autónoma de Sinaloa, C/Paseo Claussen s/n, 82000 Mazatlan (Sinaloa), Mexico
^ Depart Bioloxia Animal, Fac de Bioloxia Universidade de Santiago, E-15706, Santiago (La Corufia), Spain
^ Depart de Recursos Naturais e Medio Ambiente, Fac de Ciencias do Mar, Universidade de Vigo, Vigo, Spain
KEYWORDS. Bivalves, synecology, physicochemical parameters, Ria de Ferrol, Spain
MOTS CLEFS. Bivalves, synécologie, facteurs physico-chimiques, Ria de Ferrol, Espagne
ABSTRACT. This paper presents a synecological study of the dominant bivalve species in the
Ensenada do Bafio (Ria de Ferrol, NW Spain), and reports on relationships between the distribution of
these species and physicochemical parameters (particle size, carbonate content, organic matter
content, sorting coefficient and depth/ height with respect to tidal zero) We conclude that the most
important factors govermng species distribution are grain size and depth/height
RÉSUMÉ. Une étude gynécologique des bivalves dominants de 1' Anse do Bano (Ria de Ferrol, NO
Espagne) est présentée Cette étude montre les relations entre leur distribution et les conditions
physico-chimiques du miheu (granulométne, teneur en carbonates et en matière orgamque, coefficient
de sélection et profondeur) Cette étude a permis de mettre en évidence que les facteurs déterminant
de la distribution des bivalves sont le gradient sedimentaire et la profondeur ou la hauteur par rapport
au mveau 0 de la marée
INTRODUCTION
In early studies on the biology of benthic faunas, an
understanding of sedimentological parameters proved
to be of utmost importance, due to their effect on the
faunal composition of commumties and to the close
relationship between sediment vanables and the
ecological preferences of the different species This is
particularly true for infaunal species, which the nature
of the sediment determines life style as well as trophic
and reproductive habits
In a number of studies, tlie primary goal has been to
gather information on relationships between mollusc
distributions and the physicochemical properties of die
sediment It has been observed that the relationship
between mollusc distnbutions and tlie sedimentary
environment is tlie result of a dynamic interdependence
among physical, chemical and microbiological
sediment factors (BADER, 1954) Important studies in
tlus field include those of LANDE (1975), TUNBERG
(1981) and CORNET (1985, 1986) on the distribution
and ecology of bivalve commumties of European
Atlantic coast, and those of DRISCOLL & BRANDON
(1973), FRANZ (1976), FRANZ & MERRIIL (1980) on
tlie American Atlantic coast in which bentliic
molluscan assemblages in relation to sediment were
studied Previous studies about distribution and
ecology of molluscs of the coasts of northern Spain
include tliose of FIGUERAS (1956), VIEITEZ (1976),
PLANAS & MORA (1984), LABORDA & MAZE (1987),
MAZE & LABORDA (1988), BORJA
TRONCOSO & URGORRI (1992)
(1988, 1991) and
Despite of abundance of malacological studies on the
Galician coasts, there is a scarcity of research on
sinecology of molluscs For that, we decided to extend
the knowledge of this group, particularly in the Ria de
Ferrol, where this group has been poorly studied In the
present study, we investigated relationships between
bivalve distnbutions and physicochemical factors in the
Ria de Ferrol The study was earned out in the
Ensenada de Bano (Baflo Inlet), which contains a wide
range of sediment types (including mud, muddy sand,
shell gravel, coarse sand and maerl)
METHODS
Tlie study area is located on the southern side of the
Ria de Fenol (NW Spain), between Punta do Faro da
Palma (43°27'52"N, 08°16'49"W) and Punta Piteira
(43°27'57"N, 08°15'37"W), and has an area of 0 5 km^
andamaximumdepthof 18 m (Fig 1)
81
APEX
13(3) 81-93,20 juil 1998
Bivalves and relationships with environmental parameters
The inlet is oriented in direction NNE-SSW, the
prevailing winds are southwesterlies for most of the
year, except in summer when northeasterlies become
dominant The mean tidal range in tlie na is 2,7 m, and
tidal effects give rise to strong currents (up to 1,5 m/s
in the ria's central channel) Outward movement of
water from the na provokes movement to tlie SE witlun
the inlet, while movement into the na provokes
movement to tlie SSW within tlie inlet These currents,
which are stronger at the mouth of the inlet than at
more distal points, are tlic dominant factor affecting
sediment distnbution within the inlet
Mollusc were sampled between July 1991 and June
1992 at 40 intertidal and 35 subtidal stations (one
sample per station) Sampling points were selected
along 12 parallel transects drawn across the inlet at
100 m inter\'als, taking samples at the points that were
judged by visual examination to show a change in
nature, texture or substrate co\ering In the subtidal
zone, tlie samples were collected by scuba diving At
each point, a 0,25 m^ square sample was taken, to a
depth of approximately 20 cm, using a rectangular
shovel The tidal range at intertidal stations was
2 29 m The intertidal samples were additionally
collected at tlie ends of each transect and, in the inner
intertidal zone, samples were also taken every 100 m
along each transect (OLABARRIA et al, 1996) All
samples were subsequently wet-sieved tlirough a series
of sieves with 10, 2, and 0 5 mm mesh Finally the
sieved samples were transported to the laboratory to be
sorted by the remounting technique (Ros, 1975)
Surface sediment samples were also collected from
each sampling point, for granulometric analysis and for
determination of orgamc matter and carbonate content
by the method of GUITIAN & C-VRBAILAS (1976)
(Table 1)
For each species and each environmental factor,
possible relationships between population density
(number of individuals in the sample) and the level of
that factor were investigated by Spearman rank
correlation analysis (SOKAL & ROHLF, 1979) (Table 2)
RESULTS
Distribution of individual species with respect
to sediment characteristics
The samples yielded a total of "7579 specimens of
bivalves belonging to 52 species, of which 11 (Mytilus
edulis, Thvasira Jlexuosa, Afysella bidentata,
Papilhcardium papillosum, Panncardiuin exiguuni,
Cerastoderma eaule, Ahra alba, I'enus verrucosa
Dosinia exoleta, '/eneruvis senegalensis and Hiatella
arctica) represented 80 8% of tlie total, witli Mvsella
bidentata being the most representative species
,35 6%) (Table 3)
!Àvtilus edulis occurred most commonly in the
intertidal /one (93 3%). of individuals, versus 6 7% in
the subtidal zone reaching its highest densities in
coarse sand bottoms located m me intertidal zone on
the border of the inlet (Fig 2A) The density of
82
OLADARRIA & al
individuals in the intertidal zone was positively
correlated with gravel, coarse sand, and carbonate
contents, and negatively correlated with fine sand
content (Table 2)
Thvasira jlexuosa was found almost exclusively in
tlie subtidal zone (99 4% of individuals), reaching its
highest densities in tlie eastern area of the inlet (Fig
2B), on fine sand bottoms with silt-clay contents of
over 10% and orgamc matter contents of 1-2% There
was a strong positive correlation between the density of
this species m tlie subtidal /one and fine sand and
organic matter contents, and a strong negative
correlation with coarse sand and carbonate contents
(Table 2)
Klysella bidentata was tlie most abundant and widely
distributed bivalve, witli a broad distnbution
tlu-oughout the inlet and a large number of individuals
in the subtidal zone (Fig 2C) Correlation imalysis did
not reveal any relationslup with physicochemical
parameters in the subtidal zone, due to the widespread
occurrence of tins species on all types of bottom In the
intertidal zone, however, Üie density of this species
correlated positively with coarse sand and gravel
contents, and negatively with fine sand content (Table
2)
Papillicardium papillosum occurred most commonly
m the subtidal zone (96 7% of individuals) The highest
densities were tliose observed in the outer subtidal zone
(Fig 2D), dominated by coarse sand and medium sand
bottoms with organic matter contents of less than 1% in
most cases The density of tins species in the subtidal
zone was positively correlated with coarse sand content
and deptli, and negatively correlated witli fine sand
content (Table 2)
Par\'icardium exiguum was commonest in the
intertidal zone (86 4% of individuals) The highest
densities were found in the mid-intertidal zone where
there is a Zostera noltii meadow (Fig 3 A) The density
of tlus species m the subtidal zone showed a significant
though weak positive correlation with medium and fine
sand contents, and a sigmficant negative correlation
with gravel and carbonate contents In the intertidal
zone, the density of this species was negatively
correlated with tidal height (Table 2)
Cerastoderma edule was present only in tlie intertidal
zone, and reached its highest densities in tlie timer
intertidal /one (Fig 3B), where tlie bottoms are mostly
medium and fine sand with orgamc matter content
ranging between 0 5 and 1% Correlation analysis did
not reveal significant relationships with tiie
physicochemical oarameters, except for a negative
correlation with tidal height (Table 2)
Abra alba was most frequent in the «ubtidal /one
(84 S% of individuals) However it was wiaely
distributed in the inlet (Fig 3C), Oeing most common
on bottoms with particle si/e smaller than 0 5 iraii and
orgamc matter content greater than l"/i The density of
this species in the subtidal /one correlated positively
with the sorting coefficient tmd less stronglv with
orgamc matter content, and negatively with coarse sand
Bivalves and relationships with environmental parameters
OLABARRIA & al
APEX 13(3) 81-93, 20 juil 1998
Ria de FERROL
Ensenada
do Bano
8°14'W
D
43-28' N
Punta
Redonda
S115
Faro
oSioi
da Painna 0SI02
Punta Pitcira
0S10"
M'îiN-csioï
Mugardos
8°16'W
Fig. 1. Location of the study area and the sampling sites A Spam, B Galicia, C Rfa de Ferrol, D Ensenada do
BaPio
83
APEX 13(3) 81-93, 20 juil 1998
Bivalves and relationships with environmental parameters
content In the intertidal zone, density showed a weak
but significant positive correlation with silt-clay
content (Table 2)
Venus verrucosa occurred largely in the subtidal
zone (94 5% of individuals), and reached its highest
densities on bottoms with coarse sediments and varying
percentages of organic matter (Fig 3D) Tlie density of
this species in the subtidal zone was negatively
correlated with fine sand content In the intertidal zone,
however, a positive correlation was observed between
the density of this species and both coarse sand content
and the sorting coefficient (Table 2)
Dofinia exoleta occurred most commonly in the
subtidal zone (96 8% of individuals), and reached its
OIABARRIA&O/
highest densities in the outer part of the inlet on coarse
sand bottoms with variable organic matter content (0 4I 7%) (Fig 4A) The density of this species correlated
positively with coarse sand content and to a lesser
extent with carbonate content, and negatively with fine
sand content (Table 2)
Venerupis senegalensis was slightly more frequent in
the subtidal zone (61 8% of individuals), attaining its
lughest densities in the outer inlet In tlie intertidal zone
It was distributed homogeneously throughout tlie whole
area In both cases, it occurred on bottoms of varied
physicochemical characteristics (Fig 4B) In the
intertidal /one, density was negatively correlated witli
tidal height (Table 2)
Site
Qso
s-c
So
CA
OM
D/H
Site
Qso
S-C
s„
CA
OM
SlOl
102
10 2
24
30 2
04
10 25
1103
1 30
10 6
•-2 5
196
06
0,80
SI 02
0 71
20 3
27
31 1
05
7 25
1104
130
16
18
20 6
04
0,21
S103
041
20 7
17
33 3
04
4 25
1105
0 32
54
16
94
07
1,75
S104
0 15
35 3
60
182
1
103
1106
0 65
25
26
129
04
0,74
S105
231
20 2
48
34 7
07
11
1107
0 65
47
25
26
05
0,52
S106
0 53
27
84
89
1
9
1108
0 40
48
19
21
05
00
S107
2 90
20 6
64
32 4
19
5
1109
38
>1 6
17
06
0,55
S108
3 00
142
22
34 7
12
43
1110
0 80
5
37
86
2
1,13
S109
0 09
45 7
96
29 3
1 5
72
1114
1 80
15
>13
17
02
0,84
2
D/H
SllO
1 90
115
27
32 9
07
13 2
1115
0 28
62
18
1
05
0,70
Sill
0 18
36 9
02
32
17
13
1116
0 45
175
50
03
14
0,74
S112
0 25
319
21 7
13 8
1 1
17
1117
1 40
114
37
26 7
06
0,10
S113
0 44
77
25
13 8
09
17
1118
0 38
44
29
16 3
03
0,98
S114
0 11
44 6
20 9
21 3
14
14
1119
0 18
55
16
08
06
1,91
sns
0 85
114
20
34 7
04
155
1120
0 13
87
15
03
09
0 16
S116
0 49
12 8
17
34 7
06
11
1121
1 80
44
>2 5
08
09
1,30
S117
0 65
12 5
21
49
03
2
1122
0 12
159
15
17
14
0,91
8118
0 34
27 3
95
24 9
1 5
4
1123
0 16
65
19
03
06
0,94
S119
175
13 2
26
173
04
8
1124
0 13
10 9
14
02
08
0,08
S120
139
146
34
184
06
13
1125
Oil
107
14
03
08
0,27
S121
3 00
6
25
27 6
09
18
1126
0 14
56
13
1
04
0,57
S122
121
23 4
75
30 2
06
16
1127
0 32
10
23
09
05
0,80
8123
1 55
13 2
>2 3
16 4
04
5
1128
0 34
66
22
03
08
0,38
S124
140
11 4
>3 3
30 2
07
10
1129
0 15
35
14
09
1
0,81
8125
0 16
40
100
35 6
09
13
1130
0 13
9
03
03
12
0,92
8126
>2 00
77
>3 9
22 6
13
10
1131
0 24
27 7
43
09
05
1,03
8127
0 09
13 3
>1 8
22
18
12
1132
0 13
66
14
02
07
1,67
8128
1 55
54
>3 5
63
03
45
1133
0 13
76
14
03
09
1,45
S129
0 13
37 9
85
173
18
98
1134
Oil
54
13
02
09
1,78
S130
0 06
49 8
9
25 8
15
12
1135
0 26
47
15
1
05
1,78
S131
0 03
53 1
85
163
2
76
1136
0 19
47
17
02
04
1,05
S132
0 23
10 4
16
13
06
15
1137
0 12
11
14
02
09
1,63
8133
0 06
46
52
62
2
58
1138
0 18
55
37
02
08
1,20
S134
0 75
13 1
>3 5
19
09
64
1139
0 36
7
39
09
07
1,59
8135
0 19
17
17
09
04
2
1140
0 13
27 9
72
09
06
0,84
1101
>2
09
1 1
12
02
0 35
1141
0 90
55
30
43
07
0,68
1102
0 35
59
18
I4
04
2 29
1142
0 32
47
16
24 9
04
0,96
1143
0 36
97
36
14 3
08
0,78
Table 1. Characteristics of the sampling sites Qso median particle size (mm), S-C silt and clay contents (% \NI\N),
So sorting coefficient, CA carbonate content (% w/w), OM organic matter content (% w/w), D depth (m) with
respect to tidal zero (subtidal sites), H height (m) with respect to tidal zero (intertidal sites)
84
OLABARRIA&O/
Bivalves and relationslups with environmental {-«rameters
APEX 13(3) 81-93,20 juil 1998
Fig. 2. Estimated densities (individuals per m^) of Mytilus edulis (A), Thyasira flexuosa (B), Mysella bidentata (C)
and Papillicardium papillosum (D) at sites at which that species was found
85
APEX 13(3) 81-93,20juil 1998
Bivalves and relatronships with environmental parameters
Hiatella arctica was likewise slightly more frequent
in the subtidal zone (65 5% of individuals), largely
occurring on bottoms with a particle size greater Üian
0 5 nun, both in the subtidal and intertidal /one (Fig
4C) The density of this species in the subtidal /one
showed a slight positne correlation with gravel content
and deptli In tlic intertidal zone the density of this
species correlated positively with coarse sand,
carbonate and gravel contents, and negatively with
organic matter and fine sand contents (Table 2)
Among species relationships
In the subtidal zone, extensive overlap was observed
among the distribution of ffialella arctica. I'einis
verrucosa and I'enerupis \enegalensis (Fig 5A), and
similarly among tlie distnbution oiAbra alha, 'Ih\asira
Ol ABARRIA & al
Jlexuom and Mv^ella hidentata (Fig 5B) though note
that the latter was very common throughout tlic
subtidal zone Thvasira Jlexuosa and Dosinia exoleta
were not found together (Fig 5B). since D exoleta
occurs on infralittoral gravel and 7 flexuo\a on muddy
sands or muds Papillicardiiim papillosum showed high
densities (up to 150 individuals/m^) on the deepest
bottoms dominated by coarse sands
In the intertidal zone, extensive overlap was
observed between Hiatella arctica and I'enus
verrucosa and between Par\'icardium exiguuni and
J'enerupis senegolensis (Fig 5A) I' verrucosa und H
arctica occurred in the same types of habitat (coarse
sands and gravels), whereas I' exiguuin and I
senegalensis both occurred on a wide range of bottom
types Cerastoderina edule occurred most commonly at
intermediate tidal levels, with the lughest densities at
SUBTroAL
Species
Mylilw: eduUs
Thyasiraflexiiosa
G
C'S
MS
I'S
SC'
OM
C'A
K
n
0 10^ '•'^
-0 004 ^"^
-0 060 ^"^
-OMI^'^
-0 028 '"''
oov, "^^
0 14^ "••"
-0 2^8 ^"^
0 048"^
-0 359*
0 595**
0 067 '^''
0619**
0 7^^ NS
0 584**
0 412*
0 430*
0 025 '"''
0 001 '^•'
-0 240 "^^
0 198 ^^
0 ns"'"'
0 082 ^"^
0 182'""^
-0 O^W """'
0 198 ^''
0 196 '-''
-0 045 "^^
0 543**
0 071 ^"^
•0 449**
-0 157^"^
-0 295 ^ ' '
0 164^"^
-0 002 '"•^
0 443**
0 425 -
-0 278 "~~'
0 385*
0 356*
0 2>7 ^'^
0 1962 "'"'
0 3754*
0 05^^^
0 048'""''
Ahra alba
-0 295 ^^
0 378*
0 ^.01 '^•^
0 15^"^
0 272 ^^
0 348*
-0 266^^^
0481**
-0 0 6 ^ ^ ' '
Venn v verrucosa
0 S26 "^^
-0 064 f^^
-0 099 ''•'
0 382*
0 126^^
0 199^^
0 247 f"^
0 152^^
-0 0 ^ 8 ^ ^
Dosinia
0 009'"'''
0 486**
0 126'^'^
0 497**
-0 078 "^''
-0 296 "-^
0 392*
-0 ^29 "'''
-0 1 1 6 ^ ^
0 004 ^"^
0 102 ^'^
0 261^^^
-OMl^^
-0 192 N"^
0 05^^^
0 152^-^
-0 12^ "=>
-0 059'^''
0 382-
-0 0^4 ^"^
-0 102f'"'
-0 195 •^•^
0 092"^'^
0 160^^
0 125 ^"^
0 07^ '~^~'
0471**
c\
^
I)/1I
Af) sella
hidentata
Papilhcardnim
papillo'tiim
Parvtcardiuw
exiguuni
Cerastoderma
edule
exoleta
Venerupis
Hiatella
senegalensis
arctica
INTERTIDAL
G
Species
Ktytilus
edulis
Thya lira flex uosa
My sella
hidentata
Papilhcardium
papillosum
cs
MS
FS
S(
OM
0 333-
0 347*
-0 069 ""^
0431**
-0 128 '^^
-0 086'^^
0 397*
0 288 '''''
-0 058'^''
-on2'"~'
0 215^"^
0 17-,NS
-0 104 ^^
0 069 " ^
-0 222 "^^
0 048 ^'"
-0 008 ^^
0 271 "^"^
0321*
0 468**
0 060 "^^
0 357*
-OII7NS
-0 284'''^
0 388*
0 2-.^ ^^
-0 211 f^"^
0 245"^
0 086 '^'^
-0 020 ^"^
-0 174'•^~'
-0 087''''^
-0 158 f"^
-0 08^ '•''^
0 015 ^ ' '
-0 048^"^
Parvicardium
exiguum
0 052 f"^
on6'''^
0 04^^^^
0 000 ^"^
0 072 ^^
-0 008 "••'
0 119 ^•^
0 05-. ^^
0 373*
Cerastoderma
edule
0 008"^
0 094''^^
0 201 "=>
-0 085 ^"^
-0 062 ""^
-0 220 " ^
-0 044 '''"'
0 250 ••"^
0 369*
Ahra alha
0 00^^ "^'^
-0 031'^•'
-0 214^^^
0 082 "^'^
0 324*
0 185^^
0012'^'"
-0 024 "-^
-0 2-.7 - ^
Venus
veirucosa
0 150^'^
0 367*
0 02-. NS
-0 178 ^"^
0 161 NS
-0 145 N'''
0 259 '^'^
0 344*
-0 078 ^"^
Dosinia
exoleta
-0 19"^ '•"'^
0 078 """'
0 201 '"^
-0 1 1 9 ^ ^
-0 0-.7 '"•'
-0 119 ''^
0 066 '""'
0 014^^^
-0 152"""'
0 244 N^
0 197 '^•'
0 011 ^^
-0 205 "'^
0 161 N^
-0 009 ^'^
0 -.04 ^^
0 228 ^"^
0 577**
0 352*
0 518"*
-0 214"^^
•0 397*
-0 054 '"''
0 319*
0 446**
0
Venenipis
Hiatella
senegalen\is
arctica
\M)^^
j
-0 192 '•"'
Table 2. Coefficients of rank correlation (Is) between densities of the different species (number of individuals in the
sample) and physicochemical factors (G gravel content, CS coarse sand content MS medium sand content
FS fine sand content, SC silt-clay content OM organic matter content, CA carbonate content So sorting
coefficient, D/H depth/height with respect to tidal zero) NS Not significant (p> 0 05) * p< 0,05 ** p< 0 01
86
OLABARRiA&a/
Bivalves and relationships With environmental parameters
APEX 13(3) 81-93, 20 juil 1998
A
Fig. 3. Estimated densities (individuals per m^) of Parvicardium exiguum (A), Cerastoderma edule (B), Abra alba
(C) and Venus verrucosa (D) at sites at wtiich that species was found
87
APEX 13(3) 81-93, 20 jml 1998
Bivalves and reltitionships \Mth environmenUil [wriiiiietcrs
between 0 10 m and 0 94 m Aîvtilus edulis was found
in coarse sands and gravels, at densities of up to 100
individuals/m^
Generalij speaking, the factors most strongh
influencing bnalve distribution were grain size and
depth though carbonate content was also an important
Specie*
Nucula nitida Sowcrh),, 1833
Area wnagona Poll, 1795
Stnatca lactea (I innaeus, 1758)
Mytilus edulis galloprovineialis L amartk, 1818
Musculus subpicttif (Cdntrame, 1835)
Pecten maximus (Limiaeus, 1758)
Aiiomia ephtppium 1 iiuiaeiis, 1758
Podoiiesmus squamula (Limiaeus, 1758)
Moiiia patellifomus (Linnaeus, 1767)
Ostrea edulis Lmndcu% 1758
Crassostrea gigas ( fhunberg, 1793)
Pisidium caset-tanum (Poll, 1791)
Loripes lacteus (Linnaeus, 1758)
Lucnioma borealis (Liimdeus, 1767)
Myrtea spmifera QAoïAagu, 1803)
Lucmella divancata (Linnaeus, 1758)
Tliyasim flexuosa (Montagu, 1803)
Lasaea tiibia (Montagu, 1803)
Kellia suborbiculans (Montagu, 1803;
Moiiiaaita substnata (Montagu, 1808)
Mvsella bidentata (Montagu, 1803)
Digitana digitana (Linnaeus, 1758)
Goodallia tnangulans (Montagu, 1803)
Acaiitliocardiapaucicostata (Sowerby, 1841)
Papillicardium papillosum (Poll, 1795)
Parvicardium exiguum (Gmelin, 1791)
()l ABARRIA & al
factor (possibh related to the positive correlation
observed between carbonate contents ;md particle size,
Ts = 0 478. p < 0 01) An>wa> A/ hidentola, C edule
and r senegalensis seemed to be less specific in their
choice of sediment t>pes
RA%
Species
RA%
0 20
0 04
0 03
Pan'icatdium nodosum (Turton, 1822)
Ceiastodemia edule (Linnaeus, 1758)
Spnula eUiptica (Urowii, 1827)
/ ultana lutiana (I imweus, 1758)
Pbaxas pelliicidwi (Pennant, 1977)
Moeielladonacwa(l iimaeus, 1758)
Moeiella pusilla (Philippi, 1836)
Gobtaeus tellmella (Lamarck, 1818)
Gobtaeiis depiessa (Pennant 1777)
Setobiculana plana (da Costa, 1778)
Abia nitida (O I Muller, 1776)
W,a alba (Wood, 1802)
( enui veniicosa Linnaeus, 1758
Gouldia minima (Montagu, 1803)
Dosinia exoleta (Linnaeus, 1758)
lapes decussatus(\ imiaeus, 1758)
I enenipis thomboides (Pennant, 1777)
( enenipis saxaiilis (rieuriau de Bcllevue, 1802)
I enenipis senegalensis (Gmelin, 1791 )
Cliamelea smo/i/to (da Costa, 1778)
( 'lausinella fasciata (da Costa 1778)
limoclea o\ata (Peimant, 1777)
Cotbulagibba (0\\\i, 1792)
Ilialella aiclica (Linnaeus, 1767)
Mototeiedo non egica (Splenger, 1792)
Thniciapapvracea (Poll, 1791)
0 73
19 50
1 22
0 33
1 4
1 5
0 1
041
001
001
0 18
0 13
102
0 02
3.9
0 04
1 21
0 01
35 62
0 19
0 03
0 01
4.59
2.53
2 68
0 01
0 03
001
0 37
0 01
1 02
1 01
0 04
0 22
2 27
1.73
0 81
2.06
0 03
1 12
1 01
5 63
0 44
0 75
0 04
1 02
180
0 11
1 11
Table 3. List of the species detected in the present study showing overall relative abundance (i e percentage of the
total nunnber of individuals found in all samples)
DISCUSSION
Interpretation of spatial vanations m the abundance of
bcnthic species is difficult, m view of the large number
of environmental factors which may act on bentluc
communities PEARSON & ROSENBERG (1978) studied
the factors involved in structiu"ing the marine benthos,
and highlighted the importance of food availability as a
determinant of community structure They concluded
that depth, latitude and water current speed are tlie
factors which have the strongest effect on food
availability PETERSON (1979) reported that tlie factors
affecting abundance m the bentlios may be divided into
density-dependent factors (such as competition,
prédation, and adult-larva interactions) and tlie physical
properties of the sediment
88
In our stud> area, tlic most important environmental
factors affecting the distnbution of bivalves were
particle size and deptli/ height The current regime was
not investigated, tliough it is clearly determinant of the
distribution of sediment types
Tlie dominant species m the mtertidal area, Mytilus
edulis, Pan'icardium exiguum and Cerastoderma
edule, showed a relationship with physicochemical
factors tliat was consistent witli their autoccology A/
edulis, which feeds on suspended detntus and
phytoplankton, is found primarily on coarse sediments
tliat allow it to attach itself by its byssus (TEBBLI-,
1966) In tlie present study, llie density of this species
correlated positively with coarse sediment content and
negatively with fine sand content Both P exiguum and
OLABARRIA & al
Bivalves and rcldlionslnps with environmental parameters
APEX 13(3) 81-93, 20 juil 1998
Fig. 4. Estimated densities (individuals per m^) of Dosinia exoleta (A), Venerupis senegalensis (B), and Hiatella
arctica (C) at sites at which that species was found
89
APEX 13(3) 81-93, 20juil 1998
Bivalves ami relationships with environmental f)aranieters
C edule are highly tolerant of variations m salinit>.
and are typically indifferent to the type of substrate
(TEBBLE, 1966), tJie most important factors governing
their distnbution are the emersion time and water
current speed, both related to food availability
(FiGUERAS, 1956), since they are fiUer-feeders that can
only feed when submerged (LABORDA, 1986) In the
present study we found that the densities of both
species m tlie intertidal /one were negativel> correlated
with height witli respect to tidal level zero, while tliere
were no sigmficant correlations with the other
environmental parameters I'enerupis <ieiiegalensis was
also abundant in the intertidal domain, with the most
important factor in its distnbution being height like
most venerids. it is adapted to the lower levels of the
intertidal zone or to the subtidal zone The importance
of tidal level and zoning has been discussed at length
by other autliors (Woi PH. 1971. R.AI \i 111 & BtnLi.
1986, JUNOV & VIEITE/, 1990) The distribution of this
species did not show an\ clear relationship with
sediment characteristics, in accordance with previous
reports TtBBiF (1966), for example, found that this
species that inhabits all kinds of bottoms (sand, sand>
gravel, silty gravel, and silty sand), wlule in Kilkieran
Bay in Ireland, KPK;AN (1974) reported the presence
of this species in a great varietv of biotopes. including
bottoms with clean sand, siltv sand, maerl and on rare
occasions even conchiferous gravel However, a studv
bv MORA (1980) in the Ria de Arousa (in southern
Galicia), found this species to be limited to clean sand
and gravel
Of the dominant species in tlie subtidal zone, \h sella
hidentata had a broad distribution tliroughout the inlet,
with high densities of individuals Tlie dcnsitv of this
species in tlie subtidal zone showed no correlation with
any of the phjsicochemical parameters in accordance
with the fact tliat it is a highlv ubiquitous species, able
to exploit a wide varictv of env iromnents. from sandv
to those with high contents of fine particles It is also
charactenzed b> its feeding behavior, which changes
depending on developmental stage juveniles are
deposit-feeders while adults are filter-feeders
(OCKELMA.\N & Ml I s. 1978) Tin astro flexiiosa
showed a strong positive correlation with fine sand and
organic matter contents, similarlv, other authors such
as LOPEZ-JA.MAR et al (1987) have reported that this
species inhabits silty sediments with a relativelv high
orgamc matter content This species has morphological
adaptations that prevent clogging of the branchial filter
b> large particles m suspension (ALLr\. 1958)
Endosvmbiont bacteria, which probabh contribute to
Its diet, are found m the gills (D-WDO et al. 1985) In
our studv area, the density of Abra alba correlated
positivelv with the sorting coefficient (which indicates
tliat it appears in poorlv sorted sediments, with a wide
diversity of particles) and to a lesser extent with
organic matter content G I I M A R I C (1971) reports on
the presence of this species in heterogeneous siltv
facies According to DUIVIN & GiMii (1989). it is
plentiful in silt and sand sediments tolerates
ph>sicochcmical changes in the sediment verv well.
90
Ol ABARRIA & al
and IS rapidlv adaptable (strategist r) LANDF (1975)
highlights the presence of this species in heterogeneous
sediments, and CORMFI (1985) states that it can live on
highlv varied bottoms, and that substrate granulometrv
is not a decisive factor, although it requires a laver of
suspended detritus m tlie water-sedmient interphase as
a source of food (Gl EMARLC, 1964)
I'eniis verrucosa, Dosinia exolela and I/iatella
orclicn are species tliat live on bottoms charactenzed
bv coarse sand silt gravel or conchiferous gravel
(TEBBLE, 1966) In our studv area, tliev occurred
largely on coarse sand and gravel, and tlie densities of
tliese species were negativel> correlated with fine sand
content
The obsened correlations between the densities of
the different species and particle size and organic
matter content appear to be related to feeding
behaviour For example, tlie densities of / flexuosa
and 1 alba, which are burrowing detritus feeders,
correlated positivelv with organic matter and fine sand
contents, whereas tlie remaimng species (with the
exception of M bidentata wluch mav change its
feeding mechanism depending on its developmental
stage) fed on particles in suspension, so that their
distribution correlates positively with sediments having
a larger particle size According to CORNU (1986).
filter-feeders take over from detntus-feeders species
when the proportion of fine particles decreases
LI \ IN roN (1977) reports tliat deposit-feeders dominate
in ecosystems with fine, sou sediments and that their
presence is linked to tlie silt-clay fraction, although tins
latter has not been venfied in our study area By
contrast, filter-feeders dominate in sandv sediments
(SViNDLRS, 1958) and their distribution may be
governed more bv hvdrodvnamic processes, which
determine sediment characteristics, than bv the
charactenstics of the sediment itself
The marked overlap in the distribution of. 1 alba and
7 flexuosa is as expected given that these species
charactcnsticallv form part of a well-defined subtidal
zone communilv (see THORSON. 1957) Mvsella
bidentala. which likewise showed considerable overlap
with these two species, is not characteristic of tins
communitv but is ubiquitous and broadly distnbuted m
our study area ffiatella arctica, I' verrucosa and I'
senegalensis.
siimlîirly
showed
overlapping
distributions, and all tliree occurred at high densities on
a maerl bed near Punta Redonda This bed is made up
of Lithothamniom corallioides and Phymatolithon
calcareuni. on a shell-gravel bottom with a small
amount of silt According to UROORRI et al (1992).
these bottoms offer stable substrates which provide
good shelter for manv species of small molluscs
including the juveniles of certain species, so that the
maerl acts as a hatchery
The similar distributions in some areas of I' exiguuin
and r senegalensis may be explained by the fact that
these species are charactcnstic of the intertidal facies
occupied by Zostera noltii within the limited
community ofMacoinohalthicaÇTuORSO^. 1957)
Bivdhes and relationships vMth environmental parameters
OLABARRIA & al
Apt x n ( 3 ) Sl-Q'?, 20juil 1998
D Hiatella arctica • Venerupis senegalensis B Venus verrucosa • Parvicardium exiguum |
o
(Ö
o
W
o
»
o
U>
o
^
Subtidal stations
D Dosinia exoleta
W
M
W
W
W
W
W
W
Ï
Intertidal stations
m Abra aiba
to
W
Subtidal stations
W
W
O Mysella bidentata
• Thyasira flexuosa
W
Intertidal stations
Fig 5 Plots illustrating the overlaps m the distributions of Hiatella arctica Venus verrucosa Venerupis
senegalensis and Parvicardium exiguum (A) and Abra alba Mysella bidentata Thyasira flexuosa and Dosinia
exoleta (B) The horizontal axis shows sample number The vertical axis shows relative abundance here defined as
the number of individuals in that sample expressed as a percentage of the maximum number of individuals per
sample recorded for that species
91
APEX
13(3) 81-93,20]uil 1998
Bivalves and relationships with environmental parameters
This has likewise been reported by CURRAS & MORA
(1991) in the Ria de Ribadeo (likewise on the north
coast of northwest Spain), where P exiguuw and I '
senegalensis were found on muddy sand or sandy mud
bottoms covered by Z noltii This phanerogam gives
rise to a more diversified habitat, and its rhi/omes and
roots compact the sediment and provide protection
from predators (ECKMAN, 1987) Both population
densities and species riclmess are thus typically higher
Finally, / / nrctica and I verrucosa showed closcl>
overlapping distnbutions since both occurred in tlie
dumping area of the dredging operations earned out in
the chaimel of the na The dumped material is
charactenzed by coarse gravel and conchiferous gravel.
which are topical habitats for tliese species
AcKNOWLEDGP:MKNrs. This research form part of
project XUGA 20005B95, and was partiallj financed
by a Predoctoral Grant from the Xunta de Galicia
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