210
Rapp. Comm. int. Mer Médit., 36,2001
Introduction
The problem of faecal pollution in the coastal seawa
t
e
r, present in urban
centers, has an effect on the sanitary quality of organisms living in such
areas. Being sessile organisms the biva
l
ves are permanently present in a cer-
tain area, and can not avoid stress situations by active moving. The rate of
concentration of food particles in biva
l
ves undoubtedly depends on the rate
of filtration of seawater (1,2), which is determined by a number of fa
c
t
o
r
s
such as food concentrations, ?ow rate, size of biva
l
ves or life cycles of
b
iva
l
ves (3,4,5). How
eve
r, one of the most important environmental fa
c
t
o
r
s
which control filtration rate in biva
l
ves is temperature (2,4). High fil
t
r
a
t
i
o
n
rate does not always mean high concentration of food particles in shellfis
h
because of its low concentration in seawa
t
e
r. Similarly, high concentration
of food particles in seawater does not always mean its higher concentration
in shellfish, because at high food concentration decrease filtration rate as
well as feeding effi
c
i
e
n
cy (decrease retention rate and increase rate of
p
s
e
u
d
o
faeces production occurs). From a practical point of view the most
important question should be which concentrations of faecal pollution indi-
cators in shellfish could be expected in particular conditions. In this paper,
the effect of temperature on the rate of concentration of faecal coliforms
(FC) in mussels as well as leve
l
-
o
ff concentration of FC in dependence on
temperature and FC concentrations in seawater were studied.
Material and methods
Mussels (Mytilus galloprov
i
n
c
i
a
l
i
s) were taken from the shellfish ga
r-
dens near Split, and were held at ambient temperature in the laboratory until
use. The experiments were carried out in 30 l fib
e
rglass trays containing 15l
of seawater with biva
l
ves of uniform size (4-5 cm). Each tray was aerated
and termostated at experimental temperature. Ambient temperatures were
changed to temperature of experiments at the rate of 0.5°C per day. A
f
t
e
r
the experimental temperatures were reached, the biva
l
ves were allowed to
acclimate for at least two days. In the experiments, three temperatures and
three concentrations of FC in trays were combined, and each ex
p
e
r
i
m
e
n
t
a
l
combination was carried out in several replications (3-6). The numbers of
FC in biva
l
ves were checked every hour until they reached plateau. Te
m-
peratures used in experiments were 12°C (mean winter temperature), 24°C
(mean summer temperature), and 18°C (the temperature between these two
extremes). Concentrations of FC in experimental trays were 10-10
3
FC L
-
1
(“unpolluted” seawater), 10
3
-
1
0
5
FC L
-
1
(moderately polluted seawa
t
e
r
)
,
and 10
5
-
1
0
7
FC L
-
1
(high polluted seawater). The beginning concentrations
of FC (concentrations in the moment when experiments started) were low
and varied between 0 and 13 FC per gram of ?e
s
h
.
Results and discussion
In all experiments the rates of FC concentration in bivalves were high at
the beginning of the experiments, when the initial concentrations of FC in
b
iva
l
ves were low, and decreased as the concentration in biva
l
ve
s
increased. Finally, at certain concentration of FC in bivalves (level-off con-
centration), bivalves ceased to concentrate FC (rate of concentration; k=0)
(Tab.1). Neither, the temperature nor concentration of FC in seawater
changed this pattern, but both in?uenced the values of concentration rate
as well as the slope of its decrease.At low initial concentrations of FC in
mussels, the rate of concentration increased with the temperature. As con-
centration of FC in mussels increased, the rates of FC concentration
decreased more rapidly at the higher temperature. As a result, at certain
concentration (“turning-point concentration”) of FC in mussels, or its nar-
row range, the rates of FC concentrations in mussels were similar at all
temperatures (Tab.1). As the FC concentration in mussels kept on growing
the rate of concentration became inversely proportional with temperature.
As a consequence, the lower temperature, the higher was the level-off con-
centration (which is the maximal concentration of FC present in mussels),
and more time was needed to reach that concentration (Tab.1). The con-
centration of FC in seawater (in experimental trays) had no effect on the
pattern of temperature effect. However, the values of concentration rate,
slope of its decrease and “turning point concentration” (concentration of
FC in mussels at which positive correlation between concentration rate and
temperature turns into negative correlation) varied in dependence on con-
centration of FC in seawater.At low initial concentration of FC in mussels,
the rate of concentration of FC in bivalves increased with their concentra-
tion in seawater.As concentration of FC in mussels increased, the rates of
concentration decreased more rapidly at higher concentrations of FC in
seawater (Tab.1). Thus, mussels needed more time to reach the level-off
concentration (maximal concentration of FC present in bivalves), at which
mussels stopped concentrating FC (k = 0). Finally, the increase of FC num-
ber in seawater was also accompanied with the decrease of “turning point
concentration”. Contrary to temperature, which affected the values of max-
imal concentration of FC observed in mussels (inverse relationship was
found), level-off concentration of FC in mussels did not significantly dif-
fered in dependence on concentration of FC in seawater. However, level-
off concentrations were reached earlier as concentration of FC in seawater
increased.
Our study showed that higher concentration of food particles as well as
change of temperature toward optimum, increased the rate of bacterial con-
centration in biva
l
ves. At the same time, as concentration of bacteria in
b
iva
l
ves increases, the concentration rate decreases more rapidly as the con-
centration of bacteria in seawater increases and as the temperature is closer
to optimum. Therefore, in conditions which are closer to optimal, biva
l
ve
s
need less time to reach leve
l
-
o
ff concentrations of bacteria and to become
i
n
e
fficient in feeding (decrease retention rate and increase the rate of pseud-
o
faeces production). Finally, due to the fact that bacteria are not only, and
very probably not the most important food for biva
l
ves, the rates of FC con-
centration, as well as the values of leve
l
-
o
ff concentration are primarily
determined by concentration of particulate organic matter, detritus and other
particles suspended in the surrounding wa
t
e
r. Thus, the results of this study
could be interesting rather as qualitative than quantitative model.
References
1 - Thompson R.J. and Bayne B.L., 1972. Active metabolism associated with
feeding in the mussel Mytilus edulis.J. exp. mar. Biol. Ecol.9: 111-124.
2 - Schulte E.H., 1975. In?uence of algal concentration and temperature on the
filtration rate of Mytilus edulis. Mar. Biol. 30: 331-341.
3 - Jorgensen C.B., 1966. Biology of Suspension Feeding. Pergamon Press, London,
357 pp.
4 - Walne P.R., 1972. The in?uence of current speed, body size and water
temperature on the filtration rate of five species of bivalves.J. mar. biol. Ass. U.K.
52: 345-374.
5 - Tenore K.R. and Dunstan W.M., 1973. Comparison of feeding and biodeposition
of three bivalves at different food levels.Mar. Biol. 21: 190-195
EFFECT OF TEMPERATURE ON THE RATE OF CONCENTRATION OF FAECAL COLIFORMS
IN MUSSELS
M. Solic* and N. Krstulovic
Institute of Oceanography and Fisheries, Split, Croatia - solic@izor.hr
Abstract
The effects of different temperatures (12°C, 18°C, 24°C) on the rate of concentration of faecal coliforms (FC) in mussels were studied in
experimental conditions at different concentrations of FC in seawater.At low initial concentrations of FC in mussels the rate of FC
concentration increased with concentration of FC in seawater and with changes of temperature toward optimum. As concentration of FC
in mussels increased, the rate of FC concentration decreased more rapidly as the concentration of FC in seawater increased and as the
temperature was closer to optimum. Maximum concentrations of FC observed in mussels (level-off concentrations) were the highest at
minimum temperature (at which rates of FC concentration were the lowest), whereas concentration of FC in seawater had no effect on
level-off concentrations of FC in bivalves.
Key words: bacteria, bivalves, temperature
Conc. of
Level-off“TP”k (h)
FC inTemp
conc.(logTimeconc. (logat
seawater(°C)
FC g
-1
(h)FCg
-1
“TP”
y-intsloper
2
Low121.35- 0.420.873.255.54
10 - 10
3
181.90- 0.680.952.753.332.130.48
FC1
-1
243.12- 1.250.882.501.85
Moderate123.35- 0.940.813.562.45
10
3
- 10
5
184.00- 1.370.982.921.681.452.00
FC1
-1
244.99- 2.080.982.401.11
High125.17- 1.520.913.401.51
10
5
- 10
7
185.88- 2.090.872.821.101.303.20
FC1
-1
247.48- 3.250.912.300.71
Tab. 1. The effect of temperature on the rate of concentration of faecal
coliforms (FC) in mussels at different concentrations of FC in seawater
[Linear regression statistics: x = logarithm of concentration of FC in mussels,
y = rate of concentration of FC in mussels (hours), y-int (intercept) = rate of
concentration of FC at initial concentration of FC in mussels, r2 = coefficient
of determination; Level-off concentration = maximal concentration of FC pre-
sent in mussels at which concentration rate is zero (k = 0); Time = time need-
ed for mussels to reach maximum concentration of FC in their bodies; “TP”
(“turning-point concentration”) = concentration of FC in mussels at which pos-
Linear regression
statistics
