animals were served as controls. The respiration rate of each individual was calculated
y1
Ž .
as mg O h
. Energy absorbed was calculated from absorbed rate AR using a
2 y1
Ž .
conversion factor of 20.78 J mg POM
Crisp, 1971 and energy expended on
y1
Ž .
respiration was expressed using a conversion factor of 13.98 J mg O
Ivlev, 1934 .
2
SFG of each individual was obtained by subtracting energy expended on respiration from the correspondent AR.
Enzymatic activities in digestive glands and crystalline styles of the same group of experimental animals used in the respiration study were also determined. The amylase
Ž and cellulase activity was determined by the Nelson–Somogyi Method Nelson, 1944;
. Somogyi, 1952 . Digestive glands and crystalline styles were collected in situ at the
experimental site, put into liquid nitrogen, transported back to the laboratory and stored at y308C for in vitro enzymatic assays. Wet weights of the digestive glands and
crystalline styles were recorded just before the enzymatic assays. One digestive gland or
Ž two crystalline styles were homogenised in cold 20 mM phosphate buffer pH 6.9 and
. pH 6.5 for the digestive gland and crystalline style, respectively containing 20 mM
NaCl, then centrifuged for 15 min at 4000 = g. The clear supernatants were used to determine a-amylase and cellulase activities. Standard calibration curves were set up
with glucose. The substrates for the determination of a-amylase and cellulase were
Ž .
Ž .
starch 1 and carboxymethylcellulose 1 , respectively, and were made up with the corresponding phosphate buffer for digestive glands and crystalline styles, respectively.
Mass of gland and crystalline style were estimated as protein using the method of Lowry Ž
. et al. 1951 and the standard calibration curve was set up using bovine serum albumin
Ž .
y1 y1
BSA . The enzyme activity was expressed in mg glucose h mg
protein. Ž
. Statistical methods used include one-way analysis of variance ANOVA , multiple
comparison of Student–Newman–Keuls Test, and multiple stepwise regression analyses Ž
. of simple linear and non-linear procedures Zar, 1984 . Any regression analysis per-
formed in this paper depended on the most appropriate function to be fitted in each case, following standard least square procedures.
3. Results
3.1. Hydrological conditions and seasonal seston characteristics in Kat O Fig. 2 shows the annual hydrological data in Kat O from December 1997 to
November 1998. Temperature varied from about 188C in February to about 308C in August. Dissolved oxygen level was higher in winter when temperature was lower
Ž .
Ž November to April and lower in summer when temperature was higher May to
. October 1998 . Salinity remained relatively constant at about 30‰ except in July
Ž .
25‰ . Fig. 3 shows monthly variations of seston at the study site. All seston Ž
. parameters, i.e., TPM, POM, PIM and f underwent temporal variations P - 0.001 .
Two peaks were identified for TPM, POM and PIM, the first and the major one Ž
. Ž
. occurring in spring MarchrApril and a minor one in autumn September . TPM varied
from about 2 mg l
y1
in January to a maximum value of about 12 mg l
y1
in March
Ž .
Fig. 2. Monthly variations in temperature, salinity and dissolved oxygen meanSE, ns9 in Kat O.
whereas f varied from 0.30 in April to 0.62 in January. Relationships between PIM, POM, TPM and f are shown in Fig. 4. There were positive linear relationships between
POM, PIM and TPM that is best described by the following equations
POM s 0.282 = TPM q 0.716 n s 338, R
2
s 0.624, P - 0.001
Ž .
PIM s 0.718 = TPM y 0.716 n s 338, R
2
s 0.915, P - 0.001 .
Ž .
The contributions of POM and PIM for TPM were 28.2 and 71.8, respectively. The relationship between f and TPM was best described by a negative power function
f s 0.56 = TPM
y0 .21
n s 338, R
2
s 0.13, P - 0.001 .
Ž .
3.2. Annual feeding rates, SFG and amylase actiÕity of mussels Monthly variations in CR, AR and AE are shown in Table 2. Higher values of CR
Ž .
Ž .
were obtained from summer September to early winter January and lower values Ž
. Ž
. from winter February to early spring April . Higher values of AE were also obtained
in winter, however, lower values were obtained in summer. For AR, higher values were recorded from October to January. In the present study, no pseudofaeces was produced
except in January when seven individuals out of 42 produced pseudofaeces. RR of these individuals varied from 0.1 to 0.4 mg h
y1
. Both respiration rate and SFG varied significantly with time, with highest values
being obtained in October and lowest values in February. There was no significant difference in the amylase and cellulase activity in the crystalline style among the four
Ž .
seasons Table 3 . Significantly higher activities of amylase and cellulase activity in the
Fig. 3. Temporal variations in the concentration of TPM, POM, PIM, and organic content of suspended solid Ž . Ž
. f
meanSE in Kat O.
digestive gland, however, were obtained from May to October. There was no significant Ž
. difference in the activity of amylase P 0.05 between digestive gland and crystalline
style, cellulase activity in digestive gland, however, was significantly higher than that in Ž
. crystalline style P - 0.001 .
3.3. Relationships between feeding rates, SFG, amylase actiÕity and food aÕailability Ž
. Ž .
Food availability, both in terms of quantity TPM and quality f , was shown to be a Ž
. significant factor determining feeding and ARs Table 4 . CR was a negative power
Ž . Fig. 4. Relationships between TPM, POM, PIM, and organic content of suspended solid f in Kat O.
Table 2 Ž
. Temporal variations meanSE in CR, AE, AR, respiration rate and SFG in P. Õiridis
y1 y1
y1 y1
Ž .
Ž .
Ž .
Ž .
Items CR mg h
AE mg h AR mg h
Respiration rate SFG J h
y1
Ž .
mg O h
2 b
c ab
Dec. 1997 0.840.20
0.480.07 0.780.15
d c
b
Jan. 1998 2.500.39
0.580.08 0.940.13
ab b
a a
a
Feb. 1998 0.560.11
0.330.07 0.200.07
0.290.02 0.200.31
a b
ab
Mar. 1998 0.340.02
0.330.07 0.400.09
a ab
a
Apr. 1998 0.360.03
0.180.14 0.160.09
ab ab
ab c
ab
May. 1998 0.610.05
0.310.06 0.600.10
0.740.08 2.120.42
ab ab
ab
Jun. 1998 0.620.08
0.200.09 0.560.14
b ab
ab b
ab
Jul. 1998 0.730.17
0.230.07 0.400.10
0.400.07 2.690.47
b a
ab
Aug. 1998 0.820.06
0.160.15 0.340.18
b ab
ab
Sep. 1998 0.890.17
0.290.06 0.550.09
b ab
b d
b
Oct. 1998 0.860.07
0.270.07 0.990.15
1.000.10 6.640.69
c c
c
Nov. 1998 1.190.17
0.590.06 2.210.22
Ž .
Note: within columns, treatment means followed by different letters are significantly different P - 0.05 . Table 3
Ž Amylase activity in digestive gland and crystalline style MeanSE, ns 36 for digestive glands and ns18
. for crystalline styles
Items Enzyme activity in digestive gland
Enzyme activity in crystalline style
y1 y1
y1 y1
Ž .
Ž .
mg glucose h mg
protein mg glucose h
mg protein
Amylase activity Cellulase activity
Amylase activity Cellulase activity
a a
Feb. 1998 2.530.19
1.690.09 3.260.34
2.120.33
c b
May. 1998 4.520.20
2.250.16 3.390.30
2.840.57
b c
Jul. 1998 3.900.18
3.560.13 3.320.39
2.270.24
c b
Oct. 1998 4.890.17
2.230.08 4.160.39
1.620.07 Ž
. Note: within columns, treatment means followed by different letters are significantly different P - 0.05 .
Table 4 Relationships between food availability and enzymatic activity
2
Ž .
Items n
Food availability TPMr f R
P
y0 .724
CR 468
s 2.402=TPM 0.364
- 0.001
Ž .
AE 468
sy0.168=Ln TPM q0.591 0.163
- 0.001
2
AR 468
sy0.006=TPM q0.21=TPMq0.738 0.061
- 0.001
SFG 158
sy0.301=TPMq3.736 0.006
0.05
a
Amylase in digestive gland 4
s 0.646=TPMy0.269 0.951
- 0.01
a
Cellulase in digestive gland 4
s 0.245=TPMq0.896 0.238
0.05
1.006
CR 468
s1.750= f 0.141
- 0.001
2
AE 468
sy1.853= f q2.259= f y0.313 0.362
- 0.001
2q
AR 468
sy4.954= f 7.643= f y1.749
0.128 -
0.001 SFG
158 s 38.724= f y15.201
0.191 -
0.001
a
Amylase in digestive gland 4
s10.731= f y0.816 0.158
0.05
a
Cellulase in digestive gland 4
sy10.14= f q7.008 0.249
0.05
a
The averaged monthly enzyme activity and the averaged monthly values of TPM and f were used here. Since there was no temporal change in the enzyme activity in crystalline style, only activity in the digestive
gland was considered.
function of TPM and a positive linear function of f. AEs and ARs showed logarithmic relationships with TPM and varied as a polynomial function of f. SFG increased as a
linear function of f but varied independently with TPM. In contrast to SFG, the amylase activity in the digestive gland showed significant relationship with TPM, but not f.
Cellulase activity in the digestive gland was not significantly correlated with either TPM or f.
4. Discussions
