Application of dual stable isotopes in investigating the utilization of two wild dominant filamentous algae as food sources for Daphnia magna

Figures & data

Figure 1. Light photomicrographs of strains of Oscillatoria sp. nov.

Table 1. Daphnia-algae feeding treatments. The ratio of unlabeled S. obliquus to labeled filaments was 1:10.

Treatments	Zooplankton	Labeled algae	Unlabeled S. obliquus
S	D. magna	S. obliquus	Not added
M1	D. magna	M. granulata	Not added
M2	D. magna	M. granulata	Added
O1	D. magna	Oscillatoria sp.	Not added
O2	D. magna	Oscillatoria sp.	Added

Figure 2. Growth of D. magna in each beaker, which fed by sole S. obliquus (S, as control), sole M. granulata (M₁), M. granulata mixed with S. obliquus (M₂), sole Oscillatoria sp. (O₁) and Oscillatoria sp. mixed with S. obliquus (O₂) during the 96-h experiment. Each symbol represents the mean value in the D. magna-algae feeding treatment, with the error bar representing the standard deviation.

Table 2. One-way ANOVA for the mean of growth rate (k) of the five different D. magna-algae feeding treatments.

Dependent variable	Factor	df	Mean square	F	P
K	Between group	4	0.06	309.12	<0.01**
	Within group	10	0.00
	Total	1

Note: The significance levels are *p < 0.05 and **p < 0.01.

Table 3. The results of LSD post hoc for comparing the mean of growth rate (k) of the five different D. magna-algae feeding treatments.

Treatments (i)	Treatments (j)	Mean difference (i − j)	P
S	M1	0.396	<0.01**
	M2	0.184	<0.01**
	O1	0.230	<0.01**
	O2	0.243	<0.01**
M1	M2	−0.212	<0.01**
	O1	−0.166	<0.01**
	O2	−0.152	<0.01**
M2	O1	0.046	<0.01**
	O2	0.060	<0.01**
O1	O2	0.014	>0.05

Note: The significance levels are *p < 0.05 and **p < 0.01.

Table 4. One-way ANOVA for the mean of survival rate of the rest four different D. magna-algae feeding treatments.

Dependent variable	Factor	df	Mean square	F	P
Survival rate	Between group	3	0.157	62.155	<0.01**
	Within group	8	0.003
	Total	11

Note: The significance levels are *p < 0.05 and **p < 0.01.

Table 5. The results of LSD post hoc test for comparing the mean survival rate of the remaining four different D. magna-algae feeding treatments.

Treatments (i)	Treatments (j)	Mean difference (i − j)	P
M1	M2	0.007	>0.05
	O1	0.460	<0.01**
	O2	0.310	<0.01**
M2	O1	0.453	<0.01**
	O2	0.303	<0.01**
O1	O2	−0.150	<0.01**

Note: The significance levels are *p < 0.05 and **p < 0.01.

Table 6. Growth rate (k), final survival rate and catabolic tissue turnover rate (m) estimated for the five different D. magna-algae feeding treatments.

Treatments	Survival rate	k ()	k% ()	m% ()
S	100% ± 0%	0.422 ± 0.007	42.3%	57.7%
M1	98% ± 1.5%	0.026 ± 0.005	2.7%	97.3%
M2	97% ± 1.7%	0.240 ± 0.025	23.9%	76.1%
O1	50% ± 7.6%	0.192 ± 0.013	19.3%	80.7%
O2	66.7% ± 6.1%	0.180 ± 0.010	17.9%	82.1%

Table 7. Isotopic turnover modeling parameters estimated of the five different D. magna-algae feeding treatments.

					P
^13C
S	1.048	0.0003	0.0243 ± 0.0008	0.999	<0.001	28.53
M1	2.054	0.0005	0.0072 ± 0.0015	0.995	<0.001	95.74
M2	0.989	0.0008	0.0338 ± 0.0018	0.999	<0.001	20.54
O1	0.908	0.0103	0.0215 ± 0.0046	0.969	<0.001	32.22
O2	0.630	0.0038	0.0903 ± 0.0193	0.955	<0.001	7.679
^15N
S	1.157	0.0002	0.0190 ± 0.0008	0.999	<0.001	36.40
M1	1.641	0.0005	0.0091 ± 0.0011	0.996	<0.001	75.88
M2	1.540	0.0004	0.0111 ± 0.0008	0.999	<0.001	62.30
O1	1.042	0.0003	0.0182 ± 0.0040	0.979	<0.001	38.02
O2	0.637	0.0007	0.0516 ± 0.0159	0.914	<0.005	13.44

Figure 3. Changes in ¹³C and ¹⁵N values of D. magna fed by sole S. obliquus (S, as control), sole M. granulata (M₁), M. granulata mixed with S. obliquus (M₂), sole Oscillatoria sp. (O₁) and Oscillatoria sp. mixed with S. obliquus (O₂) during the 96-h experiment. Each symbol represents the mean value in the D. magna-algae feeding treatment, with the error bar representing the standard deviation.