Relative Community Metabolism(RCM)
To investigate the ecological impacts of a widely used antibiotic, oxytetracycline
(OTC), on the population abundance of composite species, gross primary productivity (GPP) and community respiration (CR) were considered. The population
abundance, GPP, and CR were linked to understand the relationship among these
measures. First, the experimental respiration rate of heterotrophs (HE exp ) was
obtained from CR less algal respiration calculated from 0.35 Â GPP. Next, the
population respiration of each heterotroph was calculated from the direct measure of
population abundance and the assumed constant of per capita respiration. The sum
of the population respirations across all heterotrophs was defined as the theoretical
respiration rate of heterotrophs (HR theo ). Finally, the relative community metabolism
(RCM) of the heterotrophic community was obtained by calculating the ratio of
HR exp to HR theo , which indicates changes in the specific respiration rates as a whole
within the community. The influence of OTC on the RCM was greater than on CR,
and thus the effect of OTC on the metabolism of heterotrophs was far more severe
than expected from CR. The rate of change in the original data can be magnified by
RCM, which facilitates the detection of influences in ecotoxicological studies
(Shibata et al. 2014).
The concentration of DO in the culture medium was continuously measured with
a handheld optical DO meter (ProODO; YSI/Nanotec Inc., Kawasaki, Japan). The
oxygen flux at the atmosphere/medium interface was corrected according to Odum
(1956). The respiration under light, which could not be measured directly, was
estimated by assuming it to be equivalent to the respiration in the dark. The amount
of oxygen consumed during the dark period (12 h) was doubled to indicate the
oxygen consumption during an entire 24-h period and defined as the CR. The
oxygen consumed during the dark period was combined with the amount of oxygen
produced during the light period and defined as the GPP (McConnel 1962). Algal
respiration (AR) was obtained from Duarte and Cebrian (1996) using the equation
AR ¼ 0.35 Â GPP. The HR exp was calculated as CR less AR:
HR exp ¼ CR À AR:
The respiration rate of each heterotrophic organism was estimated using body
size and population abundance. Respiration of the bacterial community, dominated
by Bacillus cereus, was estimated by the mean metabolic rate of Firmicutes
(Makarieva et al. 2012); the bacterial CFU count was assumed as being equal to
the cell count. The SR of Cyclidium glaucoma was calculated from the cell volume
using the equation of Fenchel and Finlay (1983). The cell volume was calculated
from their cell length and width measurements (n ¼ 20) using an ellipsoid formula.
The SRs of Lecane sp., Philodina erythrophthalma, and Aeolosoma hemprichi were
calculated from their dry weights using the equation of Galkovskaya (1995). The dry
weights of Lepadella patella and Rotaria rotatoria + Philodina roseola Ehrbg
reported by Dumont et al. (1975) were used for the dry weights of Lecane sp. and
220
Appendices
To investigate the ecological impacts of a widely used antibiotic, oxytetracycline
(OTC), on the population abundance of composite species, gross primary productivity (GPP) and community respiration (CR) were considered. The population
abundance, GPP, and CR were linked to understand the relationship among these
measures. First, the experimental respiration rate of heterotrophs (HE exp ) was
obtained from CR less algal respiration calculated from 0.35 Â GPP. Next, the
population respiration of each heterotroph was calculated from the direct measure of
population abundance and the assumed constant of per capita respiration. The sum
of the population respirations across all heterotrophs was defined as the theoretical
respiration rate of heterotrophs (HR theo ). Finally, the relative community metabolism
(RCM) of the heterotrophic community was obtained by calculating the ratio of
HR exp to HR theo , which indicates changes in the specific respiration rates as a whole
within the community. The influence of OTC on the RCM was greater than on CR,
and thus the effect of OTC on the metabolism of heterotrophs was far more severe
than expected from CR. The rate of change in the original data can be magnified by
RCM, which facilitates the detection of influences in ecotoxicological studies
(Shibata et al. 2014).
The concentration of DO in the culture medium was continuously measured with
a handheld optical DO meter (ProODO; YSI/Nanotec Inc., Kawasaki, Japan). The
oxygen flux at the atmosphere/medium interface was corrected according to Odum
(1956). The respiration under light, which could not be measured directly, was
estimated by assuming it to be equivalent to the respiration in the dark. The amount
of oxygen consumed during the dark period (12 h) was doubled to indicate the
oxygen consumption during an entire 24-h period and defined as the CR. The
oxygen consumed during the dark period was combined with the amount of oxygen
produced during the light period and defined as the GPP (McConnel 1962). Algal
respiration (AR) was obtained from Duarte and Cebrian (1996) using the equation
AR ¼ 0.35 Â GPP. The HR exp was calculated as CR less AR:
HR exp ¼ CR À AR:
The respiration rate of each heterotrophic organism was estimated using body
size and population abundance. Respiration of the bacterial community, dominated
by Bacillus cereus, was estimated by the mean metabolic rate of Firmicutes
(Makarieva et al. 2012); the bacterial CFU count was assumed as being equal to
the cell count. The SR of Cyclidium glaucoma was calculated from the cell volume
using the equation of Fenchel and Finlay (1983). The cell volume was calculated
from their cell length and width measurements (n ¼ 20) using an ellipsoid formula.
The SRs of Lecane sp., Philodina erythrophthalma, and Aeolosoma hemprichi were
calculated from their dry weights using the equation of Galkovskaya (1995). The dry
weights of Lepadella patella and Rotaria rotatoria + Philodina roseola Ehrbg
reported by Dumont et al. (1975) were used for the dry weights of Lecane sp. and
220
Appendices