benthic biomass(Fig. 2). However, the question still remains open, which of the benthic
organisms were responsible for the increase in biomass, since bacterial number and
biomass remained almost constant during this period. Consequently, bacterial ATP as
percentage of the total ATP strongly decreased from 43 % (anoxic conditions) to 18 %
(oxic conditions). With decreasing redox potential towards the beginning of November,
however, bacterial ATP again increased (up to 40% of the total ATP) indicating an
increasing importance of bacteria in benthic metabolism under anoxic and suboxic
conditions (Meyer-Reil 1983). The inhibition of protein decomposition under anoxic
conditions is not easy understandable. Under the same conditions, the decomposition of
carbohydrates is much less affected as it could be shown by laboratory experiments
(Meyer-Reil, unpublished data).
A utumn and spring input
The input of the phytoplankton blooms in autumn and spring, respectively, represent
external food supplies for the benthos which generally reacted with an outburst in activity
and subsequent biomass production (Fig. 2). However, the specificity of the benthic
response is caused by differences in the food supply, the physical properties of the
sediment, and the composition of the benthic community.
During the “autumn input” a peak in protein succeeded a peak in carbohydrate. In spring,
however, the first peak in organic material was an enrichment of carbohydrate which was
followed by protein. As an immediate response to the availability of organic material,
heat production culminated. It is interesting to note that the peaks in heat production
coincided with peaks in protein, but not with peaks in carbohydrate (Fig. 1,2). Decomposition rates of carbohydrate (activity of α-amylase) were closely related to the enrichment
of carbohydrate in the sediment. Enzymatic responses turned out to be much higher in
autumn as compared to spring. This is obviously a reflection of both the higher temperature and the higher benthic biomass in autumn. Due to an induction of enzymatic activity
with increasing substrate concentrations, a stimulation of enzymatic decomposition rates
already occurred when concentrations of carbohydrate started to increase in the sediment
surface. Since exoenzymatic activities are thought to be a minor component of the overall
heat loss in sediments (Pamatmat 1982) both activity parameters showed no correlation
(Fig. 2).
Whereas heat production comprises all types of benthic metabolism, electron transport
activity (ETS ; for data cf. Graf et al. 1983) relates to the activity of respiratory chains
(oxygen-, nitrate, and most likely sulfate-respiration). The quotient between heat production and ETS-activity should therefore serve as an indicator for changes in the type of
metabolism (Pamatmat 1982). A strong increase of this quotient following the “autumn-”
and“spring-input”, respectively, demonstrated a shift in the type of benthic metabolism
towards fermentation. This coincided with suboxic conditions mainly caused by biological oxygen consumption (Graf et al. 1983).
The stimulation of benthic activity resulted in subsequent biomass production. Prior to
peaks in total benthic biomass (ATP measurements) however, bacterial biomass accumulated (Fig. 2). Bacteria primarily reacted to the availability of organic material with an
immediate and strong increase in cell volume (biomass production). Deviating from the
“normaP’distribution of bacterial biomass, medium and large size cells dominated. Subsequently, bacteria responded with cell division (increase in cell number), re-establishing
the normal biomass distribution : small-size cells (volume <0,3 µm 3 ) again dominated the
bacterial biomass followed by medium and large-size cells (volume 0,3-0,6µm 3 and >0,6
yum 3 , respectively ; Meyer-Reil 1983).
58
organisms were responsible for the increase in biomass, since bacterial number and
biomass remained almost constant during this period. Consequently, bacterial ATP as
percentage of the total ATP strongly decreased from 43 % (anoxic conditions) to 18 %
(oxic conditions). With decreasing redox potential towards the beginning of November,
however, bacterial ATP again increased (up to 40% of the total ATP) indicating an
increasing importance of bacteria in benthic metabolism under anoxic and suboxic
conditions (Meyer-Reil 1983). The inhibition of protein decomposition under anoxic
conditions is not easy understandable. Under the same conditions, the decomposition of
carbohydrates is much less affected as it could be shown by laboratory experiments
(Meyer-Reil, unpublished data).
A utumn and spring input
The input of the phytoplankton blooms in autumn and spring, respectively, represent
external food supplies for the benthos which generally reacted with an outburst in activity
and subsequent biomass production (Fig. 2). However, the specificity of the benthic
response is caused by differences in the food supply, the physical properties of the
sediment, and the composition of the benthic community.
During the “autumn input” a peak in protein succeeded a peak in carbohydrate. In spring,
however, the first peak in organic material was an enrichment of carbohydrate which was
followed by protein. As an immediate response to the availability of organic material,
heat production culminated. It is interesting to note that the peaks in heat production
coincided with peaks in protein, but not with peaks in carbohydrate (Fig. 1,2). Decomposition rates of carbohydrate (activity of α-amylase) were closely related to the enrichment
of carbohydrate in the sediment. Enzymatic responses turned out to be much higher in
autumn as compared to spring. This is obviously a reflection of both the higher temperature and the higher benthic biomass in autumn. Due to an induction of enzymatic activity
with increasing substrate concentrations, a stimulation of enzymatic decomposition rates
already occurred when concentrations of carbohydrate started to increase in the sediment
surface. Since exoenzymatic activities are thought to be a minor component of the overall
heat loss in sediments (Pamatmat 1982) both activity parameters showed no correlation
(Fig. 2).
Whereas heat production comprises all types of benthic metabolism, electron transport
activity (ETS ; for data cf. Graf et al. 1983) relates to the activity of respiratory chains
(oxygen-, nitrate, and most likely sulfate-respiration). The quotient between heat production and ETS-activity should therefore serve as an indicator for changes in the type of
metabolism (Pamatmat 1982). A strong increase of this quotient following the “autumn-”
and“spring-input”, respectively, demonstrated a shift in the type of benthic metabolism
towards fermentation. This coincided with suboxic conditions mainly caused by biological oxygen consumption (Graf et al. 1983).
The stimulation of benthic activity resulted in subsequent biomass production. Prior to
peaks in total benthic biomass (ATP measurements) however, bacterial biomass accumulated (Fig. 2). Bacteria primarily reacted to the availability of organic material with an
immediate and strong increase in cell volume (biomass production). Deviating from the
“normaP’distribution of bacterial biomass, medium and large size cells dominated. Subsequently, bacteria responded with cell division (increase in cell number), re-establishing
the normal biomass distribution : small-size cells (volume <0,3 µm 3 ) again dominated the
bacterial biomass followed by medium and large-size cells (volume 0,3-0,6µm 3 and >0,6
yum 3 , respectively ; Meyer-Reil 1983).
58