School of Engineering and Science - Jacobs University

CHAPTER III
incubation bottles without added nutrients (Landry, 1993, Caron, 2000); negative values
of g were set to zero for calculation. Based on the coefficients obtained for µ 0 and g
applied on the initial phytoplankton biomass C t0 , the loss of phytoplankton standing
crop per day P i and the percentage loss of potential phytoplankton production P p of each
species were calculated according to equation (6) and (7) (Quinlan et al., 2009).
P
i
C
t0
( e
C
t0
g
1)
100
(6)
P
p
C
t0
[( e
µ 0
C
t0
1) ( e
( e
µ 0
( µ 0 g )
1)
1)]
100
(7)
Copepod grazing - correcting for trophic cascade effects
The uncorrected grazing coefficient g cop,p of T. longicornis was calculated for each prey
type p after Frost (1972) at average prey concentrations, whereby the undiluted seawater
incubation bottles of the dilution experiment served as control. The corrected copepod
grazing coefficient (g corr,p , equation (8)) was calculated after the general method of
Nejstgaard (2001) by adding a correction factor k p for reduced microzooplankton
grazing rates due to predation by T. longicornis to g cop,p :
g
corr,
p
gcop,
p
k
p
(8)
k
p
g
micro,
p
[ C
predator
] [ C
[ C
predator
predator
]
]*
(9)
whereby [C predator ] in equation (9) is the mean microzooplankton carbon concentration
in the undiluted seawater from the dilution series and [C predator ]* is the mean
microzooplankton carbon concentration in the T. longicornis bottles. Only significant
microzooplankton grazing rates were used for the correction, negative grazing rates
were set to zero. Carbon specific grazing (g c ) and filtration rates (F c ) and carbon
specific ingestion rates (I c ) (phytoplankton and microzooplankton prey) of the added T.
longicornis were calculated as described above for the microzooplankton.
Microzooplankton growth was assumed not to be influenced by nutrient addition and
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