5. Lipid Dietary Dependencies in Zooplankton
103
(A)
CONCENTRATION
Cry ptomonas marssonii
6
2
3
0
(8)
PHOTOSYNTHESIS
( relativized to "Lake")
:
. .
• 90 . I II
· 0 8 .
;
·
Synura petersenii
7
I
2r----.------------~
.
~.
~--~--=!:
o
4L---~--------~
oL-__ -L ____________
Aphanizomenon flos-aquae
= 5
2r----r-------------,
.§
E
E
o
.0
Lake Containers
Containers
TREATMENTS ( "+" : 20 Daphnia· L- 1 )
FIGURE 5.1. Response of algal concentrations (A) and relative photosynthetic rates (B) to
grazing and inorganic nutrient additions (Lake Waynewood, October 1989). Algal counts
from the control (C) and nitrogen plus phosphorus treatments (NP), each with ("+") and
without Daphnia, demonstrate significant stimulation of growth in Cryptomonas (P <.001
from ANOCOVA) and Synura (P <.05), which were both significantly grazed (P <.001
and <.01, respectively). The cyanobacterium Aphanizomenon was neither grazed nor
nutrient limited. The homogeneity of photosynthetic rates across all nutrient and grazer
treatments suggests an absence of strong nutrient limitations. In each graph, container
results for the third day of incubation are compared with cell counts and photosynthetic
rates of algae in water freshly collected on day 3 ("lake" treatment to left of vertical
divider).