9780521861724htl 1..2

removal of fish had no effect on chlorophyll in two experimental lakes (though

the colonization of a fishless lake byDaphniadid result in reduced algal biomass

(Sarnelle & Knapp,2005)). This is in contrast to the situation in more productive

environments, where cascading effects can be seen in lakes of varying (high)

the yield; chlorophyll:TP was similar in lakes with and without fish

(E. Jeppesenet al., unpublished data). Canonical correspondence analysis indi-

cates changes in community structure of phytoplankton (K. Christoffersen

et al., unpublished data) along the fish gradient. These results suggest that the

strong impact of fish on zooplankton abundance and body size in these

oligotrophic lakes is not translated to total phytoplankton biomass, which

is likely to be determined mainly by nutrient availability (Jeppesenet al.,

2003a).

Zooplankton (

μg ind

–1)

Cladocerans (

μg ind

–1)

Rotifers (

μg ind

–1)

Chlorophyll

a (

μg l

–1)

Cyclopoids (

μg ind

–1)

Ciliates (

μg ind

–1)

Total phosphorus (

μg l

–1)

Calanoids (

μg ind

–1)

Zoophyt (dw dw

–1)

EG WEG

–F +F –F +F

EG WEG

–F +F –F +F

EG WEG

–F +F –F +F

0

2

4

6

8

10

0

10

5

20

15

30

25

0

2

4

6

8

10

0

0.5

1.5

2.5

1.0

2.0

3.0

0

0.02

0.04

0.06

0.08

0.10

0

1

2

3

4

0

0.5

1.0

1.5

2.0

2.5

0

1

2

3

4

0

10

20

30

40

50

Figure 7.2Boxplot showing various environmental data from 40 lakes

sampled in high Arctic NE Greenland (EG) and 42 lakes in Arctic W Greenland

(WEG). In each region roughly half of the lakes were fish free (F). Sampling

was conducted in late July–early August. ‘Zoophyt’ is the zooplankton:

phytoplankton ratio. For further details see Jeppesenet al. (2003a).

124 J. I. JONES AND E. JEPPESEN