Community Ecology Processes, Models, and Applications

fishes had little effect on algal biomass initially, per-
haps because sea urchin grazing compensated for
the reduced fish grazing (Hay 1984; Hughes 1994;
Jacksonet al. 2001). But when sea urchins suffered
mass mortality from disease, algal biomass exploded
(Carpenter 1990). Macroalgal blooms proliferated
only after both fishes and sea urchins were reduced.

These observed patterns are consistent with experi-

ments and comparisons among protected and fished

areas on Kenyan reefs, which showed that sea urch-

ins were more abundant on overfished reefs than in

protected areas, but that experimental reduction of

urchins allowed large macroalgae to dominate only

on fished reefs, where herbivorous fishes were

0.80

0.60

0.40

0.20

0.00

0.80

1.00

0.60

0.40

0.20

0.00

0.80

1.00

0.60

0.40

0.20

0.00

0.12

0.15

Sole

Cod

Whiting

Norway pout

Herring All species

Sandeel

Saithe

Haddock

Plaice

0.09

0.06

0.03

0.00

5.00

4.00

3.00

2.00

1.00

0.00

5.00

4.00

3.00

2.00

1.00

0.00

16.0

12.0

8.0

4.0

0.0

1.60

1.20

0.80

0.40

0.00

1.20

1.00

0.80

0.60

0.40

0.20

0.00

1.50

1.20

0.90

0.60

0.20

0.00

1976 1980 1984 1988 1992

1976 1980 1984 1988 1992

1976 1980 1984 1988 1992

1976 1980 1984 1988 1992

1976 1980 1984

Year Year

1976 1980 1984 1988 1992 1988 1992

1976 1980 1984 1988 1992

1976 1980 1984 1988 1992

1976 1980 1984 1988 1992

Biomass (tonnes x 10 1976 1980

6 )

Biomass (tonnes x 10

6 )

Biomass (tonnes x 10

6 )

Biomass (tonnes x 10

6 )

Biomass (tonnes x 10

6 )

1984 1988 1992

Figure 8.5Biodiversity begets stability. The temporal trend in aggregate fish biomass (bottom right) is substantially less
variable than the time series for any individual species. Reproduced with permission from Jennings and Kaiser (1998).

106 APPLICATIONS