Influence of habitat condition and competition
on foraging behaviour of parrotfishes
Kirsty Nash, Nick Graham, Fraser Januchowski-Hartley & David Bellwood
ARC CoE Coral Reef Studies, James Cook University
Herbivores: providers of ecosystem
process
Ontogenetic
Variation
Inter-specific
Variation
Temporal
Variation
Abundance
& Biomass ≠
Grazing
Intensity
Spatial
Variation
Herbivores: providers of ecosystem
process
Ontogenetic
Variation
Inter-specific
Variation
Temporal
Variation
Abundance
& Biomass ≠
Grazing
Intensity
Spatial
Variation
Spatial variation in herbivory
 To date primarily focused on changes in bite rate, bite
area...
 Little work looking at area covered whilst foraging
Vs.
Vs.
Aims
Using short-term assessments of foraging range
 Quantify space use by foraging parrotfish
 Compare use of space by feeding fish among sites with
varying reef condition
Trunk Reef
Rib Reef
John Brewer Reef
Wheeler Reef
Davies Reef
Methods
 Study Species
 Initial phase Scarus niger and Scarus frenatus
 In-water metrics – targets foraging behaviour
 Complexity, benthic cover
 Predator and competitor abundance
Photos: Randall, 1997 FishBase
2
3
5
4
1
Nash et al, in press, MEPS
Results: Influence of Coral Cover
Scarus niger
Scarus frenatus
Inter-Foray Distance (cm)
200
900
1400
800
100
700
1200
600
1000
400
0
500
800
200
-100
300
600
0
400
-200
-200
100
200
-400
0
20
40
60
Coral Cover (%)
80
0
20
40
60
Coral Cover (%)
80
Nash et al, in press, MEPS
Results: Influence of Coral Cover
Scarus niger
Scarus frenatus
Compactness Ratio
27
1.04
15
0.53
03
0.02
-11
-0.51
-2
-1.00
0
20
40
60
Coral Cover (%)
80
0
20
40
60
Coral Cover (%)
80
Nash et al, in press, MEPS
Results: Influence of Competition
Scarus niger
Scarus frenatus
Compactness Ratio
27
1.04
15
0.53
03
0.02
-11
-0.51
-2
1.5
2.0
2.5
3.0
3.5
Ln Parrotfish Abundance
4.0
1.5
2.0
2.5
3.0
3.5
Ln Parrotfish Abundance
4.0
Outcomes
 Coral cover & complexity at colony scale are key drivers
 Competition effects weak
 Need multiple metrics to assess foraging behaviour
Implications
 Cannot make assumptions of uniform foraging across
space
 Herbivory likely to change as habitat condition
changes
How do these small scale behavioural changes scale up
to broadscale patterns of herbivory....
Implications
Neutral
Negative
Feedback ›
Compensatory
Mechanisms
Positive
Feedback ›
Further
degradation
Implications
Degradation
Compensation
Diluted
grazing
intensity
Increased
grazing
intensity
Macroalgal
refuges
Contiguous
cover of reef
surface
Thank you
Credits
Graham Lab
Bellwood Lab
Fieldwork funded by
Queensland Smart Futures Fund and Australian Research Council
For more information:
Nash KL, Graham NAJ, Januchowski-Hartley FA, Bellwood DR. 2012.
Influence of habitat condition and competition on foraging behaviour of
parrotfishes. MEPS 457: 113-124.