Download 1015 Johansson C

Herbivory and sea urchin predation
for ecosystem resilience
By Charlotte Johansson, David Bellwood and Martial Depczynski
Introduction

Coral reefs under pressure

Human impacts

Increasing disturbance to reefs

Loss of vital functions (ecological
roles)

Gradual erosion of resilience
Introduction
Resilience
“the capacity of a system to absorb disturbance and reorganize
while undergoing change so as to still retain essentially the
same function, structure, identity and feedbacks”
(Walker et al 2004)
To understand how ecosystem processes will be affected by
disturbances we need to look at the species that contribute to
them and what the strength of their combined functional role is
Introduction
 Functions are;
 Processes (feeding) – movement or
storage of materials or energy
(Bellwood et al 2004)
 Functional groups;
 A collection of species that perform or
influence the same function,
irrespective of their taxonomic affinities
(e.g. herbivores, nitrogen fixers etc)
(Bellwood et al 2004)
Introduction
4 roving herbivorous groups
Herbivores
Macroalgae
Browsers
Turfalgae
Grazers
Scrapers
Excavators
Introduction
Fine scale approach when evaluating resilience:
1. Alternative organism (coral/algae)
2. Herbivorous fish
 Functional redundancy (same functional role)
 Functional diversity (different functional role)
 Responses
3. Non-fish herbivores (sea urchins)
Aim
1. Quantify the distribution of:
 Macroalgae
 Herbivorous fish
 Non-fish herbivores (sea urchins)
2. Evaluate the extent to which herbivorous fish and urchins are
likely to control macroalgae
Study location
Ningaloo Reef, Western Australia
1. Alternative organisms
Proportion ± SE
0.6
0.6
Coral
0.4
0.4
0.2
0.2
0.0
0.0
Slope
Back
Lagoon
Macroalgae
Slope
Back
Lagoon
2. Herbivorous fish
Density (100m-2 ) ± SE
10
Density of herbivores
8
Browsers
Excavators
Grazers
Scrapers
6
4
2
0
Slope
Back
Lagoon
2. Herbivorous fish
Excavators
SR = 2
FD = 1
1.0
SR = 2
FD = 1
SR = 2
FD = 1
Abundance (%)
0.5
0.0
C. sordidus
C. microrhinos
C. sordidus
C. sordidus
C. microrhinos
C. microrhinos
Grazers
1.0
SR = 13
FD = 5
SR = 16
FD = 5
SR = 8
FD = 4
0.5
0.0
Slope
Back
Lagoon
Abundance
Bioerosion
300
16
Eroded material (kg.m-2.yr-1: ± SE)
Density (100m2) ± SE
3. Non-fish herbivores
200
100
0
Slope
Back
Lagoon
C. microrhinos
C. sordidus
E. mathaei
12
8
4
0
Slope
Back
Lagoon
3. Non-fish herbivores

Important role on Ningaloo Reef

What is driving the pattern of
urchins, especially on the slope

Is it a lack of predators?

Urchins = reef degradation
3. Non-fish herbivores
10
Successful
8
6
4
2
0
3. Non-fish herbivores
Density 100m-2 ± SE
0.4
0.640
0.537
0.3
Balistidae
Labridae
Lethrinidae
Tetradontidae
0.423
0.2
0.1
0
Slope
Back
Lagoon
Conclusion

Macroalgae abundant in lagoon (despite herbivores)

Urchins abundant on slope (despite predators - except specialist
balistids)

Urchins and algae often signs of degradation - here they appear
to not be

Ningaloo Reef, although relatively intact, appears to be
functionally distinct to other reef systems
Acknowledgements

Prof D. Bellwood, Dr. M. Depczynski,
Dr. A. Hoey and I. van de Leemput

JCU, ARC Centre of Excellence

AIMS, AIMS@JCU, DEC

Colleagues in the lab and field