This study examined the effects of ocean acidification on the early development of epaulette sharks (Hemiscyllium ocellatum). The researcher measured growth, yolk usage, movement, ventilation rate, and survival of embryos exposed to current or elevated CO2 levels. Results showed no significant differences in growth, yolk usage, movement, or ventilation between the two CO2 conditions. However, survival rates before hatching and after 30 days post-hatching tended to be lower under elevated CO2, indicating some stress on the embryos, though the cause was not identified by the parameters measured. While adult epaulette sharks can tolerate changing ocean chemistry, their early life stages may be more vulnerable, with implications for future

1. Will ocean acidification affect the early ontogeny of a tropical
oviparous elasmobranch (Hemiscyllium ocellatum)?
By Martijn Johnson
Supervisor: Dr. Jodie Rummer

2. Outline
Introduction Aims Methods Results Conclusions
- Problem
- Why sharks
- Background
research
- Animal welfare
- Research design
- Stats
- Growth
- Yolk usage
- Animal
physiology
- Survival
- The big
picture
- Importance
- Aims
- Objectives

3. Ocean Acidification
Introduction Aims Methods Results Conclusions
• Current day CO₂ ~400 μatm
• pH ~ 8.1
• Predicted CO₂ ~1000 μatm by 2100
• pH ~ 7.8
• Change of pH by 0.3-0.4 units by
2100
• Negative effects on marine life
Modified from IPCC 2007
2015: Current day 2100

4. Introduction Aims Methods Results Conclusions
What’s known?

5. Why study elasmobranchs
Introduction Aims Methods Results Conclusions

6. • A quarter of all sharks are
threatened by extinction
• Different factors threatening species
• In combination of life history
characteristics
• Low fecundity
• Late sexual maturity
• Fewer offspring
• Longer gestation time
Introduction Aims Methods Results Conclusions
Why study elasmobranchs?
• Where to start?

7. Introduction Aims Methods Results Conclusions
Epaulette sharks
(Hemiscyllium ocellatum)
• Commonly found on reef
flats
• Small species
• Can withstand low oxygen
for a period of time
• Oviparous (egg laying)
• But what about the eggs
and embryos?

8. Aims
• To determine if the early ontogeny of epaulette sharks have a
developmental tolerance or intolerance to elevated PCO₂
Objective
• To determine if growth parameters and following physiological
parameters are impacted during embryonic development by high
PCO₂ conditions.
Introduction Aims Methods Results Conclusions

9. Introduction Aims Methods Results Conclusions
• Removed fibrous layer
• Candled for age and dev stage
Research design & treatment
Treatment
PCO2
(μatm)
pH
Temperature
(°C)
Control
n=16
422.61
± 4.769
8.14
±0.004
28.49
±0.03
Elevated CO2
n= 20
945.40
±13.668
7.88
±0.003
28.29
±0.040
• Randomly placed in each tank
and treatment
• Eggs were candled every 3 days
to view embryo and yolk
YolkEmbryo

10. Data analysis
Introduction Aims Methods Results Conclusions
Measurements
• Growth ( cm2 day-1 )
• Yolk Usage ( cm2 day-1 )
• Tail undulations (min-1 )
• Ventilation Rate (min-1 )

11. Introduction Aims Methods Results Conclusions
Growth
0
3
6
9
12
15
18
21
24
10 16 22 28 34 40 46 52 58 64 70 76 82 88
Averagegrowth(cm²)
Days post fertilization (dpf)
Control CO₂
MLM
p = 0.168
• MLM= Mixed linear models
Hatched

12. Introduction Aims Methods Results Conclusions
Yolk Usage
0
10
20
30
40
50
60
70
80
90
100
19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67
AverageYolkused(%)
days post fertilization (dpf)
Control CO₂
MLM
p = 0.699
Small
amount
of yolk

13. Introduction Aims Methods Results Conclusions
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
10 16 22 28 34 40 46 52 58 64 70 76 82
Averageventilationrate(gillmovementsminˉ¹)
AverageTailMovement(Oscillationsminˉ¹)
Days post fertilization (dpf)
0
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
10 16 22 28 34 40 46 52 58 64 70 76 82
Days post fertilization (dpf)
Control Treatment CO₂ Treatment
MLM
Tail undulations, p = 0.961
Ventilation rate, p = 0.094
Movement

14. Introduction Aims Methods Results Conclusions
30 day Post hatching survival (n=19)Pre-hatching survival (n=36)
ᵡ²
p=0.55
ᵡ²
p = 0.08
Survival
0
10
20
30
40
50
60
70
80
90
100
Control CO₂
Survival(%)
0
10
20
30
40
50
60
70
80
90
100
Control CO₂
(n=16) (n=20) (n=11) (n=8)

15. • Growth = NS
• Yolk Usage = NS
• Tail Undulations = NS
• Ventilation rate = NS
• Pre-hatching survival = NS
• Post hatching survival = NS
Introduction Aims Methods Results Conclusions
Summary of Results

16. • Growth & yolk consumption rates
similar
• No extra time in egg case
• Tail movement used for gas/oxygen
exchange in early development
• Gill development (major milestone)
Introduction Aims Methods Results Conclusions
The big picture: Growth & Physiology

17. • Mortality always occurred
before gill development
• Survival reduced under
elevated CO₂ conditions
• Indicating some sort of stressor
occurring in embryo
• Not seen in our parameters
Introduction Aims Methods Results Conclusions
The big picture: Survival

18. Overall Outlook
• Adult epaulette sharks can tolerate
changing ocean chemistry
• vulnerable stage- first month after fertilization
• Decreased survival- could have implications
for future populations
• What about other species of elasmobranchs
• vital in understanding the effects OA has on egg
laying species
Introduction Aims Methods Results Conclusions

19. People to thank !!
• Dr. Jodie Rummer
• The wonderful Rummer lab group
• Dan Kraver
• Prof. Gillian Renshaw
• Munday lab group
• MARFU

20. Thanks for your attention
10 dpf 25 dpf
40 dpf
55 dpf
70 dpf
Hatched 88 dpf