Will ocean acidification affect the early ontogeny of a tropical oviparous elasmobranch (Hemiscyllium ocellatum)?

By Martijn Johnson

Supervisor: Dr. Jodie Rummer

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

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

Introduction Aims Methods Results Conclusions

What’s known?

Why study elasmobranchs

Introduction Aims Methods Results Conclusions

• 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?

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?

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

Introduction Aims Methods Results Conclusions

• Removed fibrous layer• Candled for age and dev stage

Research design & treatment

TreatmentPCO2

(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

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 )

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

Ave

rage

gro

wth

(cm

²)

Days post fertilization (dpf)

Control CO₂

MLMp = 0.168

• MLM= Mixed linear models

Hatched

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

Ave

rage

Yo

lk u

sed

(%

)

days post fertilization (dpf)

Control CO₂

MLMp = 0.699

Small amount of yolk

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

Ave

rage

ven

tila

tio

n r

ate

(gill

mo

vem

ents

min

ˉ¹)

Ave

rage

Tai

l Mo

vem

ent

(Osc

illat

ion

s m

inˉ¹)

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

MLMTail undulations, p = 0.961Ventilation rate, p = 0.094

Movement

Introduction Aims Methods Results Conclusions

30 day Post hatching survival (n=19)Pre-hatching survival (n=36)

ᵡ²p=0.55

ᵡ²p = 0.08

Survival

0

10

20

30

40

50

60

70

80

90

100

Control CO₂

Surv

ival

(%

)

0

10

20

30

40

50

60

70

80

90

100

Control CO₂(n=16) (n=20) (n=11) (n=8)

• 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

• 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

• 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

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

People to thank !!

• Dr. Jodie Rummer

• The wonderful Rummer lab group

• Dan Kraver

• Prof. Gillian Renshaw

• Munday lab group

• MARFU

Thanks for your attention

10 dpf 25 dpf40 dpf

55 dpf

70 dpfHatched 88 dpf