Are habitats important in mediating range shifts in tropical fishes?

Hayden BeckPhD Candidate

Supervisors: Prof. David Booth and Dr David Feary

GREAT BARRIER REEFEAST AUSTRALIAN

CURRENT

• Recruitment of tropical reef fishes along SE Australian coast during summer

• Hotspot of climate change: establishment of permanent populations

• Importance of physical habitats for early life stages of tropical fishes?

Model System: SE Australia

1500km

AUSTRALIA

1. Selection for habitat generalists (i.e. no coral dwellers)

Predictions: importance of habitats in core range

2. Larger-scales: organisation of distributions by interactions between wave-exposure and swimming abilities

3. Finer-scales: association with specific benthic habitats

Result 1. Only habitat generalists observed• 5695 individuals belonging to 30 species (Underwater surveys: 2

years, 4 latitudes, estuarine and coastal reef sites – 100s m apart)

NO CORAL DWELLERSPlanktivores (51%) Invertivores (24%)

Grazers (24%) Piscivores (1%)Images: D. Harasti and Australian museum

Result 2. Association with wave-exposure

0 0.05 0.1 0.15 0.2 0.25 0.3 0.350

50

100

150

200

250

300

350

400

450

500

Wave-exposure (Index 0-1)

Den

sity

(Ind

ivid

uals

/100

0m²)

• Significant correlation of densities of tropical fishes with wave-exposure on larger-scales

Result 2. Association with wave-exposure

0 0.05 0.1 0.15 0.2 0.25 0.3 0.350

5

10

15

20

25

Wave-exposure (Index 0-1)

Spec

ies

Rich

ness

(Spe

cies

/100

0m²)

• Significant correlation of species richness of tropical fishes with wave-exposure on larger-scales

• No correlation with water temperatures, benthic complexity, predator densities or substrate composition

Result 3: Swimming modes match wave-exposure

Pectoral Pectoral-Caudal Caudal0

10

20

30

40

50

60

70

80

90

100 95.7998211902358

16.1660937396936

3.38363501474252

Primary swimming mode

Mea

n (±

SE) p

ropo

rtion

of a

ssem

blag

e (%

)

*

* Coastal reefs

High swimming performance

*

Poor swimming performances

Estuarine reefs

Result 4. Association with sea urchin barrens• 1028 individuals belonging to 15 species (Underwater surveys: 2

years, 7 coastal reef sites; barrens and kelp habitats - 10s m apart)

NO species associated with kelp habitat

Images: D. Harasti

Conclusions

•4

Within new range lacking coral: • Habitat generalists successful

• Wave-exposure: strong structuring mechanism on larger-scales

• Benthic habitat: organise finer-scale distribution