Effects of conspecifics on lobster recruitment – Insights from larval behaviour experiments and multi-

scale population monitoring.

Victoria Burdett-Coutts*1, Richard Wahle2, Paul Snelgrove1

*MSc Candidate1 Memorial University of Newfoundland, St John’s, Canada

2 Bigelow Laboratory for Ocean Science, West Boothbay Harbor, USA

Effects of conspecifics on lobster recruitment

• recruitment drivers at different spatial scales

• American lobster

• patterns: long term recruitment time series

• mechanisms: behavioural experiments

• conclusions

Recruitment drivers over different spatial scales

Behaviour

Inter- and Intra-specific interactions

Benthic movements/migrations

Be

nth

ic

po

st-s

ett

lem

en

t p

roce

ss

es

Pe

lag

ic

pre

-se

ttle

me

nt

pro

ces

ses

Passive Transport

Ocean gyresBoundary layer turbulence

Swimming ability

Habitat selection

Vertical horizontal movement

Predation, competition

spatial scale +- 104 m10-2

American lobsterHomarus americanus

PelagicPelagic

BenthicBenthic

5-39mm

Early Benthic Phase Early Benthic Phase (EBP)(EBP)

Adolescent Phase Adolescent Phase (AP)(AP)

40-89mm40-89mm

Reproductive Phase Reproductive Phase (RP)(RP)

90+mm90+mm

3-8 weeks3-8 weeks

Stage IStage I

8 mm8 mm

9 mm9 mm

11 mm11 mm

11 mm11 mm

Stage IIStage II Stage IIIStage III

Stage IVStage IV

What is the relationship between Young-of-Year (YoY) and older conspecific juvenile (OCJ) density at different spatial scales ?

Does this relationship have a behavioural basis?

REGIONS100 km

QUADRATS1 m

2002 - 2008

SITES10 km

Nested Sampling Design

Evaluate patterns & processes operating at

different spatial scales

Develop hypotheses for mechanisms

year n  R2 p-value

2002 12 0.73 < 0.0001

2003 11 0.89 < 0.0001

2004 11 0.66 < 0.0001

2005 12 0.52 < 0.0001

2006 11 0.69 < 0.0001

2007 12 0.58 < 0.0001

2008 14 0.90 << 0.0001

1.8

1.2

0.6

0 3.5 7.0

Regional scale

OCJ density ( n / m 2 )

Yo

Y d

ensi

ty (

n /

m 2

)

RI

Site scale

OCJ density ( n / m 2 )

Yo

Y d

ensi

ty (

n /

m 2

)

3.0

1.5

0 5.0 10.0

• frequency of quad with/without YoY densities of OCJ

Quadrat scale

# of OCJ

pres abs sumpresprop

0 46 396 442 0.10

1 52 111 163 0.32

2 24 46 70 0.34

3 19 24 43 0.44

4 16 8 24 0.67

<5 10 7 17 0.59

0

1

2

3

4

0 2 4 6 8 10

OCJ density ( n / m 2 )

Yo

Y d

ensi

ty (

n /

m 2

)

0.70

0.35

0.000 1 2 3 4 5+

pro

po

rtio

n o

f q

uad

rats

# of OCJ / quadrat

year  χ2 P

2002 103.749 <0.001

2003 156.802 <0.001

2004 107.332 <0.001

2005 113.927 <0.001

2006 59.338 <0.001

2007 12.728 0.026

2008  90.896  <0.001

observed expected

Quadrat scale

YoY with OCJ

• consistent circulation-driven spatial differences in larval supply and settlement

• similar habitat requirements, postlarvae select for cobble/boulder habitat

How do stage IV lobsters respond to the presence of older conspecific juveniles during settlement?

• Boudreau et al (1993) • + swimming orientation toward conspecifics

• Behaviour is cost – benefit • cost

• cannibalism, competition• benefit

• indicators of suitable habitat

Recruitment drivers over different spatial scales

+ association between YoY and OCJ at all scales (regional, site, quadrat)

behaviour experiments to identify small scale mechanisms

Experimental design

• independent – presence/absence of OCJ• dependent – settlement response of individual stage IV postlarvae

• sandy bottom, juvenile containers, YoY shelters

• short term and long term exp

4 minutes - immediateproportion of time on bottom

24 hour – long term recorded at 0, 6, 12, 18, 24h swimming / on bottom

presentn = 48

absentn = 46

0.5

0.25

0

Pro

port

ion

Short term – 4 minute

Proportion of time on bottom

t95 = 1.66P = 0.02

OCJ present absent

HO = HA

Long term – 24 hourProportion settled

HO ≠ HA

pro

po

rtio

n

time (hours)

0.35

0 2418126 0

0.70

Passive ocean processes

Preference for habitat R

eg

ress

ion

A

na

lys

is• effect didn’t persist with time ? hierarchical cue? other cue variables? i.e. with / without cobble

ConclusionsB

eh

avio

ur

exp

eri

me

nts Initial

propensity to settle

Strong YoY – OCJ association at all spatial scales

?

spatial scale +- 104 m10-2

AcknowledgementsAcknowledgements

• NSERC, Darling Marine Center, Bonne Bay Marine NSERC, Darling Marine Center, Bonne Bay Marine Station, Stonington Zone C hatchery, NOAA / Sea Grant, Station, Stonington Zone C hatchery, NOAA / Sea Grant, DFO, CURRADFO, CURRA

• Rachel Lasley, Hannah Blossom, Charlene Bergeron, Rachel Lasley, Hannah Blossom, Charlene Bergeron, Martina Kluge, Don Saunders, Benoit BruneauMartina Kluge, Don Saunders, Benoit Bruneau