V) Factors affecting recruitment B) Determinants of larval delivery V ...

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recruitment and recovery b) 3 Hypotheses: HA1– whole plants carried to reef, then release spores. V) Factors affecting recruitment. B) Determinants of larval ...
b) 3 Hypotheses:

V) Factors affecting recruitment B) Determinants of larval delivery

HA2– “seed bank” of dormant spores - but out-plant studies by Reed suggests very short longevity (rapid loss to grazers)

iii) Episodic events storms (Reed 1988 Ecology)

HA3– storms cause propagule transport to distant locations (for kelps) a) Pattern: following storms there is catastrophic loss of kelpbed area, followed by quick, widespread recruitment and recovery

- but, previous work indicated that dispersal was on the order of 1 meter

b) 3 Hypotheses: HA1– whole plants carried to reef, then release spores Macrocystis sporophylls at base of plant < 1m

- but broad-scale, uniform pattern of recruitment inconsistent with pattern predicted by plant swept across reef

c) Test:

Pterygophora

V) Factors affecting recruitment

Current

K e l p

B) Determinants of larval delivery

Sand

iv) Larval depletion - ecological filters Predation Gaines and Roughgarden 1987 Science

10 m 100 m

1000 m

a1) Pattern: from year-to-year, recruitment of B. glandula was negatively correlated with kelp abundance offshore Ö kelp or something associated with it may affect settlement… supply?

barnacle recruitment (no. / cm2 / wk)

d) Results: (Pterygophora) calm conditions

storms

kelp canopy area (m2)

b1) Hypothesis: if supply, larval abundance should be lower on inside edge of kelp bed than outside it

Settlement of spores on slides 10 m 100 m

1000 m

10 m 100 m

1000 m

e) Conclusion: During storms, long range dispersal can occur, spores get mixed, advected up into the water column, transported away

S h o r e

X inshore

K e l p

Current

X offshore

No. competent larvae per hr

inshore

offshore

1

iv) Larval depletion - ecological filters

iv) Larval depletion - ecological filters

c1) Test: sample larval concentrations with plankton pump inshore and offshore of kelp bed

Predation Gaines and Roughgarden 1987 Science b2) Possible hypotheses for pattern:

d1) Results:

1) simple hydrodynamic effects (of kelp)

i) Cyprid larvae - the settlement stage for Barnacles

i) water slows down – particles sink

No. competent larvae per hr

Confirmed: 70 times greater concentration offshore than inshore!

ii) get entrained in kelp 2) predation by kelp-associated planktivores inshore

offshore

ii) Nauplius larvae - pre-settlement stage - released by adults Opposite pattern! S h o r e

nauplii

K e l p

No. competent larvae per hr

cyprids

c2) Test: looked at distribution of particles that were same size and shape as barnacle larvae but that were not living or edible = molts of larval barnacles! d2) Results:

inshore

offshore

iv) Larval depletion - ecological filters

No difference!

– suggests predation is responsible, and

c3) Test: looked at the relationship between abundance of juvenile rockfish (Sebastes) and Balanus glandula recruitment over a three year period.

1983 1984 1985

Balanus recruitment #/cm2

“recruitment shadow” Gaines et al. 1985 Oecologia a) Hypothesis: as a bath of larvae pass over a site, settlement causes there to be a decrease in the # of larvae available to settlement down current: propagules

kelp bed area

0.7

3.7

7.2

1.4

33,000 m2

0.05

46,500 m2

236

offshore

iv) Larval depletion – ecological filters

b3) New hypothesis: predation by juvenile rockfish filters cyprids

rockfish density # observed / min

inshore

– kelpbed itself is not responsible → only edible things were affected

Predation Gaines and Roughgarden 1987 Science

Year

No. cyprid molts Per volume

8,500 m2

d3) Results: Rockfish hypothesis not rejected but change in kelp bed size—complicates the interpretation a bit

I b) Predictions:

II

III

1) cyprid concentration should decrease with distance 2) settlement should decrease

c) Tests: 1) counted cyprid concentration (supply) in water column 2) followed settlement at Hopkins Marine Station at three sites along a unidirectional current

2

Processes affecting larval supply

iv) Larval depletion – ecological filters “recruitment shadow” Gaines et al. 1985 Oecologia d) Results:

1. Variable production i) species traits ii) environmental variation (in productivity)

cyprid concentration

settlement rates #/cm2/day

I

2. Physical oceanographic processes i) biogeographic scale

III

II

I

II

site

III

site

Results were consistent with “larval depletion hypothesis”, but other hypotheses not rejected (assumption that change in cyprid # = depletion)

Particularly likely alternative:

ii) intermediate scale processes a) internal waves b) upwelling 3. Episodic events - storms 4. Mortality and Depletion

hydrodynamic -- difference in cyprid # caused by hydrodynamic reasons (e.g., greater water movement/exchange at site 1 → more water → more cyprids → more settlement)

i) rockfish predation ii) hydrodynamic influence of kelp iii) larval depletion

Sources of spatial and temporal variation in recruitment 100 yrs

Temporal scale

1 decade

Larval dispersal, mortality Seagrass beds

1 year

Seasonal current shifts

PDO

ENSO

Kelp forests Seasonal upwelling Mesoscale eddies Coastally Small-scale trapped fonts, plumes, waves runoff

1 month 1 week 1 day

Plankton migration

Surface tides

1 hour Langmuir cells 1 min

Coastal filaments, Upwelling / relaxation

Internal waves Internal tides

Turbulent eddies Surface waves 1 cm

1 dm

1m

10 m

100 m

Settlement

1 km

10 km

100 km 1000 km 10000 km

Linear spatial scales After T. Dickey, unpublished

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V) Factors affecting recruitment C) Processes affecting settlement

Larval Behavior Æ Pre-settlement Æ Settlement I. Some types of larval behavior

1) Physical processes (e.g., turbulence, current speed) a) Phototaxis — response to light (e.g., bryozoans, corals, fish)

2) Larval behavior I) types

b) Geotaxis — swim up or swim down (many inverts and fish) c) Rheotaxis — currents (many inverts and fish)

II) history of larval behavior studies - barnacles

d) Rugotaxis — surface texture (inverts, not fish)

III) conditions for evolution of behavioral cues (settlement)

e) Chemotaxis — water or surface chemistry (inverts and fish)

IV) contribution to vertical zonation

II. Early work on larval behavior (mostly barnacles) Golden age 1950-1960 when received a lot of attention and great advances

Example 1: Gregarious settlement — Knight Jones 1953 b) Hypothesis: Gregarious settlement response is species specific (i.e., “conspecific facilitation”)

(e.g., Crisp, Knight Jones, Ryland (bryozoans), Barnes) Most of the work was motivated by field observations but generally done in lab with field collected or cultured larvae

Example 1: Gregarious settlement — Knight Jones 1953 a) Pattern: Barnacle aggregations on shoreline seemed to be species-specific (like settled next to like)

c) Test: In laboratory aquaria, presented cyprids (barnacle larvae) with choice of settling on surfaces with either: 1) adults of own species, or 2) another species, or 3) no barnacles

System- 3 species of barnacles in the rocky “you know where”…

4

d) Results…. 2 general results! Settlement of: 100

(1) B. balanoides

Why settle gregariously? Benefits:

(2) B. crenatus

98

(3) E. modestus

2) Benefit in numbers (e.g., swamp predators)

85

82

fertilization, reproductive success

3) Higher likelihood of finding mates

% settlement

Surface with adults of:

1) Indicates good habitat

I

0

0

2

0

18

I

0 2

0

15

I

0 3

1) Strong conspecific attraction 2) No settlement in absence of barnacles i.e. no settlement without some sort of cue (inducer)! e) Conclusions: 1) Settlement much greater in presence of inducer 2) Inducer is species specific (⇒ gregarious)

Example 2: Territoriality at settlement - Crisp 1960

Distance between neighbors

0

But, what is the relationship between gregarious settlement and post-settlement growth and mortality? (what does gregarious behavior do ⇒

post-settlement growth, survivorship

minimize distance to nearest neighbor)

Distance between neighbors

3 types of distributions are possible… generated by 3 behavioral mechanisms:

a) Species: Balanus balanoides b) Pattern: 1) just showed that B. balanoides settle gregariously 2) however, at smaller spatial scale, individuals seem to be spaced out more than expected by purely gregarious settlement. c) Hypothesis: pattern of settlement at smaller spatial scale different from gregarious

Dispersion:

clumped

random

uniform

Mechanism:

gregariousness

no behavior

territoriality

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d) Test: sampled settlement distribution of B. balanoides to test for these predicted frequency distributions of distance

Anderson et al. 2005 MEPS

a) System Blue damselfish, Chromis cyanea on coral reefs in Bahamas

clumped uniform

random

% frequency of occurrence

Example 3) Facilitative settlement in coral reef fishes

b) Pattern: highly aggregated distribution, especially recently settled juveniles far

short distance to nearest neighbor (mm)

e) Results: normally distributed frequency distribution… uniform f) Conclusions: Territorial behavior at settlement - backed up w/observations of larvae settling in the lab.

2) Strong positive relationship between settlement rate and number of residents

f) Conclusion: Conspecific residents facilitate settlement

Mean no. settlers / Mean no. settlers / head coral head

1) No settlement in absence of resident adults or recruits

d) Test: establish different densities of resident species and determine if settlement rate increases with resident density level

a

10

5

0

0

Present

b

20

Cumulative no. settlers / coral head/ head Cumulative no. settlers

e) Results:

c) Hypothesis: aggregations created by facilitative settlement: behavioral preference to settle with resident conspecifics

Absent

Residents Absent Present Residents

15

10

5

0 0

10

20

30

40

Mean no. residents / head

Mean no. residents / coral head

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