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
3
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
5
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
6
