Stable isotope analysis! - Hawaii Coral Reef Initiative

Population level impact of the introduced
grouper roi (Cephalopholis argus)
on native reef fishes in Hawaii
HCRI talk 1: Project outline and rationale
Charles Birkeland (UH Zoology)
Jan Dierking (UH Zoology)
HCRI talk 1: Project outline and rationale
• Background
• Key project questions
• Project structure
• Key results of completed research
• Rationale & status of ongoing research
Background
Introduced in
1956
Background
– Situation today
• Roi widespread
and abundant
14
12
Density (individuals/1000m2)
• Still increasing in numbers
(6 years of WHAP data)
10
8
6
4
2
0
The perception of the people
“Don’t eat it, it’s ciguatoxic!”
“Roi is a ferocious predator & harms
native reef fishes!”
Hawaii Skindiver Magazine
Kona coast divers
Dierking
Key project questions
1. Feeding biology
•
What is the qualitative and quantitative nature of roi predation?
2. Ciguatera
1. Is the problem as bad as perceived by the public?
2. Which factors determine the ciguatoxicity of roi individuals?
Key management issues: • Evaluation of roi impact
• Feasibility of roi fishery in Hawai'i
Project structure
2. Ciguatera
Ciguatera
analysis
1. Feeding biology
Stomach content
analysis
Stable
isotope
Æ Completed
components
• Key
analysis data
results & available
Consumption/
Digestion
experiments
Roi impact
modeling
Æ Ongoing research
• Rationale
and status
End of this talk: How does everything fit together?
Sampling
• 304 roi from 23 locations (spearfishing)
• body length
• weight
• otoliths Æ age
• sex
• sample site
• sampling time
• tissue samples
• stomach contents
• 15 live roi (Kaneohe barrier net collection)
• body length, weight
• average food consumption ad libidum
• digestion rates
Key results from completed work
Feeding biology
Stomach content analysis
(Æ What does roi feed on in Hawai’i?)
Consumption/Digestion experiments
(Æ How much prey does roi consume?)
Stomach content analysis
Gilded Triggerfish
Belted Wrasse
Lavender Tang
Pyramid Butterflyfish
Orangemouth Lizardfish
Palenose Surgeonfish
Stomach content analysis
Fish and
Crustacean
6%
Crustacean
9%
Fish
85%
Empty
43%
Full
57%
Stomach content analysis
Stomach content analysis
Available data:
• Prey dimensions (length, depth)
• Weight
• Volume
• Digestion status
• ID
• Photo
• Link through databaseFish
toand
corresponding roi individual
Crustacean
6%
Crustacean
9%
Empty
43%
Full
57%
Fish
85%
Consumption/Digestion experiments
Consumption experiment
400
Food consumed (g)
Data for 12 individuals pooled
300
200
100
0
0
5
10
15
Average food consumption/day
(in terms of % of body weight):
1.30%
20
25
30
35
Literature values for other native predators
(incl. Carangidae, Labridae, Lutjanidae):
Range: 3.6% - 6%
Digestion experiment
Intervals
up to
72h
Digestion experiment
Proportion of initial prey remaining (by Weight)
100.0%
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
0.0
12.0
24.0
36.0
Time (h)
48.0
60.0
72.0
Digestion experiment
100.0%
Proportion of initial prey remaining
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
R2 = 0.959
30.0%
20.0%
10.0%
0.0%
0.0
12.0
24.0
36.0
Time (h)
48.0
60.0
72.0
Consumption/Digestion experiments
Available data:
• Average daily ad libidum consumption rates of roi
• Understanding of digestion process in roi
Ciguatera
Measure of relative ciguatoxin concentration in roi tissue:
• scores: 0 (not detectable) to 6 (high concentration)
• score classes: 4 classes, from “safe for consumption” to “likely to cause incident”
Overall sample
+
Ciguatera level
14%
4%
36%
0-0.5
1-2
2.5-4
4.5-6
46%
n = 292
Ciguatoxin level and location
100%
F re q u en c y
80%
Strong pos.
60%
Positive
40%
Marginal
20%
Negative
K-
M
K-
ah
u
ko
n
Ki a
ho
K- lo
L
K - on e
Go
K - l de n
Ko
lo
K- ko
Ka
K - iw i
K - Pu
Ho a k
na o
un
K- au
Ko
n
K- a
K - Re
d
Al
ah
ak
a
OK2
OK4
O- O -K
Ko
6
ol
in
a
2
Al
l
0%
Site
• Sites differ significantly in Ciguatoxin levels (p<0.002)
• Many sites with low mean Ciguatoxin concentrations have outliers
Mean score:
1.55
Mean score:
0.73
100%
F req u e n c y
80%
Strong pos.
60%
Positive
40%
Marginal
20%
Negative
K-
M
K-
ah
u
ko
n
Ki a
ho
K- lo
Lo
K- n e
Go
l
K - de n
Ko
lo
K- ko
Ka
K - iw i
K - Pu
Ho a k
na o
un
K- au
Ko
n
K- a
K - Re
d
Al
ah
ak
a
OK2
OK4
O- O-K
Ko
6
ol
in
a
2
Al
l
0%
Site
Æ Oahu roi have significantly lower Ciguatoxin levels than Big Island roi
(p<0.001)
Ciguatoxin level and roi size
6
C ig u a te ra s c o re
5
4
3
2
1
0
12
17
22
27
32
Total length (cm)
37
42
Ciguatoxin level and roi size
6
C ig u a te ra s c o re
5
4
3
R2 = 2.7%
2
1
0
12
17
22
27
32
37
42
Total length (cm)
• Significant positive association of fish length and ciguatoxicity (p = 0.004),
2.7% of variation in toxicity explained by fish length
Ciguatera
Available data:
• Ciguatoxin concentrations for 292 roi
• Link through database to roi length, age, location, tissue
samples, prey item
• Information about the role of location & roi size in ciguatoxicity
Rationale & status, proposed research
1. Feeding biology
•
Qualitative and quantitative nature of roi predation in Hawaii
Æ Qualitative: completed project parts
Æ Quantitative: unknown. How does individual consumption scale up to
population consumption and impact?
Æ Population consumption & impact model!
Population consumption & impact model
Annual consumption of particular species in particular region by roi
= (size of area) * (density of roi) * (average weight of roi) *
(daily individual consumption rate) * (ratio of diet consisting of particular species) * 365
•Previous applications (examples):
• 2 species of Jacks, NWHI (Sudekum et al. (1991)
• Atlantic mackerel (Scomber scombrus) (Overholtz et al. 2000)
• Several studies of consumption of marine mammals (e.g., Kenney et al. 1997)
Population consumption & impact model
Annual consumption of particular species in particular region by roi
= (size of area) * (density of roi) * (average weight of roi) *
(daily individual consumption rate) * (ratio of diet consisting of particular species) * 365
• Data availability discussion
Required data
Source
Size of reef area
NOAA habitat maps
Benthic habitat characterizations from monitoring studies
Roi density
WHAP
CRAMP
Average roi weight
Length distribution data from monitoring
studies; L-W correlation from our study
Daily consumption rate
Diet composition
Our completed study
Our completed study
Population consumption & impact model
Annual consumption of particular species in particular region by roi
= (size of area) * (density of roi) * (average weight of roi) *
(daily individual consumption rate) * (ratio of diet consisting of particular species) * 365
• Data availability discussion
Required data
Source
Size of reef area
NOAA habitat maps
Benthic habitat characterizations from monitoring studies
Roi density
WHAP
CRAMP
Average roi weight
Length distribution data from monitoring studies; L-W
correlation from our study
Daily consumption rate Our completed study
Diet composition
Our completed study
Rationale & status, proposed research
2. Ciguatera
1. Is the problem as bad as perceived by the public?
2. Which factors determine the ciguatoxicity of roi individuals?
Æ Better understanding from completed project; but what could
explain the variability in ciguatoxicity not explained by geographic
variation, roi size & age?
Æ Most likely factor is longterm average diet of roi.
Æ Stable isotope analysis!
Stable isotope analysis
• Method potential:
• Average trophic feeding level of individuals
(Æ δ15N, predictable enrichment (DeNiro & Epstein 1978, 1981))
• Determination of average importance of functional prey groups in diet
(Æ δ13C, constant ratio from prey to predator (Peterson & Fry 1987))
• Roi related questions:
• Average trophic feeding level of roi
• Importance of functional prey groups in average diet of roi
Stable isotope analysis
• Test of method validity:
• Signal to noise ratio ÆVariability on different levels:
- Within muscle tissue of roi:
Variability w ithin m uscle tissue, 15N
11.00
10.50
Stdev (‰)
15N
13C
15N
Sample
10.00
9.50
9.00
OA163
0.06
0.09
Acceptable: ±0.3‰
8.50
8.00
OA163-1
OA163-3
OA163-4
OA163-5
Sam ple
-Good! Æ Will facilitate analysis of intrapopulation &
interpopulation differences
OA163-6
Stable isotope analysis status
• Method validation tests run successfully – analysis valid for roi tissue
• ~ 12 samples each from Oahu and Kona run:
15N - Trophic level
13C - Food sources
0
10
20
30
13.0
40
-11.0
12.0
-12.0
13c (0/00)
13C Kona
-14.0
13C Oahu
!5N (0/00)
11.0
-13.0
15N Kona
10.0
15N Oahu
9.0
-15.0
8.0
-16.0
7.0
0
-17.0
Standard length roi (cm )
10
20
30
Standard length roi (cm )
• all 304 roi samples & 45 prey samples prepped for analysis
• will present full results of SIA at next HCRI meeting
40
How does all this fit together?
Ciguatera
Ciguatera
analysis
Feeding biology
Stomach content
analysis
Stable isotope
analysis
Underlying issues
Roi fishery
Consumption/
Digestion
experiments
Roi impact
modeling
WHAP
Habitat
maps
Roi impact
evaluation
Timeline
Time period
Project component scheduled
08/05 – 12/05
12/05 – 02/06
09/05, 12/05
09/05 – 01/05
01/06 – 04/06
04/06 – 08/06
09/05 – 12/06
Sample preparation for Stable isotope analysis
Stable isotope testing of roi and prey item tissues
Meetings with DAR Kona to coordinate WHAP data use
Data extraction from WHAP
Stable isotope results: analysis and write-up
Population impact assessment
Statistical analyses and work on manuscripts for publication
Acknowledgements
• Hawai'i Coral Reef Initiative (HCRI)
• UH Ecology, Evolution & Conservation biology program
• Hawai'i Institute of Marine Biology (Albert Tacon, Joanne Leong)
• Sheila Conant, Yoshitsugi Hokama, Bob Kinzie, Ivor Williams, William
Walsh
• Amanda, Tim, Lance, Craig, Sasa, Courtney, Shawn
Questions?
Stable isotope analysis: principle of determination of
importance of functional prey groups in diet
Carbon and Nitrogen (Mean +- 2SE)
0.0
2.0
4.0
6.0
8.0
10.0
-8.0
-9.0
-10.0
13C
-11.0
-12.0
-13.0
-14.0
Scaridae
-15.0
-16.0
roi
-17.0
15N
12.0
Rationale & status, proposed research
1. Feeding biology
•
Qualitative and quantitative nature of roi predation in Hawaii
Æ Qualitative: completed project parts; quantitative: not known – how do
individual consumption scales up to population consumption and impact?
Æ Population consumption & impact model!
2. Ciguatera
1. Is the problem as bad as perceived by the public?
2. Which factors determine the ciguatoxicity of roi individuals?
Æ Better understanding from completed project; but what could
explain the variability in ciguatoxicity not explained by geographic
variation, roi size & age?
Æ Most likely factor is longterm average diet of roi.
Æ Stable isotope analysis!