1. Benthic Invertebrates – habitats, human impacts, management

2. Presentation Outline Importance of benthic invertebrates
Population based model
Approach
Limitations
Individual based model
Combining with population model
Genetic variability
Concluding Remarks

3. Benthic Invertebrates
Important components of estuarine and coastal food webs – sentinel species, many long lived
Provide coupling between benthic and pelagic systems
Post-settlement and larval phases of life history
Filtering water
Regulate food concentrations (phytoplankton)
Nutrient cycling
Shellfish important to carbonate balance
Many are commercially important
Important to local history and culture

4. Benthic Invertebrates
Included in models as loss/gain term via boundary conditions
Loss of phytoplankton via filtration rate
Nutrient addition term
Population that grows and declines in response to various forcing functions
Coupled circulation-biological model focused on larvae - usually transport pathways
Coupled circulation-biological model that includes larvae and post-settlement populations
Importance of understanding ecology, physiology and life history of organism

5. General Characteristics
Most models track energy – given by difference between assimilation and respiration
Reproduction is energy loss but provides recruits
Mortality – natural, disease, predation, starvation
Movement – pelagic phase to life history – need circulation
Range of responses within species in rates – genetic variability
Multiple species – focus on ones with data

6. Population Dynamics Modeling - The Past
Population-based model of the average individual
Based on animal physiology
Parameterized for average physiology
Allows projection of responses to environmental conditions

7. Aspects of Population Dynamics
Animal grows
Somatic tissue
Reproductive tissue
Reproduces – biological and environmental cues
Environmental inputs
Animal filtration rate sets up assimilation and respiration
Animal can gain and loose mass
Model usually in terms of energy or carbon

8. Requires conversion between weight and length
Size Class Approach
Requires conversion between weight and length
Nonlinear size scale

9. Size Class Model – Governing Equation
Net production NPj = Pgj + Prj = Aj – Rj j = size class dOj/dt = Pgj + Prj + gain j-1 – loss j+1 Gain and loss are inputs from current size class to/from larger and smaller size classes Transfers scaled by animal weight so mass and energy are conserved in terms of animal numbers

10. Shrinkage due to poor environmental conditions
Reproductive tissue accounts for 30-50% of body weight
Spawning is a loss of mass and energy for size class
Larvae provide new recruits and connect to pelagic system

11. Size Class Model – Governing Equation
Net production NPj = Pgj + Prj = Aj – Rj j = size class dOj/dt = Pgj + Prj + gain j-1 – loss j+1 + gain j+1 – loss j-1 Gain and loss are inputs from current size class via shrinkage from larger and to smaller size classes Scale transfers to conserve numbers

12. oyster population size structure Time history of
Results – what learned
Simulated change in
oyster population size
structure
Time history of
reproductive tissue and
occurrence of spawning
events

13. Limitations
Average individual – does not allow consideration of variability in physiological responses
Larvae incorporated as a loss of mass and input of mass to smallest size class – not altering characteristics of post-settlement population
Gain/loss in weight requires a
gain/loss in length

14. Population Dynamics Modeling The Recent Present
Animal
Individual-based model
Multiple cohorts of phenotypically varying individuals
Allows phenotypic variation to determine population response to environment
Age-size decoupled so that age-frequency and size-frequency distributions can be independently described

15. Given age can
have a range of
lengths
Given size can
ages
Represents genetic
variability of
population
Nonlinear
age-length
relationship
Age-length
distribution

16. Net production is
apportioned between
reproductive and
somatic tissue
Increase in weight
only if NP is positive
Condition index
determines if
length increase
can occur – positive
scope for growth
Allows an increase in
mass without an
increase in length

17. Governing Equations Calculate increase in weight
Calculate condition index
Calculate length
increase

18. Simulated hard clam growth
Increase/decrease in weight without change in length - spawning events

19. Investigate effects of environmental conditions on clam weight and length
Starvation period imposed in years 3-5 via low food conditions
Change in clam condition over time
Management implications

20. Successful How to extend beyond individual?
Apply a Gaussian function to produce
a distribution of individuals with range
of characteristics
Successful
Individual hard clam results are extended to cohort and population
levels

21. Track spawning events – gives individuals
Vary characteristics such as assimilation efficiency,
respiration rate, initial egg size to produce a cohort
Construct cohort with individuals with a range of variability

22. Extend Cohorts to Population
Uses broodstock-recruitment relationship

23. Limitations
Population variability is based on probability distribution
Cannot determine cause and effect of variability
Introduction of new traits and/or modifications to existing traits not possible
Want to be able to track genetic variability

24. }L1 }L2 G3 G1 G4 G2 Population Dynamics Modeling The Present
Integrate Population and
Genetic Processes
Model allows for
genetically determined
phenotypically-based
physiology
Phenotypic response
modulated by
genotypic constraints
Phenotype response to
environmental conditions
controls population
response
Animal G3 G1 G4 G2
}L1
}L2
N Chromosome pairs
Nx2 Chromosomes
Multiple loci per
chromosome
Multiple alleles per
gene
Genotype doesn’t respond to environmental conditions – the phenotype does.
The ability of the phenotype to respond determines the genotypic response which then controls the population response in the subsequent generation

25. Characteristics of Oysters
High fecundity – 106 eggs per spawn with multiple spawnings per season
Protandic – male when young, small size and become female when older and larger
Sex ratio of the population changes as it ages
High load of lethal mutations
Potentially subject to sweepstakes reproductive success events

26. Inclusion of Explicit Genetics
Track trajectory of individual alleles over time which gives a measure of genetic drift and loss of alleles
Effective population number
Introduction of new genetic traits
Relevance – pH effects,
disease resistance,
warming temperatures

27. Tracking individual alleles

28. Population trajectory Population characteristics AND
Model framework
provides
Population trajectory
Population characteristics
AND
Genetic composition
Example Application
Simulate introduction of specific genes into a population
Allele frequency on each chromosome

29. Larval dispersal – moves individuals
Larval Behavior
Physical Transport
© John Norton (
Pelagic phase
Benthic phase

30. Vertical Velocity, Size,
Model Framework
Genetics Model
Circulation Model
(3D and time)
LARVAL MODEL
Atmospheric
Tides
River Discharge
Temperature
Salinity
Currents
Temperature
Salinity
Larval
Growth
Particle Tracking
Module
Larval
Behavior
Settlement
330 um
Modified Particle
Tracking Module
Vertical Velocity, Size,
Temperature, Salinity
Post-settlement
Population

31. Population Connectivity Matrix
Allows determining connection
between spawning and
settlement areas
Allows tracking of specific genes
and genotypes

32. 1 2 3 4
Larval Dispersal obtained from coupled circulation-larvae model From Narváez
Area 1
Area 2
Area 3
Area 4
Area 1 to:
11%
54%
27% 8%
Area 2 to: 6%
56%
29% 9%
Area 3 to: 3%
40%
28%
Area 4 to:
19%
14%
64%
Munroe et al. (n press)

33. Transport of Alleles via Oyster Larvae
Base Case
2000’s
Even Dispersal
All 4 Areas
Reverse Larval
Dispersal
Low Salinity
Larval Disp.
No Self-Recruits
Equal Disp 1 2 3 4
Larvae not effective at moving and introducing new alleles
Munroe et al, in press

34. Adult Population Transfer of Alleles
Base Case
2000’s
Even Abundance
Via Mortality
1970’s Simulation
Via Carrying Cap.
Adult Population Transfer of Alleles 1 2 3 4
Adult mortality controls movement and introduction of alleles
Munroe et al., in press

35. Shells provide habitat
Shell Budget
Shells provide habitat
Carbonate source

36. Concluding Remarks Understanding and tools allow
consideration of interactions of ecology,
biology and genetics
Shellfish models are extendable to other invertebrate species – understand species and have data
Consider combined effects of environment, growth, behavior in projections of effects of climate change

37. Concluding Remarks Use complex models to develop
parameterizations for larger scale ecosystem models
Models are sufficiently robust to provide useful inputs for management - shell repletion in estuaries
Genetic basis allows consideration of adaptation to changing environmental conditions

38. QUESTIONS?