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Benthic Invertebrates – habitats, human impacts, management

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Presentation on theme: "Benthic Invertebrates – habitats, human impacts, management"— Presentation transcript:

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 (http://www.mdsg.umd.edu) 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?


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