# Eelgrass Model v2.10

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## WHAT IS IT?

This model explores Zostera marina L. (eelgrass) restoration efforts by modeling the seasonal growth and spread of eelgrass in a shallow coastal area in the Chesapeake Bay or adjacent Delmarva Coast.

## HOW IT WORKS

This model simulates growth and reproduction of newly planted eelgrass. Eelgrass is planted (the initial pattern is shown visually as yellow eelgrass clumps) and season growth and dieback is simulated for a number of years with each tick representing one month of time.

Eelgrass growth and reproduction are modeled using adapted mathmatical metabolic growth models published by the Virginia Institute of Marine Science researchers (Jarvis et al, 2014; Buzzelli et al, 1999; Wetzel & Neckles, 1986). Eelgrass will continue to grow and reproduce as long as environmental conditions permit and as long as it is not eaten by grazing animals.

The environment is a tidal area with a gently sloping sand bottom from 0.5m deep (top of the screen) to 2m deep (bottom of the screen) and the incoming tide rising to the right. Water temperatures are based upon long-term average temperatures for the region.

This model begins by planting a number of patches of eelgrass in a set pattern similar to those used 1999-2008 restoration efforts. The eelgrasses germinate in early winter, grow through the spring and early summer, and die off in the late summer. Mature healthy plants spread by rhizome growth a random short distance and direction. Mature healthy plants more than one year old release seeds in the late summer, most of which are carried by the rising tide and some of which are randomly distributed.

Green Turtles are modeled as grazing predators, migrating into the Chesapeake Bay area in Spring and migrating south in early Fall. These turtles will seek out and eat the nearest eelgrass. Each turtle feeds 30 times per month. If a turtle does not find enough grass to eat, it will die (leave).

## HOW TO USE IT

- Select one of the seed patterns from the drop-down list.
- Use the Planting-Year slider to select which year to begin the simulation
- Use the months-of-experiment slider to select the number of months to run the model
- Select whether to keep water temperatures nominal (0C) or to simulate global warming by increasing water tempreature a number of degrees Celcius.
- Select the number of green turtles which will migrage each year.
- Select how much eelgrass each turtle will eat.
If desired, adjust the model calibration sliders. Default selections were found from previous modeling to yield a model that closely resembled real-world experimental results.

Press Setup to reset the model and plant the seeds (seed planting locations shown in yellow)

- If desired, use free-plant mode by depressing the free plant mode button and manually drawing eelgrass clumps using your mouse. This may be done even if another pattern has been selected.
- Press the Go button to run the simulation. Alternately, you may press the Step One Month button to go one month at a time.

EELGRASS-PATTERN: the pattern in which eelgrass seeds will be planted PLANTING-YEAR: seeds will be modeled as germinating in November of this year MONTHS-OF-EXPERIMENT: selectable in 12 month increments, the model will be run this number of months GLOBAL-WARMING: water temperature, in degrees celcius, that will be added to the typical average bay water temperature MIGRATING-GREEN-TURTLES: the number of green turtles that migrate in each year. TURTLES-EAT: how much eegrass shoot biomass is eaten each day by each green turtle TD-CALIBRATION: calibration coefficient for the amount of biomass translocated down from shoots to rhizomes. RZMS-CALIBRATION: calibration coefficient for shoot respiration RZMR-CALIBRATION: calibration coefficient for rhizome respiration SEED-SURVIVAL: calibration coefficient for what fraction of seeds survive MORTALITY-CALIBRATION: calibration coefficient for what fraction of shoots randomly die MAX-CLUMPS-PER-PATCH: calibration coefficient for limiting density by limiting the number of eelgrass clumps permitted in each 1x1m patch. RHIZOME-SHOOT-DISTANCE: calibration coefficient for how far new shoots are created by rhizome spread

## THINGS TO NOTICE

Do you see the exponential growth? Do you see the difference between newer and older beds after several years of growth, or do they appear the same?

Do you notice the difference in growth between different seed patterns for different amounts of time? Are there similarities? What are the differences?

## THINGS TO TRY

Try adjusting the number of sea turtles to see the impact on smaller beds. Does the impact lessen as the bed grows? Is there a significant difference when many turtles are added or if they're hungrier?

Try using free plant mode to see how your pattern grows.

Try using BehaviorSpace to compare the results of different models.

## EXTENDING THE MODEL

This model only included the basic metabolic model and does not include many real-world limitations such as nitrogen reduction, CO2 reduction, and turbidity. Implementation of the full model developed by Jarvis et al (2014) is anticipated to yield much higher quality results.

Can you add other predators and stressors such as fowl, crownose rays, and crabs?

Can you add stressful events, like hurricanes?

## VERSION CHANGES

2.10: -Added dotted versions of the squares and circle with 5m spacing between clumps

2.9: -Added free plant mode -Added additional code comments and documentation -Added error trapping for when green turtles eat all the eelgrass -Corrected conservation of rhizome mass during asexual reproduction

2.8: -Added additional code comments

2.7: -Added seed broadcast to model

2.6: -Adjusted dates to 2002-2008 to match Orth (2009) restoration records of the DelMarVa -Adjusted size to match actual Chesapeake planting patterns. Added 50m circle. -Changed sea turtles to migration pattern

2.5: -Removed Epiphyte code -Added factor into rhysome respiration to replicate real-life winter reduction of biomass -Added depth impact to PAR -Added rhizome reproduction back in

2.0 - 2.4: -Incremental model development

2.0: -Changed patch-based eelgrass sections to turtle-based eelgrass clumps.

1.0: -Early developmental model

## REFERENCES AND CREDITS

This model was created in NetLogo by Stephen Fehr, Old Dominion University, June 2016.

Thank you to Nima Shahriari and Adrian Gheorghe of Old Dominion University for the insights and instruction used to develop this model and to Uri Wilensky for developing Netlogo. Special thanks to the Virginia Institute of Marine Science team and all involved in Chesapeake Bay SAV restoration.

Buzzelli, C., Wetzel, R., Meyers, M. (1999). A Linked Physical and Biological Framework to Assess Biogeochemical Dynamics in a Shallow Estuarine Ecosystem. Estuarine, Coastal and Shelf Science 49.

Jarvis, J., Brush, M., Moore, K. (2014). Modeling loss and recovery of Zostera marina beds in the Chesapeake Bay: The role of seedlinks and seed-bank viability. Aquatic Botany 113.

Orth, R., et al (2009) Restoration of Seagrasses in Virginia Seaside Bays Year 6 (Oct 1, 2007, to Dec 31, 2008) and Summary FY 2007 Task 10.01. doi: 10.1.1.570.1755

Railsback, S., Grimm, V. (2012). Agent-Based and Individual-Based Modeling: A Practical Introduction. Princeton University Press: Princeton, NJ.

Wetzel, R., Neckles, H. (1986). A Model of Zostera Marina Photosynthesis and Growth: Simulated Effects of Selected Physical-Chemical Variables and Biological Interactions. Aquatic Botany, 26.

Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University. Evanston, IL.

## Comments and Questions

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;; VARIABLE DECLARATIONS ;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; extensions [array] globals [ x y ; x and y coordinates, in meters month ; integer representing the month (from 0-12) month-name ; array of month names, from JAN-DEC temperature ; average water temperature, in C initial-extent-eelgrass ; count of how many seedlings we planted max-extent-eelgrass ; the maximum extent of the meadow (largest veg-mass amount) seed-germination ; the probability of seed germination and survival (decimal) simulation-started ; alerts the free draw mode that the simulation is actively running ] breed [eelgrasses eelgrass] ; each eelgrass turtle is a clump of eelgrass representing many shoots breed [green-turtles green-turtle] ; each green-turtle turtle is a literal sea turtle eelgrasses-own [ veg-mass ; the biomass of eelgrass shoots, in gC/m2 rhizome-mass ; the biomass of eelgrass root & rhizomes, in gC/m2 epiphyte ; the biomass of epiphyte growth, in gC/m2 age ; the birth month (planting month) of the eelgrass seedling (tick) seeds ; the maximum biomass of the eelgrass clump (used for computing seeds) ] green-turtles-own [energy] ; energy represents the turtles' stomach and fat stores turtles-own [] patches-own [ depth ; mean water depth, neglecting tides [Wetzel (1986) found no tidal impact] ] ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;; MODEL SETUP ;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to setup clear-all ; reset everything to NetLogo default reset-ticks ; reset ticks to 0 set simulation-started false ; alerts free draw mode that we're in setup mode ;; Set up the calendar and initial water temperature set month 10 ;Calendar month in ordinal numbers: 10=October. set temperature 16.25 - 13.75 * (cos(360 * (month + .5) / 12 - 25)) ; from Buzzelli et al (1999) set temperature temperature + Global-Warming ;for experiment set month-name array:from-list [ "JAN" "FEB" "MAR" "APR" "MAY" "JUN" "JUL" "AUG" "SEP" "OCT" "NOV" "DEC" ] Display-month-year ; Display the month and year so we can see it on the setup screen ;; Set the contour of the seafloor (water depth) ask patches [ setup-depth ] ;; All new turtles will be eelgrass shape unless otherwise specified set-default-shape eelgrasses "eelgrass" ;; Plant the initial crop of eelgrass in the pattern specified by the pick-list plant-initial-eelgrass-pattern ;Remember how much eelgrass we planted so that we can tell the % increase in growth set initial-extent-eelgrass count eelgrasses ; # of initial seedlings set max-extent-eelgrass initial-extent-eelgrass ; the initial max = initial seedlings end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;; MODEL GO ;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to go ;This model represents the passage of time for a small section of the Chesapeake Bay. ;Each tick represents one month in time. The water temperature changes per month. set month month + 1 if month > 12 [set month 1] ;set the water temperature depending on which month it is set temperature 16.25 - 13.75 * (cos(360 * (month + .5) / 12 - 25)) ; from Buzzelli et al (1999) Display-Month-Year ;Alert free draw mode that the simulation has started so that it will stop resetting ticks to 0 set simulation-started true ;Don't start the model if the user didn't plant any eelgrass if ticks = 0 and count eelgrasses = 0 [ user-message ["You must plant some eelgrass, either by using a preset pattern, or by using free plant mode and manually picking a pattern."] stop ] ;; Model the migration of green turtles ;; A user-specified number of green turtles will migrate into this area every spring if month = 5 [ ;Green Turtles migrate into the bay in late spring (May) set-default-shape green-turtles "turtle" create-green-turtles migrating-green-turtles ;; create the turtles, then initialize their variables [ set color black set size 1.5 ;; easier to see, though a bit exaggerated in size set energy 4 ;; Assume each turtle has some fat and has eaten a recent meal move-to one-of eelgrasses ;; Seek out the nearest eelgrass to eat ] ] ;; Green turtles migrate out of the bay in mid-Sept (deleted from the model in Oct) if month = 10 [ ask green-turtles [die] ; All green turtles either leave or die ] ;; Model the growth of eelgrass ;; Use Jarvis et al (2014), Buzzelli et al (1999) and Wetzel & Neckles (1986) model equations, ;; adapted for agent-based modeling. ask eelgrasses [ grow-eelgrass ; metabolic growth demon rhizome-eelgrass ; rhizone reproduction demon ] ;; Model the behavior of green turtles based on a simple grazing model ;; Turtles will seek out the closest eelgrass and eat it repeat 30 [ ; repeat each day for each month (30 times per tick) ask green-turtles [ move ; movement demon (move to eelgrass) set energy energy - 1 ; metabolism requires energy (digestion & fat stores) eat-eelgrass ; grazing demon death ; mortality demon ] ] ;If this was the new seasonal high for eelgrass growth, remember it let present-extent-eelgrass sum [veg-mass] of eelgrasses if present-extent-eelgrass > max-extent-eelgrass [ set max-extent-eelgrass present-extent-eelgrass ] ;Release seeds in late summer; model as released in Oct so that ;the seeds will germinate in Nov. if month = 10 [ ; Equation from Jarvis et al(2014) adapted assuming 3cm seed burial and 1.25% SOC (. ; Seed-germination represents the percent chance of seed germinating and surviving ; Seed-survival is a user-entered base probability of seed survival set seed-germination seed-survival * 0.4 / (1 + e ^ ( -0.1432 + (1.1261 * 0.03) - (1.3964 * .0125)) ) ask eelgrasses [ seed-eelgrass ; seed reproduction demon ] ] tick if ticks = Months-of-experiment [stop] ;stop after a user-input number of months, usually 60-72 months ;stop if all the eelgrasses are dead or eaten if count eelgrasses = 0 [ user-message ("All the eelgrass has died or been eaten. Very sad. Fortunately, this was just a computer simulation!") stop ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;; EELGRASS GROWTH ;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to grow-eelgrass ;; This subroutine models the growth of a particular groups of shoots of eelgrass represented by each turtle ;; This growth is based upon models by Verhagen et al and Jarvis et al (2014) ;; and varies by month, depth (vs plant height), water temperature, and water turbidity ;; ;; The maximum size of a shoot in this model is 1m, and is tracked by the turtle size property. ;; For simplification purposes, biomass is modeled as proportionate to size. ;Jarvis et al (2014) equations for Z. Marina (based on Buzzelli): ;vegatative biomass: Czms=Czms(t-dt)+(Pzms+Tczmss-Mzms-Rzms-Td)dt ;rhizome biomass: Czmr=Czmr(t-dt)+(Td+Tczmsr-Mzmr-Rzmr)dt ;Td = translocation down from shoots to roots = Tzms ; Tzms = 0.3 (unitless) ;Pzms = Z. marina shoot production = unknown ;Tczmss = transfer of seedling biomass to vegetative shoot biomass ;Tczmsr = transfer of seedling biomass to rhizome biomass ;Mzms = shoot mortality = MRzms = 0.007/day ;Mzmr = rhizome mortality = MRzmr = 0.000085/day (jan-jun) or 0.0095/day (jul-dec) ;Rzms = shoot respiration ;Rzmr = root and rhizome respiration, Arrhenius relationship at optimal 20C ; RRzmr = root respiration at 20C = 0.0005/day ; THETAzmr = root and rhizome Arrhenius constant = 1.25 (unitless) ;Td = translocation down, shoot-to-rhizome transfer = Tzms ;Tzms = Z. marine shoot-to-root transfer = 0.3 (unitless) ;Note: Jarvis calculated mortality as a fraction in the biomass model, but we will calculate it ;probabilistically and separately. ;Buzzelli et al (1999) equations for Z. Marina (based on Wetzel): ;Czs(t) = shoot carbon ; = Czs(t-dt) + (Pzs - Rzs - Mzs - Tzc)dt ;Czr(t) = rhizome carbon ; = Czr(t-dt) + (Tzc - Rzrr - Mzrr)dt ;Tzc = translocation, shoot to rhizome ;Pmzm = maximum photosynthesic rate ; = (0.0025*T + 0.0049) * (1 - (Tw-25)/10) per day ; Tw = water temperature, approximated seasonally using Wetzel's sinusoidal model (1986) ;Rzs = shoot respiration ; = PRzs*(0.00317*(Tw+0.105)+e(0.135*Tw-10.1)) per day ;Rzrr= root and rhizome respiration, Arrhenius relationship at optimal 20C ; = Rkzr & THETAzr ^ (Tw-Topt) ; = 0.0005 * 1.25 ^ (Tw - 20) ; Rkzr = root respiration at 20C = 0.0005/day ; THETAzmr = root and rhizome Arrhenius constant = 1.25 (unitless) ;FBzsc = feedback relationship between maximum and limiting shoot biomass levels ; = (Czs - Climzs) / (Cmaxzs - Climzs) ; = (Czs - 100) / 100 ;Czs = shoot biomass ;Climzs = 100 ;Cmaxzs = 200 ;Does Td = 0.3*FBzsc ?? Buzzelli describes this but doesn't explicitely show it ;Cepi = Epiphyte biomass ; = Depi(t-dt) + (Pepi - Repi - Mepi - Gepi)dt ;Pij = Photosynthesis rate coefficient ; = Pmax(t)*[PARvp / (Ik' + PARvp)] ;Gepi= grazing ;Pmepi=epiphyte photosynthesis ; =0.0091 * Tw * [1.0 - (Tw-25)/20)] ;PARzm=photosynthetically active radiation reaching the eelgrass ; =PARh * (1 - (.75 * sqrt(Cepi/Czs/2.9) ) ) ;PARh = depth corrected for habitat ; = PAR0 * e^(-kd*hhab) ; kd= light extinction coefficient, function of chlorophyll, POC and DOC ; = 0.04 ; hhab= habitat depth (m) ;Wetzel & Neckles (1986) equations for Z. Marina (based on Wiegart): ;Fij = Carbon transfer from CO2 into eelgrass leaves, general form ; = Pij*Xj*[1-FBij)(1-(GBjj*Cjj))] ; Xj = Leaf biomass ; Cij= metabolic correction rate ; = 1.0 - (Rj / Pij) ;Pmax= linear statistically fitted function represented light-saturated rate at tempereature (t) ;PARvp = photosynthetically active radiation, or intensity of light reaching the leaves ;Ik' = half-saturation PAR intensity, based upon assumption that fresh new leaves were epiphyte-free ;FBij=non-linear feedback function of CO2 concentration ; =1 - [(Xi - Gij) / (Aij - Gij)] ; Xi =CO2 concentration ; Aij=CO2 concentration below which carbon became limiting ; Gij=CO2 concentration at which photosynthesis by eelgrass became zero ;FBjj=non-linear feedback function of metabolic limitations (crowding, nutrients, etc.) ;NOTE: Wetzel assumed Td was 17% of net leaf organic matter production, reduced ;when either above or below-ground compartments became limiting. ;Wetzel found epiphye:eelgrass biomass ratio was 0.04 during early spring and 1.5 during the late-summer decline ;PAR reaching the plant was reduced 22% due to epiphytes and another 10% due to epiphyte-limited CO2 diffusion. ;Maximum density was set at 150gC/m2 in the density feedback as this is the densest observed in the Chesapeake ;; Programming note: these calibration levels worked well during model validation. ;Td-Calibration = 4.1 ;Rzms-Calibration = 1.0 ;Rzmr-Calibration = 3.3 ;mortality-calibration = 0.1 ;max-clumps-per-patch = 10 ;Rhizome-shoot-distance = .50 ;;Eelgrass metabolic equations let PARzm e ^ (-0.4 * ([depth] of patch-here)) * (1 - .32) ;represents light decrease from epiphytes and depth, from Wetzel 1986. let Pzms PARzm * (0.0025 * (temperature - 10 ) + 0.0049) * (1 - (temperature - 35) / 10) ;adapted from Buzzelli et al (1999) if Pzms < 0 [set Pzms 0] let Tczmss 0 ;transfer of seedling biomass to vegetative shoot biomass let Rzms Pzms * veg-mass * Rzms-calibration * (0.00317 * (temperature + 0.105) + e ^ (0.135 * temperature - 10.1)) ;from Buzzelli et al (1999) *Pzms?? ;if temperature <= 14 [set Rzms 0] ;Jarvis et al 2014: reduce respiration to 0 below 14C. let Rzmr 0.0005 * rhizome-mass * Rzmr-calibration * (1.25 ^ (temperature - 20) + 2) ;adapted from Buzzelli et al (1999) let MRzms 0.0095 ; (jul-dec) if month < 7 [set MRzms 0.000085] ; (jan-jun) set MRzms MRzms * mortality-calibration let Tflower 0 ;Initially assume no flower/seed production if month >= 6 and temperature < 21 and age > 12 [set Tflower veg-mass * .1] ;Calculate flower / seed production for flowering plants ;Td = translocate down biomass from shoots to rhizome let Td .3 * Td-calibration * (veg-mass) / 100 ;adapted from Jarvis et al (2014) and Buzzelli et al (1999) if Td < 0 [set Td 0] ;no translocation up, just translocation down if veg-mass > 0 or month < 7 [ ;Inhibit regrowth of died-off shoots in late summer/fall set veg-mass veg-mass + 30 * (Pzms - Rzms - Tflower) ; adapted Jarvis et al (2014) equation ] if veg-mass < 0 [set veg-mass 0] ; cannot have negative vegetative mass ifelse (veg-mass > (30 * Td)) ; if there is shoot biomass to translocate into the rhizome [ set veg-mass veg-mass - 30 * Td] ;translocate shoot biomass into the rhizome if that biomass exists [ set Td veg-mass / 30 ;translocate all remaining shoot biomass to translocate set veg-mass 0] set rhizome-mass rhizome-mass + 30 * (Td - Rzmr) ; Jarvis et al (2014) equation ;let calibration-constant .1 ;converts biomass equations to model clumps - not yet fully implemented ;Check for random mortality based on Jarvis et al values if random-float 1 < MRzms * 30 [die] ;Estimate the amount of seeds as proportionate to the maximum vegetative mass of the eelgrass. if veg-mass > seeds and (ticks - age) > 12 [set seeds veg-mass] ;Render the visual model based on shoot biomass, but not smaller than size 0.5. set color green - 2 ifelse veg-mass > 1.5 [set size veg-mass / 3] [set size .5] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;; EELGRASS RHIZOME GROWTH ;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to rhizome-eelgrass ; Simulates new rhizome reproduction sprouting at a random point near the parent shoot ; A new sprout is hatched if the plant is mature enough and the immediate area is not already overcrowded if ((veg-mass > .8) or (veg-mass > .8 * [depth] of patch-here)) and count eelgrasses-here <= Max-clumps-per-patch [ hatch-eelgrasses 1 [ ; create a new clone of this clump set veg-mass 0 ; Starts off with no shoots (yet) set epiphyte 0 ; No epiphtye without shoots to grow on set rhizome-mass .01 ; Model a small piece of rhizome as a new plant set heading random 360 ; Sets the random direction the new clump will be forward (random-float (Rhizome-shoot-distance) + Rhizome-shoot-distance / 2) ;sets the random distance the new clump will be set size .1 ; Render as a very small dot set heading 0 ; Reset heading to 0 so that the eelgrass turtle looks like grass when it renders ] if rhizome-mass > 0.01 [set rhizome-mass rhizome-mass - 0.01] ;This rhizome mass just transferred to the new clump. ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;; EELGRASS SEED PROPAGATION ;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to seed-eelgrass ;; algorithm model for ellgrass sexual reproduction through seeds ; Flowers and seeds grow between may/june and sept. (http://seagrant.mit.edu/eelgrass/eelgrassscience/biology.html) ; germination is initiated below 20C, typically in November. ; Floating flowering shoots spread seeds throughout the bay. ; Eelgrass in the Chesapeake doesn't flower the first year (Jarvis et al, 2014). ; 10% of shoot density flowers when it's <21C in June. ; .33 seed predation rate ;The seeds variable stored information about vegetative mass of flower-producing shoots ;if seeds > 0, then this shoot flowered. if seeds > 0 [ set seeds seeds / 3 ;reduce # of seeds due to predation (Jarvis et al, 2014) ;Estimate the probability of seed germination based on # of seeds in the clump ;The individual germination rate is very low but is multiplied by the # of seeds ;in each clump. if random-float (1) > (1 - seed-germination ^ seeds) [ ifelse random (100) < 5 ;Assume 5% of seeds are distributed purely randomly [ set x random (max-pxcor * 2 ) + min-pxcor set y random (max-pycor * 2 ) + min-pycor ;If this seed did not land in an overpopulated area, create a new eelgrass clump if count eelgrasses-at x y <= Max-clumps-per-patch and x <= max-pxcor [ hatch-eelgrasses 1 [ set veg-mass 0 set epiphyte 0 set rhizome-mass .01 set xcor x set ycor y set size .1 set heading 0 ] ] ] ;Assume prevailing rising tides normally carry seeds a logarithmic distance to the left [ let seed-angle 90 + random-float (10) - 5 ;Assume seeds are carried by the rising tide in the direction seed-angle let seed-distance e ^ random-float (5) ;Seeds drop to the bottom after a random distance, seed-distance set x xcor + seed-distance * cos (seed-angle) ;Convert polar coordinate to (x,y) set y ycor + seed-distance * sin (seed-angle) ;Convert polar coordinate to (x,y) ;If this seed did not land in an overpopulated area or outside of the model area, create a new eelgrass clump if count eelgrasses-at x y <= Max-clumps-per-patch and x <= max-pxcor [ hatch-eelgrasses 1 [ set veg-mass 0 set epiphyte 0 set rhizome-mass .01 set heading seed-angle forward seed-distance set size .1 set heading 0 ] ] ] ] ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;; PLANT EELGRASS ;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to plant-eelgrass create-eelgrasses 1 ;plant an eelgrass clump [ set color yellow ;; Color it yellow for visualization so that it's easy to see set shape "eelgrass" ;; Make it eelgrass-shaped set veg-mass 0 ;; Starts off with no grass set rhizome-mass .01 ;; Starts off with a small amount of seedling/rhizome mass set size 1.5 ;; Exaggerate the size for visualization so that it's easy to see setxy x y ;; Place the eelgrass at the coordinates x,y (global variables set before calling this subroutine) set heading 0 ;; Orient the eelgrass for display purposes so that it looks more realistic set age ticks ;; Remember what month this eelgrass was planted ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;; EELGRASS MISC ;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to graze-eelgrass ;; algorithm representing grazing by waterfowl and other consumers. This is not yet fully implemented. ; little grazing activity in the Chesapeake from NOV-MAR when water temps are <10C. (Wetzel, 1986) ; grazing populations decline mid-summer as predatory fish increase. (Wetzel, 1986) ; Green Turtle grazing handled via the eat-eelgrass subroutine end to stress-eelgrass ;;algorithm representing environmental stress on eelgrass from water quality, waves, etc. ; at temps above 20C respiration increases at a greater rate than photosynthesis. mortality above 25C. ; epophytic growth blocks sunlight end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;; SEA TURTLE BEHAVIOR ;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to move ;; turtle procedure if count eelgrasses > 0 [ ; If there are eelgrasses face min-one-of eelgrasses [distance myself] ; turn towards the closes eelgrass fd 1 ; swim 1 meter ] end to eat-eelgrass ;; herbivious animal procedure ;In this procedure, the animal eats a piece of eelgrass in its patch. let meal one-of eelgrasses-here ; Look for random nearby eelgrass if meal != nobody [ ; If there is some eelgrass here, ask meal [ ; eat some eelgrass. set veg-mass veg-mass - turtles-eat ; Reduce the eelgrass by what the turtle just ate. if veg-mass <= 0 [ die ] ; The eelgrass clump dies if the turtle ate all of it. ] set energy energy + 2 ; Put that eelgrass in the turtle's belly. if energy > 20 [set energy 20] ; Don't exceed 20 energy (stomach + fat). ] end to death ;; turtle procedure ;; when energy dips below zero, die if energy < 0 [ die ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;; SETUP ROUTINES ;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to setup-depth ;Create a slope to the bay floor. Per Wetzel (1986), tidal variations do not influence ;estimated modeling coefficients in the Chesapeake, so depth is estimated as static. set depth (0 - pycor) / max-pycor * 0.75 + 1.25 ;Set depth at .5m (top of window) slowing linearally to 2.0m (bottom of window) set pcolor scale-color cyan depth 2.5 -1 ;Display deeper depths as a darker shade of cyan end to Display-month-year ;; Display the month, year, and temperature (C) in the upper-right corner ask patch (max-pxcor - 1) (max-pycor - 3) [ set plabel array:item month-name (month - 1) set plabel word word word word word plabel " " (floor ((ticks - 2) / 12) + Planting-Year + 1) ", " round temperature "C" ] end to plant-initial-eelgrass-pattern ;; Eelgrass is planted in the pattern specified by the picklist ;; Plant a single clump in the center of the model if eelgrass-pattern = "Single clump" [ set x 0 set y 0 plant-eelgrass ] ;; Plant a spaced 100m square with clumps every 5m if eelgrass-pattern = "100m Dotted Square" or eelgrass-pattern = "100m Dotted Inscribed Square" [ set x -50 set y -50 repeat 21 [ plant-eelgrass set y y + 5 ] set x 50 set y -50 repeat 21 [ plant-eelgrass set y y + 5 ] set x -45 set y -50 repeat 19 [ plant-eelgrass set x x + 5 ] set x -45 set y 50 repeat 19 [ plant-eelgrass set x x + 5 ] ] ;; Plant a spaced 100m line with clumps every 5m if eelgrass-pattern = "100m Dotted Line" [ set x 0 set y -50 repeat 21 [ plant-eelgrass set y y + 5 ] ] ;; Plant a 100m square with clumps every 1m if eelgrass-pattern = "100m Square" or eelgrass-pattern = "100m Inscribed Square" [ set x -50 set y -50 repeat 101 [ plant-eelgrass set y y + 1 ] set x 50 set y -50 repeat 101 [ plant-eelgrass set y y + 1 ] set x -49 set y -50 repeat 99 [ plant-eelgrass set x x + 1 ] set x -49 set y 50 repeat 99 [ plant-eelgrass set x x + 1 ] ] ;; Plant a 50m circle with clumps every 1m if eelgrass-pattern = "50m Circle" or eelgrass-pattern = "100m Inscribed Square" [ let theta 0 repeat 157 [ ; A 50m circle has a circumference of 157 and requires 157 clumps set x 25 * sin (theta) ; Convert polar coordinates to cartesian for planting set y 25 * cos (theta) ; Convert polar coordinates to cartesian for planting plant-eelgrass set theta theta + 2.293 ; At 25m radius, 2.293 degrees is a 1m arclength. ] ] ;; Plant a 50m circle with clumps every 5m if eelgrass-pattern = "50m Dotted Circle" or eelgrass-pattern = "100m Dotted Inscribed Square" [ let theta 0 repeat 31 [ ; A 50m circle has a circumference of 157 and requires 31 clumps 5.064, apart set x 25 * sin (theta) ; Convert polar coordinates to cartesian for planting set y 25 * cos (theta) ; Convert polar coordinates to cartesian for planting plant-eelgrass set theta theta + 11.612 ; At 25m radius, 2.293 degrees is a 1m arclength. ] ] ;; Plant a 50m grid with clumps 7m apart (actually 49m, not 50m) if eelgrass-pattern = "50m Checkerboard" [ set x -24.5 repeat 7 [ set y -24.5 repeat 7 [ plant-eelgrass set y y + 7 ] set x x + 7 ] ] end ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;; FREE PLANT MODE ;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; to free-plant ;If the user clicks while in free plant mode, plant a clump where the user clicked if mouse-down? [ set x mouse-xcor set y mouse-ycor plant-eelgrass ] ;We tick to render the new seedling so the user can see it, but only if the model hasn't already been started if not simulation-started [ ;Remember how much eelgrass we planted so that we can tell the % increase in growth set initial-extent-eelgrass count eelgrasses ; # of initial seedlings set max-extent-eelgrass initial-extent-eelgrass ; the initial max = initial seedlings tick ; refresh the display so the user can see the new seedling reset-ticks ; set ticks back to 0 clear-plot ; clears the output plot ] end

There is only one version of this model, created about 4 years ago by Steve Fehr.

## Attached files

File | Type | Description | Last updated | |
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Eelgrass Model v2.10.png | preview | Preview for 'Eelgrass Model v2.10' | about 4 years ago, by Steve Fehr | Download |

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