176
9. Modeling Eelgrass (Zostera marina L.) Distributions in Great Bay
TABLE 9.1. Parameters in the Plant Model
Name
Latitude
Max Shoot Den sity
Per of Total Light
Ratio
Descripti on
Latitude of the Grea t Bay Estuary
Maximum area shoot den sity.
Percentage of surface light that reaches eelgrass.
Ratio of new shoots to new leaves.
Va lue
55
1000
1
1.8
is more pronounced in the spring (Olesen 1999). However, most seedlings
resulting from spring rep rodu ction are shaded out during the summer.
Therefore, vegetative propagation is more important for the growth and
mainten ance of eelgrass beds (Olesen 1999). As such, while a seed bank is
built up in the current model, seeds do not germinate into new plants.
Now that all the pieces of the model are assembled , let us investigate in
the following section two scenarios: a base scenario and a light-depletion
scenario in which the maximum light that reaches the eelgrass is reduc ed
by 60% for the second year of the model run .
9.3.1 . Base-Run Results
The model captures four years of eelgrass plant/bed growt h using one-day
time steps and Euler's method of integration . Base-run results are provided
in Figures 9.9-9 .11. As shown in Figure 9.9, shoots demonstrate an annual
summer peak in abundance. Roots and rhizomes do not follow the same
summer peak, and instead show a more variable growth pattern . The transfer of sugar appears to be more dominant from shoo ts to roots and rhizomes, as shown in Figure 9.10. However, some exchange of sugar from
roots and rhizomes to shoo ts takes place towards the end of each year as
shoots decrease in abundance . Relative sugar conce ntrations are provided
in Figure 9.11. The sugar concentration in roots and rhizomes demonstrates
the same variable pattern as the annual growth pattern shown in Figure 9.9.
However, the sugar concentration in shoo ts appears to be more abundant
in late summer.
Nam e
Description
Ske w weathe r
PI Mod el
PI Discard
Weather data
Plastoch ro ne inte rval for leaf de velopment
Plastoch ron e interv al for leaf loss
Roots and Rhizomes Submodel
Dyoff Rate
Die-off rate of roots and rhizomes
Shoots Submodel
Nr of Leaves Mean '
Repro Season
Tran s Growth
Annual mean numbe r of leaves
Shoots reproduc tive season
Hormo nal growt h not attributed to light , tem perature , or nutrien ts
9. Modeling Eelgrass (Zostera marina L.) Distributions in Great Bay
TABLE 9.1. Parameters in the Plant Model
Name
Latitude
Max Shoot Den sity
Per of Total Light
Ratio
Descripti on
Latitude of the Grea t Bay Estuary
Maximum area shoot den sity.
Percentage of surface light that reaches eelgrass.
Ratio of new shoots to new leaves.
Va lue
55
1000
1
1.8
is more pronounced in the spring (Olesen 1999). However, most seedlings
resulting from spring rep rodu ction are shaded out during the summer.
Therefore, vegetative propagation is more important for the growth and
mainten ance of eelgrass beds (Olesen 1999). As such, while a seed bank is
built up in the current model, seeds do not germinate into new plants.
Now that all the pieces of the model are assembled , let us investigate in
the following section two scenarios: a base scenario and a light-depletion
scenario in which the maximum light that reaches the eelgrass is reduc ed
by 60% for the second year of the model run .
9.3.1 . Base-Run Results
The model captures four years of eelgrass plant/bed growt h using one-day
time steps and Euler's method of integration . Base-run results are provided
in Figures 9.9-9 .11. As shown in Figure 9.9, shoots demonstrate an annual
summer peak in abundance. Roots and rhizomes do not follow the same
summer peak, and instead show a more variable growth pattern . The transfer of sugar appears to be more dominant from shoo ts to roots and rhizomes, as shown in Figure 9.10. However, some exchange of sugar from
roots and rhizomes to shoo ts takes place towards the end of each year as
shoots decrease in abundance . Relative sugar conce ntrations are provided
in Figure 9.11. The sugar concentration in roots and rhizomes demonstrates
the same variable pattern as the annual growth pattern shown in Figure 9.9.
However, the sugar concentration in shoo ts appears to be more abundant
in late summer.
Nam e
Description
Ske w weathe r
PI Mod el
PI Discard
Weather data
Plastoch ro ne inte rval for leaf de velopment
Plastoch ron e interv al for leaf loss
Roots and Rhizomes Submodel
Dyoff Rate
Die-off rate of roots and rhizomes
Shoots Submodel
Nr of Leaves Mean '
Repro Season
Tran s Growth
Annual mean numbe r of leaves
Shoots reproduc tive season
Hormo nal growt h not attributed to light , tem perature , or nutrien ts