Ecosystem Simulations by an End-to-end Model
Coupling MEC-Ocean Model and EwE Model
Yiming Xia, Shigeru Tabeta
Dept. Environment systems, The University of Tokyo,Kashiwa, Japan1

Overview

Introduction
Methodology
Case study 1
Case study 2
Conclusion
2

Introduction

Discharge

Humanactivity

Physicalconditions

For decades, modeling of marine ecosystems has beenhandled by two different scientific communities[1].
fishingHigh
trophiclevelLow
trophiclevel

Ecosystem

1. Fisheries model: focused on high trophic level species,and fishery impact but the effects of abiotic factors werenot considered.
2. Physical and biogeochemical model: understanding
carbon fluxes and plankton dynamics in variable
environments of ocean but hard to extend to hightrophic level species

Demand: the model should progressively integrate the dynamics of the food web withenvironmental forcing of the marine ecosystem to improve the ability to understand theclimate and fishery impact on ecosystem .
3Introduction
End-to-end model refers to a specific approach to ecosystem modelling which

Fishery(1) represent the entire food web and the associated abiotic environment
factors,EwE
Model(2) Integrate physical and biological processes at different scales,(3) assesse the effects of climate change and fishing on ecosystem dynamics

Low
trophiclevel

simultaneously.

Few single Models can satisfy these requests, so we need integrate
several suitable models to construct this end-to-end model.

Hightrophiclevel

MEC
OceanModel

Physicalconditions
4

Methodology: MEC Ocean Model
MEC Ocean model(developed by Marine Environmental Committee of Japan ) [2]o A 3D hydrodynamic model with a z-coordinate system basedon a finite difference schemeo Calculate physical environmental factor (currents, T, S….)o Calculate biological factor while combined with Low trophic
Ecosystem model

FisheryHightrophiclevel
Low
trophiclevel

MEC
Ocean
Model

Physicalconditions

Lower trophic ecosystem model5

Methodology: EwE ModelEwE model
A dynamic of food web model capable of exploring fishing based on
the ecosystem trophic mass-balance (biomass and flow) analysis [3]Fishery
EwE
Model

impacts

Trophic level

Mass-balance
Production = catch + predation + net migration + biomass accumulation + other mortality

Biomass flow basedon diet compositionHigh
trophiclevel
Low
trophiclevel

Physicalconditions
Trophic relationships of functional groups in the ECS ecosystem

6Methodology: Link two models
Data 1 from literature

EnvironmentalConditions

Basic input

Diet composition

input

Ecosystem
model

Detritus fate

input

MEC-NESTMEC Ocean modelhydrodynamic modelData
3Dto 0D
Data tansform

transform

EwE Model
Ecopathmodel

Output result basedon data 1 and 2

outputZooplankton

Phyplankton

POC

DOC

DO

Sediment POC

Data 2!"#$ =Link two models: 1) data transform

Time scale: S-1

Year-1, Month-1

Space scale: 3D0D1× ) !* ×∆,'!"-$". = ) !"#$ ×∆/!-$0 =1× ) !"-$". ×151234

Link two models: 2) include the effect of physical conditions (DO, T) on some groups

7

Case study
1. Large scale
Advantage:

Ignore the immigration of some species

Disadvantage: Hard to involve DO effect as the average DO was used in Model

2. Small scale
Advantage:

More accurate simulation result

Disadvantage: Ecological system is incomplete8Case study 1: Large scale
East China Sea
situated in the eastern Pacific between the subtropical and temperate zones
Multiple Impact:
1.

the nutrient load from Yangtze River2.

The large fishing pressure

9Google map

Case study 1: computational domain

WinterSpring
Summerwater percent from Yangtze river(%)

autumnLatitude:E117-E132
MEC Computational domain longitude : N24-E41
Grid number: 180204

the computational area of East China Sea

EwE Computational domain

Latitude:longitude :E119-E126
N30-E36
10Case study 1: Large scale
Construct the food-web model of ecosystem in East China Sea

22 function groups in East China Sea ecosystem
11Case study 1: Large scale
Fishing.22 . 2.2.

.

2 1.

.2.2
2 1.

22 2.

Nutrient load
22 function groups in East China Sea ecosystem

12Case study 1: fishing data
Fishing pressure

Capture yield of 4 species from East China Sea[4]Relative fishing effort for other species [5]fishing data of 4 groups as the main product in ECS , and a typical tendency of fishingeffort which are used to set the fish catch of other species are shown13

Case study 1: Large scale
Fishing.
)((((. (((((22( 1()based on the simulation result ofnutrient load impact by MEC
Ocean Model

Nutrient load

14

Case study 1: dynamic data of plankton and detritus
Plankton and detritus dynamics from MEC Modelinter-annual variation of Plankton, detritus
caused by nutrient influx change fromYangtze Riverseasonal variations of zooplankton from MEC model

seasonal variation of relative biomass ofzooplankton
15

Case study 1: Large scale
Fishing.

1.

.

.1)

Nutrient load

111 -- 1)-) 1.

-1 ) (-)))) 1)) .

) )-)) 2)- 11)

16-Case study 1: result

Simulation result of Relative Biomass change(a) only nutrient load from Yangtze River,(b) only fishery influence,(c) both of nutrient load and fishery

Scenario c of yellow croaker and Hailteil areclose to actual situation[5].

17Case study 1: Result
Simulation result of Relative Biomass change(a) only nutrient load from Yangtze River,(b) only fishery influence,(c) both of nutrient load and fishery18

Case study 1: Discussion
By applying end-to-end model, we evaluate multiple impacts including nutrient influx ofYangtze River and fishery on the ecosystem in East China Sea

a. the increase of nutrition input slow the decline tendency.
b. Fishery is the main reason of ecosystem recessionc. Low trophic species are more sensitive with seasonal variations.
Only including how the nutrient influx effect on primary productions,

It is hard to involve DO effect on ecosystem because the scale is too large
Case study of small scale

19Case study 2: Small Scale
1. Nutrient load

T-P load (t/day)

T-N load (t/day)Tokyo bay

2. Fishing in Tokyo Bay
12108642

depthComputational domain

0
1930

1940

1950

1960

1970

1980

1990

Fishing-small pelagic

Fishing-small demersal

Fishing-piscivorous fish

Fishing-other benthos

2000

2010

Case study 2: Small Scale
Divided Tokyo Bay into three parts based on river influx, hypoxia, and fishing port.

Inner
part

Mid
part

Out
part

Left: The spatial distribution of bottom hypoxia (dissolved oxygen concentration 2ml/l or less; shaded area);
Mid: The fishing port distribution along the coastal line of Tokyo Bay;
Right: Division of Tokyo Bay into three parts.
21

Case study 2 :effects of hypoxia
The effects of hypoxia on each benthos group

Annual-DO-bottom
87

monthly survival rate (Si in %) and dissolved oxygen (DO in ppm):

6

Si = 100

5if DO>=DOth,i4= (100/DOth,i)DO

3
2

While DOth,i is the threshold level of DO (the level above which all

101935

if DO<=DOth,i1949

1962
DO2_out

1976
DO2_mid

1990

2004

2017

individuals were assumed to survive hypoxia).

DO2_in22

Case study 2: Small ScaleFishing
3 .22 .32

333.2 33.

2 1.

Hypoxia.

.22 1.

32 32 2.

.

functional groups of ecosystem in Tokyo Bay.

Nutrient load233

Case study 2: Result
inner part(a)
Simulation result of Relative Biomass change in
the inner part(a) only nutrient load,(b) nutrient load and hypoxia,(c) Nutrient load , hypoxia, and fishery(Mid part is very similar with inner part)

(b)

(c)

24

Case study 2: Result
Out part(a)Simulation result of Relative Biomass change inthe out part(a) only nutrient load,(b) nutrient load and same fishing pressure withinner part,(c) nutrient load and double fishing pressure

(b)
(c)

25

Case study 2: Small Scale
By end-to-end model, we evaluate multiple impacts including nutrient load, DO and fisheryon the ecosystem of three parts in Tokyo bay

a. Inside part and Mid part ecosystem affected by both hypoxia andoverfishing;b. Out part ecosystem dominated by fishing .
c. Nutrient load are a double-edged sword which can increaseprimary production but also bring the hypoxia.

26

Conclusion

1. Developed an end-to-end model combining MEC Ocean model and EwEmodel
2. By using this model, we evaluate multiple impacts including nutrient load,
DO and fishery on the ecosystem at different scales.
3.Nutrient load, DO and fishery have different functions in different
environment conditions.

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Thanks for listening!

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