3. Characteristics of Nature Restoration Technologies and their Trends
In nature restoration projects, the restoration technologies must be appropriately
selected, applied and evaluated based on the characteristics of coastal ecosystems.
3.1 Characteristics of coastal ecosystems(1) Coastal ecosystem
Coastal ecosystems are the interface of terrestrial and marine ecosystems. They
consist of various biotic and abiotic components which work as an integrated
whole, as well as in unison with wide-ranging environments surrounding them.
This unique composition of ecosystems provides them with various structural andfunctional diversity.
An ecosystem includes biotic and abiotic components, as well as the environments
surrounding them. Living organisms, which make up the biotic component, havetheir own unique behavioral patterns, as an individual, a species and a population,
contributing largely to the interactions among individuals, populations andcommunities. For instance, a tidal ecosystem has the structure of the “eat–or-to-be-eaten” relationship as seen in Figure 3-1. With birds on the top level, thematerial is circulated through the interactions among these organisms. This
schematic structure of such relationships is known as a food web, a distinctive
feature of an ecosystem.
This hierarchical structure of ecosystems serves their own unique functions. In one
example, tidal flat ecosystems have nitrogen or phosphate cycling networks,
making resources to be redistributed or produced.
In addition, biological activities, which are directly or indirectly supported by solar
energy, also allow an ecosystem to serve as a system that can utilize and consume
energy.
The aforementioned attributes are commonly seen in ecosystems in general,
however, costal ecosystems, which are surrounded by environments encompassing
marine and terrestrial areas, demonstrate wide spatial and temporal variations.

25

Figure 3-1 Schematic relationships of tidal flat ecosystem26

(2) Environments surrounding coastal ecosystems and their changes
The environments surrounding coastal ecosystems change dynamically in response
to external forces including tidal movements. The living organisms inhabiting such
ecosystems adopt various sorts of survival strategies.
One of the environmental aspects of coastal ecosystems significantly different fromthe ones of other ecosystems is the dynamic changes associated with topographic
and environmental factors. When classifying these factors by energies transportingwater or sediment, the distinctive features are observed by temporal and spatial
scales, as shown in Figure 3-2. This seems to indicate that living organisms
inhabiting such environments select various survival strategies.

Figure 3-2 Transportation energy distribution in the coastal area
1. wind and wave 2.swell 3. harbor seiche 4.tsunami 5.seiche in open sea
6. topographic vortex flow 7. quarter-diurnal tide 8. semi-diurnal tide
9. diurnal tide 10. floods / high water 11. drift current 12.tidal residual current
13. density current 14. seasonal variation 15. secular variation
1) Dynamic equilibrium
Being influenced by energies with ranging scales, the topographic features of sandbeaches and tidal flats are constantly being changed by erosion and deposition. In
sand beaches, such topographic changes are controlled by sediment transportation27

to offshore, which is associated with wave movement, providing beach slopes with acertain gradient towards their shorelines. Such topography can approximately beconsidered as being in a state of static equilibrium. Conversely in a tidal flat, thecross-sections of topography towards shorelines are not constant in shape. The
horizontal transportation of wave and sediment is constantly taking place and thus
its topography is changing to restore its former features with seasonal variations if
applicable. This is a prime example of a topography being in a state of dynamic
equilibrium. Consequently, if they lack the factors necessary to be in dynamic
equilibrium, thereby leading to a minimal or no supply of sandy-mud or the
reduction in tidal flat areas, such topography will have little chance of being stably
sustained.
In a marine water environment, such dynamic equilibrium should also be taken
into account when studying material cycling. For example, the detailed
examination of the nutriment in the water flooding a tidal flat, can provide
nutrient distribution towards the offshore as well as its temporal changes. This isconsidered to be due to the fact that the distribution and changes are subject to not
only tidal advection but also to biological activities and sediments being stirred up
from the sea floor.
The fact that environmental factors are in dynamic equilibrium means that carefulconsideration must be afforded in the planning, designing, construction andmanagement of a restoration project. This indicates that the target values formonitoring environmental improvement in the management process should bedetermined leaving some scope for flexibility in view of this dynamic variation. If
the situation allows, the approach using the self-designing of nature (or the
topographic stability by natural process) should be actively employed, taking
advantage of its ability to maintain dynamic equilibrium.
Breton Island, located in the estuary of the Mississippi, has been drastically erodedby hurricanes, hence efforts to restore beaches were attempted, by placing dredged
sand and soil on the gulf side of the island to restore the land area in the hope thatthe dredged material would be naturally defused to the whole island. This project
saw success with the island’s precious features being restored.

28

Column: Topographic restoration in Breton Island, LA, USA
Location; Breton Island, near the outlet of the Mississippi River, Louisiana.
Period: 1993Objectives: Restoring former topography and ecosystems of Breton Island, using
sand and soil dredged in the MRGO projects.
Methods: Muddy sediment of 0.01mm in grain size was dredged by a pump anddirectly deposited to the site using a horizontal pipe. The deposited material wasthen transferred by ocean current to other parts of the island, returning the island
to its original shape.

Before erosion by the hurricane (1995),

Post- project (2000)

Figure 3-3 Features of major tidal flats in Japan29

offshore 低

offshore 低

高 shoreebb tide

flood tide
PO4(μ M)

4

2

Stn.3

Stn.2
5:00

NH4 +NOX(μ M)

30

6:00

7:00

8:00

20

時間とともに上昇

0

Stn.3

Stn.2

Stn.1

Stn.3
15:00

30

ebb tide

10

2

0

Stn.1

NH4 +NOX(μ M)

PO4(μ M)

40

高 shore

Stn.2
16:00

Stn.1
17:00

18:00

flood tide

20

時間とともに低下

10

0

Stn.3

Stn.2

Stn.1

Figure 3-4 Change in nutrients distribution by tidal water2) Survival strategies of living organisms
The survival strategies of living organisms making up ecosystems are classified
into two strategies: r-strategy and k-strategy. The r-strategy is characterized by ashort generation time and high rates of reproduction. The k-strategy, in contrast, ischaracterized by a longer generation time and relatively low rates of reproduction.
The seasonal habitat density in shallow water zones, where r-strategy species andk-strategy species coexist, showed the following observations.
・The r-strategy species are predominant in drastically changing environments,and show a rapid recovery from population reduction (sandworm etc.)

The k-strategy species are predominant in relatively stable environments, andshow a slow recovery from population reduction (sea turtles etc.).
The results also showed that small-sized species are dominant in r-strategy species,
whereas in k- strategy species, many large-sized species were observed.
When the objectives of a nature restoration project are targeted on ecological
function value, the selection of the sites or the formulation of management
strategies should be carried out with utmost care, with a correct understanding of
the survival strategy of the target species and the environmental factors suitable
for such a strategy. Attention should also be paid to the reduction/elimination of a
species due to the competition between target species and non-target species aswell as the invasion of foreign species.
If the project includes the conservation of k-strategy species, the target species
・30

must be provided with an appropriate habitat for each growth stage. Furthermore,
careful monitoring should be done on the fluctuation range of environmental
factors.
(3) Structure of coastal ecosystems
Coastal ecosystems consist of spatial and temporal structural levels.
The structure of coastal ecosystems is characterized by various spatial andtemporal levels of hierarchy, such as the “eat –or-to-be-eaten” biological hierarchy.
This hierarchy is governed by feeding habit of component species, species size,
spatial distribution of species by habitat segregation, and changing of habitats due
to a species’ life history.
1) Difference in size
Coastal areas are inhabited by various living organisms of different sizes (Table
3-1). A tendency has been observed wherein the smaller the individual organism,
the larger the number and species variation present. They also feature anenormous macro biota, something not commonly observed in terrestrial
ecosystems.
Table 3-1 Living organisms by size
Size
Flora
Bacillariophyceae
Small
Large

Seagrass, Seaweed
Mangrove

Fauna
Bacteria
Copopoda, Protozoa
Polychaeta, sellfish
Shrimp, Fish, Birds

2) Habitat segregation
Habitat segregation is considered to occur primarily due to acclimatization to theenvironment. The zonal distribution of periphyton (/sessile organisms) observed on
shoreline rocks or seawalls, is a good example of habitat segregation. Suchzonation is caused by differences in the extent of wave splash, the length,
submergence time and light intensity. Other examples on a larger scale areobserved in the distribution of benthic organisms (Figure 3-6) that are largely
affected by sediment environments, or the difference in the mangrove treecomposition by the distance from a shoreline (Figure 3-7). In both cases, theenvironmental conditions governing the distribution are not just conditions at a31

single point in time, but the accumulation of conditions that are constantly
changing by time. It therefore requires attention to examine the biologicaldistribution together with variable environmental factors, such as water quality or
wave motion. Biological distributions are also considered to be controlled byenvironmental factors triggered by natural events, including low salinity inducedby typhoons or river flush, or incursion of an anoxic water mass. Figure 3-8
illustrates the sediment distribution around the Port of Baltimore and theresistance distribution of sediment disturbance. This case exemplifies theenvironmental changes that happen only a few times a year and yet determine thecharacteristics of the habitat. Changes in sediment type brings with it changes inthe structure of the species inhabiting that area. This case demonstrates that
ecosystems can be determined by the occurrence of event-like environmental
changes for example typhoons or river flushes

Figure 3-5 Zonal distribution of living organisms around a breakwater
40

40

30COD

30

20

20

10

10

Fraction of
Sand>2mm %

mg/dry-g22

Figure 3-6 SCOD and the distribution of Polychaeta and Batillariidae(left) / Sand
grain size and the distribution of clam and Prionospio (right)

32

Soneratia,
Avicenia

Bruguiera
Rhizophora
Ceriops

Lumnitzera Nypa

HWL
MWL

Figure 3-7 Mangrove distribution on the shore

Figure 3-8 Sediment distribution near the Port of Baltimore (left: sedimentcontent , unit:%) :Resistance distribution of sediment disturbance (right: basal shearing stress, unit:
Pa)3) Life history
The structural properties of ecosystems observed by life history can easily beillustrated by the species with a planktonic larval stage. Figure 3-9, profiles the life
history of clams. Clam larvae are in a planktonic stage for up to two to three weeks
after being hatched, when they undergo metamorphosis as larvae. They then cometo settle on the tidal flat area, move within the tidal flats as they grow, and spawn
as adults when they reach the size of 2 to 3cm. From this it can be seen that theclam has a life history traversing the different environments of sea areas and tidal

33

flats. It can also be deduced that the existence of clams whose life histories havesuch a straddling structure, enables a tidal flat ecosystem not only to sustain its
own system but also to maintain interactions with other systems in tidal flats. In
other words, it can be referred as an ecological network in which ecosystemcomponents are interactively linked.

Figure 3-9 Life History of clams

Figure 3-10 Distribution charts of planktonic clam larvae in coastal water.

344) Ecological network
An ecological network consists of; core areas (preserved areas), in which diverse
ecosystems are sustained with fully exercised functions; buffer zones that surroundcore areas with restricted human activities; and corridors that link core areas andact as thoroughfares for species traffic. The ecological network is designed toenhance ecosystems in the whole target area by restoring habits in core areas andconnecting them to one another. The scale and allocation of core areas or the ways
to connect them have already been studied and suggested in network plans, which
are also founded on the basic theories of Landscape Ecology or Conservation
Ecology.
European countries, including Germany and the Netherlands, havealready taken on such environmental approaches in their land use policies.
(Domoto, 1998). With the extension of such a paradigm to marine environment
conservation, the term “ ecological network” in marine environment therefore, isdefined by the concept that each individual marine ecosystem, including thesystem in a tidal flat or in a seagrass bed, is interlinked rather than just being asingle closed system. In such a network, it is important to clarify the relationshipbetween linkage routes and each node (base). In the study of marine environments,
the term “ ecological network” is still new and has not yet been given a clear
meaning in usage, and has been used as a term to describe ecological continuity,
such as reed community-tidal flat-seagrass bed, or as a term describing therelationships in a wide habitat area represented by the interactions of species
dispersed in a harbor. Both contexts, however, are regarded to show important
ecological networks. As yet, there is limited knowledge on concrete demonstration
research of ecological networks, or on management or restoration methods inwhich such networks work effectively. The recent study on clams in Tokyo Bay
has shed light on the life history of clams in this region, revealing the fact thatplanktonic clam larvae migrate within the whole bay area and that the larval
supply or recruitment take place between several tidal flats.
The advancement of such studies still remains a challenge, requiring a further
accumulation of knowledge through the implementation of nature restoration
projects.

35

(4) Coastal ecosystem function
The coastal ecosystem function includes; 1) habits for living organisms, 2) water
purification and material cycling, 3) biological productivity, 4) provision ofwaterfronts with easy access,5) others

Being surrounded by diverse environments and furnished with manifold system
structures, ecosystems are considered to offer a wide variety of functions andvalues in accordance with the biological activities of their component species or thecharacteristics of their location. The term “function” in this section is referred towhat is exercised in physical, chemical and biological processes, and includes thefollowing: 1) habits for living organisms, 2) water purification and material cycling,3) biological productivity, 4) provision of waterfronts with easy access, 5) others
functions (hydraulic buffers etc.) . On the other hand, values are to be defined by
the purposes for which the coastal ecosystem is used, and thereby different values
are given to the same function. Let’s take 1) habitats for living organisms, forexample. If the purpose is to secure biological diversity, a high evaluation will begiven to an ecosystem where many species can coexist. If the purpose is to promote
the population of a specific rare species, or culture commercial fish, the objectives
are set to increase the productivity of a single species, thus the establishment of an
ecosystem with such productivity will be highly evaluated. This would be seen as acontradictory value.
Table 3-2 shows the functions displayed by each coastal ecosystem.
The details will be discussed in the other volumes comprised for each ecosystem.
In evaluating ecosystem function, various methods have been proposed and studied,including a numerical calculation model. (Please refer to Chapter 3.3 (2)Development of prediction methods for coastal ecosystem)

36

Table 3-2

Ecosystem function
Ecosystem type

Function

Biological habitation

Water/sedimentpurification

Water accessibility

Hydrologic adjustment

Tidal flat, mangrove

Sand beachReed community

Seaweeds andseagrass beds
Recharging area Habitat for shallowwater species,
for diverse
species, linkage breeding groundof ecosystems,
feeding ground
Coral reefs

Environmental
Buffer zone
diversity associated between
with tidal movement, terrestrial andmangrove dependent marine species,
species, rich inbreeding groundnutrients
for juveniles,
stopovers for
migrating birds

securing
biodiversity,
buffer zone
betweenterrestrial andmarine species

Nutrient cycling,organic matterdecomposition

Nutrient cycling,organic matterdecomposition

Nutrient cycling, Recharging area Nutrient fixation
organic matter for filter-feeding
decomposition, species
pollutant trap

Limited use by
citizens, clam
digging, leisurefishing
Buffer zone forsurface water level,
land erosion
prevention inflooding,, sediment
trap

Bathing, strolling,
bird watching

Bird watching

Scuba diving

Land erosion
prevention inflooding

Buffer zone forsurface waterlevel, landerosionprevention inflooding,,
sediment trap

Surface water
control, wave
control

Stabilization ofbottom sediment by
seagrass/seaweeds

3.2 Technological background needed for nature restoration(1) Basis for successful nature restoration
Restoration of coastal ecosystems can succeed through the analysis of theenvironmental factors that support the system, the appropriate selection of sites,
the realistic planning and goal setting, as well as the careful implementation of the
project.
Considering the marine environments in our country, as well as the attributes ofcoastal ecosystems and species inhabiting them, the following features areobserved:i) Coastal marine environments have a high nutrient load originating from land,
and thus rendering great biological productivity.
ii) Coastal ecosystems are located in areas with drastic environmental changes as characterized in intertidal zones(tidal flats etc.).

iii) Hierarchical structures, which were formed by slight differences ofenvironmental factors, are observed in coastal ecosystems (tidal zones etc.).
iv) The species well adaptable to environmental changes, small in size, and with ashort span of reproduction, like r-strategy species or opportunistic species, are37

more likely to be predominant.
v) Coastal ecosystems are more likely to go through the constant changes ofdisturbance, recovery and growth, rather than being stable and reaching climax.
These aspects have been previously reported (Kurihara, 1993, Alongi 1997).
In view of the relationship between human activities and the coastal environment, and in particular tidal flats andseagrass beds, the following features can be seen.
vi) Due to a high biological productivity, coastal seas have been used as fishing grounds or clam digging sites.

vii) Some areas have seen the active involvement of human beings as incommercial fishing grounds for clams, laver seaweeds, or aqua farming.
viii) Common reeds and seagrass (Zostera) have been used as craft material or fertilizer.

These aspects portray that people have utilized marine products from tidal flats orshallow water zones, and that such human activities have maintained water
quality and fishing productivity in such a region.
At the head of Tokyo Bay exists a huge shallow water zone called Sanbanse. Further into the head, a tidal flat called
Funabashi Bay Park is located.

Although this flat is sometimes introduced as a natural tidal flat, it was actuallyformed through reclamation. It is perceived as a prosperous tidal flat that serves asa habitat for waterfowl as well as a clam digging site, among other flats or shallow
waters suffering environmental degradation in the vicinity including Sanbanse.
This is a successful example of coastal restoration, where various environmental
factors supporting tidal flats, such as wave impact and grain size of sand, havebeen well matched to the conditions of the area, and have not only succeeded ingiving the flat stability but also functioned as a habitat for benthic organisms.
Some developed tidal flats have been washed away or have subsided, no longer
fulfilling their function.
With these in mind, the restoration of coastal ecosystems can be successful if: the environmental factorsthat support

the target ecosystem (water quality, sediment, wave, and currents) are correctly analyzed; the appropriate sites forsuch factors are selected; the realistic planning and goals are formulated; and the project is implemented carefully.
It also requires a flexible approach in management to the developed site, in ways such as by allowing for adjustments
over time.

The coastal ecosystem features described above, are generally seen in the coastal
environments existing in the temperate regions of Honshu, the main island ofJapan, as these areas have long been developed. On the contrary ecosystems ofsubtropical regions, such as mangrove forests, seagrasss beds and coral reefs, have38

often been created in relatively oligotrophic environments over a long period oftime, thus requiring more careful and long-time restoration approaches. Attention
should also be paid to the diversity both on species and genetic levels.
Furthermore, in the recent studies on tidal flats, seagrass beds, and thesurrounding inner bay environment, the roles of such ecosystems in inner bay
environments as a whole has drawn attention, rather than each individual role asa closed system. Some of the focuses of such studies are as follows:ix) Interdependent or complementary relationships between two or among several
tidal flatsx) The ideas of zoning where the positioning of tidal flats and seagrass beds, ortheir optimum layouts are discussedxi) Concepts of Ecotone where the ecosystem is treated as a transitional system,
such as; backshore (reed community) －tidal flat－seagrass bed (Zostera bed)－planktonic ecosystem in an inner bay.; or the idea that such systems create acompound ecosystem through interaction.
With these perspectives in mind, the efforts are being made to reexamine of therole of each habitat.

39

Figure 3-11 Diagram of the experimental tidal facilities in the Port and Airport
Research Institute (above). Recovery of benthic life following sediment disturbance.
In the experiment, the surface layer of sediment (up to 30cm) was agitated. The
benthic species showed recovery in a period of about six months.

40

Figure 3-12 Fishermen releasing juvenile shell (Tokyo Bay: 1945-1955)

Figure 3-13 Fisherman collecting eelgrass (Nakaumi: 1945-1955)41

(2) Key factors for ecosystem restoration and factors controllable by man
A successful ecosystem restoration requires a stable base as a biohabitat, andoptimum environmental conditions. If the conditions are not met, methods toartificially adjust them must be discussed, with careful consideration being
afforded to the self-designing ability of nature as well as to the impact on thesurrounding environments.
For successful ecosystem restoration, the existence of a physically stablesettlement base (substratum), as well as the environmental conditions appropriate
for recruitment, settlement, growth and reproduction of species, are essential.
The key factors to be considered are as follows:i) Physical factors contributing to the physical stability of a habitat base (substratum)・・

Geological factors: coastal landscape, water depth, sea bottom gradient etc.
Oceanographic factors: wave, tide level, tidal current, disturbance andshearing stress etc.

・・

Meteorological factors: wind, precipitation etc.
Sediment and ground condition: grain size, specific gravity, water content,
silt content, soil property etc.

・River inflow in the vicinity: flow rate, flow velocity, water level, suspended
solid, estuarine landscape etc.

ii) Environmental factors appropriate for biohabitats ( for larval recruitment,
settlement, growth and reproduction)
・Water quality: water temperature, salinity, dissolved oxygen levels, pH;concentration levels and fluxes of suspended matter, organic matter, nutrients,
and growth inhibiting matter・Sediment and ground condition: grain size (median grain size, grain size
distribution), specific gravity, water content, silt content, pH, oxidation-reduction
potential, hardness, soil property, water depth of substrate, direction of substratesurface etc.

・Weather & Meteorological factors: wave, tide level, tidal current, disturbanceand shearing stress, wind, precipitation, solar irradiation (turbidity,
underwater visibility, underwater light intensity).

・

Ecology of target species: existence of recruitment, life history, adaptability andcontinuity of the site, predation pressure, and fishing pressure.

42

・

Habitats and ecosystems in the vicinity: supply of nutrients or food (bottom-up),
predator (top-down), biological competition or inhibition, recruitment sources
for a damaged system.

The above factors, however, must be considered through habitat observations and the cause analysis on habitat loss
or expansion. In restoring nature, it is essential to improve or repair the substrata so that they could satisfy theenvironmental requirements. If the requirements are not met, it is important to contrive methods to aid in the fulfillmentof such requirements while taking into consideration the self-designing ability of nature. Special attention should
also be paid to the impact posed by such methods on the whole ecosystem, along with the matters affected by the managementlabor or cost-efficiency inherent to the methods.
Such an approach in learning from surrounding geographic features or from the habitat conditions is integral to theestablishment of technologies for nature restoration. When creating tidal flats, the property of tidal flats should
be well understood. Table 3-3 shows the specification of major natural tidal flats in Japan. Sediment type and wave
condition are the primary factors for physical stabilization. If the restoration is for a specific species, it isnecessary to consider the environmental conditions not only for the present life stage but also for all the stages
in its life history.

As an example, the ecological aspects of clam habitat are shown in Table 3-4.

43

Table 3-3 Features of major tidal flats in Japan

干潟名
(所在地)
柳川(福岡県)
諫早(長崎県)
大牟田(福岡県)
佐賀(福岡県)
小櫃川河口(千葉県)
千鳥浜(山口県)

面積(ha)
1191.5
860.0
470.0
368.0
311.0
226.0

球磨川河口(熊本県)
大海湾(山口県)
木曽川河口(三重県)

勾配
1/560~1/100
1/520
1/400
1/360
1/1010
1/730

潮位差
（ｍ）
4.45
4.45
4.45
4.45
1.58
2.06

有 義 波 高
（ｍ）
2.0
2.0
2.5
2.0
3.0
1.0

158.2
125.6
39.1

1/220~1/90
1/400~1/300
1/120

3.25
1.92
1.89

1.0
4.0

一宮川河口(千葉県)

22.8

1/110

0.89

5.0

大井川河口(静岡県)
夷隅川河口(千葉県)
相模川河口(神奈川県)

9.8
6.8
6.3

1/6250
1/190
1/180

0.12
0.89
1.11

4.5
5.0
6.5

底質粒径(mm)，分布
シルト・粘土シルト・粘土0.004~0.25
シルト・粘土0.06~0.25
0.5~1.0(34％)
0.25~0.5(28％)
0.125~0.25(16％)
0.06~0.25
0.004~0.06
0.25~0.5(26％)
0.125~0.25(43％)<0.0625(25%)
0.25~0.5(30％)
0.125~0.25(45％)<0.0625(15%)
砂質土
砂泥質
砂質土

Table 3-4 Summary of ecological data(example: clam)

環境要因等

地形

底

生

期

水域から底質へ
着底最適水深：大潮干潮時60～90cm 付近，
一日の干出時間 2 時間以下
致死水温－2℃以下
40℃では生存時間 5 時間

底質(水深 0~6m)
生息最適地盤高－1～＋１ｍ付近
0～37℃で生息
約 15～30℃で速やかな
成長
10℃以下で緩慢
適 塩 分
20.7 ～
37.6PSU(15℃換算)

ピーク時(6，10 月)
:20℃

塩分

殻長 3.0～4.5mm：30℃以
上では塩分 24.6 であっても 3 日間で 100％斃死
植物プランクトン
デトリタス，珪藻類，ギョウ脚類
1.0ml/l 以上，0.2～0.4ml/l の海水では一週間で 70～
80％の個体が斃死
泥率 8％以上，泥分率 30％ 砂泥海岸(東京湾：泥率になると激減20～30％)
中央粒径 0．07mm 以上
カモ類，タコ類，タマガイ類，ツメタガイ類，魚類

栄養
溶存酸素
底質

外敵

底生移行期

水温

水 質

環 境 要 因

時期
場所

生 活 史
浮 遊 期
5~11 月の 2～３週間
水域(3) Technologies for habitat base44

Civil engineering technologies play crucial roles in the establishment of a stablebase for habitats (substrata). In the creation of the base accommodating several
types of habitats, new challenges focusing on the compound of ecosystems, such as
demonstration experiments on their layouts or combinations, are also being
attempted.
As described in the previous section, the factors including geological, oceanographic, and meteorological conditions,sediment, ground, as well as river inflow, are key elements to the development of a stable habitat base (substratum).
The methods to control these factors have largely been supported by civil engineering technologies. If the waves are
too strong, civil engineering technologies could allow for the construction of a submerged mound off the tidal flat.
The versatility of civil engineering can be seen here with its array of technologies embracing both work on the
improvement of surroundings as well as countermeasures against wave motion. The technologies employed when dealing
with the stabilization of the substrata, such as ground settlement prevention or scour protection, rank among the mostimportant technologies being used.

Furthermore, the development or the improvement of habitats in the past has
mostly been focusing on a sole ecosystem, however, the development of a compoundsystem, such as the concurrent development of a tidal flat or a seagrass bed, will
become crucial technological challenges. Also, well-designed zoning in ports or bay
areas should not be eliminated.
One of such developments is seen in the Port of Amagasaki, where an experiment on effective combination or a “bestmix “of elemental technologies is underway, in order to restore healthy material cycling. In this experiment, thetechnologies for an artificial tidal flat, the seagrass bed development, an artificial lagoon surrounded by banks,
and a stair-stepped structure called Eco-Wharf, were chosen as element technologies to create habitat bases. Other
technologies including the ones for controlling physical flow between the elements, and for the energy recovery systemby which seagrass is collected as a resource, are also incorporated into the experiment. Having such environmental
technologies combined, this experimental project is now underway in the actual sea environment. Although the project
has still to be fully implemented, the complementary relationships between each technology’s functions in the project
are outlined in Figure 3-14.

45

海砂代替材の開発
ヨシ原
流況制御

人工干潟

生物生息場
アマモ場

生 物
プラント

アオサ利用
栄養塩循環

ラグーン

アオサ利用
栄養塩循環

海藻胞子等
供給
海藻胞子等
供給

筏式藻場

アオサ
バイオマ
ス利用

Figure 3-14 Complementary relationships of each technology’s functions seen in
the “Best mix” project in Amagasaki Port.

(4) Technologies providing suitable environmental conditions for habitats
The environmental conditions needed for the habitat creation should fulfill therequirements for each tidal flat, seagrass bed or coral reef ecosystem.
The environmental conditions suitable for biohabitats should be adequately arranged, through careful studies on thepreviously mentioned factors of water quality, landscape, sediment, weather, oceanographic aspects, ecology of target
species, and habitats or ecosystems in the vicinity.

These conditions are to be designed in accordance with the habitable conditions foreach species. The material properties or numerical values should therefore varydepending on the target ecosystem. The examples for tidal flats, seagrass beds andcoral reefs are shown as follows.
The factors needed for designing a tidal flat are shown in Figure 3-15.
Table 3-5 shows the technologies enabling each environmental factor to be suitable for the development of seagrassbeds. The technologies for conservation, restoration and utilization of coral reefs are summarized in Table 3-6.

46

A detailed description of each appears in other volumes dealing with eachecosystem in turn.
干潟設計の考え方

設計条件

設計内容

干 潟

生物の生息基盤とし

波浪条件

平面形

ての干潟地形の設計

流速

勾配

勾配

投入土砂の安定の 設
計
生物生息のための工

潮位・地盤高

微地形

夫

底質

植栽

Figure 3-15 Contents for the design of a tidal flat47

Table 3-5 Technologies facilitating favorable environmental conditions

Environmental factors

Technologies

Wave

Submerged mound, breakwater

Light

Water depth adjustment (incl. Artificial sea bottom, increase of underwater
penetration, water purification

Substrate stability

Wave control, Installation of large substrate, artificial sea bottom

Substrate hardness

Substrate installation, substrate modification

Nutrients

Fertilizer, Artificial upwelling, facilitation of flow

Toxic substance

Additional soil

Herbivores

Elimination, installation of obstacles, supply of foodCompeting species

Elimination, substrate installation

Supply of seagrass species Transplantation, seeding
Littoral drift

Substrate installation

48

Table 3-6 Technologies for conservation, restoration and utilization of coral reefs
Technologies
Conservation

Consideration on analignment plan

Substrates
installation

Creation ofshallow flats
Creation ofsubstrates

Surfaceprocessing

Restoration
technologies
Directintroductionof corals

Installation of stable substrate

Install stable substrates including stones and blocks on a
gravel or sandy sea bottoms unsuitable for coral growth

Installing substrate in deep flats to
reduce water depth

Place stones and blocks in deep water to create ashallower flat so as for coral to settle and growGently sloping breakwater wall

Increase shallow water areas by introducing a gentle
declivity in wave-dissipating block conformation on the

Stair-steps on breakwater walls

Increase shallow water zones by building stair-steps on
breakwater slopes outside a harbor

Mound raising

Extend shallow water zones by raising breakwater moundon the harbor side

Gently sloping sea banks

Give slope declivity to sea banks or create shallow waterzones in front of them when they are not provided forberth.

Unevenly- surfaced blocks

Apply uneven surface processing to wave-dissipating
blocks or other structures to facilitate coral settlement

Uneven processing on vertical walls of
caissons

Provide protrusions or terraces on the vertical walls of
breakwaters so as to secure the bases for coral settlement

Substrate with chemically processedsurface

Apply growth promoting substances of coral settlement tothe surfaces of structures including wave-dissipating
blocks (*developmental stage)

Release of coral larvaeCollect, culture and release coral larvae so that a large
quantity and successful coral settlement can be madeTransplantation of coral larvae

Transplant corals polyps on to coastal structures or tonatural reefs scarce in coral cover to encourage
multiplication

Transplantation of coral fragments

Transplant coral fragments onto coastal structures or tonatural reefs scarce in coral cover to encourage
multiplication

Relocation of coral assemblages

Relocate a coral assemblage when it's under the risk ofbeing destroyed by landfill or breakwater construction

Diversephysicalenvironment

Placing caissons in uneven alignments

Place caissons in uneven alignments so as to promotecoral reef regeneration

Allowing space between caissons

Space caissons to allow sea water exchange; or use wavedissipating blocks for breakwater walls instead of caissons

Caissons with water channels

Create water channels on caisson walls for better
circulation of seawater

EnvironmentalBetterimprovement
circulation ofsea water

Directintroductionof corals

Release of coral larvaeCollect, culture and release coral larvae so that a large
quantity and successful coral settlement can be madeTransplantation of coral fragments

Transplant coral fragments onto coastal structures or tonatural reefs scarce in coral cover to encourage
multiplication

Relocation of coral assemblages

Relocate a coral assemblage when it's under the risk ofbeing destroyed by landfill or breakwater construction

Breakwaters with easy access to water
Underwater observation tower
Utilization

Make arrangements on alignment plans for reclamationor breakwater construction projects, when coral reefs arefound on such sites.

Bathing areas off the coast

Nature observation facilities

Create promenade type breakwaters for harbor
viewing or other marine activities
Construct facilities from which coral reefs can bedirectly observed (underwater observation tower,
underwater tunnel)
Set aside areas on the harbor side of breakwaters or
on natural reefs off the coast, for bathing or for
scuba diving
Designate areas for observing marine life or wild
birds, that feature a nature observation facility (nature center), an ecosystem exhibition facility(aquarium) and observation instructors (ranger)49

3. 3 Recent developments and challenges of restoration technologies(1) Technological development in base material used for creating biohabitats
The material indigenous to the region or natural material has been experimented
on in the creation of biohabitats.
The selection of artificial structures as well as the material suitable for biohabitation is as important in itself
for restoration technologies as habitat stability and appropriate environmental conditions.

As for the technologies deployed in creating tidal flats, the foundation work such as
the placement of sand or soil on the sea bottom constitutes the fundamental part,and the sand types used in the surface layer characterize the flats. When creating
an artificial tidal flat, it is desirable to use the same type of sandy-mud sediment
found in natural tidal flats existing in the vicinity. In the project of “Omori
Furusato no Hamabe Seibi Jigyo” in Tokyo, however, the applicability of sediment
was compared between the sand from the proposed site, dredged soil, andpurchased sand, confirming that the sand from the proposed site found the earlier
inhabitation of living organisms (Nikkei BP, 2002). Other technologicaldevelopment includes the use of wooden piles, structural variations of shore
protection and retaining walls, as well as the development of microtopography.
With regard to the seaweed and seagrass bed development, technologies areroughly classified into two areas; the seeding/planting of seagrass or seaweeds, andthe transplantation of adult plants. In the use of artificial material, such as matsused in eelgrass seeding, or the placement of blocks in which to create sargassum
forest, the focus of technological development has also been placed on the
alleviation of stress posed on the surrounding environments associated with thesetechnologies, as well as on the improvement of survival rates.
The technologies creating coral habitats include the ones for securing optimum
water depths, submerged mounds, the creation of calm sea area by breakwaters
and the stable substratum for coral growth. Besides these civil engineering aspects,
technologies considering biological habitation have also been promoted, such ascoral transplantation, coral relocation and the release of coral larvae. Thesemethods are taking advantage of the properties of coral, of which coral species
serve both as base material and a restoration target.
(2) Development of prediction methods for coastal ecosystem
Methods for predicting changes in coastal ecosystems have been studied using
various models, including models for physical environmental factors, material
50

cycling, and ecosystems.
Methods for predicting changes in coastal ecosystems have been studied using
various models, including models to simulate physical environmental factors,
material cycling, and ecosystems. The following are the examples of various
approaches employed for a tidal flat ecosystem using such models.
1) Models for physical environmental factors
Tidal flat topography, which has been largely affected by waves and currents,changes its features through erosions and depositions. The topography is also
affected by the influx of soil from rivers, which combined with the above, can cause
both, temporary or permanent changes. (Uchiyama, 2000;Furukawa et al., 2000).
The transport of such sandy-mud has been analyzed through hydraulic modelexperiments or numerical calculations. When the sediment type used is sand, thegradient that stabilizes the flat is estimated using prediction methods for littoral
drift. However, the prediction methods for three dimensional or local topographic
changes have not yet been established. Furthermore, besides such sandy-mud
transport, the ground subsidence induced by the consolidation pressure of mud isalso found in some artificial tidal flats, witnessing new proposals for predictive
experiments for such phenomena.
In addition to the topographic changes, the attempts to clarify the relationships
between biohabitation and the environmental factors controlling tidal flat surface
conditions, such as wave, current, sediment, and water quality, have been largely
addressed.
2) Roles of tidal flats and the modeling of tidal flats
The water purification function of tidal flats has been indicated as a distinctiverole for the surrounding marine environment, and its study has been pursued inparallel with the study on material cycling in tidal flat ecosystems. As part of theresearch on the cleansing function and biological productivity in and aroundintertidal zones, the studies on the organic matter decomposition by marine
bacteria, the bacterial decomposition of organic matter in sandy-mud,
phytoplankton, zooplankton, meiobenthos, as well as macrobenthos have been
carried out. Having gained insight from these studies, as well as focusing on thecleansing function of tidal flats, the following have been noted:
・・・

Estimated cleansing effect of organic matter
Filtration function of Bivalvia
Importance of the intake of nutrients by large-sized seaweeds

51

・Permeability of seafloor sediment anddecomposition of organic matter involved

theimportanceofbacterial

Hosokawa and his group (1996) measured the cleansing function of an artificial tidal flat created in the experimental
tidal flat facilities, confirming that the artificial tidal flat can record a high removal effect of organic matter.

For such cleansing functions, several models were developed, including a model
incorporating both a planktonic and a sedimentological system, which wasdeveloped from the models for the DO consumption mechanism or the oxygen layer
creation mechanism on mud surfaces. A model to numerically simulate thematerial diffusion processes in benthic boundary layers was also developed.
Table 3-7 Primary ecosystem models
Modelliterature

Low trophic level ecosystem model
Sediment model
Population dynamics model
DO modelMulti-box model3) Habitat segregation of tidal flat species
With regard to prediction methods for habitat segregation of tidal flat species,
various discussions have been had from the analytical methods to theestablishment of biological indicators based on such segregation.
There have been no clear guidelines for biological distribution surveys; however, Sakai and his group (1983) conductedsurveys on standing stock of benthic organisms in Omi Bay, Yamaguchi prefecture, and emphasized the necessity thatthe surveys be conducted more than 6 times a year in order to gain a better understanding of seasonal variations.

The spatial allocation of survey stations should also be determined in considerationof the distribution patterns of target species (Kurihara et al., 1988).
The habitat segregation has also been described focusing on the feeding patterns and the sediments for habitation,
indicating that interactive processes found between sediments and species inhabiting them have a significant role insediment ecosystems. This is known as bioturbation, and its effect has been observed in a report stating that sulfide
production was restricted by the bioturbation by Polychaeta.

Other studies on habitat segregation include the experiment conducted on
biological recruitment in the Mesocosm experimental facilities, where species
variation, rates of recruitment or renewal of the species are being studied (Kuwae
et al., 2002), along with the development of a model incorporating parameters for52

active preference or avoidance of species over environmental conditions.
4) Anoxic water mass and the biological response to it
Unfavorable environments for living organisms mean inhabitable environments.
Water temperature or dryness could become the threatening factors to the survivalof marine organisms in tidal flats. In the environments of inner bays, an anoxic
water mass occurring in summer creates extremely severe environmental
conditions, affecting species survival.
The mechanism for the production of an anoxic water mass has been studied bymany researchers as reported by Yanagi (1989). These include the macroscopic
studies on the production mechanism in bay or calm sea environments, or the
microscopic examination on the mechanism of fine particles and water in benthic
boundary layers existing between the bottom mud and water.
When such an anoxic water mass emerges, the r-strategy species increase theirreproduction rates, thereby creating a temporal segregation from the k-strategy
species that have lower reproduction rates and a longer generation time
(Imabayashi, 1989).

53

(3) Development of evaluation methods for coastal ecosystem
The methods to evaluate coastal ecosystems are divided into two categories;
methods to evaluate environmental function, and methods to evaluate biological
function. Various numerical models have been developed and are used for such
evaluations.
The evaluation of coastal ecosystems must be carried out based on the structure ofeach ecosystem and the simulation level of evaluation, such as individual,
population, community and ecosystem. The scale of the ecosystem, ranging from alittle nesting hole to a wide bay area, also differentiates the evaluation methods
used. The evaluation methods available for such purposes are classified into two
types: functional evaluation and biological evaluation. The features of thesemethods are shown in Table 3-8.
Table 3-8 Evaluation methods for coastal ecosystem
Functional evaluation Biological evaluation
Evaluation item

Species structure
Habitat condition
External force
Spatialdistribution
Temporal change

HEP

WET

HGM
○
○
○
×

Material
cycling model×○○○

Biohabitation
model
○
○
○
○

○
×
×
×

○
○
×
×

×

△

×

○

○

1) Functional evaluation methods
Functional evaluation methods have been developed as the tools to evaluate
environmental impacts in coastal development, as well as the quantitativeevaluation methods for environmental mitigation. HEP (Habitat Evaluation
Procedure), WET (Wetland Evaluation Techniques), and HGM (HydroGeoMorphic
Approach) are the most commonly used in functional evaluation (National
Research Institute of Fisheries Engineering, 2000; Bartoldus, 1999).
In these methods, the suitability of an area as a habitat is represented as the
product of the suitability of such area as an ecosystem and its areal extent. The
area’s suitability as an ecosystem is quantified as an index. If the area hasenvironmental conditions capable of increasing biomass or the number of species, it54

is given a high index. If it has the conditions for the opposite effects, the index islowered. As such, the environmental conditions including water quality, sediment,
topography, water depth, and external force are evaluated as suitability indices.
The equation is as follows:
Suitability as a habitat = Suitability as an ecosystem

X

Areal extent

In HEP, the habitat suitability is called HIS (Habitat Suitability Index) and thesuitability as an ecosystem is called SI (Suitability Index). The HIS to evaluate aclam habitat is suggested by the following equation.
HIS =Sediment SI (medium gradient size, mud content, ignition loss, the minimum
SI value in oxygen-reduction potential)
X water quality SI (the product of water temperature SI and salinity SI)
X exposure time SI
X wave action SI
If the environmental suitability appearing on the right-hand side is estimated bynumerical models, such as wave/current models or a material cycling model, suchmodels would be applicable to the site-selecting system for seagrass beds and tidal
flats.
2) Biological evaluation methods
In biological evaluation methods, functions related to biological activities(metabolism, secretion, respiration), and life history as well as ecological functions
are being modeled and evaluated by parameters such as material transport ormaterial cycling in ecosystems.
For instance, by relating the growth and metabolism of species to the values for thequality of water and sediment obtained from a material cycling model, “thesuitability as an ecosystem”, which has been experimentally or inductively
determined in the functional evaluation methods, can be determined deductively.
The biological evaluation methods are classified into two types depending on theparameters used for evaluation; methods using parameters focused on theecosystem’s health or the constitutive property of material cycling, and methods
using parameters that gauge the function of each individual species, such as theturbidity filtration function of Bivalvia (Sugita et al., 2002).

553) Application of evaluation methods
Following various evaluation methods being suggested for coastal ecosystems,
together with the increased high precision of simulation models, such evaluation
methods have begun to be utilized in detailed examinations or monitoring
programs. But they come with their disadvantages as well as their advantages.
The biological evaluation methods can provide objective values on ecosystem
function; but for the species whose life history or habitat conditions are notclarified, the parameters have to be set through experiments or observations,which in turn would require a large amount of time for the completion ofevaluation.
While the functional evaluation methods enable the quantitative assessment in a
relatively short period of time; however, a number of surveys are required toincrease reliability of data, and thus may encounter an increase in evaluation cost.
Also the results of evaluations may vary depending on the species being studied.
When selecting evaluation methods, it is important to give ample consideration to
the evaluation purposes, and seek a comprehensive evaluation of the target habitatby harnessing the features of each approach. Some cases may require thesimultaneous or complementary use of these methods for better appreciation.

56