Expanding walls and shrinking beaches:
loss of natural coastline in Okinawa
Island, Japan
Giovanni Diego Masucci1 and James D. Reimer1 ,2
1

Molecular Invertebrate Systematics and Ecology Laboratory, Graduate School of Engineering and Science,
University of the Ryukyus, Nishihara, Okinawa, Japan2
Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Okinawa, Japan

ABSTRACT

Submitted 30 May 2019
Accepted 19 July 2019
Published 6 September 2019
Corresponding author
Giovanni Diego Masucci,
giovannimasucci@me.com
Academic editor
Xavier Pochon
Additional Information and
Declarations can be found on
page 15
DOI 10.7717/peerj.7520
Copyright
2019 Masucci and Reimer
Distributed under
Creative Commons CC-BY 4.0

Okinawa is the largest and most populated island of the Ryukyu Archipelago in southern
Japan and is renowned for its natural resources and beauty. Similar as to what has been
happening in the rest of the country, Okinawa Island has been affected by an increasing
amount of development and construction work. The trend has been particularly acuteafter reversion to Japanese sovereignty in 1972, following 27 years of post-war American
administration. A coastline once characterized by extended sandy beaches surroundedby coral reefs now includes tracts delimited by seawalls, revetments, and other humanmade hardening structures. Additionally, part of coastal Okinawa Island was obtainedby land-filling shallow ocean areas (land reclamation). Nevertheless, the current
extension of the artificial coastline, as well as the level of fragmentation of the natural
coastline are unclear, due to the lack of both published studies and easily accessible andupdated datasets. The aims of this research were to quantify the extension of coastline
alterations in Okinawa Island, including the amount of land-filling performed over thelast 41 years, and to describe the coastlines that have been altered the most as well as
those that are still relatively pristine. The analyses were performed using a reference mapof Okinawa Island based on GIS vector data extracted from the OpenStreetMap (OSM)
coastline dataset (average node distance for Okinawa Island = 24 m), in addition tosatellite and aerial photography from multiple providers. We measured 431.8 km ofaltered coastline, equal to about 63% of the total length of coastline in Okinawa Island.
Habitat fragmentation is also an issue as the remaining natural coastline was broken
into 239 distinct tracts (mean length = 1.05 km). Finally, 21.03 km2 of the island’s
surface were of land reclaimed over the last 41 years. The west coast has been altered
the most, while the east coast is in relatively more natural conditions, particularly thenorthern part, which has the largest amount of uninterrupted natural coastline. Given
the importance of the ecosystem services that coastal and marine ecosystems provide to
local populations of subtropical islands, including significant economic income fromtourism, conservation of remaining natural coastlines should be given high priority.

Subjects Biodiversity, Conservation Biology, Coupled Natural and Human Systems,

Environmental Impacts, Spatial and Geographic Information Science
Keywords Habitat loss, Habitat fragmentation, Land reclamation, Coastal armoring, Coral reefs,
Okinawa Island, Japan, Land-filling, Anthropic impact, Remote sensing

OPEN ACCESSHow to cite this article Masucci GD, Reimer JD. 2019. Expanding walls and shrinking beaches: loss of natural coastline in Okinawa Island, Japan. PeerJ 7:e7520 http://doi.org/10.7717/peerj.7520

INTRODUCTION
Japan is renowned worldwide both for its economic, industrial, and technologicalachievements, and for its cultural and natural heritage. Unfortunately, a consequence of theJapanese development model has been the destruction of portions of the country’s naturalenvironments, both terrestrial and marine (McCormack, 1999; Kerr, 2001). After WorldWar II, Japan has increasingly invested public money in projects related to modificationsof the natural landscape (Walker & Mossa, 1986). This included the alteration of 110
out of its 113 major rivers with numerous dams and concrete enclosures, in addition
to minor streams across the country, and the creation of numerous mountain roads forthe forestry industry, which has contributed to the eradication of around 40% of Japan’snative forest (Kerr, 2001). During the 1990s, the production of concrete in Japan rose,reaching the highest cement consumption per capita in the world and the highest percapita construction-related debt (U8 million; Kingston, 2005). This increase was seemingly
unaffected by the recession that the country was facing, which, instead, accelerated the
production: between 1992 and 1999, the country invested U120 trillion to boost theeconomy, of which ∼60% was spent on construction projects (Kingston, 2005), producing
as much concrete per year as the United States (Kerr, 2001; Kingston, 2005). During thistime, local and international commenters began describing Japan as the ‘doken kokka’, theconstruction state (McCormack, 1999; Kerr, 2001; Kingston, 2005; Nam, 2019).
Perhaps the most well-known and evident impact of construction can be seen on the
coastline, where numerous civil engineering projects have been performed, either by theplacement of bulkheads, seawalls, breakwaters, revetments, and groins, with the purposeof protecting human-made buildings and coastal roads from erosion and wave action(shoreline hardening, or armoring), or by extending the coastline seaward by filling theocean with soil, rocks, cement, or combinations of these materials, in a process knownas ‘‘land reclamation’’ or ‘‘land-filling’’. Both of these expressions are not without issues:
the term ‘‘land reclamation’’ has also been associated with a wide range of humanmade alterations, generally with the aim of converting disturbed land to productive uses
(Powter, 2002). In a similar way, the term ‘‘land-filling’’ overlaps with the practice ofdisposing garbage by burial on land. In the context of this research, the meanings of thetwo expressions are identical, but we here use the more neutral and descriptive term‘‘land-filling’’.
When a coastline is eroding, coastal armoring can interfere with natural beach
upslope migration, triggering a passive erosion of the shoreline that can lead to beachnarrowing or loss (Griggs, Tait & Corona, 1994; Dugan et al., 2008), a phenomenon which
has been defined as ‘‘coastal squeeze’’ (Pat, 2004). In terms of impacts on the marine
ecosystems, shoreline hardening reduces habitat complexity and uniqueness, affecting
species composition, and decreasing abundance and diversity (Seitz et al., 2006; Duganet al., 2008; Gittman et al., 2016; Aguilera, 2017). The effects of land-filling the marine
environment include habitat loss (Lai et al., 2015; Heery et al., 2018) and a degradation ofenvironmental parameters levels, particularly higher nutrients, sedimentation rates, andMasucci and Reimer (2019), PeerJ, DOI 10.7717/peerj.7520

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turbidity, which can negatively impact the survival of coral reefs (Chou, Yu & Loh, 2004;
Dikou & Van Woesik, 2006).
Japan’s ‘‘Environmental Impact Assessment (EIA) Law’’ was enacted in 1997 andimplemented in 1999, providing legal power to deny authorization to construction projects
exerting excessive impacts on the environment (Ministry of the Environment of Japan,2019). Although an important achievement, the law has some limitations that need to beconsidered. Only large-scale construction projects require EIAs. For medium-scale works,
the necessity of an EIA is judged by the national government for each individual project,while smaller-scale projects do not require any assessment by national law. In the caseof land-filling, an EIA is only required for projects involving over 50 ha (0.5 km2 ) ofreclamation. For land-fills between 40 and 50 ha (0.4–0.5 km2 ), the decision is taken on a
per-project basis, and below 40 ha (0.4 km2 ) there is no requirement. If the reclamation is
performed to build harbors and ports, the limit for no EIA is extended to 300 ha (3 km2 ).
Although the size of a project is an important factor, it is not the only one: EIA only
regulates specific categories of construction works. While land-filling is one of the covered
categories, coastal armoring is not included and can therefore proceed without any EIA(see Ministry of the Environment of Japan (2019) for a detailed list of categories and sizes
subject to EIA Law).
EIAs are performed by the project proponent and sent to an authorizing agency(commonly the Ministry of Infrastructure, Land and Transport, or the Ministry of
Economy, Trade and Industry), which makes the final decision. Because the authorizing
agency and the proponents can share similar interests, the Ministry of the Environment(MoE) can be requested to express an opinion. However, a positive MoE opinion is not
required for the final approval.
Finally, there is no requirement for follow-up surveys that would provide data on thequality of the initial EIA and on the impacts of the construction work on the naturalenvironment (Ministry of the Environment of Japan, 2019). This is one of the reasons why
the impacts on the natural environment of coastal construction projects in Japan are
generally unreported, and thus unclear or unknown. EIAs are not the only legislative
instruments that regulate construction works; in the case of land-filling, a permit fromthe local government is needed, making the role of prefectural governors important in the
final decision (Okinawa Prefectural Government, 2014; Ministry of Land, Infrastructure andTransport of Japan, 2001).
The Ryukyus (also Nansei Islands), a subtropical archipelago located in southwesternJapan, consist of approximately 160 islands. They include the most extensive coral reefsof the country, hosting almost 90% of the scleractinian coral species found in Japan(∼360 species out of ∼415; Nishihira, 2004), and have high levels of marine diversity andendemism (Cowman et al., 2017). Okinawa Island, or Okinawa-jima in Japanese (Fig. 1), is
the largest and most populated island in the archipelago (area = 1,208 km2 ; Japan Statistics
Bureau, 2014; population = 1.3M people; Okinawa Prefectural Government, 2019a).
The beauty of Okinawa’s natural sandy beaches, rocky cliffs, and marine environment
has provided significant economic income from tourism, and there has been a rapid
growth in the number of visitors in recent years, surpassing those of Hawaii in 2017 (total

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Japan
East
China
Sea

Pacific
Ocean

East
China
Sea

Okinawa Island

Pacific
Ocean

N
20 km

Figure 1 Okinawa Island and surrounding areas in southern Japan, northwestern Pacific Ocean. The
map includes locations discussed in this research.
Full-size DOI: 10.7717/peerj.7520/fig-1

number = 9,579,900 visitors; Ryukyu Shimpo, 2018). However, the natural environment
has also been damaged by human activities, including deforestation, urban sprawl, coastal
development, coastal hardening, and land-filling (McCormack, 1999; Nakano, 2004; Reimer
et al., 2015; Heery et al., 2018).
Since 1972, the year Okinawa Prefecture reverted to Japanese control, construction
projects have profoundly modified and reshaped the island landscape and topography(McCormack, 1998; McCormack, 1999; Kerr, 2001). By 1992, more than 1,600 ha of reef had
been destroyed due to land-filling and dredging, roughly equal to the 6% of the total coral
cover around the island (Nakano, 2004). The high influx of tourists has contributed to thebuilding of new infrastructure along the coastline and on reclaimed land (McCormack,
1998; Tada, 2015). Despite the difficulties in estimating general trends and local impacts
due to the lack of post-work assessments and published studies, construction has been
pursued to such an extent that civil engineering has been described as the main cause ofcoral reef destruction in the region (Nakano, 2004). Today, the development in Okinawa
Island continues and, as of January 2019, three major land-filling projects are underway:
the construction of a second runway at Naha Airport (1.6 km2 of reclaimed land; Flyteam
Japan, 2013), the creation of a harbor, residential facilities, resorts, and artificial beaches
at the Awase Tidal Flats (2.66 km2 ; Nakano, 2004), and the building of a new US militarybase at Cape Henoko/Oura Bay (1.6 km2 ; Okinawa Defense Bureau, 2012).
In this research, using GIS software and remote sensing technologies, specificallysatellite imagery and aerial photography, we described the current state of the Okinawa
Island coastline, with three main objectives:

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(1) To quantify the amount of coastline that has been altered as of the end of 2018, andto categorize such alterations. This included a comparison between the east and west
coasts, as we hypothesized higher levels of impact and habitat fragmentation on thewest side of the island, due to the presence of the capital and largest city Naha and of
National Route 58, a coastal road constituting the main connection between the northand south of Okinawa Island.
(2) To generate a map allowing easy visualization of the current status of the island
coastline, including habitat fragmentation, and to identify which parts of the island
have lost the largest amounts of natural coastline, and which locations have the highest
amount of preserved coastal environment.
(3) To determine the amount (area) and locations of land-filling performed during thelast 41 years of Japanese administration of Okinawa Island (1977–2018).
Both the maps generated in this study and the underlying dataset provide a baseline
for future studies and can be used as an additional tool when performing evaluations on
projects potentially impacting the island’s natural coastal environments.

MATERIALS & METHODS
According to a survey conducted by the Japanese Coast Guard in 1986 (Japan Statistics
Bureau, 2014), Okinawa Island has 476 km of coastline. However, there are two issues withthis number. Firstly, the extension of a coastline is not fixed in time and can be affected bynatural factors, like erosion or, at shorter time scales, by human activities, including coastal
hardening and land-filling. Secondly, the extension of a coastline depends on the scale atwhich the measurements are done. The more detailed the scale of a map, the longer themeasured coastline will be, tending towards infinite (coastline paradox; Richardson, 1961;
Mandelbrot, 1967), with no clear-cut gap between what is useful and unrequired detail.
Because coastlines are fractals with properties of self-similarity, it is not possible to state thelength of a coastline without referring to a specific reference map or to a scale and accuracyof unit of measurement. In other words, numbers referring to the length of a coastline that
do not report this additional information are of little use (Mandelbrot, 1967).
For these reasons, to assess the amount of altered coastline in a way that will makepossible for future studies to make comparisons at different times or with other locations,
our measures were performed over a base layer of LineString data (polylines vectors
connecting georeferenced points) extracted from the OpenStreetMap (OSM) coastline
dataset (Haklay & Weber, 2008) at maximum detail (visualized at a scale of 1:1,000,
WGS-84/long datum, dataset acquired on January 26, 2019). OpenStreetMap data provide
key advantages compared to datasets from numerous other sources: (1) They are easily
accessible and can be freely used for research purposes, (2) they are constantly updated,allowing us to conduct repeated surveys over the years to monitor trends and changes in
the coastlines, and (3) they are not specific to one country or region, which means thatthey can be used for future comparisons with other islands or coastlines.
The OpenStreetMap coastline dataset (tag: natural=coastline) includes worldwide
vector data delineating the sea edge, which is marked by the mean high water spring

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line. Coastline information is acquired from satellite data (such as NASA Landsat; see
https://wiki.openstreetmap.org/wiki/Potential_Datasources#Shoreline_databases for acomprehensive list) and automatically converted into vectors using automatic image
recognition algorithms. The acquired vector lines are then quality-checked and refined by
the members of the OSM community. Being a vector dataset, scale (or spatial resolution)is represented by the average distance between nodes (GFC, Kansas State University, 2019).
In the OSM coastline dataset, average node distance varies with location on a scale that
goes from tens to a few hundreds of meters. Node density is particularly high in Europe
and Japan, and lower where baseline data are more inaccurate and local contributors arefewer, such as Antarctica. Overall, the average global spatial resolution of the OMS dataset
has been measured at 66 m (Hormann, 2013). Coastal generalization algorithms may be
used when comparing regions of the world with different spatial resolution.
The base layer of the Okinawa coastline was imported into QGIS (version 3.6.0-Noosa;
QGIS Geographic Information System, 2019) and updated with minimal modifications totake into account new and ongoing land-filling works not yet indexed by the OSM project,including Naha Airport, Awase, and Oura Bay/Henoko. The total coastline included
Okinawa Island and artificial land-fills connected to the main Island. Naturally occurring
islands connected via bridges to Okinawa Island were not included. However, naturalislands that became merged via land-fills were included in the analyses. The total coastline
was then divided into west and east coasts using the northernmost (GPS = 26.875525,
128.257702, Cape Hedo) and southernmost (GPS = 26.074467, 127.676570, Cape Arasaki)
points of the island, to allow comparisons between the two. Altered portions of the
Okinawan coastline were tagged over the base map layer with the help of satellite data andaerial photography from ESRI, Google, Bing, and the Okinawa Prefectural Government
historical GIS dataset. Where image data were unclear, observations from the 5th basic
survey on conservation of the natural environment from the Biodiversity Center of Japan,
Ministry of the Environment (1998) were referenced. Finally, visits to locations to confirm
information were conducted as needed. Collectively, these sources allowed us to draw a
map reflecting the situation of Okinawa Island at the end of year 2018. The altered coastline
was obtained by tracing LineStrings over the base layer and tagging them accordingly within
defined ‘alteration’ categories. This process was done using the GIS software Map Plus for
iOS (version 2.8.5, Duwei Technology, 2019).
Each coastline LineString was included into one the following alteration categories(Fig. 2):
1. Natural. The shore (beach or rocky shore) and the terrestrial area immediately behindthe shore have been preserved, allowing the existence of a buffer zone made byvegetation and/or dunes.
2. Soft armoring. The shore has been hardened by walls or other human-madeconstructions. Hardening blocks are on land and the components of the natural
coastline (vegetation, sand, intertidal zone, etc.) are still preserved.
3. Hard armoring. The shore has been hardened by seawalls, breakwaters, or other humanmade constructions, placed into the water and/or at the interface between water andland. One or more components of the former natural coastline have been compromised

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Figure 2 Coastline categories. (A) Natural (east Kunigami). Vegetation acts as buffer between shoreline and road. (B) Soft armoring (Odo). Beach and vegetation preserved but disconnected due to the presence of human-made structures above the intertidal zone. (C) Hard armoring (west Kunigami). Roadsor buildings built next to the coastline. Presence of seawalls and/or breakwaters. (D) Land-filling (Agarihama/Agarizaki). Shallow waters turned into land to increase the space available for human activities. The
yellow line indicates the original shoreline before reclamation. For each category, color choices are consistent with those used in Fig. 3. Map data c 2019 Google.
Full-size DOI: 10.7717/peerj.7520/fig-2

by something human-made (roads, seawalls, coastal buildings, breakwaters, etc.), sothat simply removing the hardening would not restore the natural coastline.
4. Land-filling. A tract of hardened coastline obtained from human-made land
reclamation of the intertidal and, in some cases, subtidal zones.
It is important to note that both the map of human-made alterations and the underlying
data are conservative, mainly due to two reasons. First of all, it is possible, especially inthe case of soft armoring, for vegetation to grow around barriers, making them hard to
confirm from satellite images. Secondly, blocks placed in the subtidal zone and completely
submerged, although used in Okinawa Prefecture, could not be accounted for in our
analyses as they were not reliably visible in satellite images.

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LineStrings were grouped in their respective categories and imported into QGIS, where
their length in kilometers was summed to obtain the total lengths (km) of each group and thepercentages of each category on the total coastline. Moreover, in order to examine coastline
fragmentation and the relative contributions to fragmentation (assuming all coastline wasoriginally natural) from each coastal category above, the number of LineStrings and
LineStrings mean length were calculated for the natural coastline, for the whole altered
coastline, and within each category of alteration.
Descriptive statistics were performed using R software (version 3.5.3; R Development
Core Team, 2019). As the dataset included the totality of LineStrings composing the
Okinawa coastline, no statistical test was performed to compare west and east coast
LineString mean lengths, as a statistical test would only make sense for sample data, as
opposed to population parameters.
Finally, to assess the amount of land-filling performed in Okinawa Island in the last
41 years, historical aerial photography data from 1977 were acquired from the Okinawa
Prefectural Government GIS webpage (Okinawa Prefectural Government, 2019b) andgeoreferenced. The tracts of coastline that differed from year 2018 were manually traced as
vectors using QGIS. The total amount of land added by reclamation activities was obtainedby subtracting the area of Okinawa Island in 1977 from that of Okinawa Island in 2018.
Maps figures were generated using the QGIS PDF vector export function.

RESULTSThe length of the coastline layer imported from the OSM dataset was 656.9 km, with anaverage node distance (spatial resolution) of 24 m. After adding the most recent coastal
developments, the total coastline reached 682.8 km, at the same spatial resolution. 431.8 kmof coastline were altered, equal to 63.2% of the total length, leaving 251.0 km in a naturalstate (36.8%). The most common category of coastal alteration, in terms of length in km,
was land-filling (309.2 km, 45.3%), followed by hard armoring (98.9 km, 14.5%), and thensoft armoring (23.7 km, 3.4%) (Fig. 3).
The west coast (347.5 km) was the most affected by coastal development: 251.4 km werealtered (72.3%), of which 186.3 km by land-filling (53.6%), 52.8 km by hard armoring(15.2%), and 12.2 km by soft armoring (3.5%). 96.1 km were in a natural state, equal
to 27.7% of the total length of the west coast. The east coast (335.3 km) was relatively
more preserved: 180.5 km were altered (53.8%), of which 122.9 km (36.6%) were alteredby land-filling, 46.1 km (13.7%) by hard armoring, and 11.5 (3.4%) by soft armoring.
154.8 km (46.2%) were still in a natural state (Fig. 4).
Regarding habitat fragmentation, the number of LineStrings associated with coastal
alterations was 427, meaning there were overall 427 distinct sectors of the coastline, ofvariable length, presenting human-made alterations and contributing to the fragmentationof the natural coast. Of these, 229 were on the west coast and 198 on the east coast.
Interestingly, while land-filled LineStrings had the largest mean length (169 LineStrings,
mean length = 1.83 km, sd = 4.27 km), armored tracts with no land-filling, although

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36.8%NaturalSoft armoring
Hard armoring
Land-filling

45.3%
3.4%
14.5%

N
10 km
Base layer map data
© OpenStreetMap contributors

Figure 3 Map of human-made alterations to the Okinawa Island coastline. Different alteration categories are represented by different colors and summarized in the pie chart, which shows their relative
abundances (%). Base layer map data c OpenStreetMap contributors.
Full-size DOI: 10.7717/peerj.7520/fig-3

shorter, were more numerous (258 LineStrings, mean length = 0.48 km, sd = 0.54 km; see
Table 1 for split data between soft and hard armoring).
The natural coastline was composed of 238 LineStrings. The mean length of natural
LineStrings was 1.05 km (sd = 1.78 km). In other words, on average, a tract of natural
coastline in Okinawa Island was found to be interrupted by coastal armoring or land-filling
every 1.05 km. The natural coastal environment was more fragmented in the west coast,
where 96.1 km were composed of 129 distinct LineStrings (mean length = 0.75 km, sd= 1.08 km). The east coast had instead lower levels of fragmentation: 109 LineStrings for
154.8 km of natural coastline (mean length = 1.42 km, sd = 2.31 km). Overall, in the west
coast, the natural coastline was composed of more LineStrings of shorter mean length, andMasucci and Reimer (2019), PeerJ, DOI 10.7717/peerj.7520

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100%
90%

Coastline length (%)

80%
70%
60%

Land-filling

50%

Hard armoring
Soft armoring

40%

Natural
30%
20%
10%
0%

West coast

East coast

Figure 4 Coastal development categories divided between the east and west coasts of Okinawa Island.
Full-size DOI: 10.7717/peerj.7520/fig-4

Table 1 Summary of coastal alteration and fragmentation data.

West coast

East coast

Total coastline

NaturalSoft
armoring

Length (km)

96.1

12.2

% of West coast

27.7

3.5

LineStrings number

129

32

LineStrings mean length (km)

0.75

0.38

Standard deviation (km)

1.08

0.29

Length (km)

154.8

11.5

% of East coast

46.2

3.4

LineStrings number

109

31

LineStrings mean length (km)

1.42

0.37

Standard deviation (km)

2.31

0.31

Length (km)

251.0

23.7

% of Total coastline

36.8

3.5

LineStrings number

238

63

LineStrings mean length (km)

1.05

0.38

Standard deviation (km)

1.78

0.30

Hard
armoring

Landfilling

Total
altered

52.8

186.3

251.4

15.2

53.6

72.3

110

87

229

0.48

2.14

1.10

0.62

5.66

3.60

46.1

122.9

180.5

13.7

36.6

53.8

85

82

198

0.54

1.50

0.91

0.55

1.90

1.37

98.9

309.2

431.8

14.5

45.3

63.2

195

169

427

0.51

1.83

1.01

0.59

4.27

2.79

therefore was more affected by habitat fragmentation (Fig. 5 and, for a summary of coastal
alteration and fragmentation data, Table 1).
The longest tract of uninterrupted natural coastline (10.71 km) was measured in thenortheast area of the island, in the Kunigami District (GPS = 26.844964, 128.296063–
26.794411, 128.317441). The same area hosted two additional tracts of similar length(∼10 km). The northeast of the island, from Teima, Oura Bay (GPS = 26.552018,
128.065038), to Cape Hedo (GPS = 26.875525, 128.257702), was overall the most preserved,

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12

A) West coast(mean length = 0.75 ± 1.08 km)

1110B) East coast(mean length = 1.42 ± 2.31 km)

9Length (km)

8
7

n=1

6

n=9

5
4
3
2
1
0
1

129

1

109

Number of natural LineStrings

Figure 5 Natural LineStrings in Okinawa Island and their length (km). (A) West coast. (B) East coast.
The horizontal dashed line highlights the presence of a single LineString above five km on the west coast,
compared to 9 LineStrings for the east coast.
Full-size DOI: 10.7717/peerj.7520/fig-5

with 82.7% of the coastline in a natural state (84.96/102.70 km). This same area also hosted
the majority of natural coastline tracts above five km (8 out of 10 totals, 9 of which wereon the east coast; Figure 5). For the west coast, the longest tract of uninterrupted natural
coastline (6.67 km) was in the Nakijin Area (GPS = 26.703180, 127.934848–26.696041,
127.971799) with no other tracts above five km in length.
The area of Okinawa Island at the end of year 2018 was measured at 1213.35 km2 , 5.35
square kilometers more than reported in the Japan Statistics Bureau (2014). This number
includes land-fills detached from the main coastline (from ∼100 m to ∼1,000 m distancefrom shore), and connected to it via multiple bridges: on the west coast the Toyosaki land-fill(Tomigusuku; 1.41 km2 ; GPS = 26.156254, 127.654746), on the east coast, from north tosouth, the Suzaki land-fill (3.47 km2 ; GPS = 26.333432, 127.855115), the Awase land-fill(measured at 0.93 km2 , reclamation works still ongoing; GPS = 26.303966, 127.840715),
and the Agarihama/Agarizaki land-fill (1.14 km2 ; GPS = 26.207607, 127.765247). In 1977,
the measured area was 1,192.32 km2 . Hence, the island’s expansion, accountable to theland-filling projects performed over a period of 41 years, was measured at 21.03 km2 , themajority of which have occurred in the southern part of the island on both the east andwest coasts: 18.83 km2 , or ∼90% of the land-filled area was located south of the Tancha,
Onna Village and Yaka, Kin Town districts (Fig. 6). On the west coast, the area surrounding
Naha, the prefectural capital has been particularly affected by coastal land-filling: from
Itoman (GPS = 26.114724, 127.664448) to the Kadena US military base (GPS = 26.339156,
127.746935) the entire coastline (112.2 km) was altered, and 107 km of its length werecategorized as land-filled (∼95%).

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A

B

Tancha

Yaka

N
10 km
Base layer map data (2018)© OpenStreetMap contributors

N
10 km
Base layer map data (2018)© OpenStreetMap contributors

Figure 6 Map of the land-filling that occurred in Okinawa Island over a period of 41 years (1977–2018). (A) South part of Okinawa Island (south of Tancha and Yaka). Base layer map data (2018) c
OpenStreetMap contributors. (B) North part of Okinawa Island (north of Tancha and Yaka). The areafrom 1977 is colored in grey, newer expansions from 2018 are highlighted in red. Base layer map data
(2018) c OpenStreetMap contributors.
Full-size DOI: 10.7717/peerj.7520/fig-6

DISCUSSION
The results of this study revealed that over 63% of the original Okinawan coastline has
been lost or altered by numerous coastal engineering projects, and that what remains is
now fragmented into numerous segments divided by land-filled and armored tracts.
Land-filling, or land reclamation, was found to be the main contributor to the amount ofcoastline alterations (45% of the total coastline), especially in the highly urbanized south of
the island, where the capital city Naha and most of the population are located. Reclamation isa direct cause of habitat loss, in particular for coral reefs and mangrove meadows. Although
habitat loss as a problem is not unique to Okinawa, the situation in Okinawa Island isnoteworthy, for at least two reasons: between 1993 and 1998, the largest increase (47.99%)
in the amount of artificial coastline in Japan occurred in Okinawa Prefecture (Biodiversity
Center of Japan, Ministry of the Environment, 1998). Secondly, unlike mainland Japan,
Okinawa Island is subtropical, characterized by the presence of a well-developed fringing
reef along its coastline (Reimer et al., 2019). Construction has mainly happened in theshallow waters of the inner reef, over lagoons and reef flats. Being located in the vicinityof river mouths or in the inner reef, mangrove forests and seagrass meadows have also
been targets of development. In a coral reef environment, reef formations themselves are
an important element in the protection of the coastline: according to Ferrario et al. (2014),
coral reefs can provide significant protection from storms, dissipating on average 97% ofwave energy. The economic benefit of the coastal protection provided by Japanese coral
reefs has been estimated to be of 172 million USD/year (Cesar, Burke & Pet-Soede, 2003),
but by reclaiming shallow reefs, this ecosystem service is inevitably lost, leaving the coastline
more vulnerable and in need of artificial protection.
Similarly, seagrass meadows and mangrove forests are known to provide important
ecosystem services: both, particularly seagrass meadows, act as nurseries for valuable fish
species (Whitfield, 2016 provides a review on the topic). Moreover, mangrove forests offer

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valuable protection from coastal disasters by significantly reducing economic and humanlife losses during storms and tsunamis (Das & Vincent, 2009). Kathiresan & Rajendran(2005) suggested the adoption of a dense buffer zone made of mangroves and othercoastal vegetation of at least one km between the ocean and the first human settlements
at Parangipettai, Tamil Nadu, India. However, in Okinawa Island, numerous roads andbuildings have been built just a few meters from the coastline. Several coastal roads havesuffered the effects of erosion or damage due to their proximity to the ocean. In a few cases,
access had to be restricted, or expensive repairs and improvements have been required forthe road to remain functional, usually in the form of additional armoring (Nakano, 2004).
In the northwestern part of the island, despite this being a rural area of low population
density (0–100 residents/km2 ; Okinawa Prefectural Government, 2019b) with abundant
space available to build roads, National Route 58 runs for kilometers just a few metersfrom the coastline (Fig. 2C). This route was built so close to the ocean that it required theemployment of hard armoring, usually in the forms of seawalls and tetrapods, tetrahedral
blocks of various sizes made of concrete placed in front of seawalls or piled up to form
breakwaters (Hesse, 2007). This combination of coastal roads coupled with seawalls andconcrete blocks have altered several tracts of natural coastline in Okinawa Island. In the caseof National Route 58 and also in the north Kunigami Area, the artificial landscape extends,
with only sporadic interruptions, from the northern part of the Motobu Peninsula (GPS:26.630022, 128.029791) until Ginama Fishing Port (GPS: 26.848042, 128.253570), after
which the route deviates from the shoreline. In the same northern region, but on the east
coast, National Route 70 connects the north and the south of the island. Because National
Route 70 was built inland, leaving a buffer space of vegetation between the road itself
and the shoreline, the natural profile of the original coastline has been largely preserved(Fig. 2A). This is an important example of how different engineering approaches to similar
problems can affect the environment in different ways. The different state of the east andwest coasts of the north Kunigami Area shows that it is possible to build roads without
sacrificing the natural coastline. In a subtropical island where tourism is the most importanteconomic asset, and the local government aspires to become a World Natural Heritage Site
(Okinawa Prefectural Government, 2019c), there should be a strong government interest inlimiting the loss of beaches and natural scenery.
Although coastal armoring exerts impacts on the natural environment (Seitz et al., 2006;
Sane et al., 2007; Dugan et al., 2008; Dethier, Toft & Shipman, 2017; Gittman et al., 2016;
Aguilera, 2017), beyond habitat loss and fragmentation it is unclear how it can affect thegeneral health of a coral reef ecosystem, or how communities inhabiting the surroundingsof coastal armoring compare with those inhabiting natural areas. If artificial barriers actively
harm corals and the wider coral reef community, then armoring a coastline would mean,in the long term, an increase in artificial defense at the expense of the protection alreadynaturally provided by the reef. Therefore, future research should investigate in detail how
shoreline armoring affects coastal ecosystems. Japan is an ideal candidate for such study, as
tetrapods have been widely deployed across different prefectures (Kerr, 2001), and yet very
little international peer-reviewed studies on their effects on marine communities have been

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published. It is clear that more research is needed to fill gaps in our knowledge, on thisissue and with other coral reef conservation concerns in the region (Reimer et al., 2019).
The overall benefits of the Japanese coral reefs have been estimated as equivalent to1665 million USD/year (Cesar, Burke & Pet-Soede, 2003). Realizing the importance of ahealthy reef ecosystem, since 2012, the Okinawa Prefectural Government has been investing
significant resources in coral reef restoration (6.25 million USD for the first three years of
implementation; Okubo & Onuma, 2015). However, reef restoration still provides benefits
estimated to be six orders of magnitude lower than the amount of damage occurring(Okubo & Onuma, 2015), and restoration results are often uncertain and, in some cases,
counterproductive (Casey, Connolly & Ainsworth, 2015). For these reasons, as progress ismade in restoration research and public money is invested on the effort, it is important toalso better integrate conservation concerns into development plans in order to spare reefs
from further destruction. Finally, it is noteworthy, in this context, that the national action
plan for the conservation of Japanese coral reef ecosystems (Ministry of the Environmentof Japan, 2010) mentions coastal development as a cause of habitat loss and coral reef
mortality, and proposes the establishment of Marine Protected Areas (MPAs) and nationalparks in coral reef regions as a solution. However, as of June 2019, no Marine Protected
Area exists in Okinawa Island.

CONCLUSIONSThe coast of Okinawa Island has been subject to significant alterations leading to habitat
loss (63.2% of the coastline artificially altered) and fragmentation (remaining coastline
divided in 239 distinct tracts of mean length = 1.05 km). As hypothesized, the west coasthas been the most impacted by human development.
It is our opinion that the northeast Kunigami coast of the island should be considered
as an MPA candidate, being located in an area of low human population, with a relatively
pristine coastline, both in terms of amount and fragmentation, and with a biodiversity thatis still largely understudied (Reimer et al., 2019).
In the future, coastal restoration/rehabilitation initiatives will need to be evaluated. We
live in an era of unprecedented attention to environmental issues. In Singapore, a country
where less than 20% of the coastline remains natural, mangroves have been planted with
the intent of rehabilitating artificial habitats (Lai et al., 2015) and research has been made tocreate more variable armored intertidal zones (Loke et al., 2014; Loke et al., 2015). Several
states in the US, such as North and South Carolina, have restricted or banned the use ofadditional coastal armoring and are planning or have performed block removals (Kerr,
2001; Miller et al., 2012; Dethier, Toft & Shipman, 2017). The ‘‘soft armoring’’ category of
our map includes several locations where restoration activities could be feasible. In someinstances (Fig. 2C) such works would be limited to the removal of old walls no longer
used, reducing habitat fragmentation and restoring connectivity between land and ocean.
Such restoration activities would benefit species that depend on ocean-land connectivity
and have been impacted by habitat loss and fragmentation, like sea turtles for their nesting(Rizkalla & Savage, 2010), and coconut crabs to release fertilized eggs (Sato & Yoseda,

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2013). Walls and barriers built years ago to protect buildings that are now abandoned,or roads no longer used and overgrown by vegetation could also be included in similar
initiatives. It is anticipated this work will focus attention on the current status of the
Okinawa Island coastline and be utilized as a tool for further evaluations and monitoring,
tracking changes in time and allowing comparisons with other regions, in Japan or abroad.

ACKNOWLEDGEMENTS
The authors would like to thank Masaru Mizuyama for his suggestions that greatly
contributed to the improvement of this work, Zax Zeng from Duwei Technology forproviding help on acquiring and geotagging historical aerial photography data, Kohei
Hamamoto for his help in translating parts of the cited Japanese literature, and Piera
Biondi for her comments on early versions of the manuscript. We would like to thank the
OpenStreetMap, QGIS and R software communities, whose hard work made this researchpossible. Comments and suggestions from Dr. Mariko Abe and two anonymous reviewers
greatly improved an earlier version of this work.

ADDITIONAL INFORMATION AND DECLARATIONS
Funding
The authors received no funding for this work.

Competing Interests
James D. Reimer is an Academic and Section Editor for PeerJ.

Author Contributions• Giovanni Diego Masucci and James D. Reimer conceived and designed the experiments,
performed the experiments, analyzed the data, contributed reagents/materials/analysis
tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved
the final draft, final English check.

Data Availability
The following information was supplied regarding data availability:
The raw data (GIS vector shape files) are available in Dataset S1. Dataset S1 includes
LineStrings divided per category, and Polygons representing the whole Area of Okinawa
Island in 2018 and 1977.

Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.7520#supplemental-information.

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