Deterioration of Coastal Ecosystem: A Case Study of the Banana Bay Ecological Reserve in Taiwan

Abstract

Due to the increasing pressure on the environment from human activities, there is a growing need to understand the relationship between species and the environment. Therefore, this study constructs life cycle and niche from a geographic perspective, aiming to explain how existing spatial configurations affect the deterioration of coastal ecosystems. This research mainly adopts the method of literature analysis and field investigation, and then carries out four steps of reading, sorting, integration and analysis. In this study, the road kill data and living environment data of land crabs were integrated, and two results were obtained on the relationship between spatial conflict areas and land crab populations. The first is that the life cycle of land crabs is disturbed by TPH 26, thus confirming the spatial conflict hypothesis; the peak period of traffic flow at TPH 26 overlapped with the peak period of land crab larvae release, indicating that the spatial configuration of the reserve is not only a spatial conflict, but also a spatial-temporal conflict. Second, the land crab is an important indicator of coastal forests, and its niche also reflects geographic diversity, especially in features such as topographic structure, geological stability, and environmental humidity.

1. Introduction

Tropical islands have been a focal point of the study of biological evolution since Charles Darwin. Island biogeographic theory suggests that a key feature in predicting species richness is the tendency of some particular areas to have more species than others [1,2]. This concept advances the understanding of the geographic pattern and dynamic distribution of species abundance as a quantitative approach [3]. Since it was proposed half a century ago, the theory has attracted many researchers to test the validity of its models and the distribution of biodiversity on a global scale; it shows that with optimized data and analytical tools, its assumptions can be tested more accurately [4,5]. However, the impact of biogeographical processes on small-scale habitats remains largely unexplored beyond macroscopic analysis. Understanding the mechanisms that generate diversity patterns requires analysis at both spatial and temporal scales to understand the dispersal capabilities and ecological requirements of organisms [5].

Published studies have pointed out that biodiversity is the result of global, as well as regional and local, processes and that to conserve the biodiversity of one biogeographic realm might require the conservation of processes of others as well, both wet and dry, and the coastal zone unifies the two, but it is not merely a narrow transition between dry and wet [6]. In Japan, the “Mori wa Umi no Koibito” movement (hereafter referred to the as “Forest and Sea” movement), appeals to the need to think about environmental conservation from a continuous and integrated perspective of forests, rivers, and the sea [7,8]. However, the rapid development of the tropics has already greatly threatened the conservation of biodiversity, including the extinction of species [9], the reduction in forest areas, and the damage caused by population expansion [10,11]. The isolation and size limitation of small tropical islands makes them more likely to experience species extinction [12]. The ecological literature is full of examples of esoteric relationships between species that only become apparent when the decline or disappearance of one species has cascading adverse effects on others [13]. Although ecological reserves are one of the key human interventions in biological conservation [11], even a large protected area cannot be completely isolated, not to mention that a small protected area requires strict management to maintain the health of the ecosystem. Therefore, protected areas based on traditional biogeography must be supplemented by diversity-sensitive criteria [13].

Taiwan is located between the tropics and subtropics; although the land area is not large, it has both geographic diversity and biodiversity. Because of the action of tectonic plates and early glaciers, the whole island is covered with mountains and valleys; and the vertical height difference is nearly 4000 m. It has the characteristics of various climatic zones and a complex topography; it retains the characteristics of relict species of the Ice Age, has developed a diverse ecological environment, and is surrounded by the sea on all sides, nurturing a variety of habitat types and biological resources [14].

At present, the area that has been designated as a nature reserve in Taiwan is 6944 km², accounting for about 19.18% of the total land area of the island [15]. However, Taiwan is a high-mountain island with topographical features that are long from north to south and narrow from east to west; the plain area only accounts for 30% of the island [16], and due to topographic constraints, more than 90% of Taiwan’s population lives in the western plains [17]. Therefore, the high development of coastal plains and the establishment of protected areas along the coast mean that biodiversity conservation is subject to spatial tension and conflict. Published studies pointed out that humans are changing the earth system and these changes include habitat destruction, biotic homogenization, increased species invasions, and accelerated extinctions [18], more biodiversity hotspots and a higher plant extinction rate, mainly due to urbanization, agriculture and invasion [19].

Taiwan is a hotspot of biodiversity. Located in Kenting National Park in the southern part of the island, there is the only Banana Bay Ecological Reserve in Taiwan for the purpose of protecting coastal forests. In the small reserve, there are 115 species of woody plants, and more than 200 vascular plants and it is composed of typical seaside plants, tropical rainforest characteristic plants, monsoon forest acupuncture plants and common plants brought in by animals [20,21]. Therefore, the main characteristics of Banana Bay Reserve are small and high species diversity. However, in recent years, the forest in the reserve has seriously deteriorated, and measures must be taken to maintain the original appearance of the coastal forest. Causes of deterioration include invasive alien species [22], fructose nibbling, habitat fragmentation, and frequent typhoon disturbances [23]. Land crabs are an important species that inhabit coastal forests and affect the material cycle of coastal forest ecosystems. Since its staple food is the leaves, flowers and fruits of coastal forests, it is the dominant species in the plant community [24,25,26,27]. At present, there have been many research results on the reasons for the deterioration of vegetation in coastal forests. The road kill of land crabs is a significantly affecting the population of land crabs [28,29]. However, there are no relevant research reports on the relationship between land crabs and coastal forest flora succession [26].

Published studies on the road kill of land crabs, such as those comparing the size of land crabs in road kill areas and non-road kill areas, found that land crabs in road kill areas were smaller in size [29], Other studies compare the larger-scale habitat types, and analyze the relationship between land crabs and different types of tropical coastal forest recruitment [27].

However, from the qualitative point of view of island geography, food and niche are also factors that affect species diversity, but related research on land crabs is still lacking. Therefore, the aim of this study is to combine the structure of life cycles and niche from a geographic perspective and to explain how the existing spatial configuration affects the deterioration of coastal ecosystems. Spatial analysis of land-marine integration can contribute to integrative thinking.

2. Materials and Methods

2.1. Study Framework and Design

The field survey of this study found the phenomenon of road killing of land crabs and very few land crabs crossing the road (the survey time was 9:00–9:30 p.m., 15 September 2019, two days after the full moon). Hypothetically, it is the conflict between the spatial configuration of the road and the life cycles, such as the release and recruitment of land crabs, that may affect the ecosystem of coastal forests (Figure 1).

We cannot draw the micro-habitat map or spatial distribution map of land crabs because of their hidden living habits, and there is also a lack of spatial correspondence between coastal forests and land crabs. Therefore, this study made an integrated map of the spatial distribution of the existing land crab road kill data and the environmental description data of the land crabs’ location, and further explains the issue of land crab road kill and coastal ecosystem deterioration.

2.2. The Land Crabs in Hengchun Peninsula, Taiwan

The distribution of land crabs depends on specific geography [30,31]. The adult crabs need tropical, subtropical, island, and mainland habitats. The ovigerous crabs need to go between the land and the sea for larval release migration. The zoeal and megalops travel between the habitats along the ocean current. Therefore, the life cycle of land crabs reflects macroevolution [32,33]. The destruction of habitats is the main cause of biodiversity loss in tropical islands. Therefore, scholars call for geographical research that characterizes the ecological environment of the crab population [27,34,35].

Most land crabs studies on Banana Bay focus on species classification and characteristics [36], newly published species [37,38,39], comparison of regional differences in species [40]; as well as population and reproduction of a single species [41]. However, the study of life cycles has gained importance recently [42,43,44]. This shows that the ecological geography and microhabitat of land crabs have been given more attention.

The research objects include the following broad characteristics of land crabs: they are able to survive out of the water, need to migrate for larval release, can develop and grow in fresh water, have a high tolerance to environmental changes, burrow, and emerge in the daytime and at night [30,44,45,46,47,48]. There are 40 species of land crabs, belonging to 7 families in Hengchun Peninsula, Taiwan, with the highest species diversity among the known coastal forest habitats in the world [49,50]. However, the sharp decrease in population in recent years has attracted the attention of the ecological community; the results point to habitat destruction, human capture, climate change, and invasive species [51,52,53].

2.3. Study Area

The Hengchun Peninsula at the southernmost tip of Taiwan has a complex terrain, including various ecological habitats, and because it is the first thrust of the Kuroshio to the north, it is one of the areas with the highest marine biodiversity in Taiwan. The Banana Bay Reserve was established on the peninsula in 1973. It is also the only coastal forest reserve in Taiwan, with a total length of about 1150 m, a width of about 250 m, and an area of about 28 ha (Figure 2).

Banana Bay Ecological Reserve is located at 37–39.4 km of Taiwan Provincial Highway (TPH 26), and the terrain is northwest–southeast. The entire protected area is divided into two sections by TPH 26. The terrain in the northern section is a cliff and is bounded by TPH 26. The length along the boundary is about 1150 m, and the width on both sides is about 200 m. The middle section is narrower, with a width of about 120 m and an area of about 5500 m². The southern section extends seaward with TPH 26 as the northern boundary, with a length of about 650 m and a width of about 100 m [54].

Banana Bay Tropical Coastal Forest has a long history of protection. During the Japanese occupation, it was designated as a natural memorial forest in 1933. At that time, it was more than 10 km long from Eluanbi to Kenting, all covered with dense coastal forest. Since 1945, due to reclamation and construction, the forest land has been shrinking. In particular, in 1950, the coastal forests were reclaimed for hemp plantations to make ropes and burlap bags to supply the needs of Taiwan’s booming industries, and the coastal forests were destroyed.

In 1973, the coastal forest of Banana Bay was designated as a nature reserve, but in 1979, due to the construction of a nuclear power plant, the only road, which was originally 4 m wide, was widened to 20 m, and the coastal forest became even thinner. After the establishment of Kenting National Park in 1982, the remaining coastal forests were designated as a reserve. The land crabs in Hengchun Peninsula have attracted the attention of researchers since 1992, but the numbers of land crabs in Banana Bay have only been investigated since 1998 [55,56]. According to a literature review, 35 species of land crabs have been surveyed and registered over the years (Table 1). The survival range of these land crabs is concentrated in the 2 km (21°55′43″ N, 120°49′41″ E, 21°54′55″ N, 120°49′41″ E) from 39.5 km + 000 to 41.5 km + 000 on TPH 26. The species diversity of land crabs in this area is the highest in the same type of habitat in the world, and has the characteristics of a small population but with high diversity [26,51,53]. Even Christmas Island, which is famous for red crabs, has only 20 species of land crabs [57].

In terms of climate, Banana Bay belongs to the tropical monsoon climate zone, and the temperature and rainfall are similar to those of tropical rain forests [20]. In terms of topography, the northern section is a cliff topography, composed of uplifted high-level coral reefs. In the whole area, there are many large coral reefs that have collapsed or remnants, and the terrain is rugged. The southern section is the fringing reef terrain of the sea grooves, and between the sea grooves, there are coral skeletons, reef gravel and coarse-grained shell sand. Geologically, Banana Bay Ecological Reserve is located in a low-lying tectonic zone, a high-permeability sand dune cover, and a porous coral reef [54]. The bioclastic layer in the reserve provides a good living environment for land crabs, with caves for easy hiding. The protected area is located on the Hengchun Peninsula, at the junction of the Eurasian plate and the Philippine Sea plate. The continuous change in coral reef has, at different times, had different effects on the sea surface stagnation and plate extrusion caused by the sea formation platform, as we can observed from the profile map (Figure 3). The beach sand layer, bioclastic debris, and biodebris sedimentary surface layer are covered in turn [58].

Table 1. Land crab species investigated in the study area and their number of records (1998–2020).

Family	Species	Category of Living Environment	2002	2003	2007	2009	2010	2015	2019	2020	Total Number of Single Crabs	Total Number of Times the Crab Has Been Investigated
Gecarcinidae	Cardisoma rotundum	Terrestrial	352	377		160	182	37		9	1117	6
	Cardisoma hirtipes	Terrestrial	36	26	132	1	383	5	596	13	1192	8
	Cardisoma carnifex	Terrestrial			11	1			3	1	16	4
	Gecarcoidea lalandii	Terrestrial	53	420	4	329	227	12	185	168	1398	8
	Epigrapsus politus (2002)	Terrestrial	1		923	74	3	7	1	24	1033	7
	Epigrapsus notatus (1998)	Terrestrial	191		521	26	2	13	386	82	1221	7
Grapsidae	Geograpsus crinipes	Terrestrial	3	7		1	1	1	1	1	15	7
	Geograpsus grayi	Terrestrial	6	6		1	5	3	12	1	34	7
	Grapsus albolineatus	Terrestrial							3		3	1
	Geograpsus stormi	Terrestrial				1				1	2	2
	Metopograpsus thukuhar	Semiterrestrial				1	1				2	2
Sesarmidae	Labuanium scandens (2003)	Terrestrial	43	18		1	7	6	4	1	80	7
	Sesarmops impressum	Semiterrestrial	3	3	130	95	478	73	1085	8	1875	8
	Metasesarma obesum	Terrestrial	27	1		1	10	45	1	1	86	7
	Metasesarma aubryi	Terrestrial	1452	5438		1	3544	346	5166	1191	17138	7
	Parasesarma pictum	Semiterrestrial	1			1				1	3	3
	Steigistra stomi (1999)	Terrestrial	2							1	3	2
	Scandarma lintou (2003)	Terrestrial	13			1		7		1	22	4
	Chiromantes obtusifrons	Terrestrial	2			1	1				4	3
	Chiromantes eurymerus	Terrestrial								1	1	1
	Sesarmops intermedium	Terrestrial					1	1	9		11	3
	Geosesarma hednon (2004)	Terrestrial				1		1			2	2
	Lithoselatium pulchrum (1998)	Semiterrestrial					9	1			10	2
	Neosarmatium rotundifrons	Terrestrial				1	1				2	2
Coenobitidae	Coenobita brevimanus	Semiterrestrial	100			1	18	59	45	1	224	6
	Birgus latro	Semiterrestrial	3			1	1	1	2	1	9	6
	Coenobita rugosus	Semiterrestrial				1	1		30	10	42	4
	Coenobita cavipes	Semiterrestrial				1	1		62	1	65	4
	Coenobita violascens	Semiterrestrial						7			7	1
Varunidae	Varuna litterata	Aquatic						9	9	1	19	3
Ocypodidae	Ocypode sinensis	Terrestrial			1141	263		0	3		1407	4
Potamidae	Geothelphusa albogilva (1994)	Terrestrial			9	1	1	101	91	1	204	6
	Eriphia sebana	Terrestrial						1	1		2	2
	Candidiopotamon rathbunae	Semiterrestrial				1	1	18		1	21	4
	Geothelphusa ferruginea	Aquatic				1	1			1	3	3
	Total crab number of the year		2288	6296	2871	968	4879	754	7695	1522
	Total species of the year		17	9	8	27	23	23	21	25

(Note: data from [42] (2002, 2003); [59] (2007, 2009); [51] (2010); [52] (2015, 2019); [53] (2020)).

Table 1. Land crab species investigated in the study area and their number of records (1998–2020).

Family	Species	Category of Living Environment	2002	2003	2007	2009	2010	2015	2019	2020	Total Number of Single Crabs	Total Number of Times the Crab Has Been Investigated
Gecarcinidae	Cardisoma rotundum	Terrestrial	352	377		160	182	37		9	1117	6
	Cardisoma hirtipes	Terrestrial	36	26	132	1	383	5	596	13	1192	8
	Cardisoma carnifex	Terrestrial			11	1			3	1	16	4
	Gecarcoidea lalandii	Terrestrial	53	420	4	329	227	12	185	168	1398	8
	Epigrapsus politus (2002)	Terrestrial	1		923	74	3	7	1	24	1033	7
	Epigrapsus notatus (1998)	Terrestrial	191		521	26	2	13	386	82	1221	7
Grapsidae	Geograpsus crinipes	Terrestrial	3	7		1	1	1	1	1	15	7
	Geograpsus grayi	Terrestrial	6	6		1	5	3	12	1	34	7
	Grapsus albolineatus	Terrestrial							3		3	1
	Geograpsus stormi	Terrestrial				1				1	2	2
	Metopograpsus thukuhar	Semiterrestrial				1	1				2	2
Sesarmidae	Labuanium scandens (2003)	Terrestrial	43	18		1	7	6	4	1	80	7
	Sesarmops impressum	Semiterrestrial	3	3	130	95	478	73	1085	8	1875	8
	Metasesarma obesum	Terrestrial	27	1		1	10	45	1	1	86	7
	Metasesarma aubryi	Terrestrial	1452	5438		1	3544	346	5166	1191	17138	7
	Parasesarma pictum	Semiterrestrial	1			1				1	3	3
	Steigistra stomi (1999)	Terrestrial	2							1	3	2
	Scandarma lintou (2003)	Terrestrial	13			1		7		1	22	4
	Chiromantes obtusifrons	Terrestrial	2			1	1				4	3
	Chiromantes eurymerus	Terrestrial								1	1	1
	Sesarmops intermedium	Terrestrial					1	1	9		11	3
	Geosesarma hednon (2004)	Terrestrial				1		1			2	2
	Lithoselatium pulchrum (1998)	Semiterrestrial					9	1			10	2
	Neosarmatium rotundifrons	Terrestrial				1	1				2	2
Coenobitidae	Coenobita brevimanus	Semiterrestrial	100			1	18	59	45	1	224	6
	Birgus latro	Semiterrestrial	3			1	1	1	2	1	9	6
	Coenobita rugosus	Semiterrestrial				1	1		30	10	42	4
	Coenobita cavipes	Semiterrestrial				1	1		62	1	65	4
	Coenobita violascens	Semiterrestrial						7			7	1
Varunidae	Varuna litterata	Aquatic						9	9	1	19	3
Ocypodidae	Ocypode sinensis	Terrestrial			1141	263		0	3		1407	4
Potamidae	Geothelphusa albogilva (1994)	Terrestrial			9	1	1	101	91	1	204	6
	Eriphia sebana	Terrestrial						1	1		2	2
	Candidiopotamon rathbunae	Semiterrestrial				1	1	18		1	21	4
	Geothelphusa ferruginea	Aquatic				1	1			1	3	3
	Total crab number of the year		2288	6296	2871	968	4879	754	7695	1522
	Total species of the year		17	9	8	27	23	23	21	25

(Note: data from [42] (2002, 2003); [59] (2007, 2009); [51] (2010); [52] (2015, 2019); [53] (2020)).

2.4. Study Method: Literature Analysis and Field Investigation

This study mainly uses the literature analysis method. The main documents collected include survey reports, books, journals and academic papers, etc. Then, we proceeded with the following four steps: reading, sorting, integration and analysis. The survey time was 9:00–9:30 p.m., 15 September 2019, two days after the full moon. The latest research has proposed a spatial distribution map of the dominant land crab species (at the macroscale) [53]. However, the textual descriptions of the living environments of different land crabs are scattered in the research of different disciplines, and there is still a lack of further research and graphic descriptions of land crabs’ microhabitats (at the microscale). The literature used in this study is shown in Table S1. The most important information is the land crab roadkill achievement report completed in 2019 [52]. This report records all land crab road kill data from 26 June 2019 to 28 November 2019, which are the only land crab road kill survey data so far. In order to construct the habitat of land crabs in Banana Bay Reserve, it is necessary to integrate the spatial distribution of the living environment of land crabs from the scattered data (

Table 2. Description data of the living environment of land crabs.

Family	Species	Microhabitat Factor	Notes
Gecarcinidae	Cardisoma rotundum	Distribution is limited by the coastal vegetation of the reef [60]; it inhabits the coastal shrub belt and coastal forest [59].
	Cardisoma hirtipes (Discoplax hirtipes)	It lives in the reef and coastal forest [60]; inhabits land near the inland waters, 0.62 km from the sea [52]; inhabits a muddy environment, digging deep holes to live in, all the way to where there is groundwater [59]. Caves appear near water, including coastal forests, banana plantations, and roadsides, and the water at the bottom of the cave is freshwater [51]. Nests are often found in deciduous and fruit-rich environments, and the tree species investigated include Amaranth, Macaranga tanarius, Hibiscus tiliaceus, Pandanus odoratissimus, Ficus septica, etc. [43].	n = 989 (2017), (12 days) n = 486 (2018), (9 days) n = 596 (2019), (18 days)
	Cardisoma carnifex	The habitat is closer to the sea and located near the grass or some estuary meadows of coastal forests, but there are also individuals living in coastal forests, currently recorded as far away from the sea as 300 m [52]; inhabiting a muddy environment [60]; the cave is very deep, all the way to where there is groundwater [59]; the water in the cave is brackish or pure freshwater [51].	70.5 ± 6.6 mm (2009, 2010) 80.0 ± 8.3 mm (2015)
	Gecarcoidea lalandii	It inhabits coastal shrub and coastal forest, 3.35 km from the sea [52]. It prefers to live in coastal forest with coral reef limestone, hide under the limestone reef, or dig holes to live in; the holes are dry and waterless [51,59].	n = 386 (2003) 57 ± 7 mm n = 227 (2010) n = 146 (2019) 53.4 ± 7.2 mm
	E. politus	The distribution is limited by the coastal vegetation of the reef, perched on the outskirts of the coastal forest, under ready-made high coral reef caves and shallow rocks, rarely digging [60]; inhabiting the pores or reefs of coastal thickets and edge rocks or coral reefs, usually not more than 50 m away from the sea pass [51,52].
	Epigrapsus notatus	The distribution is limited by the coastal vegetation of the reef, perched on the outskirts of the coastal forest, under ready-made high coral reef caves and shallow rocks, with some digging [60]; inhabits many coral reef rock formations under coastal thickets and coastal forests, the furthest from the sea being about 0.5–1 km away [52]; some dig holes to live in, or perch under a reef [51,59]. Most captured males are found by turning rocks in the forest, but females can be easily found in the littoral zone during larval release period [41].
Grapsidae	G. cranipes	The microhabitat is located from the high tide line to the coastal shrub area, and does not include the coastal forest. The distance from the habitat to the sea is usually less than 50 m [51,52].
	Geograpsus grayi	The habitat is quite complex, including coastal forest, coastal shrub, and coastal grasses. Generally, they live in places where there are many rocks and coral reefs. They usually hide under reefs or in crevices between reefs. They are the species that can live the farthest from the sea. At present, the maximum recorded distance from the sea is 400 m [52,53,60].
	Grapsus albolineatus	Species that inhabit the high tide line of the reef coast and hide in the pores of the reef [52].
	Geograpsus stormi	It lives near the high tide line and in the pores of coral reefs. It is the closest species to the sea [51,52].
	Metopograpsus thukuhar	Inhabits crevices or lives under rocks from the intertidal zone to low tide line.
Sesarmidae	Labuanium scandens	Inhabiting caves in coastal forest trees, it is an indicator species of mature coastal forests [51] and must go to the beach to release the larvae [59].
	Sesarmops impressum	Lives in a fresh water environment near the sea [51,59], including pools above the high tide line in coastal areas and streams or pools near the coast. At present, the farthest distance recorded from the sea is 1.3 km. They are semiterrestrial crabs, hiding underwater or in riparian stone pores, or digging holes in the riparian habitat [52].	30.5 ± 4.6 mm (2013) 29.0 ± 4.1 mm (2019)
	Etasesarma obesum	It is distributed under the coastal shrub and the edge of the coastal forest near the sea, and its habitat density is higher under the coastal forest with many coral reefs [51,59].
	Etasesarma aubryi	They live under the coastal forest, in the crevices of coral reef limestone, under fallen trees, or near the roots of big trees [51,59]. They also dig caves in muddy soil to inhabit. They can live in coastal forest 180 m away from the sea, but only a few large individuals can cross the road to the coastal forest on the inland side. In dry season, they will hide in deeper caves; in the rainy season, they often leave the caves and hide in fallen leaves [52].
	Parasesarma pictum	It inhabits gravel areas near the high tide line of a reef coast, estuary, or mangrove swamp; under the stones or among forest leaves and other deposits, and rarely digs holes.
	Steigistra stomi (1999)	Not recorded yet.
	Scandarma lintou	The Lintou land crab inhabits the shrubbery under coastal forests, especially in the base of the hydrops petiole of Lintou and Gupo taro or in dead branches and leaves [59].
	Chiromantes obtusifrons	It inhabits the coastal shrubbery area between the high tide line and the edge of the coastal forest, or in the crevices of reefs or under rocks [59].
	Chiromantes eurymerus	Not recorded yet.
	Sesarmops intermedium	Lives in estuaries or coastal wetlands, not too far away from fresh water [51,59]; the habitat can be as far as 3.5 km from the sea [52].
	Geosesarma hednon	Not recorded yet.
	Lithoselatium pulchrum	Inhabits the reef near the high tide line of the reef coast and the gap between the rocks above [37].
	Lithoselatium pulchrum	Not recorded yet.
Coenobitidae	Coenobita brevimanus	It lives inland and often appears under coastal forest [52].
	Birgus latro	It lives in the coastal forest of coral reef and limestone.
	Coenobita rugosus	It inhabits the high tide line of sandy or gravel beach to the coastal shrub area [52].
	Coenobita cavipes	It lives inland and is often found on the edge of coastal forest [52].
	Coenobita violascens	It lives in underground spring areas [52].
Varunidae	Varuna litterata	It prefers to live in a watery environment and only crawls out of the water to cross the road when breeding at the sea. The microhabitat includes the pool above the high tide line in the coastal area, and it also inhabits the middle and lower reaches of the river. At present, the farthest distance recorded from the sea is 19.5 km [52].
Ocypodidae	Ocypode sinensis	The habitat extends from the upper part of the high tide line to the grass growing area, the shrub area, and the sandy land under the coastal forest. Living in caves, hiding in caves during the day, going out at night; omnivorous [52,53,60].
Potamidae	Geothelphusa albogilva	It lives in inland forest [52]. Adult crabs can be found near the water in the dry season and they live at the bottom of the forest in the rainy season [59]. They do not need to go to the seaside to release larvae, and sometimes can be found in streams [59].
	Eriphia sebana	Lives near the high tide line of reef coasts and hiding in reef pores [52].
	Candidiopotamon rathbunae	They live near freshwater streams and often move out of water at night. They can also be seen on roads near streams [59].
	Geothelphusa ferruginea	They live in caves under rocks beside streams.

); and then, once integrated with the road kill data, it can become a spatial distribution map.

3. Results

3.1. Not Just a Spatial Conflict, but a Spatial-Temporal Conflict

Kenting National Park is an international tourist hotspot because of its tropical landscape conditions, attracting more than 4 million visitors a year since 2000 and 8.3 million in 2014 alone, with an average annual traffic volume of about 630,000 vehicles (includes buses, vans, sedans, and motorcycles) (Figure 4). The main means of transport are private cars and motorcycles, and the only way to get around is the TPH 26. According to the report in 2010 and 2011, April (spring music festival) and July–September (summer vacation) are peak periods for tourists and traffic in Kenting National Park (Figure 5) [61,62]. The larvae release period of female crabs is from May to September (the start time depends on the rainy season) [43]. It shows that the peak traffic period and the larvae release period highly overlap.

Every year, when ovigerous land crabs embark on their larval release migration (May–October), many are killed on the road in the Banana Bay section. According to the latest report from 2019, more than 50 species of animals have been killed on the road, with a total number of 3315 (

Table 3. Investigation of all roadkill incidents at Banana Bay in 2019.

	Content	Species	Roadkill	Percentage
Type
Land crabs		19	3210	96.83
Reptiles		11	47	1.42
Birds		9	25	0.75
Mammals		6	22	0.66
Amphibians		1	6	0.18
Others		4	5	0.15
Total		50	3315	100.00

(Note: data from [52]).

), including 3210 land crabs. Land crabs, thus, accounted for 96.84% of all roadkill species, and the number of ovigerous crabs (n = 802) accounted for 24.98% of all land crabs killed on the road (Figure 6). Comparing the road kill data of land crabs in 2010 and 2019, it shows that land crabs with large populations also have high road kill rates, such as Metasesarma aubryi and Sesarmops impressum. It is also worth paying attention to species such as Cardisoma hirtipes, Gecarcoidea lalandii, Sesarmops impressum, etc., as the total number of road kill and the number of road-killed ovigerous crabs were high for these land crabs in both years. According to public research reports, the road kill hotspots for these three types of land crabs are all on the mountainside of the road in the spring water area [52], as the living environment characteristics of these three types of land crabs mean that they rely on spring water, so they must cross TPH 26 to release larvae Metasesarma aubryi is the dominant crab species in the reserve, and its road kill hotspot is on the road of the mountainside. Because of its terrestrial characteristics, large individuals will cross TPH 26 to inhabit the coastal forest on the inner side of the road and choose a dry place to hide [52]. The above shows the spatial correlation between the road kill hotspots of land crabs and their microhabitat characteristics.

According to the traffic flow survey on 26 August 2019, 7:45–8:45 p.m., there were 7 buses, 138 private cars, and 65 scooters in 1 h, with a total of 210 trips, with an average of 3.5 trips per minute passing through the Banana Bay section [63]. The study found that the average time for female crabs to cross the road was 4.37 min. [43]. In other words, during the time when the female crab crosses the road, it must pass the obstacle of 15,295 vehicles before it can cross the road. At present, the National Park implements traffic control measures from July to September during the peak period of land crab larvae release, that is, three days before and after the full moon, a total of 9 days, every day from 18:30 to 20:30, reducing the road width to 8 m and the traffic must stop for 10 min and are able to drive through for 10 min [64]. However, research from South Korea pointed out that during the high tide, vehicles should be prohibited from evening to midnight, which can improve the survival ability of land crab populations [28].

In this study, the road kill data and living environment data of land crabs were integrated (Figure 7), which provided two results regarding the relationship of the spatial conflict zone and the population of land crabs. (1) According to the integrated graph of living environment and road kill data, the ratio of road kill numbers of mountainside to coast land crabs is 2:1 (2112:1098). (2) The omnivorous biological nature of land crabs is the main cause of road kill [52], which can be inferred from the high mortality (n = 702) of hermit crabs, living on both sides of the road. Since land crabs are mostly omnivorous, the smell of road-killing animal carcasses will attract land crabs (especially hermit crabs, n = 669) to forage, thereby aggravating the road-killing of land crabs.

This study found that the road kill rate of land crabs that inhabit the mountain side of the protected area was twice that of the coast. The main reason is that the life cycle of land crabs that inhabit the mountainside must undergo a bidirectional transition of freshwater, brackish water and salt water, and this life cycle is disturbed by TPH 26, thus confirming the spatial conflict hypothesis. In addition, the peak period of traffic flow on the TPH 26 overlaps with the peak period of land crab larvae release, indicating that the current spatial configuration of the ecological reserve is not only a spatial conflict, but also a spatial-temporal conflict.

3.2. Constructing the Life Cycle and Niche of Land Crabs

3.2.1. Life Cycle of Land Crabs: Messengers between Tropical Islands

The life cycle of land crabs is mainly a cyclic process, linking the reproductive and breeding phases [65], planktonic larval phase [45], and molting [66]. The breeding female crabs will hold the eggs (ovigerous crabs) until the eggs are mature (larvae) and start to migrate to the seaside to release them (larvae release). As soon as the eggs touch the sea water, they will crack and become zoeal. If the timing of releasing the eggs is missed, reproduction will fail. Most land crabs have the same sort of aquatic larval development as their marine ancestors, with several zoeal stages, and come ashore as megalops or in the first crab stages [30]. During the molting process of zoeal into megalops, they develop in the ocean and usually drift with ocean currents. The megalops must go through several molts to become baby crabs and find a suitable habitat, then go ashore [31].

The life cycle of land crabs is dynamic and is closely related to their niche (Figure 8). Land crabs transition from marine plankton larvae (zoeal), to life in the benthic (megalops), to larvae, to baby crabs in inland brackish water (CW < 10 mm), to adult crabs on land, and through the breeding phase (mating), where female crabs undertake larval release migration to the sea during the annual rainy season, and complete their life cycle via the process of sea–land transition [43,60]. Among the land crabs living in the coastal forests of Banana Bay, except for the four species of the family Potamidae, the larvae from the eggs of the other land crabs must live a planktonic life in the ocean, and turn into megalops after molting, and then return to land in the baby crab stage [52].

Ovigerous crabs migrate to the coast for larvae release, allowing land crab plankton to spread across vast tropical islands, such as Guam in the western Pacific and Malpelo Island in the eastern Pacific, as well as Clipperton Island, Socorro Island, Jamaica [67,68,69,70], Australia’s Christmas Island [57], and Japan’s Ryukyu Islands [71,72]. The role of land crabs as messengers in the marine space can be determined from their geographical distribution [73].

The geographical location of the Hengchun Peninsula is not only connected to the Pacific islands in terms of space, but is also interwoven with island characteristics and the geographical edge of the tropical north. It is also located in an important position for the propagation chain of land crabs; the research points out that temperature is an important survival index of planktonic larvae [73]. The larvae of the forest crabs in the non-release season collected in 2010 are presumed to arrive from Southeast Asia along the warm Kuroshio [42]; and the idea that the Kuroshio can transport the larvae from Southeast Asia to Taiwan and Japan has been confirmed [74,75,76]. The relative stability of the physical and chemical environment in the oceans is good for the spread of larvae over long distances [77], so most land crab larvae can make connections in vast tropical islands. A study has compiled the distribution of six species of land crabs in India and the Western Pacific [60], while the new species of land crabs on the Hengchun Peninsula have a highly correlated geo-relationship with the Philippines and Indonesia [39].

However, in the early stages of life, land crabs are faced with new ecological conditions and selection factors. For example, the brackish water seedbed is a typical transient and heterogeneous habitat, with unpredictable and fluctuating abiotic conditions [32] and it was around 5–10 years before the emergence of a land crab population was documented [78,79,80]. The population recruitment of land crabs is extremely unstable, which may be related to several factors, for example, a large number of larvae come ashore in a large tide [60]. Environmental factors, such as low water temperature, mold infection, and water quality, can cause marine plankton larvae to fail to develop and die [81,82,83]. The development of land crab embryos is greatly affected by temperature [65]. The population recruitment of land crabs is limited by various conditions and is unpredictable, so it is difficult for the population to recover once the population ecology disappears [66]. Compared with land crabs living in estuaries or sand banks, the larvae of land crabs in the supratidal zone find it more difficult to return to the land [42].

3.2.2. The Niche of Land Crabs

Studies on European green crabs pointed out that environmental factors affect species’ habitat selection, use, and distribution in diverse spatial scales [84]. The environmental characteristics of land crabs in Banana Bay Reserve include benthic topography (depth, hiding place), biological characteristics (vegetation, food source, and activity), and hydrology (salt water, brackish water, fresh water, dissolved oxygen, annual average humidity, and monthly average evaporation). The results show that the surface of the habitat and the microhabitat of various land crabs are arranged according to the following factors: the amount of water, the temperature, the height of the groundwater table, the wave impact (discharge), and the substrate (bottom type) (Table 4). It was found that spring water is an important factor in the habitat of crabs.

A study pointed out that the water intake and water conservation of crabs are characteristics of the evolution from ocean to land [31], and are entirely dependent on the complete transition of water conditions. For example, the length of the breeding season of some land crabs is positively related to the cave water level [45], the spatial distribution of land crabs is affected by the level of the water table [80], and female crabs choose to avoid dehydration death during the rainy season [85]. Juvenile crabs need to follow the gradual transition from saline water to brackish water to fresh water, which is a key evolutionary process [32].

The bioclastic debris layer, spring water, and coastal forest are important factors in land crabs’ microhabitats and provide burrow habitats, fresh water for survival, fruits and fleshy leaves, a humid environment to reduce the loss of body water, and dark space. The three factors form an excellent living environment that supports a diversity of land crab species (Figure 8). The crab species that depend on underground springs include Sesarmops impressum, Varuna litterata, Geothelphusa albogilva, Geothelphusa ferruginea, Candidiopotamon rathbunae, and Coenobita violascens. The humid environment around underground spring waters mean that they are an important habitat for land crabs such as Cardisoma hirtipes and Geothelphusa albogilva, as well as for a variety of shellfish, freshwater shrimp, and fish [52,86].

Studies have pointed out that the water environment is the most critical ecological condition and selection factor in the early life cycle stage of land crabs, because land crabs require salt water, brackish water, and fresh water for their transformation [32]. The climatic conditions of Banana Bay Reserve are characterized by high rainfall and high humidity, forming the characteristics of a tropical rainforest [26]. In addition, it is located in a low-lying structural belt, and consists of high-permeability sand dunes and porous coral reefs, so the amount of spring water is abundant [54]. In addition, stable spring water is an important condition for land crab restoration [53].

Table 4. Environmental factors that affect the microhabitat of Banana Bay land crabs in the reviewed literature.

Category	Factor	Explanation
Bottom topography	Depth	Banana Bay is a coastal terrace of uplifted coral reef. The topography inclines to the east of the bay for about 6° and the sand is mainly composed of shell fragments, coral fragments, aragonite, and high-magnesium calcite that benefits benthic foraminifera and crustaceans. The content of calcium carbonate is as high as 97.68% [52].
	Shelter	Land crabs live in coastal forests, the pores of reef limestone crevices, under fallen trees, or near the root of trees; and dig caves in muddy soil.
Biotic features	Vegetation	From the coral reef shrub above the high tide line to the forest in the inland direction, including (1) coastal coral reef vegetation zone (Pemphis acidula J.R. & G. Forst., Fimbristylis cymosa R. Br., Ischaemum indicum (Houtt.) Merr., Hedyotis strigulosa Bartl. Messerschmidia argentea (L. f.) Johnston., Ficus tinctoria Forst. f. (2) Herbaceous plant belt in sandy land: Ipomoea pes-caprae, Vitex rotundifolia L. f., Canavalia rosea, Vigna marina (Burm.) Merr., Cassytha filiformis Linn., Wedelia biflora (L.) DC. (3) Coastal shrub plant zone: Messerschmidia argentea, Scaevola sericea Vahl., Clerodendrum inerme (L.) Gaerth., Pandanus odoratissimus Linn. f., Sophora flavescens, Excoecaria agallocha L., Hibiscus tiliaceus L., Premna serratifolia (4) Coastal forest plant zone: Barringtonia asiatica, Hernandia nymphiifolia (Presl) Kubitzki Pongamia pinnata, Terminalia catappa Linn. Hibiscus tiliaceus, Diospyros discolor Willd., Heritiera littoralis Dryand., Pisonia umbellifera (Forst.) Seem., Calophyllum inophyllum, Bischofia javanica Blume., Ficus subpisocarpa, Ficus virgata, Ficus microcarpa. [20].
	Food source	The food of land crabs is fruits and seedlings, fallen leaves, corpses, excrement, and algae [42].
	Agonistics	Land crabs come out at night to reduce the water evapotranspiration in their bodies. They are mainly active at night and during June to October when the rainfall is high [60]. Most land crabs in the reserve must migrate to the coast to release larvae (except for the four species of the family Potamida), and the start of the breeding season is related to the start of rainy season [65,87]. Most species of land crabs descend on the sea and undertake larval release migration, often in sync with the environmental cycle, releasing larvae at the full moon and high tide.
Hydrography	Salinity water	Zoeal salinity 33 ppt. [60], Zoeal (Cardisoma carnifex). The survival rate at a salinity of 25% or 30% is the best; 5–40% of land crabs can survive for three days, and can adapt to the low salinity of the estuary [88].
	Brackish water	Not recorded yet.
	Fresh water pH	Not recorded yet. The Banana Bay springs located at 21°55′30.69″ N, 120°50′5.16″ E and 21° 55′30.07″ N, 120°50′4.92″ E will not be exhausted. There is also a northern gushing point with a small amount of water in this spring area, which is inaccessible, so it is impossible to determine the exact coordinates. There are also springs on the south side of the Banana Bay marine terraces: 21°55′27.40″ N, 120°50′5.63″ E and 21°55′27.66″ N, 120°50′5.67″E. The water volume of the springs here is small, and in the dry season, it will dry up [52].
	Dissolved oxygen	Not recorded yet.
	Annual average relative humidity	78% [20]
	Monthly average evaporation	1991.44 mm [20]
	Temperature	20–28 °C, Zoeal 27 °C [60].
	Rainy season	Rainy season, May–November.
	Underground water level	37–37.6 km = −1 m, 37.6–38.2 km = −5 m, 38.2 km = −4 m, 38.5 km = 0 m, 38.8–39.4 km = −2 m [43].
Exposure	Flow	Kuroshio current [74], and high humidity [26].
Substrate	Bottom type	Coral reef, bioclastic debris, beach sand layer, tree coral fossil debris.

Note: These are grouped into five overlying environmental categories, adapted from [84,89].

Table 4. Environmental factors that affect the microhabitat of Banana Bay land crabs in the reviewed literature.

Category	Factor	Explanation
Bottom topography	Depth	Banana Bay is a coastal terrace of uplifted coral reef. The topography inclines to the east of the bay for about 6° and the sand is mainly composed of shell fragments, coral fragments, aragonite, and high-magnesium calcite that benefits benthic foraminifera and crustaceans. The content of calcium carbonate is as high as 97.68% [52].
	Shelter	Land crabs live in coastal forests, the pores of reef limestone crevices, under fallen trees, or near the root of trees; and dig caves in muddy soil.
Biotic features	Vegetation	From the coral reef shrub above the high tide line to the forest in the inland direction, including (1) coastal coral reef vegetation zone (Pemphis acidula J.R. & G. Forst., Fimbristylis cymosa R. Br., Ischaemum indicum (Houtt.) Merr., Hedyotis strigulosa Bartl. Messerschmidia argentea (L. f.) Johnston., Ficus tinctoria Forst. f. (2) Herbaceous plant belt in sandy land: Ipomoea pes-caprae, Vitex rotundifolia L. f., Canavalia rosea, Vigna marina (Burm.) Merr., Cassytha filiformis Linn., Wedelia biflora (L.) DC. (3) Coastal shrub plant zone: Messerschmidia argentea, Scaevola sericea Vahl., Clerodendrum inerme (L.) Gaerth., Pandanus odoratissimus Linn. f., Sophora flavescens, Excoecaria agallocha L., Hibiscus tiliaceus L., Premna serratifolia (4) Coastal forest plant zone: Barringtonia asiatica, Hernandia nymphiifolia (Presl) Kubitzki Pongamia pinnata, Terminalia catappa Linn. Hibiscus tiliaceus, Diospyros discolor Willd., Heritiera littoralis Dryand., Pisonia umbellifera (Forst.) Seem., Calophyllum inophyllum, Bischofia javanica Blume., Ficus subpisocarpa, Ficus virgata, Ficus microcarpa. [20].
	Food source	The food of land crabs is fruits and seedlings, fallen leaves, corpses, excrement, and algae [42].
	Agonistics	Land crabs come out at night to reduce the water evapotranspiration in their bodies. They are mainly active at night and during June to October when the rainfall is high [60]. Most land crabs in the reserve must migrate to the coast to release larvae (except for the four species of the family Potamida), and the start of the breeding season is related to the start of rainy season [65,87]. Most species of land crabs descend on the sea and undertake larval release migration, often in sync with the environmental cycle, releasing larvae at the full moon and high tide.
Hydrography	Salinity water	Zoeal salinity 33 ppt. [60], Zoeal (Cardisoma carnifex). The survival rate at a salinity of 25% or 30% is the best; 5–40% of land crabs can survive for three days, and can adapt to the low salinity of the estuary [88].
	Brackish water	Not recorded yet.
	Fresh water pH	Not recorded yet. The Banana Bay springs located at 21°55′30.69″ N, 120°50′5.16″ E and 21° 55′30.07″ N, 120°50′4.92″ E will not be exhausted. There is also a northern gushing point with a small amount of water in this spring area, which is inaccessible, so it is impossible to determine the exact coordinates. There are also springs on the south side of the Banana Bay marine terraces: 21°55′27.40″ N, 120°50′5.63″ E and 21°55′27.66″ N, 120°50′5.67″E. The water volume of the springs here is small, and in the dry season, it will dry up [52].
	Dissolved oxygen	Not recorded yet.
	Annual average relative humidity	78% [20]
	Monthly average evaporation	1991.44 mm [20]
	Temperature	20–28 °C, Zoeal 27 °C [60].
	Rainy season	Rainy season, May–November.
	Underground water level	37–37.6 km = −1 m, 37.6–38.2 km = −5 m, 38.2 km = −4 m, 38.5 km = 0 m, 38.8–39.4 km = −2 m [43].
Exposure	Flow	Kuroshio current [74], and high humidity [26].
Substrate	Bottom type	Coral reef, bioclastic debris, beach sand layer, tree coral fossil debris.

Note: These are grouped into five overlying environmental categories, adapted from [84,89].

4. Discussion

4.1. Symbiotic Relationship between Coastal Forest and Land Crabs

Of the 115 woody plants in the Banana Bay Reserve, 57% and 48% follow the same distribution trends as in the Philippines and Malaysia, respectively [20,21,90]. The coastal forest is mainly composed of Barringtonia asiatica, Hernandia nymphiifolia (Presl) Kubitzki and Terminalia catappa Linn., the seeds of which plants have floating and protective structures and can spread with the Kuroshio current [91]. This suggests that the migration and landing paths of coastal forest crabs and land crabs are consistent. Species recruitment remains dynamically stable; when drift disseminule and plankton are exposed to the same ocean current conditions, which are sources of island biodiversity [92], this may also indirectly affect the symbiotic relationships within the reserve. Plant populations are also regulated by biological factors, in which land crabs directly affect forest composition by limiting tree establishment and recruitment [27].

A published study points out that the flora diversity of coastal forests is the main factor that affects the spatial distribution of animals [23]. It can be observed that the higher the diversity of coastal forest flora, the higher the species diversity it attracts. Moreover, the characteristics of the land crab population in the Banana Bay Reserve are that the population is small but the diversity is high [26], which is consistent with the diversity of coastal forest flora [20,21]. Coastal forests are the main habitat of land crabs and a source of food; crabs digest and decompose seeds, seedlings, and deciduous leaves from coastal forests [24], accelerating the cycle of matter and energy in the ecosystem, and dominate the plant community phases [25,27]. Land crabs also dig burrows, create mounds, aerate the soil, and create carbon-rich soil microhabitats to strengthen the flora within the reserve [27,93,94]. According to the published studies, soil organic matter content, total nitrogen content, available phosphorus and potassium content, and cation exchange capacity in the Banana Bay Reserve are much higher than those in the adjacent areas [20]. Moreover, because they exchange energy between the ocean and the land by the geographical edges, land crabs are an important source of protein for tropical island animals, making tropical birds more resilient to rats than temperate birds [34]; biologists have also explored the transition from marine life to land [46], which shows that coastal forests and land crabs are symbiotic in ecosystems.

However, there are two reasons for the change in coastal forest facies. First, in 1950, the coastal forests were reclaimed for hemp plantations to make ropes and burlap bags to supply the needs of Taiwan’s booming industries, and the coastal forests were destroyed. However, when the hemp industry declined and the fields were deserted, it was the beginning of the invasion of alien species; second, road widening gives the reserve a narrower shape [20]. According to the data, there was no Leucaena leucocephala in the coastal forest sample area in 1974 (which is ranked 46th among the top 100 ecosystem-destroying species in the IUCN Invasive Alien Species Database [95].); however, in 1985, the survey found that the relative density of acacias was 3.95% [20]. In 2005, the number of acacias in the sample area reached 75.5 per 100 m² area [90]. Even landscape fragmentation throughout Kenting National Park is highly correlated with the invasion of Leucaena leucocephala [96]. The theory of island biogeography also points out that a change in the niche will lead to the invasion of other species [2]. At present, the restoration plan in the coastal forest is almost entirely aimed at the invasion of Leucaena leucocephala [22,91,97].

Even though the landscape changes in the reserve are small, the changes in the surrounding land use have been proven to cause landscape fragmentation, especially the development of roads, which is an important factor in fragmentation [96,98]. After the widening of Taiwan Provincial Highway 26 (TPH 26), the reserve with a width of only 250 m would be within the influence range; a study pointed out that the marginal effect of cutting the habitat of the reserve in the Hengchun Peninsula by establishing the road had caused the deterioration of the coastal forest structure and composition over the past 40 years [90,99]; published studies also pointed out that the increase in roadkill land crabs will lead to a decrease in female body size, a lower proportion of female crabs, and a reduced overall population [28,29].

4.2. The Perspectives on Island Biogeography

Many complex systems cannot be analyzed using traditional mathematical tools due to their irreducible nature, such as niches. As stated by MacArthur and Wilson, “The colonization of species on islands is not only a difference in natural conditions, but also a difference in the assemblage and abundance of different species”. MacArthur and Wilson remind us that short-term changes in food and habitat can affect species assemblages [2]. This concept, which inspired qualitative thinking in island geography, focuses not on the diversity of species, but on the niche of species assemblages. Niche differences also affect the diversity of tropical forest plants, especially in terms of survival-growth and spatial distribution during the regeneration process [100]. The existing land crab diversity in the Banana Bay Reserve mirrors the characteristics of geodiversity. Therefore, the answer to the deterioration of the ecological reserve must come from diverse and integrated viewpoints.

Although the reviewed literature contains information on the spatial distribution of land crabs and tropical plant populations, the lack of accurate overlays may not allow for a complete understanding of the species–habitat relationships. Integrating management and spatial planning through overlay methods represent a bridging effort between researchers and national parks, so that all data can be combined into regional and transboundary predictions for effective conservation approaches in changing landscapes.

So far, we know that land crabs influence tree population distribution, density and size hierarchy [27]. However, the research on the succession of coastal forest facies and the distribution of land crab populations still needs increase, because land crabs are meaningful as an indicator of coastal forest restoration. [26,34], and the number of land crabs affects the composition and succession of coastal forest facies [24]. The population characteristics of land crabs in Banana Bay Reserve are small but diverse, which means that the understory surface contains deciduous and prosperous vegetation [26].

This study believes that maintaining the symbiotic relationship between coastal forests and land crabs, in addition to the balance of the ecosystem, also represents the relative stability of geographic diversity, especially in the characteristics of terrain structure, geological stability and environmental humidity. In the reserve, the average annual precipitation is 2274 mm, average annual relative humidity is 78%, except from June to September and the evapotranspiration rate is greater than the rainfall in the other months, [20] so the dense coastal forests and land crabs are highly dependent on soil moisture.

5. Conclusions

In this study, the road kill data and living environment data of land crabs were integrated, and the study found that the road kill rate of land crabs that inhabit the mountainside of the reserve was twice that of the seaside. The main reason is that the life cycle of land crabs that inhabit the mountainside must undergo a bidirectional transition of freshwater, brackish water and salt water, and this life cycle is disturbed by TPH 26, thus confirming the spatial conflict hypothesis. In addition, the peak period of traffic flow on the only road in the reserve overlaps with the peak period of land crab larvae release, indicating that the current spatial configuration of the ecological reserve is not only a spatial conflict, but also a spatial-temporal conflict. In addition, within the Banana Bay Reserve, which is narrow in shape and small in size, coastal forest facies and land crab populations are highly diverse, reflecting geographic diversity. The niche formed by this diversity attracts a variety of land crabs to maintain the succession and health of coastal forest plants by digging holes, gnawing flowers and fruit leaves, etc., and the flora of coastal forests must also provide food, dark and humid habitat conditions for land crabs. Symbiosis also shows that land crabs and coastal forest diversity must be kept in balance. Therefore, assuming that the impact of spatial-temporal conflict continues, it may cause imbalance and deterioration of the ecosystem in the reserve. The relationship between biodiversity and geographic diversity is a subject worthy of further exploration.