In Cameroon, the «Mayange na Elombo-Campo National Marine Park» has been identified as one of the regular and stable nesting and feeding sites for marine turtles. However, the latter is subject to natural and anthropogenic threats which could later lead to their alteration as well as to the disappearance of the species as Lepidochelys olivacea. The objective of the present study is to contribute to the conservation of this specie of marine turtle through a better knowledge of the biophysical characteristics of its nesting sites in the «Manyange na Elombo-Campo National Marine Park». To achieve this, survey for direct observations, consultation of documents and topographic survey using a GPS were carried out. The study revealed that the back beaches where marine turtles nest are inhabited by 9 plant species grouped into 6 families. The animal species that frequent these sites belong to 4 classes, namely crabs, mammals, birds and reptiles. The substrate of the sites is homogeneous and sandy in nature and the grain size reveals three types of sand; fine, medium and coarse whose sediment sizes are respectively >60 to < 465 µm, >465 to < 2000 µm, and > 2000 to < 4750 µm. The morphology (slope, highest and lowest altitude point, width and accessibility) of the sites differs depending on the nesting sites. Particle size shows a significantly high correlation with hatching (r²=0.95) and emergence (r²=0.97) and therefore significantly influences incubation success.

Marine turtles are reptiles that spend the majority (99%) of their lives at sea and are important consumers within trophic chains Bjorndal & Jackson, 2003. This role as consumers is important for the regulation of their prey Bjorndal et al, 2000, and as bio indicators, they provide information on different compartments of marine ecosystems. Thus, they can be qualified as umbrella species, meaning that their protection could promote the protection of a large number of other species sharing the same habitats Bourges, 2000. Just like birds and certain marine mammals, they ensure their reproduction on the continent (nesting sites). « A nesting site for marine turtles is any coastal land area where at least one female of any species has laid eggs in historical times. » Fretey & Girondot, 1996.

This terrestrial nesting habitat includes the three littoral zones of the emerged part, more or less long, of the beaches: infralittoral zone, intertidal or mediolittoral zone (foreshore), supralittoral zone. The locomotion of an adult female turtle (mainly Eretmochelys imbricata, but also sometimes Lepidochelys olivacea) can lead it to overshoot its usual floor, either voluntarily or by accident (artificial lights causing disorientation). Females D. coriacea frequent terrestrial habitats accessible via deep water and strong waves, devoid of rocky mass, beach-rocks or any other abrasive obstacle that could cause injury Fretey & Triplet, 2021.

Nesting sites are made up of two main areas: the beach itself and the backshore. The beach is divided into two sub-units: the beach of sand or other types of substrate, and an upper part of the beach more or less covered with low, creeping herbaceous vegetation. These beaches are subject to a number of physical threats, mainly natural erosion or erosion caused by port infrastructures, leading to a narrowing of the sandy strip Fuentes et al. These spaces undergo sediment erosion dynamics and strong anthropogenic pressure on the terrestrial domain, leaving little space for natural sedimentary processes Defeo et al., important for the nesting of marine turtles. Environmental parameters linked to the quality and type of substrate such as temperature, topography (slope of the beach, presence of natural barrier), particle size of the substrate, geographical location of the nest (exposure to swell, presence of vegetation), are determinants in the ultimate choice of the nesting site and the egg-laying decision by gravid females once they arrive at the nesting site Wood & Bjorndal, 2000.

In Cameroon, the “Manyange na Elombo Campo National Marine Park”, on the northern border with Equatorial Guinea, has been identified as an important nesting and feeding site for marine turtles. The park's nesting sites are home to two species of marine turtle: the Olive ridley, the Leatherback and, more sporadically, the Green Turtle. The coastal areas are frequented by juvenile Green Turtles and Hawksbill Turtles.

However, these sites are subject to natural and anthropogenic threats which could later lead to their alteration as well as the disappearance of these species; these include, among other things, pollution by tree species lying on the site; poaching; predation by animal species that frequent nesting beaches; the shrinkage of the sandy strip IUCN, 2012; flooding of nesting sites due to high tides; coastal erosion.

The present study aimed to contribute to the conservation of marine turtles through a better knowledge of the biophysical characteristics of nesting sites in the “Manyange na Elombo-Campo Marine National Park”. Specifically, these are:

• Determine the composition of animal species and woody species present on marine turtle nesting sites
• Identify the nature, determine the particle size of the substrate and the topo-morphology of marine turtle nesting sites
• Evaluate the influence of particle size on the success of incubation of sea turtle eggs.

Presentation of the Manyange na Elombo Campo Marine National Park
Created in 2021 by decree N°. 2021/4804/PM of 9 July 2021, the «Manyange na Elombo-Campo National Marine Park» is located in Cameroon's South Region, Ocean Department and Campo District. This marine park is adjacent to the maritime border with Equatorial Guinea, separated from the Rio Campo reserve by the Ntem River. It is Cameroon's first maritime and coastal protected area. It occupies the Kribi-Campo coastal strip and covers an area of 110,300 ha. It extends 42.364 km (26.5 miles) offshore, in Cameroonian territorial waters, towards the Equatorial Guinean Island of Bioko, and stops 300 meters from the coastal line of the highest tides. The park has a buffer zone of three thousand four hundred hectares (3,400 ha) reserved for community activities not harmful to biodiversity, with a maximum depth of 350 meters, bordering the marine national park on an immediate and intact coastal zone. This zone is delimited on the mainland, depending on the case, by a strip 50 or 25 meters after the highest tide line.

This zone extends over a width of 300 m into the sea and also covers the southern confluence of the Tyenjè watercourse with the Atlantic Ocean, the Cameroonian part of the mouth of the Ntem, Lake Pitché and the mangrove there adjoining (Figure 1).

Presentation of the Olive Ridley nesting sites
To the south of the National Marine Park, according to the local research and development association “Tubè Awù”, the nesting sites are named after outlying villages from Ebodjé to Campo via Bouandjo. The sites used in this study are Ebodjé, Bouandjo and Mbondo (Figure 2).

Determination of animal and woody species of marine turtle nesting sites
A structured interview was carried out with fishermen randomly selected from the different villages of the study sites. Ebodje (35 fishermen), Bouandjo (20 fishermen) and Mbondo (15 fishermen) for a total of 70 fishermen. In addition to surveys, direct observations on the beaches were made by patrols (during the day and at night depending on low tides). Animal species were identified using the French/Iyasa zoological lexicon for vertebrates by Fretey, 2003.

The quantitative inventory of Ocypode cursor crabs and other crab species frequenting the spawning sites was carried out at night in 50 x 10 m plots, covering an area of 500 m². The technique used was the artisanal fishing technique of the Iyasa community called «Mangongo». This technique consisted of escaping containers which served as traps into the sand. This technique consisted of placing containers in the sand to act as traps. To do this, it was enough to take per plot 3 containers of 15 litters with openings of diameter 30 cm and height 35 cm, then dig three holes in the sand equal to the height of the containers and equidistant by 15 m. Then, insert the containers into the holes, cover the opening of the container with green and light leaves. Bait, consisting of cassava flour or grated coconut above and around the containers. The species of crabs which live behind the beach and regularly frequent the nesting beaches were captured. All these crab species were identified using the publication for West African Brachyuran Crabs Manning & Holthuis, 1981 and the identification guide for Lagoon Crabs in South Benin, West Africa Dessouassi et al. 2018. The calculated parameter is the frequency of observation of each species on the nesting site.

The botanical inventory method consisted of inventorying tree and shrub species according to Angoni, 2005. Trees with a diameter at breast height (DBH) of at least 10 cm were recorded. The botanical inventory system was based on the establishment of three rectangular plots of 50x10 m, i.e. an area of 500 m² equidistant by one km per transect, symmetrical to the plots used for the inventory of crab species in relation to the vegetation line. The species were identified using the Picture and Plantnet applications and then revised by a botanist from the Mbalmayo National School of Water and Forests. The calculated parameter is the specific density of each species.

Identification of the nature of the substrate and determination of the grain size and topo-morphology of marine turtle nesting sites
Samples of between 500g and 1000g of sand were taken from the plots (used for the crab inventory), and preserved in A4 format plastics. Three samples were taken per transect, for a total of nine samples. These samples were analyzed at the soil science laboratory of the Faculty of Agronomy and Agricultural Sciences of the University of Dschang using the sieving method. The sieves used had respective mesh sizes of 60, 400, 2000, 5000 micrometers (0.06; 0.4; 2; 5 mm) and the visual identification key for sand was used to classify the categories of sand obtained.

The morphology of the nesting sites (the slope, the highest point and the lowest point) was measured by a topographic survey using the Garmin etrex 10 GPS device. The data was recorded in three dimensions: latitude, longitude and altitude and processed using Global maper and Google Heart software to generate the morphology of the sites.

Evaluation of the influence of particle size on the incubation success of sea turtle eggs
The nests obtained in this study belong to those of the olive ridley turtle. The nests were identified using footprints left on the sand by the species, and by direct observation of the species laying eggs (Figure 3).

The 12 nests of Olive Ridley used in this study were nests transplanted in situ (in the same natural environment). Incubation success was determined by the nest profile methodology according to Bell et al.; Maite & Agambouet, 2008. The nests were excavated two weeks after the probable hatching period. Once excavated, the contents of the nests were inspected, the number of eggs that failed to hatch was counted and the number of hatchlings that failed to emerge was also counted.

Data analysis
The data collected in this study were encoded and processed using the Excel spreadsheet. The Google Maper and Google Earth software were used to highlight the morphology of the sites and maps were produced by the Arcgis mapping software. The statistical test used to show the correlation between particle size and incubation success was that of Pearson carried out using SPSS 20.0 software.

Composition of animal species and woody species encountered on olive ridley turtle nesting sites
It appears from this table that, the spawning sites are composed of six species of crabs grouped into two families: Ocypodideae and Grapsydeae. Mammals are made up of seven species, reptiles made up of four species, and birds made up of six species.

Composition and relative density of woody species
The results obtained in the field made it possible to determine the composition of the woody species of the nesting sites and at the same time to highlight the different relative densities of these species per nesting site. In total, nine woody species were identified and divided into six families. Thus, the Clusiaceae family consists of a single species of Calophyllum inophyllum and offers the highest average relative density of 58.35%. Then comes the Arecaceae family with an average relative density of 13.63%, composed of Cocos nucifera, Elaeis guineensis Phoenix. sp; The Moraceae family with an average relative density of 8.83% is composed of species of the Ficus genus. The Combretaceae family is composed of a single woody species Terminalia catapa with an average relative density of 6.61%. The families Sapotaceae (11.07%) and Urticaceae (1.52%) are composed respectively of the species Manilkara abovata and Musanga cecropioides.

The species Calophillum inophillum, Cocos nucifera, Terminalia catapa are present on the three sites but are more abundant on the Bouandjo site with relative densities respectively of 74.13%; 11.43 and 7.62%. The species Elaeis guineensis (9.3%) is only present on the Ebodje site; the species Phoenix. sp (4.19%) is only present on the Bouandjo site; the species Ficus benjamina (4.74%) is only present on the Mbondo site, on the other hand the species Ficus saussureana is present on the Ebodje and Mbondo sites but, more abundant on the Ebodje site and offers a relative density of 17.15%, the species Manilkara abovata is present on the three sites but is more abundant on the Ebodje site and offers a relative density of 26.43%; however, the species Musanga cecropioides (4.55%) is only present on the Mbondo site.

The shrubs on the plots are essentially made up of the species Calophyllum inophyllum, hence its high relative density; moreover, the waterfront is mainly made up of this species, followed by the species Manilkara abovata, Cocos nucifera, Terminalia catapa and Ficus saussureana.

Nature and particle size of turtle nesting substrate
After sieving the substrate samples from the three sites, it appears that the size of the sediments is not less than 60 µm, which allows us to conclude that the sites are composed of a homogeneous substrate, of a sandy nature (Table 3).

Overall, it appears from Table 3 that the substrate ranges from fine to coarse sand, belonging to the respective particle size classes >60 and465 and2000 and

Sites	Slope value (%)	HP (m)	LP (m)	Width (m)	Accessibility
Ebodje	0.11-0.27	32	2	15-40	Difficult to access
Bouandjo	0.10-0.16	14	2	21-50	Easily accessible
Mbondo	0.8-0.12	10	2	13-35	Easily accessible

Classification of the contents of the 5 nests analyzed (N= 513)
Restrained new borns	68 (13.26%)	Hatched eggs
Emergence	302 (58.87%)	(N= 370)
Unhatched full-term embryos	21 (4.09%)	Eggs no
Without apparent development	57 (11.11%)	hatched (N=143)
Undetermined	31 (6.04%)
Unhatched eggs and predates	34 (6.63%)

Code of Nests	Incubation of Nests
	Outbreak Achievement	Emergence Success
N°1	81.25	76.25
N°2	79.44	71.96
N°3	80.56	72.22
N°4	61.02	38.14
N°5	50.00	23.44
Average	70.45	56.40

Incubation	Granulometry
	60-465	465-2000	2000-4750
Hatching	0.95**	- 0.95**	- 0.96**
Emergence	0.97**	- 0.97**	- 0.97**

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