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Open Access Journal of Marine Biology and Environmental Sciences Volume 1 Issue 1 ISSN: 2694-5924 Research Article Mangrove Ecosystems Rehabilitation in Cameroon: Effects of Two Abiotic Factors on the Growth of Rhizophora Seedlings Boubakarya, Leopold EKGa, Laurant NMa, Alphonse KSa, Flavien KMEa, Sarah MIb, Francois MMa and Din Na* aDepartment of Plant Biology, Faculty of Sciences, The University of Douala, Cameroon bInstitute of Agricultural Research for Development (IRAD), Specialized Research Center for Marine Ecosystems, Cameroon

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Article History: Mangrove ecosystems are undergoing anthropogenic and natural pressures worldwide. Reforestation Received: 25 October, 2019 Accepted: 12 November, 2019 projects have been developed but very few are achieving the expected goal. Data on the parameters that Published: 17 November, 2019 influence the growth and development of seedlings in natural conditions appear as key factors. The

objective of this work located in the Wouri estuary mangroves is to evaluate the impact of light and * Corresponding author: Paulo C conservation period of propagules on seedling growth of Rhizophora spp. Four packages of 120 Chagas, Department of Music, University of California, Riverside, propagules each of the above species were harvested from tree shaking and were preserved 28 days, 14 USA; Tel: + 951-827-2939; DOI: days, 7 days and 0 day respectively. A fifth package was constituted with 120 propagules gathered from https://doi.org/10.36266/JMBES/101 mangrove substrate. The propagules were distributed into three types of nurseries (lighted, semi-lighted and unlighted) and planted the same day. The development of radicles was found from the 14th day during the conservation period. No leaf appearance or perceptible color change of the seed coat were observed throughout this period. The best conservation period was 7 days associated with a semi-lighted nursery. The largest length of the seedlings in any nursery after eight weeks was 56.90 ± 6.74 cm and the average diameter is 1.32 ± 0.04 cm. The sproductions of seedlings in semi-lighted nursery appear to be the most effective approach.

Keywords: Conservation Period; Light; Nursery; Propagules; Reforestation; Wouri Estuary

Copyright: © 2019 Boubakary, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

implemented in several countries notably benin, cameroon, côte Introduction d'ivoire, kenya, nigeria, senegal [12-14]. in cameroon, these Ecosystems are worldwide subject to degradations of all kinds of mangrove restoration projects are continuing until now. Large amplitudes due to natural factors and anthropogenic pressures [1- mangrove reforestation projects implemented either fail 3]. Few coasts in the world have been subject of a mangrove completely or rarely achieve pre-established restoration objectives restoration experiment on their disaster sites. Development [5,15]. These failures are related to non-compliance with pre- conditions are however optimal, and seeds are abundant and planting, planting and post-planting procedures [16]. Most available in all seasons [4,5]. The intensification of human projects involve planting propagules in nurseries near or far from pressure is largely due to the upsurge of the regression process of the target site. Few of these projects had detailed monitoring mangrove ecosystems which is not specific to Africa. The average plans, and in most cases few documentation or recommendations annual rate of the mangroves deforestation has been estimated for modifications to the original planting plan exist [17-18]. There between 0.2 - 0.7% from 2000 to 2012 [6]. In cameroon, 53.16% is a lack of information on the biotic and abiotic parameters that of mangroves around douala city have been lost in 35 years [7]. influence the growth and development of seedlings in the specific These losses of the vegetation cover are mainly due to the mangrove ecosystem. Also, very little is known about the extension of the douala port, the exploitation of fuelwood and variation of structural and functional parameters of vegetation in mangrove wood intended to overlay the needs of fence and the mangrove ecosystem [5,19,20]. in cameroon, numerous ceiling of houses, but also for the processing of fresh fish into mangrove rehabilitation projects have been set up with the smoked fish, sampling sand and also building the huts following participation of local populations however, very few studies have rampant urbanization [8]. taken into account the impact of biotic and abiotic parameters Public and private agencies try to mitigate this trend by planting (light, temperature, humidity, chemical composition of water, mangroves [5,9,10]. Some examples of mangrove reforestation atmospheric and hydrostatic pressure, physical and chemical projects implemented around the world in recent year’s show that structure of the substrate) in reforestation of mangrove vegetation. a number of wetland functions and values can be restored [11]. In The purpose of this study is to determine, in natural conditions, africa, mangrove ecosystem rehabilitation initiatives have been the influence of light and conservation period of propagules on

Pubtexto Publishers | www.pubtexto.com 1 J Marine Biol Environ Sci Citation: Boubakary, Leopold EKG, Laurant NM, Alphonse KS, Flavien KME, Sarah MI, et al. (2019). Mangrove Ecosystems Rehabilitation in Cameroon: Effects of Two Abiotic Factors on the Growth of Rhizophora Seedlings. J Marine Biol Environ Sci (1): 101 DOI: https://doi.org/10.36266/JMBES/101

seedling growth of rhizophora spp. in the wouri estuary  the last one was harvested the day of planting. mangroves. In addition, another package of 120 propagules collected on the mud under seed trees or floating on the water were selected and Materials and Methods transplanted directly into the nursery without conservation. For Study Sites conservation, propagules was deposited on the mangrove mud in situ and surrounded by a mesh fencing with a very small mesh The work was carried out in the Wouri estuary in Douala favoring on the one hand their stability against the tidal current Cameroon (4°00'26.2 '' N and 9°40'48.6'' E). The selected study and on the other hand the normal passage of light and tidal water sites are located in Wouri Bridge where the nursery was installed (Figure 2b). The appearance of the plant and diaspores harvested because seedling need daily to be flooded and this location were was described with emphasis base on the coloring of the nearest with our laboratory to facilitate us monitoring of seedling integuments. The time of appearance of the roots and leaves was in nursery. The other sites were in “Cité Berge” and “Mbanga noted, the propagules size was also measured. Every package of Pongo” (Figure 1). The climate of the region belongs to the 120 propagules was divided into three groups of 40 individuals. equatorial domain of a particular type or Cameroonian. It is characterized by a long rainy season (March - November) with Nursery, Data Collection and Analysis abundant rains (4000 mm per year) and a short dry season Three nurseries of 2m x 2m, varying according to the intensity of (December - February), high and stable temperatures (26.7 °C), sunlight reaching the ground have been constructed in situ. The and high humidity throughout the year with a maximum always first nursery was totally opened (unprotected) favoring the arrival near 100% [21]. Tropical cyclones are unknown despite the of all the light radiation incident on the seedlings (Figure 3a). The strong influence of the tides. second nursery was established under a covered allowing the passage of soft light simulating a weak shading of shrub foliage in the natural environment (Figure 3b). This cover consists of few palms resting on a wooden frame. The third nursery consists of an opaque cover that completely prevents incident radiation from reaching the seedlings (Figure 3c). The nurseries have been arranged so that the propagules are flooded by the tides as in the natural environment. (Figure 2) Seedling: (a) Matures propagules harvested; (b) Conservation of propagules. The blocks of each conservation treatment were separated by a passage allowing the collection of data. Data collection consisted on the one hand to raise in each type of nursery and according to the block, the diameter of the seedlings with the help of a Vernier caliper and on

the other hand their length with the help of a measuring tape. The Figure 1: Map of Cameroon estuary showing the study sites [22]. variation in the number of leaves as a function of time was also Harvest and Conservation of Propagules noted. These parameters were recorded weekly and successively for eight weeks. Data analysis started with interpretation of results Data collection began with the identification of the individuals of from observations. Rhizophora spp. which can be used as seed trees. The stem size was measured with a tape and propagules were harvested from seed trees with circumference ≥ 40 cm at the upper end of the strongest stilt roots. The propagules that fell before the harvest were removed under the selected seed trees. Harvesting consisted in shaking lightly the fruited branches with hands or by the help of a stringed instrument so that only mature propagules could fall

(Figure 2a). Four packages of 120 propagules each were harvested in different Figure 2: Seedling:(a) Matures propagules harvested; (b) Conservation periods and stored as follow: of propagules.  a first package was harvested and stored for 28 days; The ANOVA test was performed to compare the different lighting  a second package was harvested after two weeks and environment (lighted, semi-lighted, unlighted) according to the kept for 14 days; conservation time. The Excel 2010 and Graph pad Prism 5  a third package was harvested after three weeks and kept software allowed to analyze the evolution of the different for 7 days; parameters studied through the graphical representation. Pubtexto Publishers | www.pubtexto.com 2 J Marine Biol Environ Sci

Citation: Boubakary, Leopold EKG, Laurant NM, Alphonse KS, Flavien KME, Sarah MI, et al. (2019). Mangrove Ecosystems Rehabilitation in Cameroon: Effects of Two Abiotic Factors on the Growth of Rhizophora Seedlings. J Marine Biol Environ Sci (1): 101 DOI: https://doi.org/10.36266/JMBES/101

Results and Discussion Effect of the Conservation Biology of Propagules Regarding the conservation period, distribution of the average heights of the seedlings is uneven (Figure 4). The situation is The 600 propagules harvested have all a tapered shape and are of similar to that occurring naturally in mangroves. Mature variable dimensions. By dividing all propagules collected into propagules that have fallen from the seed tree can either three groups (short = length ≤ 20 cm; intermediate = length [20; immediately settle in the mud or begin to grow, or float on the 50 cm] and long = length > 50 cm) as some authors used, 81% water for days, weeks, or sometimes months before finding ideal belongs to the medium group follow by the long with 13% and conditions for growth. During flotation, the tide provides nutrients the short group represents 6%. The mean length was 49.8 ± 3.4 useful for the future growth and development of propagules. The cm; the propagules of this area can be considered as long. These growth observed is better in the semi-lighted environment for the results get closer to those obtained in Gazi Bay (Kenya) where the packages of the propagules kept 7 days in situ before breeding in dispersal of two of the most widespread eastern mangrove species nursery. These results have confirmed those of [27] who observed (Ceriops tagal and Rhizophora mucronata) has provided a mean the best development of seedlings after one week of flotation in propagule size of 44.4 ± 4.3 cm [23]. full-strength seawater.

80 Lighted Semi-lighted 60

Unlighted Height (cm) Height

20 Figure 3: Different types of nurseries: (a) Without cover; (b) Slightly cover; (c) Opaque cover. 0 They are significantly different from the study carried out for the 0* 0 7 days influence of propagules float longevity and the availability of 14 days 28 days Conservation period (days) light on the development of Rhizophora mangle and Bruguiera sexangula, two introduced mangrove species in Hawaii where the Figure 4: Variation of the average heights of the seedlings in the authors found a mean propagule size between 11.7 and 36.6 cm different environment according to the conservation period. [24]. The diameter of propagules varies from 0.6 cm to 1.3 cm. These propagules have various colors: mostly brown, sometimes 1.5 Lighted green and rarely yellow. When a propagule is mature, the Semi-lighted cotyledon enveloping the plumule becomes red, and comes off Unlighted easily. It secretes on its point of attachment, a sticky liquid, 1.0 translucent and odorless. These observations are similar to those of [25] who observed germination of propagules of Rhizophora 0.5 spp. until maturity. (cm) Diameter Growth of Propagules 0.0

The coloring of the integuments did not vary and no leaf was 0* 0 observed throughout the conservation period. However, 7 days 14 days 28 days depending on the time, an appearance of the radicles is noted. Conservation period (days) Thus, 47.5% of individuals in the 14-days-old packages and 60% Figure 5: Variation of average diameter of seedlings in the different of individuals in the 28-days-old packages were found to have environment according to the conservation period. radicles. During the harvest of propagules directly transplanted in the nursery, it was found that several had been partially consumed Effect of Light by the benthic macro invertebrates. Another study has shown the One week after nursery establishment, the green and yellow impact of these benthic macro invertebrates on propagules in their staining propagules contained in previous treatments turned natural environment and highlighted their influence on seedling completely brown. All propagules harvested and collected are distribution and the limitation of competition between healthy and a germination rate of 100% has been obtained. These mangroves’ predator species [26]. results do not agree with those of [28,29] who revealed in the Growth in Heights study of rehabilitation of mangroves between Fresco and Grand- Lahou in Côte d'Ivoire, important areas for fishing that, only the Pubtexto Publishers | www.pubtexto.com 3 J Marine Biol Environ Sci

collected seedlings floating on the water have more interesting (process of renewing the water reserves of the plant) stops, the germination qualities. The appearance of the first leaves in the vacuoles retract, the cytoplasmic membranes are detached from seedlings were observed in the second week in different the wall, and the flexible parts of the plant soften. Without light, a environment: 7.5% of individuals in the lighted had leaves, 21% plant cannot photosynthesize and therefore cannot support itself. in the semi-lighted, 5% in the unlighted (Table 1). Overexposure If the plant does not have enough nutrient reserves produced by to the sun can have adverse effects on plant life. When the plant is photosynthesis, its growth stops and it dies. [30,31]. subjected to excessive light intensity the phenomenon of turgor Table 1: Appearance of the first leaf in the seedling the second week.

Conservation periods Number of individuals with leaf after two weeks

(days) Lighted Semi-lighted Unlighted 0* 0 0 0 0 0 0 0 7 8 17 2 14 1 21 2 28 6 4 6 Total 15 42 10 Table 2: Average height of seedling in each environment after 8 weeks according to conservation treatment.

Conservation periods Mean height (cm) (days) Lighted Semi-lighted Unlighted P0* 51.05 ± 6.94 51.50 ± 5.99 51.06 ± 6.11 P0 50.89 ± 6.81 48.99 ± 8.86 46.78 ± 5.80 P7 53.05 ± 7.18 56.90 ± 6.74 52.85 ± 5.47 P14 51.41 ± 6.08 47.33 ± 4.94 48.66 ± 5.24 P28 50.49 ± 6.22 46.02 ± 5.39 42.61 ± 4.08

Table 3: Average seedlings diameter in each environment as a function of treatments. Conservation periods Mean diameters (cm) (days) Lighted Semi-lighted Unlighted P0* 1.23 ± 0.05 1.25 ± 0.03 1.19 ± 0.04 P0 1.27 ± 0.06 1.19 ± 0.03 1.19 ± 0.05 P7 1.26 ± 0.06 1.32 ± 0.04 1.25 ± 0.07 P14 1.19 ± 0.06 1.21 ± 0.03 1.18 ± 0.06 P28 1.22 ± 0.01 1.21 ± 0.03 1.13 ± 0.12

Mean seedling height distribution is unevenly distributed among cm was obtained in the 7 days semi-lighted environment the three environments: lighted, semi-lighted and unlighted (Table treatment batch. Moreover, in the unlighted environment, 2). Of the three-environment studied, the semi-lighted appears to seedlings completely deprived of light grow very slowly be more favourable for the seedling height growth. The amount of compared to those of the semi-lighted. These results corroborate light that arrives is sufficient for photosynthesis of mangrove with those of [34], who showed the low growth of seedlings seedlings. These results are similar to those of [32] who showed hermetically covered by plant canopies in the mangrove. These during the study photosynthetic responses and fluorescence of results are also consistent with those of [35] who observed the chlorophyll in seedlings of Rhizophora mucronata in the shade impact of irradiance on seedling mortality of Rhizophora spp. that semi-lighted treatments provide the best condition for a good covered by canopies in their natural environment. High mortality carbon fixation capacity. These results also corroborate with those of seedlings should be attributed to unfavorable lighting of [33] who observed during the study of the adaptation of red conditions starting from the poles structure. Seedling growing in mangrove trees in the shade, the good development of seedlings full light died more rapidly than seedlings growing under in an area receiving sufficient solar radiation. However, inside the vegetation cover. Canopy cover is known to offer protection semi-lighted environment, there are differences between the against temperature extremes and excessive evapotranspiration, various treatment packages. The highest mean height 56.90 ± 6.74 although drought might be increasingly harmful under shadier

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conditions because water absorption and light capture cannot be environment for propagules kept for 7 days. For the success of a maximized simultaneously explain [36]. Mortality could be due to mangrove reforestation project, it is important to first store the several interacting factors, mainly predation and desiccation propagules in situ for one week, then to rear them in situ in semi- under extremes temperatures [31]. lighted environment for two months before planting. The results obtained in this study contributed to improve the science of Diametric Growth mangrove management in general and Cameroon in particular. Effect of the Conservation References The diameter varies from one batch of treatment to another. The greatest mean 1.32 ± 0.04 cm is obtained in the batch of 1. Lovelock CE, Cahoon DR, Friess DA, Tenspergen G, Krauss GR, propagules which have been stored for 7 days before being prick Reef KW, et al. 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