Mangroves are woody vegetation types that occur in marine and brackish environments and also are mostly restricted to the tidal zone. Mangroves have both ecological and socio-economic benefits to tropical marine biotypes and they also contribute to world’s biological and genetic diversity (Sandilyan and Kathiresan 2012). In Ghana, about 3.9% of the total coastal stretch of about 550km from Eastern to Western regions are covered by mangroves, however, they are limited to areas around lagoons and also around the lower delta of River Volta (Adda 2016; Fianko & Dodd 2019; Nunoo &Agyekumhene 2022). Communities with mangroves include Keta lagoon, Sakumono lagoon, Eture, Korle lagoon, Ada, Winneba, Apam, Shama, Half Assin, Axim, Amanzure lagoon and Takoradi.
Mangroves in Ghana fall into three main genera belonging to three families namely Rhizophora (Rhizophoraceae), Avicennia (Avicenniaceae) and Laguncularia (Combretaceae). The species represented are Rhizophora mangle (red mangroves), Avicennia germinans (black mangroves), and Laguncularia racemose (white mangroves) according to deGraft-Johnson et al. (2010) and Nunoo and Agyekumhene (2022). Many plants that grow in association with mangroves in Ghana include Thespesia populnea, Acrostichum aureum, Phoenix reclinata, Canavalia rosea, Ipomoea pes-caprae, Dalbergia escastophyllum, Sesuvium portulacastrum, Hibiscus tiliaceus, Conocarpus erectus, Drepanocarpus lunatus, Cardiospermum grandiflorum, Sporobolus pyramidalis, Terminalia catappa and Paspalum vaginatum among others, however, Conocarpus erectus records the most associated species (Uddin, Huang and Bin 2019). Other lower plants including algae that grow in association with mangroves in Ghana are Acrostichum aureum, Phoenix reclinate and Paspalum vaginatum also grow in association with mangroves (Adekanmbi and Ogundipe 2009; Olowokudejo and Ozioma 2020)
Mangroves provide habitats for many coastal organisms including birds and also help improve fish stocks. Mangroves provide employment and income for coastal communities who engage in mangrove farming (Sackey et al. 1993; Aye et al. 2019; Das et al. 2022). Mangroves serve as wind brakes and protect coastal communities against wind damage (Das and Crépin 2013; Paul et al. 2017; Onyena and Sam 2020). Fishermen in the coastal communities mend their fishing nets and also hold community meetings under shade provided by mangroves (Nunoo and Agyekumhene (2022). In some communities, mangrove shades also serve as meeting place for socializing with other fishermen where they sit to share local alcoholic beverages such as ‘pito’, play local games such as ‘Dame’ and ‘Ludu’, play music and dance together when they close from work and other special occasions (Nunoo and Agyekumhene 2022).
Despite these benefits, mangroves continually face threats to extinction if action is not taken to protect the few remaining populations. Mangroves are removed as fuel wood for domestic consumption and for charcoal production by coastal communities especially the fishing areas (Bandaranayake 1998), mangroves vegetation is cleared for construction of roads and buildings for dwellings, for salt mining, agriculture and aquaculture thereby destroying most of the vegetation (Sackey et al. 1993; Seto and Fragkias 2007; Aldon et al. 2008; Bao et al. 2013; Hamilton 2013; Liingilie et. al. 2015). Domestic animals including goats and sheep feed on seedlings of mangroves during dry season when fresh leaves are not common, some vegetation of mangroves are also lost through wildfires which mostly occur in the dry season (Sackey et al. 1993; Bandaranayake 1998; deGraft-Johnson et al. 2010). Mangroves for servicing of boat and fishing gear, furniture, tannins are used to dye leather for bags, belt and sandals production and also chemical extracts from mangroves are used as insecticides against many insects including mosquitoes (Bandaranayake 1998).
In some few cases, some coastal communities use mangroves vegetation as site for illegally disposing all types of household waste household (Numbere 2019). In Ghana, illegal mining for mineral resources especially gold which is locally called ‘‘galamsey’’ has also removed mangrove vegetation in some of the coastal communities. However, some few populations of mangroves along the coast of are naturally removed through disease and pathogenic attack and/or global warming (Bhowmik 2022; Nunoo and Agyekumhene 2022) Lack of enforcement of the existing environmental laws in the coastal areas has been one of the main drawbacks of protecting the few remaining mangrove populations from extinction in Ghana (Fianko & Dodd 2019; Nunoo and Agyekumhene 2022). In some few coastal communities, traditional leaders have introduced ‘‘traditional taboos’’ to deter encroachers from removing mangrove vegetation where it is against the gods to remove mangrove vegetation without any permit from the fetish priests, Chiefs and elders (Abeku Essel 2020; Abayie-Boaten 1998). Several attempts to restore and conserve mangrove vegetation in Ghana by government and non-governmental organizations in collaboration with coastal communities such as Songor and Keta Lagoon Complex Ramsar sites failed to due to land related issues including ownership, access and land tenure system. (Asante et al. 2017).
Many researchers have reported that Ghana has lost greater percentage of its original mangrove cover between 2002 and 2022 (Dankwa 2002; Mensah 2013; Aheto 2016; Essel et al. 2019; Dali 2020; Nunoo and Agyekumhene 2022; Dali et al. 2023). Ghana’s mangrove cover therefore needs immediate and appropriate interventions to protect the few remaining vegetation from degradation that could lead to extinction. Losing mangroves and Conocarpus vegetation may financially affect coastal communities that depend on these species for livelihood.
Mangroves and Conocarpus have many local uses. In Nigeria the leaves of these species are either eaten raw or leave extract is drunk for treatment of fever or malaria, however, root extract of the same species is boiled, cooled down and drunk for treatment of gonorrhoea, coughing and other respiratory diseases(Adda 2016). Again, latex extracted from the bark of mangroves is also used stop bleeding from wounds when there is cut on the skin (Adda 2016).
Mangroves and Conocarpus are usually shrubs of about 1.5m to 4m in height but can also grow as trees of about 20m tall (Ghate and Sridhar 2016). Other morphological features common to both species include possession of weak and brittle laterals and fine roots with dark brown colour, possession of erect or multiple trunks (Farooq et al. 2018). Both mangroves and Conocarpus possess thin corky bark of about 8mm thick which is grey or brown in colour from outside but the inner part is dark cream in colour (Farooq et al. 2018). In both species the stem in both mangroves and Conocarpus is hard, heavy and strong, however, the branches are brittle with slender yellow-green twigs (Farooq et al. 2018). The leaves of mangroves and Conocarpus are spirally arranged, elliptic, lanceolate and fleshy with measurement of about 2-10cm long which includes leaf petiole of about 3-9mm long (Farooq et al. 2018). Uddin, Huang and Bin (2019) documented that mangroves grow in association with other plant species including Conocarpus erectus in brackish water environment but there is a clear morphological indication that Conocarpus may not be the same as mangrove species. Conocarpus erectus is not much studied in the mangrove forest areas in Ghana and there have been different views, arguments and opinions in Ghana on classification of Conocarpus erectus as mangrove species. Many Ghanaians including some researchers classify Conocarpus erectus as mangroves due to some similar morphological features they share in common (Nunoo and Agyekumhene 2022). Nortey et al. (2016) used observable characters and classified Conocarpus erectus as one of the mangrove species in Ghana. Others including Boateng (2018) also used morphological feature to classify Conocarpus erectus as one of the six main mangrove species found in Ghana. Several other studies have also used similar morphological approaches including reliance on morphological characteristics of the species to classify Conocarpus erectus as mangrove species (Asuk et al. 2018; Yaney-Keller et al. 2019). However, Nascimento et al. (2016) and Aheto et al. (2016) argued that using morphological features alone might not be sufficient enough to establish a strong basis for Conocarpus erectus classification as a mangrove without any DNA analysis therefore may be scientifically wrong. The researchers further argued that morphological analysis technique alone is not sufficient enough for such classification. Distinguishing between mangroves and Cornocarpus erectus using morphological features is possible, however, it is very difficult to identify individuals in mixed populations. An estimation and description of genetic relationships such as possible hybridisation between the species and introgression of the populations in the field is difficult using morphological and phenological characters. The use of molecular markers might enhance understanding and might help distinguishing between mangroves and Cornocarpus erectus. Aheto (2016) therefore recommended the need to distinguish between the two based on DNA analysis.
This study therefore aims at using Random Amplified Polymorphic DNA (RAPD) to investigate genetic relationship between Rhizophora mangle, Avicinnea germinans, Laguncularia racemosa and Conocarpus erectus. RAPD is a PCR based technique that detects nucleotide sequence (8–12 nucleotides) polymorphisms in a DNA amplification-based assay using only a single primer of arbitrary nucleotide sequence. The RAPD technology has provided a quick and efficient screen for DNA-sequence polymorphisms at a very large number of loci. RAPD is good as it requires no prior knowledge of sequence and also a small amount of DNA is needed for amplification (Williams et al. 1990). RAPD is quick and economical for population genetics studies as compared with other molecular markers. The molecular basis for RAPD has been discussed (Hadrys et al. 1992) and may provide either single base pair changes in the primer binding sites or deletion in the region between the primer binding sites.
Though RAPD is simple, the major drawback is that, their results lack reproducibility of some amplification products. Again, RAPD is criticised in population genetics because heterozygosity cannot be determined (Williams and St. Clair 1993). Despite these criticisms, RAPD is used in population genetics studies. The objective of this paper is to use clearly amplified RAPD fragments to examine the genetic variation within and between populations of Rhizophora racemosa, Avicenna germinans, Laguncularia racemosa and Carnocarpus erectus from Shama in the Western region of Ghana. Inadequate information on mangroves in Ghana is affecting its management and protection in order to prevent the species from extinction. This study will provide information on genetic diversity of the three most common mangroves and Cornocarpus erectus in Ghana so that effective conservation strategies could be put in place to prevent the few remaining populations from extinction.