THE ROLE OF SEA BLIGHT (Suaeda monoica FORSSK. EX GMEL) IN RECOVERY OF DEGRADED MANGROVES AT MWACHE CREEK, KENYA

ABSTRACT
Given the subsequent degradation and potential encroachment of mangrove ecosystems, the slow recovery nature of these systems and huge restoration failure efforts (100% mortality after planting in some cases) of mangrove ecosystems, quantification of the role of early colonizing vegetation to mangrove systems recovery is necessary. While sea blight (Suaeda monoica) is common in the degraded sites of Mwache Creek mangrove forest in Kenya and within its growing patches a marked regeneration of mangrove seedlings, its role in mangrove forest recovery is not known. This study assessed the effects S. monoica initiates on the biotic and abiotic factors of the degraded mangrove system to enable subsequent re-entry and functional development of the system as a contribution to mangrove intertidal restoration. Using stratified systematic sampling, in sites of naturally growing Avicennia marina Forssk. (Vierh), bushes of S. monoica, adjacent open canopy and adjacent bare sites as controls respectively, measurements of sediment conditions, vegetation structure, species composition, regeneration, faunal densities and diversities, soil; structure, bulk density and carbon stocks were determinants of recovery. Except for nutrients, significant differences in all sediment conditions (p<0.05) were observed amongst the four sites. Fauna densities and diversity were higher in the vegetated sites than their respective adjacent controls and their numbers significantly different in all the sites. A. marina site had the highest juvenile mangrove vegetation density and higher live biomass proportion, but there was no significant difference (p˃0.05) in these two parameters between the vegetated sites. The bare areas had the highest bulk densities and low soil organic carbon, while the two vegetated sites had higher ecosystem carbon stocks (t ha1) than their respective controls. The results suggest that S. monoica sites are functionally developing towards and becoming more akin to the natural mangrove sites. The primary mechanism proposed for improving recovery success is sediment stabilization and hydrology moderation provided by S. monoica bushes. These findings support the use of pioneer species where natural regeneration has been impeded as a tool for management in conservation and restoration of the functional integrity of degraded mangrove habitats.

CHAPTER ONE
INTRODUCTION
Background to the Problem
Ecosystem services are indispensible to the wellbeing of all people. They include provisioning, regulating and cultural functions that directly affect people and support needed to maintain other services. Human health ultimately depends upon ecosystems (WHO, 2013). Unfortunately, human actions are depleting earth’s natural capital, putting such strain on the environment that the ability of the planet’s ecosystem to sustain future generations can no longer be taken for granted (MEA, 2005). Mangrove forests are one such ecosystem.

The term ‘mangrove’ refers to an assemblage of tropical trees and shrubs that grows in the intertidal zones. It is a diverse group of plants that are well adapted to wet and saline habitat and are circumglobaly distributed, with majority of the populations occurring between the latitudes of 320N and 380S (Tomlinson, 1986). Spalding et al., (1997) and Mitch & Gosselink, (2007); define mangroves as halophytic trees and shrubs (including ferns and palms) that are a characteristic of mudflats and banks, that grow in brackish to saline tidal waters of tropical and sub-tropical rivers and coastlines in many parts of the world. One of the most diverse forests, mangrove wetlands is known as the “rain forests by the sea” and is an important part of the marine habitat.

Mangroves are a backbone of the tropical ocean coastlines and are far more important to global ocean’s biosphere than previously thought (Dittmar et al., 2006). They play an immense role in the global carbon cycle. Further they store more carbon than most ecosystems including tropical rainforests (Donato et al., 2011). This high carbon storage suggests that mangroves may play an important role in climate change management. Mangrove ecosystems are prime nesting and migratory sites for hundreds of bird species, support extensive coastal food webs, provide shoreline stability, prevent erosion, storm protection, catch sediment and alluvial materials and protect corals and sea grass beds from siltation damages due to their filtering effect (Dittmar et al., 2006). They are also key pollutants sink at the coast. Wells et al., (2006); estimated the value of both direct (fisheries, timber, fuel-wood, fodder and tourism) and indirect benefits of mangrove ecosystems at USD 2,000 - 9,000 per hectare of mangroves per year in areas of extensive mangrove forests and areas close to and directly utilized by human populations. About 70% of wood requirements at the Kenyan coast are met by mangroves.

Despite their immense benefits to humans, mangrove forests continue to disappear all over the world. About 90% of global mangroves are growing in developing countries and they are under the condition of critically endangered and near extinction in 26 countries (Kathiresan & Qasim, 2005). Long term survival of mangroves is at a great risk and the services offered by the mangroves may likely be lost within 100 years (Duke et al., 2007). This massive loss can be attributed to, anthropogenic activities such as; urbanization and settlement, agriculture, aquaculture practices, salt manufacture (Aboudha & Kairo, 2001), cutting for timber, fuel and charcoal, oil pollution and other pollution issues as waste dumping and mining operations as well as natural phenomena. Most recently, climate change has also been proven to affect mangroves (Bosire, 2006).

The total area of mangrove has continually reduced in Kenya since 1985. According to Kirui et al., (2012); in 1985, mangrove covered an estimated 55,280ha, by 1992, this had been reduced to 51,880ha (approximately 6.2% or 0.89% yr-1 on average loss over the period). The cover stood at 46,930ha in 2000 (a further loss of 9.5% or 1.19% yr-1) and 45,590ha by 2010 (2.8% or 0.28% yr-1), with Tudor Creek recording the highest loss of 82% followed by Mwache at 46% (Olagoke, 2012; Kaino, 2013). The 1997/1998 and 2006 heavy rainfall caused massive sedimentation due to erosion of terriginous sediments that led to massive mangrove die backs. The upper region of Mwache Creek was the most affected, loosing close to 500ha of forest (Bosire, 2006). Mangroves forests situated in peri-urban settings/areas are exposed to more threats than those further away (Kaino, 2013). This makes Mwache mangroves more vulnerable as they are also impacted upon by anthropogenic activities.

Just like all ecosystems of the earth, mangroves play a critical and important role in the coastlines of the world and thus their restoration is of great importance. Restoration of marine ecosystems has many examples, but possibly a shorter history than on land (Fairweather, 2004). Management of mangroves as renewable resource poses severe problems in that natural regeneration seems to be insufficient where large scale die backs have taken place. To sustain yield of these forests, therefore, there is need to address both artificial and natural regeneration methods (Kairo, 2001). Over the years, restoration efforts through reforestation have been and are still being implemented in Kenya (Bosire, 2006; Kairo et al., 2008; Kirui et al., 2008), as well as studies on natural regeneration, but little has been done on native vegetation that establish particularly after a large scale disturbance (Kaino, 2013). Although re-colonization may be slow and unpredictable especially if there are no remote seed sources, recovery is still shaped positively or negatively by interacting component species with facilitation being largely supported as an influencing factor for plant distribution (Callaway, 1995; Bruno et al., 2003). Ecological restoration may therefore involve nurse species that improve seed trappings and establishment, attract seed carriers, enhance soil condition through organic matter or nutrient accumulation or provide protection of sensitive seedlings apart from artificial reintroduction of the original community dominant. According to McKee et al., (2007b); this approach must be based on thorough understanding of natural successional dynamics of the system as well as the growth requirements of the dominant plant species. On this account therefore, this study tried to find out the role of one such pioneer species- Suaeda monoica in supporting the recovery of degraded mangroves in Mwache Creek – Kenya that had a large die back during the 1997/98 and 2006 El Niño apart from human induced disturbances.

Statement of the Problem
International initiatives over the years have led to the appreciation of the value of mangroves and upsurge of restoration efforts but unfortunately, restoration has emphasized on planting of mangroves as the primary approach, rather than assessing wholistic recovery opportunities and how to facilitate these efforts. Consequently, the scientific resource community has been reluctant to apply facilitation to restoration practices. Naturally through succession, opportunistic species colonize areas previously occupied by mangroves. One such species is the Suaeda monoica at the Mwache Creek. A large extent of it has grown back in the area that was affected by sedimentation after the Indian Ocean Dipole effect and with its presence, there has been slow but marked regeneration of mangroves especially Avicennia marina species in such areas. Suaeda monoica is known to recolonize degraded mangrove sites, but little is known on its role, ability and extent to facilitate regeneration and recovery of mangroves in degraded areas. Moreover, few studies have experimentally examined facilitation in the context of restoration (most noted being the facilitative role of herbaceous plants in recovery of mangroves in the Caribbean and saltwort in Southwest Florida). This study therefore, sought to find out the role of S. monoica using natural regeneration, faunal colonization, carbon stocks and sediment conditions as indicators of recovery at Mwache Creek along the Kenyan coastline.

Study Objectives
Broad Objective
To understand the role of S. monoica in the recovery of degraded mangroves and mangrove ecosystems

Specific Objectives
i. To measure sediment conditions in patches with and without S. monoica in the study area.

ii. To asses faunal diversity and abundance in patches with and without S. monoica in the study area.

iii. To characterize vegetation survival and growth in patches with and without S. monoica in the study area.

iv. To measure carbon stocks in patches with and without S. monoica in the study area.

Hypotheses
i. S. monoica has an effect on sediment conditions in the study area.

ii. S. monoica has an effect on faunal diversity and abundance in the study area.

iii. S. monoica has an effect on vegetation survival and growth in the study area.

iv. S. monoica has an effect on carbon stocks in the study area.

Justification of the Study
Mangroves are considered to be one of the most endangered ecosystems in the world with approximately 35% of the original area degraded or destroyed since 1980 (Valiela et al., 2001). Kenya’s mangroves has reduced in cover over the years and Mwache Creek has lost approximately 45.4% of its cover of mangroves since 1992 (Kaino, 2013). Such losses may be reversed through application of the principle of ecological restoration. For developing countries with few resources and incentives to restore degraded forests, complimentary approaches rather than ecological engineering techniques such as facilitation can be a great opportunity for restoration at minimum cost and less effort (McKee et al., 2007b).

Mangrove ecosystems constitute of not only a critical habitat with important ecological and societal benefits, but are a system in which facilitative interactions may be applied to improve restoration techniques (McKee et al., 2007b). There had been various restoration attempts in this degraded site using various trial species; examples being: Avicennia marina, Rhizophora mucronata Lamk. and Ceriops tagal (Perr.) C. B. Robinson 1980, but this was met with great failures. The site was originally dominated by R. mucronata but site conditions such as elevation, hydrology and salinity regimes significantly changed after the sedimentation and ensuing die-back, thus making R. mucronata less suitable as a candidate species. Through various experimental trials, A. marina was found to perform better in terms of survival (Pers. Comms, Bosire). With regeneration of A. marina in the growing patches of S. monoica, therefore, there is need to document the potential for use of nurse plants to promote regeneration of mangrove in large disturbed areas where harsh conditions limit recovery (Kaino, 2013). A further understanding of how benefactors may facilitate survival and growth of mangroves will lead to identification of vegetative characteristics to screen potential candidates for restoration projects as well as provide knowledge on sustainability and management of mangrove forests which is a key component of the coastal environmental health. Restoration will help improve the lives of coastal communities who depend on the mangrove forest services and whose livelihoods have been jeopardized over time due to massive degradation of this ecosystem.

Scope of the Study
Located 20km Northwest of Mombasa city in the Coast of Kenya, Mwache Creek covers approximately 17Km2. Roughly 70% of its total 1,500ha (Bosire, 2010) area is covered with mangroves of the Avicenia marina, Rhizophora mucronata, Ceriops tagal and Sonneratia alba Sm. (Kitheka et al., 2002). This study focused on measurements of; sediment conditions, diversity of epifauna and infauna, above and below ground as well as the soil carbon stocks and growth and survivability of mangroves growing in four different treatments i.e.: plots with S. monoica, adjacent bare plots, plots of natural A. marina forest and their adjacent bare plots. The experimental plots were confined to Bonje area of the whole Creek’s mangroves where the El Niño of 1997/98 and 2006 hit (Bosire, 2010). The study gave insight on the supporting role of mangrove associate S. monoica on the recovery of degraded mangroves in a span of 11 months.

Definition of Terms
Avicennia marina: Avicenniaceae genus comprises eight species occupying diverse mangrove habitats (Tomlinson, 1986). A. marina is the widely distributed species (Duke, 1990) and it’s the only representative of the genus in Kenya (Kokwaro, 1985; Tomlinson, 1986). It is often considered to play an important pioneering role in plant succession (Osborne & Berjak, 1997). Kaino, (2013); noted that A. marina has increased in the creek, owing to its tolerance to wide range of environmental conditions (Dahdouh-Guebas et al., 2004b). It can tolerate a wide range of salinity and flooding (Tomlinson, 1986), but does poorly under shade in stands dominated by other species (Kirui, 2006).

Epifauna: Benthic animals that live in the surface of a substrate such as rocks, pilings, marine vegetation or the sea or lake floor itself. They may attach themselves to such surfaces or range freely over them as by crawling or swimming. Mussels, crabs, starfish, flounder are some Epifauna animals.

Facilitation: A succession mechanism where an early colonizing species changes the abiotic conditions thereby allowing subsequent species entries into previously intolerable habitats (Milbrandt and Tinsley, 2006).

Infauna: Benthic animals that live in the substrate of a body of water especially in a soft sea bottom. Infauna usually constructs tubes or burrows and are commonly found in deeper and subtidal waters. Clams, tube worms and burrowing crabs are some examples.

Peri-urban: The transition zone or interaction zone, where urban and rural activities are juxtaposed and landscape features are subject to rapid modification induced by anthropogenic activities.

Suaeda monoica: A shrub to 6 meters high with succulent leaves of xerophytic and brackish sites that occur in Mali, East Africa and Asia. It is halophytic, saline soil indicator and able to tolerate frequent sea-water flooding. It is used in agri-horticulture, as an indicator of soil type and water availability and for land conservation. A root decoction of this plant is drunk for sore throat in Kenya, (naso-pharyngeal medicine) (Burkill, 1985).

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