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Mangrove ecosystems are often called “makers of land” due to their ability to promote deposition, trap, and augment sediments. Accurate location- and region-specific elevation information is required to assess and mitigate threats to mangroves caused by their vulnerability to sea-level rise. The provision of land building services by mangroves is primarily sediment-dependent. It is therefore influenced by local factors, including sediment availability and supply. In the present study from Kenya, we measured and examined the variations in surface elevation in mangroves at variable distances from the creek channel using a combination of surface-elevation tables and horizon markers for three years. Elevation changes varied with distance from the creek channel (p < 0.05), with both surface loss and gains recorded. Elevation changes varied between -80 mm (most significant subsidence) and 42 mm (highest accretion) in stations closer to the creek, while farther from the creek (~200 m away), elevation changes ranged between -68 mm (most significant subsidence) and 29 mm (highest accretion). However, net surface elevation changes over the three years showed that shallow subsidence occurred in both stations closer to the creek (-45 ± 7.2 mm) and those farthest from the creek (-20 ± 7.1 mm). At the same time, an average of 18 mm of sediments were accreted above the horizon markers translating to ~9 mm yr-1 of accretion, a rate larger than both the current global rates of sea-level rise (~3.1 mm yr-1) and local measured rates of sea-level rise (3.8 mm yr-1) in Mombasa, a tide-gauge station nearest (~100 km) to the study site. Cumulatively, sediment elevation changes in Vanga indicate that they are outpacing the current rates of sea-level rise. However, they could be vulnerable to predicted and accelerated rates. It, therefore, calls for more holistic management and monitoring of the dynamics within the mangrove forests and adjacent terrestrial hinterlands.

Kipyegon JK, Obudho PA, Kairo JG. 2019. Thermal tolerance, density, and distribution of mangrove crabs, Perisesarma guttatum and Uca urvillei at Gazi Bay, Kenya. Indo Pac J Ocean Life 3: 38-50. Mangrove crabs are fundamental for the viability of mangrove forests. Therefore, the effects of climate change can impact mangrove ecosystems. The aim of this study was to determine the thermal tolerance, density, and distribution of the mangrove crabs Perisesarma guttatum (A.Milne-Edwards, 1869) and Uca urvillei (H.Milne Edwards, 1852) within Gazi Bay, Kenya. Field activities included collecting data on the density and distribution of the two crab species and environmental variables in the Rhizophora mucronata Lam., Ceriops tagal (Perr.) C.B.Rob. and Avicennia marina (Forssk.) Vierh. monospecific stands. The crabs were maintained at temperatures between 17-37°C in the laboratory, and respiration rate measurements were performed in closed chamber systems after the crabs were acclimated for 8 hours at a temperature of 27°C. The results indicate the temperature ranges for P. guttatum and U. urvillei adult crabs were 27-31°C and 27-33°C, respectively, beyond which the crabs got stressed as indicated by increased metabolism. Findings suggest that P. guttatum is more sensitive to temperature variation than U. urvillei. At the highest average densities of U. urvillei and P. guttatum crabs were recorded at 66.25±7.7/m² and 11.75±4.1/m², respectively, in the R. mucronata zone. The densities of U. urvillei and P. guttatum were strongly related to the temperature, fine sand, and organic matter using stepwise regression analysis (P

Background: Mangrove forests worldwide are highly valued for their social, ecological and environmental roles. Participatory forestry has been recognized as a tool for improvement of forest conditions. The current study assessed impacts of PFM implementation on structure and regeneration of mangroves at Gazi Bay, Kenya. Forest data was collected along belt transects perpendicular to waterline in both community and state managed blocks. Results: Basal area and standing density were significantly higher in the co-managed forests (16 m2 ha-1 and 4,341 tree ha-1) as compared to the state managed forests (eastern block 10.3 m2 ha-1 and 2,673 trees ha-1; western block 6.2 m2 ha-1 and 2,436 trees ha-1). There were significantly higher (p = 0.0068) densities of quality class poles in co-managed forest block as compared to state-managed eastern and western blocks. Natural regeneration values of 38,822 juveniles ha-1 in the co-managed central block and 23,556 and 35,061 juveniles ha-1 in the state managed eastern and western blocks respectively are considered adequate to support recovery of the forest. A higher complexity index (CI) recorded in the co-managed mangrove forest compared to the state managed eastern and western blocks is particularly due to improved stand density, tree height, and biomass resulting from increased surveillance and protection by the community. The results have wide implications in the management of mangroves for community and biodiversity benefits and climate change mitigation.Conclusion: The results support community participation for improved management of mangrove forests and are in conformity with sectoral policies on natural resources management in Kenya.

Seagrass beds occur globally in both intertidal and subtidal zones within shallow marine environments, such as bays and estuaries. These important ecosystems support fisheries production, attenuate strong wave energies, support human livelihoods and sequester large amounts of CO2 that may help mitigate the effects of climate change. At present, there is increased global interest in understanding how these ecosystems could help alleviate the challenges likely to face humanity and the environment into the future. Unlike other blue carbon ecosystems, i.e., mangroves and saltmarshes, seagrasses are less understood, especially regarding their contribution to the carbon dynamics. This is particularly true in regions with less attention and limited resources. Paucity of information is even more relevant for the subtidal meadows that are less accessible. In Kenya, much of the available information on seagrasses comes from Gazi Bay, where the focus has been on the extensive intertidal meadows. As is the case with other regions, there remains a paucity of information on subtidal meadows. This limits our understanding of the overall contribution of seagrasses in carbon capture and storage. This study provides the first assessment of the species composition and variation in carbon storage capacity of subtidal seagrass meadows within Gazi Bay. Nine seagrass species, comprising of Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule uninervis, Halophila ovalis, Halophila stipulacea, Syringodium isoetifolium, Thalassia hemprichii, and Thalassodendron ciliatum, were found. Organic carbon stocks varied between species and pools, with the mean below ground vegetation carbon (bgc) stocks (5.1 ± 0.7 Mg C ha−1) being more than three times greater than above ground carbon (agc) stocks (0.5 ± 0.1 Mg C ha−1). Mean sediment organic carbon stock (sed Corg) of the subtidal seagrass beds was 113 ± 8 Mg C ha−1. Combining this new knowledge with existing data from the intertidal and mangrove fringed areas, we estimate the total seagrass ecosystem organic carbon stocks in the bay to be 196,721 Mg C, with the intertidal seagrasses storing about 119,790 Mg C (61%), followed by the subtidal seagrasses 55,742 Mg C (28%) and seagrasses in the mangrove fringed creeks storing 21,189 Mg C (11%). These findings are important in highlighting the need to protect subtidal seagrass meadows and for building a national and global data base on seagrass contribution to global carbon dynamics.

Mangrove ecosystems along the East African coast are often characterized by a disjunct zonation pattern of seaward and landward Avicennia marina trees. This disjunct zonation may be maintained through different positions in the tidal frame, yielding different dispersal settings. The spatial configuration of the landscape and coastal processes such as tides and waves is expected to largely influence the extent of propagule transport and subsequent regeneration. We hypothesized that landward sites would keep a stronger genetic structure over short distances in comparison with enhanced gene flow among regularly flooded seaward fringes. We tested this hypothesis from densely vegetated A. marina transects of a well‐documented mangrove system (Gazi Bay, Kenya) and estimated local gene flow and kinship‐based fine‐scale genetic structure. Ten polymorphic microsatellite markers in 457 A. marina trees revealed no overall significant difference in levels of allele or gene diversities between sites that differ in hydrological proximity. Genetic structure and connectivity of A. marina populations however indicated an overall effect of geographic distance and revealed a pronounced distinction between channels and topographic setting. Migration models allowed to infer gene flow directionality among channels, and indicated a bidirectional steppingstone between seaward and nearest located landward stands. Admixed gene pools without any fine‐scale structure were found within the wider and more exposed Kidogoweni channel, suggesting open systems. Elevated kinship values and structure over 5 to 20 m distance were only detected in two distant landward and seaward transects near the mouth of the Mkurumuji River, indicating local retention and establishment. Overall, our findings show that patterns of A. marina connectivity are explained by hydrological proximity, channel network structure, and hydrokinetic energy, rather than just their positioning as disjunct landward or seaward zones., Using ten polymorphic microsatellite markers in 457 A. marina trees, we show that connectivity patterns of landward–seaward A. marina populations in Gazi Bay (Kenya) are explained by hydrological proximity, channel network structure, and hydrokinetic energy, rather than just their positioning as disjunct landward or seaward zones. Genetic structure and connectivity of A. marina populations indicated an overall effect of geographic distance and revealed a pronounced distinction between channels and topographic setting.

The functional and ecological importance of dead wood in terrestrial forests is widely recognized and researched. In contrast, much less is known about dead wood in mangrove forests, despite its known or demonstrated contribution to key ecological processes including nutrient cycling and seedling recruitment. In addition, mangrove dead wood provides an important service for millions of people; harvesting wood for fuel is widespread in mangroves and is often vital for the lives and wellbeing of people living close to these forests. Limited information on stocks and production, and the drivers of these, means that understanding and managing the supply of this service is difficult. Here we conduct a systematic review of the literature on dead wood stocks and production in mangrove ecosystems. Four hundred and seventy-five subject articles were found, with large gaps in geography, species, and forest type. After excluding records that were not relevant to our study and those from mass mortality events, 68 studies remained. We also added new data from 9 sites in Kenya, to provide overall estimates of mean (± SD) stocks of dead wood of 16.85 ± 25.35 Mg ha−1 standing and 29.92 ± 36.72 Mg ha−1 downed. Our analysis shows that potentially, higher stocks of dead wood might be found in forests without evidence of human impact. Average mean production with 95% CI was 6.30, 3.10–11.40 Mg ha−1 yr−1. Estimates of daily wood use were applied to give likely demands on wood from mangrove dependent communities. This review reveals the paucity of research on mangrove dead wood, hence these estimates of average stocks and productivity remain very limited and thus, further work on the dynamics of dead wood in mangroves and the ecological effects of its removal is needed.

Mangrove ecosystems can potentially and indirectly modulate the effects of sea level rise due to their ability to trap and retain sediments. In order to gain a better understanding of the potential sediment sources and dynamics in the mangroves of Vanga, Kenya, inter-seasonal riverine, estuarine and coastal/marine sediments together with agricultural soil and mangrove tissues were studied. Elemental ratios (C/N) and carbon (δ13C) stable isotope composition, were analysed to disentangle sources of sediment organic matter (SOM) in the Vanga, Estuary. The organic carbon (C) content, C/N ratios and δ13C values ranged between 0.1 and 2.4%, 9.9 to 35.5 and −24.8 to −19.9‰ respectively. These contents were also as expected relatively higher in mangrove tissues than in all the sediment samples. δ13C values of mangrove sediments were higher than those of the mangrove tissues, which was attributed to rapid decomposition, dilution by freshwater and mineral organic matter (OM) discharged by the Umba River as well as outwashing by ebb tides. On average, C/N ratios were also observed to be greater than 10 in all samples collected during both the dry and wet season. This has been shown to reflect a pronounced contribution of allochthonous organic matter. Using a combination of δ13C values and C/N ratio, the dominance of riverine POM was also evident from a Bayesian Stable Isotope Mixing Model in R-program (SIMMR) that indicated OM source mixing but with a dominant (∼60%) contribution of riverine OM. The observed and modeled variability of SOM in the Vanga estuary points to the hypothesized influence of the Umba River on Vanga Estuary sediments but with evidence of potential material exchange and influence of tidal fluxes within the estuary.

Fisheries are important sources of livelihoods to coastal communities. In the tropics fishing is conducted from mangroves, seagrass meadows to coral reefs. Studies on fisheries in the tropi...

Mangrove forests occur across a diversity of coastal landforms that influence their structural development and productivity. Preliminary studies in Kenya indicate that mangroves growing in the region north and south of Tana River delta have different structural attributes. We hypothesise a close relationship between mangrove distribution, climate and landform types. Floristic composition of mangroves along the coast of Kenya was characterised and differences illustrated using non-metric multidimensional scaling (nMDS). Other structural properties of mangroves such as tree height, basal area, stand density and standing biomass were also assessed and their differences tested using analysis of variance (ANOVA). A hierarchical cluster analysis was used to compare mangrove species based on structural properties. Additionally, a regression fit model was used to investigate the relationship between mangrove standing biomass and possible drivers of variability. The study revealed significant differences in mangrove tree diameter, tree height, basal area, stand density and standing biomass across the sampled sites. High values of structural complexity were observed in estuarine and deltaic settings with high influence of freshwater input whereas low levels of structural complexity were observed for peri-urban with direct human influence. Our findings suggest that structural variability of mangroves in Kenya is highly influenced by geomorphological and climatic variability along the coast as well as the past and present management regimes of the forest.

Ndirangu MD, Chira RM, Wang’ondu V, Kairo JG. 2018. Wave energy reduction and sediment stabilization by mangroves in Gazi Bay, Kenya. Biodiversitas 19: 83-94. Mangrove forests provide natural protection to the coast by attenuating wave energy and stabilizing sediments. The efficiency of coastal protection is likely to decline with increased degradation and losses of mangrove forests. Nevertheless, there are few empirical studies to test these hypotheses. The objective of the study was to investigate how wave energy and sediment stabilization vary with tree density in a monospecies stand of mangroves (Sonneratia alba) at Gazi Bay, Kenya. Seven belt transects were randomly selected along 900 m stretches of shoreline with homogenous emergent wave energy. Structural parameters, including; tree density, pneumatophores density, and basal areas were quantified using two quadrat measuring 25 m by 20 m along each transect. Three intertidal stations, each with five sampling points were sampled for wave energy using uniform plaster of Paris clod cards. Sediment stability was measured using improvised sinking metal disks made from bicycle spokes, and sediment accretion was monitored by Surface Elevation Tables (SETs). All transects showed significant difference in pneumatophores density (F (2.39) =25.15), tree density (F (2.33) =24.79), and basal area (F (2.39) = 29.66). The wave energy sampled by tree stems between stations and the correlation of wave energy reduction against tree density/ha, pneumatophores density, and basal areas per m2 also showed a significant difference. Regression analysis showed a significant difference in the sediment stability against tree density (R2 = 61%) and basal areas (R2 = 72.8%) while there was no significant difference between sediment stability and pneumatophores density (R2= 47%). Regression analysis between mean sediment accretion rates against all parameters were not significant. This study will help the managers and the government on the merit of using mangroves as bio-shields in protecting coastlines against erosion and stabilizing sediment in the wake of much anticipated global changing climate and sea-level rise.

Participatory forest management (PFM), as opposed to top down state management, is part of the decentralization process that has occurred in Africa over the past few decades. In Kenya, the process is still at its dawn with enforcing laws dating from 2005 and many pilot projects now in course. Little feedback has been given so far. This case study evaluates, for the first time, participatory management of a Kenyan protected mangrove forest. PFM, coupled with a status of protection, is believed to be an efficient way to preserve the threatened mangrove forests. Semi-structured interviews with local community members (people living within or next to the forest) and key-informants (people working in the forest management) were performed in order to measure three major components of participatory management: Knowledge, involvement, and perception of local communities. Those interviews revealed a partial and overall low involvement of local communities in the formal participatory management structure. Knowledge of the policy concerning mangrove forest management was higher for the people having a job related to natural resources from the forest (e.g. fishing or tour guiding) and for people holding at least a primary level education. The former group was also more involved in the management process. Villagers who were better informed about PFM approaches were also generally more involved in the management. Perceptions of PFM were contrasted and many criticisms were revealed at this early stage of implementation. These results are believed to evolve positively as the government regains trust among local communities who are given more power and wardenship on the forest.

Aims: Natural sedimentation rates may not affect mangrove trees adversely, but large and sometimes episodic delivery of sediment may result in decreased growth, dieback or mortality. In this study, we aim to assess the effects of different levels of partial sediment burial on mangrove tree structure and function. Methods: Trees of Avicennia marina, Ceriops tagal and Rhizophora mucronata were experimentally buried with terrestrial sediment to simulate different sedimentation levels (15, 30 and 45 cm). After 14 months, branch hydraulic conductivity, xylem structure and stomatal properties were assessed. Results: Sedimentation resulted in general increase in hydraulic conductivity following intermediate levels of burial. The process is also associated with varied anatomical modification in vessel grouping, vessel lumen size and potential conductive area in the three investigated mangrove tree species. Additionally, stomatal adjustment was observed in C. tagal with up to 37% reduction of total stomata area in leaves of buried trees. Conclusions: Although sedimentation may stimulate modification in vessel and stomatal properties of buried mangrove trees after a relatively short period of exposure, these traits may not necessarily be important in ensuring hydraulic conductivity which either increases or remains the same as in control following burial.

Githaiga MN, Kotut K, Kariuki F, Kairo JG. 2019. Structure and biomass accumulation of natural mangrove forest at Gazi Bay, Kenya. Bonorowo Wetlands 9: 18-32. The goal of this study was to determine the forest structure and estimate biomass accumulation above and below ground in the mangrove forest of Gazi Bay. The western, middle, and eastern forest blocks of the Gazi Bay mangrove forest were investigated for forest structure, whereas the western forest block was determined for biomass accumulation. To calculate below-ground biomass accumulation, in-growth cores of 80 cm long, 20 cm broad, and 60 cm deep were employed. Above-ground biomass accumulation was calculated using data on tree height and stem diameter at breast height (DBH-130). Leaf phenology was observed by tagging shoots. At the start, environmental variables were measured every four months for a year across four mangrove species zones. The linear regeneration sampling approach was used to determine the composition and distribution pattern of natural regeneration (LRS). Salinity revealed a strong negative connection with above-ground biomass accumulation among the soil environment characteristics studied. Sonneratia alba had the highest biomass accretion rate of 10.5 1.9 t ha-1 yr-1 among the four forest zones. Rhizophora mucronata (8.5 0.8 t ha-1 yr-1), Avicennia marina (5.2 1.8 t ha-1 yr-1), and Ceriops tagal (2.6 1.5 t ha-1 yr-1) were the next most abundant species. Above-ground and below-ground biomass accumulation differed significantly among zones (F (3, 8) = 5.42, p = 0.025) and (F (3, 8) = 16.03, p = 0 001), respectively. There was a significant difference in total biomass accumulation across zones (F (3, 8) =15.56, p = 0.001). For the entire forest, a root : shoot biomass accumulation ratio of 2 : 5 was calculated. This study's findings provide more accurate estimates of mangrove carbon capture and storage, which can be used in carbon credit discussions in the emerging carbon market.

Mangrove forests are among the most threatened ecosystems on earth. Some of these forests traverse national boundaries complicating their management due to differences in governance structures between countries. To improve the management of transboundary species regular monitoring is essential. Remotely sensed data were used to estimate forest cover and analyze conditions of mangroves in the proposed transboundary conservation area (TBCA) between Kenya and Tanzania. Image analysis was performed using unsupervised and supervised classification methods. The transboundary mangroves cover an estimated 11,906 ha; 55% being in Kenya, 45% in Tanzania. Ceriops tagal, Avicennia marina, and Rhizophora mucronata species co-dominate the mangroves of the transboundary area. The hotspot for loss and degradation of mangrove in the TBCA is Vanga in Kenya with a loss of 27 ha/yr. Harvesting of mangrove wood products have contributed to the loss of mangroves in the transboundary area. TBCA formation could play a critical role in ensuring sustainable mangrove resources utilization.

Seagrass habitats are important natural carbon sinks, with an average of ~14 kg C m−2 buried in their sediments. The fate of this carbon following seagrass removal or damage has major environmental implications but is poorly understood. Using a removal experiment lasting 18 months at Gazi Bay, Kenya, we investigated the impacts of seagrass loss on sediment topography, hydrodynamics, faunal community structure and carbon dynamics. Sediment pins were used to monitor surface elevation. The effects of seagrass removal on water velocity was investigated using Plaster of Paris dissolution. Sediment carbon concentration was measured at the surface and down to 50 cm. Rates of litter decay at three depths in harvested and control treatments were measured using litter bags. Drop samples, cores, and visual counts of faunal mounds and burrows were used to monitor the impact of seagrass removal on the epifaunal and infaunal communities. Whilst control plots showed sediment elevation, harvested plots were eroded (7.6 ± 0.4 and −15.8 ± 0.5 mm yr−1 respectively, mean ± 95% CI). Carbon concentration in the surface sediments was significantly reduced with a mean carbon loss of 2.21 Mg C ha−1 in the top 5 cm. Because sediment was lost from harvested plots, with a mean difference in elevation of 3 cm, an additional carbon loss of up to 2.54 Mg C ha−1 may have occurred over the 18 months. Seagrass removal had rapid and dramatic impacts on infauna and epifauna. There was a loss of diversity in harvested plots and a shift toward larger bodied, bioturbating species, with a significant increase in mounds and burrows. Buried seagrass litter decomposed significantly faster in the harvested compared with the control plots. Loss of seagrass therefore led to rapid changes in sediment dynamics and chemistry driven in part by significant alterations in the faunal community.

© 2021 The Authors. While mangroves are increasingly described as social-ecological systems (SESs), performing SES research is so much more than merely documenting local resource utilisation patterns in case studies. The aim of this paper is to review and show how ecological, human and institutional resilience could be understood and fostered in an era of uncertainty, through the adaptive cycle (AC) heuristic. Uncertainties come in many forms and shapes: climate change, social and economic dynamics, natural disasters, political and institutional disruption and ever-increasing public demands for participation. Social-ecological studies form windows of experimentation that can provide insights beyond their case-specific context. In order to synthesise and structure the cumulative knowledge base arising from existing and future studies, the need for a suitable overarching framework arose. Here, the AC heuristic represents the connectedness between variables of the mangrove SES versus the mangrove's accumulated capital (natural, built, human and social). We posit that the AC heuristic can be used to interpret spatial and temporal changes (ecological, social, economic, political) in mangrove SESs and we exemplify it by using the 2004 Indian Ocean tsunami as well as a century-long silviculture case. The AC, combined with the SES scheme, allows integration of the spato-temporal dynamics and the multi-dimensional character of mangrove SESs. We also reviewed the ecosystem functions, services and disservices of mangrove SESs, linking each of them to SES capital and variable (fast or slow) attributes, which in turn are closely linked to the different axes and phases of the AC. We call upon mangrove scientists from the natural, applied, social and human sciences to join forces in fitting diversified empirical data from multiple case studies around the world to the AC heuristic. The aim is to reflect on and understand such complex dynamic systems with stakeholders having various (mutual) relationships at risk of breaking down, and to prepare for interactive adaptive planning for mangrove forests. Belgian Science Policy Office ‘EVAMAB – Economic valuation of ecosystem services in Man & Biosphere Reserves' - BELSPO (BL/58/UN32); Erasmus Mundus Masters Course in Tropical Biodiversity and Ecosystems (TROPIMUNDO); VLIR-UOS-funded GREENDYKE Project (ZEIN2008PR347); BELSPO-funded MAMAFOREST-Project (SR/00/323); ZMT Academy travel grant; Singapore National Parks Board (NParks); TUYF Charitable Trust; HKU Seed Fund for Research; International Coral Reef Initiative (ICRI); UNEP/GEF Blue Forest Project; Pew Charitable Trust; Department of Science and Technology, India INSPIRE Faculty scheme (IFA18-LSPA111)

Key message: Large sedimentation events resulting in partial burial may negatively affect mangrove trees’ growth and survival. However, mangroves can adapt to respond dynamically within months to sediment burial, attributes which confer resilience. Abstract: Mangrove forests are generally sites of sediment deposition at the coast facilitated by the unique root structure of the trees, thus serving to help the system keep pace with rising sea level. However, at high levels it can cause anoxia in sediments and consequently tree mortality. This study evaluates the morphological and anatomical response of bark and roots of three mangrove tree species (Avicennia marina, Ceriops tagal and Rhizophora mucronata), commonly found along the Kenya coast and around the Indian Ocean, to partial burial by sediment. This was done through simulation of natural and rapid sedimentation in an experiment involving 15, 30 and 45 cm burial levels. Partial sediment burial resulted in an increase in root density which also aided survival particularly in C. tagal, where 5 of the 17 buried trees that did not form new roots in the 45 cm treatment died. Air lacunae in the root cortex became larger in pneumatophores following burial, while the ray parenchyma and cylinder of secondary xylem showed increased widths in cable roots of C. tagal. There was also an induction of the phellogen which produced more outer tissue in the buried section of stems in all three studied species (two fold increase in A. marina and C. tagal and fourfold in R. mucronata). The results suggest that the observed morpho-anatomical adaptations could lead to enhanced performance or recovery of biological processes in the burial-affected trees., SCOPUS: ar.j, info:eu-repo/semantics/published

Hamza, A.J.; Esteves, L.S.; Cvitanovic, M., and Kairo, J., 2020. Past and present utilization of mangrove resources in Eastern Africa and drivers of change In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 39–44. Coconut Creek (Florida), ISSN 0749-0208.Mangroves offer natural coastal protection and are carbon sinks, playing a key role in mitigating climate change impacts. Despite their recognized importance as the main livelihood of many coastal communities in developing countries, mangroves are being lost at fast rates impacting overwhelmingly the poorest people. The pressures of changing climate and human activities urge a better understanding of the drivers leading to mangrove loss and degradation and the effects on coastal communities. A systematic literature search was undertaken to review the current understanding of how mangroves have been used through time in Kenya and identify the key drivers of change. Results from 32 articles identified extraction of wood for construction and fuel as the major use of mangrove in Kenya. Direct needs of mangrove resources are the major cause of changes in the mangrove areas and this is due to lack of harvesting plans. The paper emphasizes the need to identify ways in which changes in mangroves can become opportunities to improve coastal communities living conditions.

Organic matter (OM) exchanges between adjacent habitats affect the dynamics and functioning of coastal systems, as well as the role of the different primary producers as energy and nutrient sources in food webs. Elemental (C, N, C : N) and isotope (δ13C) signatures and fatty acid (FA) profiles were used to assess the influence of geomorphological setting in two climatic seasons on the export and fate of mangrove OM across a tidally influenced tropical area, Gazi Bay (Kenya). The main results indicate that tidal transport, along with riverine runoff, plays a significant role in the distribution of mangrove organic matter. In particular, a marked spatial variability in the export of organic matter from mangroves to adjacent habitats was due to the different settings of the creeks flowing into the bay. Kinondo Creek acted as a mangrove retention site, where export of mangrove material was limited to the contiguous intertidal area, while Kidogoweni Creek acted as a flow-through system, from which mangrove material spreads into the bay, especially in the rainy season. This pattern was evident from the isotopic signature of primary producers, which were more 13C-depleted in the Kinondo Creek and nearby, due to the lower dilution of the dissolved inorganic carbon (DIC) pool, typically depleted as an effect of intense mangrove mineralisation. Despite the trapping efficiency of the seagrass canopy, suspended particulate OM showed the important contribution of mangroves across the whole bay, up to the coral reef, as an effect of the strong ebb tide. Overall, mixing model outcomes indicated a widespread mixed contribution of both allochthonous and autochthonous OM sources across Gazi Bay. Moreover, FAs indicated a notable contribution of brown macroalgae and bacteria in both sediment and suspended pools. These results suggest that ecological connectivity in Gazi Bay is strongly influenced by geomorphological setting, which may have far-reaching consequences for the functioning of the whole ecosystem and the local food webs.

1. Citizen science is gaining increasing prominence as a tool for science and engagement. However, despite being a potentially valuable tool for sustainable development, citizen science has little visibility in many developing countries. 2. We undertook a collaborative prioritisation process with experts in conservation and the environment to assess the potential of environmental citizen science in East Africa, including its opportunities, benefits and barriers. This provided principles that are applicable across developing countries, particularly for large‐scale citizen science. 3. We found that there was great potential for citizen science to add to our scientific knowledge of natural resources and biodiversity trends. Many of the important benefits of citizen science were for people, as well as the environment directly. Major barriers to citizen science were mostly social and institutional, although projects should also consider access to suitable technology and language barriers. 4. Policy implications. Citizen science can provide data to support decision‐making and reporting against international targets. Participation can also provide societal benefits, informing and empowering people, thus supporting the United Nations’ Sustainable Development Goals. In developing countries, innovation is needed to further develop culturally relevant citizen science that benefits participants and end users. This should be supported through regional networks of stakeholders for sharing best practice.

Recent research on participatory forest management (PFM) in the global south has highlighted the existence of a widespread “implementation gap” between the ambitious intent enshrined in legislation and the often partial, disappointing rollout of devolved forest governance on the ground. Here, through an ethnographic case study of forest officers (FOs) in Kenya, we draw on a framework of critical institutionalism to examine how key meso-level actors, or “interface bureaucrats,” negotiate and challenge this implementation gap in everyday forest governance. We go beyond consideration of institutional bricolage in isolation or as an aggregate category, to analyze how bricolage as aggregation, alteration, and/or articulation is variously driven, shaped, and constrained by FOs’ multiple accountabilities and agency. Our analysis highlights the locally specific, contingent, and mutually reinforcing nature of accountability, agency and bricolage, and their explanatory power in relation to the performance and nature of “actually existing” PFM.

Taking a coordinated, holistic approach to the governance of coastal ecosystems is widely advocated in recognition of the need to manage ecosystems as a whole. Despite commitment to approaches such as integrated coastal zone management and ecosystem-based management of fisheries, governance remains fragmented, with sectors such as environment, fisheries and forestry maintaining separate systems of governance from the national to village level. These systems include the formation of separate community-based structures, reporting directly to the respective sectoral ministry. This raises questions about how this collaborative governance approach aligns with taking a more integrated, holistic approach to management. The paper draws on findings from research in Kenya and Zanzibar-Tanzania in coastal villages where forest and fisheries management groups have been formed. The research found that the groups operate in compartmentalised ‘silos', in contrast to the interrelated ecosystems on which they depend, with little coordination of plans and priorities. In addition, these groups are not consistent in their relationship to local government, answering directly to the sectoral ministry rather than democratic local government, raising issues for accountability and sustainability. These dual challenges of a sectoral-focus and long-term sustainability must be addressed for management of ecosystems to be integrated and effective.

Mangrove forests are active carbon sinks and important for nutrient cycling in coastal ecosystems. Restoration of degraded mangrove habitats enhances return of ecosystem goods and services, including carbon sequestration. Our objective was to assess the restoration of primary productivity of reforested mangrove stands in comparison with natural reference stands in Gazi Bay, Kenya. Litter fall data were collected in nine Rhizophora mucronata and Sonneratia alba monospecific stands by use of litter traps over 2 years. Litter was emptied monthly, dried, sorted, and weighed. The reforested and natural stands showed seasonality patterns only in the production of reproductive material. Leaves constituted the highest percentage to total litter fall. Litter productivity rates for the R. mucronata stands were not significantly different and ranged from 6.61–10.15 to 8.36–11.02 t ha −1 yr −1 for the restored and natural stands, respectively. The productivity of 5 years R. mucronata stands reached 5.22 t ha −1 yr −1 and was significantly different from other stands. Litter productivity rates for S. alba stands was 7.77–7.85 for the restored stands and 10.15 t ha −1 yr −1 for the natural stand but differences were not significant. Our results indicate that plantations of at least 11 years have attained litter productivity rates comparable to the natural forests. This suggests that productivity of replanted mangroves is likely to reach complete recovery by this age under the prevailing environmental conditions.

Marine ecosystems are experiencing unprecedentedly high degradation rates than any other ecosystem on the planet, which in some instances are up to four times that of rainforests. Mangrove ecosystems have especially been impacted by compounded anthropogenic pressures leading to significant cover reductions of between 35 and 50% (equivalent to 1–2% loss pa) for the last half century. The main objective of this study was to test the hypothesis that peri-urban mangroves suffering from compounded and intense pressures may be experiencing higher degradation rates than the global mean (and/or national mean for Kenya) using Mombasa mangroves (comprising of Tudor and Mwache creeks) as a case study. Stratified sampling was used to sample along 22 and 10 belt transects in Mwache and Tudor respectively, set to capture stand heterogeneity in terms of species composition and structure in addition to perceived human pressure gradients using proximity to human habitations as a proxy. We acquired SPOT (HRV/ HRVIR/ HRS) imageries of April 1994, May 2000 and January 2009 and a vector mangrove map of 1992 at a scale of 1 : 50 000 for cover change and species composition analysis. Results from image classification of the 2009 image had 80.23% overall accuracy and Cohen's Kappa of 0.77, thus proving satisfactory for use in this context. Structural data indicate that complexity index (CI) which captures stand structural development was higher in Mwache at 1.80 compared to Tudor at 1.71. From cover change data, Tudor had lost 86.9% of the forest between 1992 and 2009, compared to Mwache at 45.4% representing very high hitherto undocumented degradation rates of 5.1 and 2.7% pa, respectively. These unprecedentedly high degradation rates, which far exceed not only the national mean (for Kenya of 0.7% pa) but the global mean as well, strongly suggest that these mangroves are highly threatened due to compounded pressures. Strengthening of governance regimes through enforcement and compliance to halt illegal wood extraction, improvement of land-use practices upstream to reduce soil erosion, restoration in areas where natural regeneration has been impaired, provision of alternative energy sources/building materials and a complete moratorium on wood extraction especially in Tudor creek to allow recovery are some of the suggested management interventions.

Despite covering only approximately 138 000 km2 , mangroves are globally important carbon sinks with carbon density values three to four times that of terrestrial forests. A key challenge in evaluating the carbon benefits from mangrove forest conservation is the lack of rigorous spatially resolved estimates of mangrove sediment carbon stocks; most mangrove carbon is stored belowground. Previous work has focused on detailed estimations of carbon stores over relatively small areas, which has obvious limitations in terms of generality and scope of application. Most studies have focused only on quantifying the top 1 m of belowground carbon (BGC). Carbon stored at depths beyond 1 m, and the effects of mangrove species, location and environmental context on these stores, are poorly studied. This study investigated these variables at two sites (Gazi and Vanga in the south of Kenya) and used the data to produce a country-specific BGC predictive model for Kenya and map BGC store estimates throughout Kenya at spatial scales relevant for climate change research, forest management and REDD+ (reduced emissions from deforestation and degradation). The results revealed that mangrove species was the most reliable predictor of BGC; Rhizophora muronata had the highest mean BGC with 1485.5 t C ha-1 . Applying the species-based predictive model to a base map of species distribution in Kenya for the year 2010 with a 2.5 m2 resolution produced an estimate of 69.41 Mt C [±9.15 95% confidence interval (C.I.)] for BGC in Kenyan mangroves. When applied to a 1992 mangrove distribution map, the BGC estimate was 75.65 Mt C (±12.21 95% C.I.), an 8.3% loss in BGC stores between 1992 and 2010 in Kenya. The country-level mangrove map provides a valuable tool for assessing carbon stocks and visualizing the distribution of BGC. Estimates at the 2.5 m2 resolution provide sufficient details for highlighting and prioritizing areas for mangrove conservation and restoration.

There is growing interest in carbon stocks and flows in seagrass ecosystems, but recent global reviews suggest a paucity of studies from Africa. This paper reviews work on seagrass productivity, biomass and sediment carbon in Africa. Most work was conducted in East Africa with a major geographical gap in West Africa. The mean above-ground, below-ground and total biomasses from all studies were 174.4, 474.6 and 514 g DW m-2, respectively with a global range of 461–738 g DW m-2. Mean annual production rate was 913 g DW m-2 year-1 (global range 816–1012 g DW m-2 year-1). No studies were found giving sediment organic carbon, demonstrating a major gap in seagrass blue carbon work. Given the small numbers of relevant papers and the large geographical areas left undescribed in Africa, any conclusions remain tentative and much remains to be done on seagrass studies in Africa.

Enhanced species richness can stimulate the productivity of plant communities; however, its effect on the belowground production of forests has scarcely been tested, despite the role of tree roots in carbon storage and ecosystem processes. Therefore, we tested for the effects of tree species richness on mangrove root biomass: thirty-two 6 m by 6 m plots were planted with zero (control), one, two or three species treatments of six-month-old Avicennia marina (A), Bruguiera gymnorrhiza (B) and Ceriops tagal (C). A monoculture of each species and the four possible combinations of the three species were used, with four replicate plots per treatment. Above- and belowground biomass was measured after three and four years' growth. In both years, the all-species mix (ABC) had significant overyielding of roots, suggesting complementarity mediated by differences in rhizosphere use amongst species. In year four, there was higher belowground than aboveground biomass in all but one treatment. Belowground biomass was strongly influenced by the presence of the most vigorously growing species, A. marina. These results demonstrate the potential for complementarity between fast- and slow-growing species to enhance belowground growth in mangrove forests, with implications for forest productivity and the potential for belowground carbon sequestration.

Anthropogenic impacts on biodiversity across a wide range of ecosystems are well docu- mented; however the responses of ecosystems to re- duced diversity are still poorly understood. We investi- gated the effects of species richness, species identity and environmental variables on aboveground biomass increment using replanted mangroves at Gazi Bay, Kenya. We planted 32 plots (36 m 2 ) with 8 treat - ments: all possible combinations of the trees Avicennia marina, Bruguiera gymnorrhiza, and Ceriops tagal and an unplanted control. Trees were planted in July and August 2004 and monitored annually until 2009. Growth was slow in the first 2 yr of the study, but by 2007 there was a significant treatment effect on aboveground biomass. A. marina showed strong competitive traits, with the best growth overall and enhanced growth of individual trees when planted in mixed species plots. The highest biomass was recorded in 3-species mixes; partitioning the net effects of species mixing showed a strong species selection effect, but there was also a complementarity effect in some of the three species plots. Biomass was positively correlated with presence of A. marina and negatively correlated with sediment salinity. We conclude that there is variation in the stages of plant development at which species richness effects manifest themselves; in addition the effects of environmental variables have a bearing on the nature and direction of the relationship between species richness and ecosystem function.

Fish assemblages of mangrove forest patches and adjacent intertidal flats in Ungwana Bay were compared using stake-net sampling in the mangrove forest and intertidal flat habitats between December 2002 and November 2003. Four forest sites were compared with paired intertidal flat sites with either sand or mud substrata. Distinct ichthyofaunal differences were found between the habitats. Pooled data indicated a significantly higher fish density and biomass in the forests compared to the intertidal flats. Mean fish densities were 0.2–2.7 fish m−2 in the forest and 0.1–2.1 fish m−2 on the flats. Thirty-five species were sampled, eight of which occurred exclusively in the forest and six were limited to the intertidal flats. However, species exclusive to either the forest or intertidal flats contributed

1. The structure, forest condition and regeneration status of nine mangrove forests in two trans-boundary areas of Mozambique bordering Tanzania and South Africa were studied. The main objective was to estimate the cutting intensity in the selected sites - Saco and Sangala in southern Mozambique; Mecufi, Pemba, Ibo, Luchete, Ulo in northern Mozambique, and Mngoji 1 and Mngoji 2 in Tanzania. 2. A total of 135, 10m x 10m quadrats were set in the outer, middle and lower parts of the mangrove forests at all sampling sites. Measurements included stem diameter at breast height (DBH) and height of adult trees (i.e. all trees with stem diameter more than 2.5 cm). Young trees (with stem diameter of less than 2.5 cm) were classified as juveniles. To assess forest condition, trees within the quadrat were classified into intact, partially cut, coppiced, die back and stump. Pole quality was appraised through the classification of the lead stem into three categories-straight, semi-straight and crooked poles. 3. The results indicate different levels of exploitation with Mngoji 1 and Mngoji 2, the most degraded sites, having stump densities of 959 stumps ha -1 and 592 stumps ha -1 , respectively. Most sites had mostly poles of inferior quality (crooked poles), but high densities of straight and semi-straight poles were found in Mngoji 1 (742 stems ha -1 ) and Saco (636 stems ha -1 ). 4. Natural regeneration was observed in most sites but not for all species, with adequate regeneration in Saco (14766 saplings ha -1 ) and Mecufi (14706 saplings ha -1 ), while low regeneration was recorded in Mngoji 1 and 2 (2212 saplings ha -1 and 4799 saplings ha -1 , respectively). 5. These results indicate the need for improved mangrove management and replanting especially in mangrove depleted conservation areas of southern Tanzania.

Economic analysis of mangrove reforestation is provided for a replanted Rhizophora mucronata plantation at Gazi Bay, Kenya. Major goods and services from a 12-year plantation were identified as: firewood and building poles, coastal protection, ecotourism, research and education, carbon sequestration and on-site fisheries. The net value of extractable wood products was estimated at US$379.17/ha/yr. For nonextractable products, however, the net value ranged from US$44.42/ha/yr in carbon sequestration to US$1,586.66/ha/yr in coastal protection. The total economic value of a 12-year-old Rhizophora plantation was therefore US$2902.87/ha/yr. Since most of these benefits cannot be internalized, there is need for governments to promote community efforts in mangrove reforestation through finding ways of marketing ecosystem services of the replanted forests.

1. This study reports above-ground biomass of 5 and 8 years old mangrove plantations in Kenya. Trees with stem diameter greater than 5.0 cm inside 100 m 2 sample plots were harvested, and then separated into stems (trunks), branches, leaves and prop roots. 2. Mean above-ground biomass was calculated at 20.25 t dry matter ha -1 for Rhizophora mucronata Lam., 11.7 t dry matter ha -1 for Avicennia marina (Forsk.) Vierh., 6.7 t dry matter ha -1 for Sonneratia alba Sm. and 3.7 t dry matter ha -1 for Ceriops tagal (Perr.) C. B. Robinson. In A. marina and R. mucronata, stems (52.19%) and prop-roots (30.28%), respectively, accounted for the highest proportion of the above-ground dry weight. While in S. alba and C. tagal, branch biomass represented the highest percentage of biomass, 48.20% and 43.62%, respectively. 3. The total above-ground biomass of R. mucronata was best estimated from regression equations using a combination of height and diameter above stilt root as the independent variables. For A. marina, C. tagal and S. alba there was no simple correlation found between the above-ground biomass and tree height or stem diameter. 4. Comparison of the regression models with those developed elsewhere gave different biomass values in these plots, further reinforcing the need for the use of site-specific allometric equations for biomass estimation.

Estimation of total biomass in woody ecosystems is important because of its relevance to nutrient turnover and the potential to store carbon. Most work on mangrove biomass, particularly in the Western Indian Ocean Region, has concentrated on the above-ground component; comparatively little is known on below-ground biomass. The current study was conducted at Gazi bay on the southern coast of Kenya. The objective was to determine the below-ground biomass of three species of mangrove, Rhizophora mucronata Lamarck, Avicennia marina (Forsk.) Vierh and Sonneratia alba J. Smith, in natural and replanted stands. The effects of distance from the tree base and of soil depth on root biomass and size distributions were also studied using coring. Live below-ground biomass (mean ± S.E.) ranged from 7.5 ± 0.4 t/ha to 35.8 ± 1.1 t/ha, 48.4 ± 0.7 t/ha to 75.5 ± 2.0 t/ha and 39.1 ± 0.7 t/ha to 43.7 ± 1.7 t/ha for R. mucronata, S. alba and A. marina, respectively, depending on the age of the stand. Including dead roots produced total biomass values of 34.9 ± 1.8–111.5 ± 5.6 t/ha, 78.9 ± 3.3–121.5 ± 7.3 t/ha and 49.4 ± 1.1–84.7 ± 5.4 t/ha for R. mucronata, S. alba and A. marina. These values imply carbon contents of live roots ranging between 3.8 ± 0.2 C t/ha and 17.9 ± 0.6 C t/ha, 24.2 ± 0.4 C t/ha and 37.7 ± 1.0 C t/ha and 19.5 ± 0.4 C t/ha and 21.9 ± 0.9 C t/ha for R. mucronata, S. alba and A. marina stands, respectively, and 17.4 ± 0.9 C t/ha and 55.7 ± 2.8 C t/ha, 39.4 ± 1.7 C t/ha and 60.7 ± 3.6 C t/ha and 24.7 ± 0.6 C t/ha and 42.4 ± 2.9 C t/ha for R. mucronata, S. alba and A. marina stands, respectively if dead roots are included. Stand densities were 4650 ± 177 stems/ha, 3800 ± 212 stems/ha and 3567 ± 398 stems/ha for R. mucronata 6-year old, 12-year-old and natural stands respectively. Mean stem diameter, and basal area were highest in the 12-year-old plantation while below-ground root biomass increased with age. Stand density for S. alba, was highest in the 12-year-old plantation (7900 ± 141 stems/ha) while the 9-year-old stand had trees with the largest diameter (7.7 ± 0.9 cm). Below-ground biomass was highest in the 12-year old (75.5 ± 2.0 t/ha) and lowest in the natural stand (48.4 ± 0.7 t/ha). Stand density for A. marina was highest in the 12-year-old plantation (4300 ± 919 stems/ha) while mean stem diameter (7.9 ± 0.7 cm) and basal area (16.2 ± 2.1 m2/ha) were highest in the natural stand. Below-ground biomass in the 12-year-old (43.7 ± 1.7 t/ha) and natural stands (39.1 ± 0.7 t/ha) was similar. Root densities decreased with soil depth and with distance from the base of trees for all species and stands. Fine roots (diameter

Stand recognition (delineation and labeling) and species mapping are cornerstones of forest inventory mapping and key elements to forest management decision making. We present an automated method for mangrove stand recognition and species mapping based on fuzzy per-pixel classification techniques. Mapping of the present distribution of the four dominant mangrove species in Gazi Bay (Kenya) was done using supervised Maximum Likelihood fuzzy classification of a QuickBird satellite image. Species recordings were obtained during a field mission in July-August 2003 with the Point-Centred-Quarter-Method (PCQM). The overall accuracy of the species map is 72%, where the two socio-economically most important species are mapped with user accuracies above 85%. Mangrove stand maps are obtained through supervised fuzzy classification of the multispectral satellite image, convolution of an appropriate window size and subsequent elimination of patches covering less than 0.05ha. The automated stand boundaries were compared to visual delineations done by an expert interpreter. The quality of the correspondence between visual and automated stand boundaries was assessed based on the quantity of overlap one has with the other. The correspondence varied from perfect, over good, to poor matches. An overall correspondence of 64% was obtained for visual labeling of stands versus automated labeling (classification) based on dominant species and total cover. When only dominant species were taken into account, the overall accuracy of stand labeling increased to 86%. Automated stand delineation and labeling are of a quality suitable for operational use in mangrove forest management.

Forest structure and productivity was investigated in a 12-year-old Rhizophora mucronata Lam. plantation at Gazi Bay, Kenya. Sampling was carried out in 22, 10 m � 10 m quadrats laid along belt transects perpendicular to the waterline. Within each quadrat all trees with stem diameter greater than 2.5 cm were identified, position marked and counted. Vegetation measurements included tree height (m), canopy cover (%) and stem diameter measured at 1.3 m above the ground (D130); from which were derived basal area (m 2 /ha); stand density (stems/ha) and biomass (t/ha). Information regarding composition and distribution of juveniles was derived using linear regeneration sampling (LRS). The replanted forest had a stand density of 5132 stems/ha; with a mean canopy height and stem diameter of 8.4 � 1.1 m (range: 3.0–11.0 m) and 6.2 � 1.87 cm (range: 2.5– 12.4 cm), respectively. The total juvenile density was 4886 saplings per hectare; 78.6% of which constituted the parental canopy. The standing biomass for the 12-year-old R. mucronata plantation was 106.7 � 24.0 t/ha, giving a biomass accumulation rate of 8.9 t/(ha year). # 2008 Elsevier B.V. All rights reserved.

Mangrove reforestation projects often suffer from low sapling survival, especially after transplanting saplings from nurseries to reforestation areas. This may be due to the sediment conditions at the target site, the planting strategy or failure to re-establish ecosystem processes. We examined experimentally the influence of environmental context, species richness and identity, sapling height and position on sapling survival and environmental variables linked to ecosystem functioning at deforested sites in Gazi Bay, Kenya. At site 1, a high shore location, 32 plots (36 m2) were planted with 8 treatments: all possible combinations of Avicennia marina, Bruguiera gymnorrhiza, and Ceriops tagal and an unplanted control (total: 3390 saplings; 4 plots/treatment). At site 2, a low shore location, the influence of sapling height, sapling position and sediment depth were tested by planting with 697 Sonneratia alba in a single monospecific plot (341 m2). After ∼2 years, there were significant differences in survival among the three species at site 1 with Bruguiera gymnorrhiza recording the lowest survival rate (29%). Survival was correlated with salinity (a strong effect) and height above chart datum (a weaker effect) at site 1. Sapling position did not significantly affect survival at either site. There was thus no evidence that early survival of transplanted saplings is influenced by the species mix in which they are grown, or by their position in the plot. Rather the tolerance of individual species to salinity was the key to their survival at the high tidal site. Species mix also had no significant effects on environmental variables in the plots. The former presence of a species at a site does not guarantee it will succeed there again if environmental degradation has exceeded species’ tolerance.

The productivity of an over-exploited and sewage polluted peri-urban mangrove was assessed through litter fall studies to establish vulnerability to human actions and climate change. Litter from three common mangrove species, Rhizophora mucronata Lam. (Rhizophoraceae), Sonneratia alba Sm. (Sonneratiaceae), and Avicennia marina (Forssk.) Vierh. (Avicenniaceae) were monitored over a period of two years. The mean annual litter fall was estimated at 12.16 ± 2.89 t ha−1yr−1. Litter fall was seasonal in both content and quantity, with high rates occurring in the dry North Easterly Monsoon (NEM) season, January-April (ca. 5.10 ± 1.36 g DW m−2 day−1) and lower rates in the cool and wet South Easterly Monsoon (SEM) season, June-October (ca. 2.53 ± 0.47 g DW m−2 day−1). Litter fall varied significantly between species, R. mucronata recording the highest annual rate (15.34 ± 3.34 t ha−1yr−1), with no significant difference between A. marina and S. alba, (11.44 ± 2.90 and 9.69 ± 5.26 t ha−1yr−1 respectively). Sewage exposure did not affect litter fall rates for all species, but affected leaf nutrient content as expressed by the leaf δ15N signature. A strong correlation between leaf C:N ratio and leaf δ15N signature was observed, indicating a more open N cycle, favouring δ15N accumulation. Sewage exposure therefore does not necessarily translate into elevated productivity in mangroves, but causes alteration of leaf nutrient content depending on species. Prevailing climatic conditions however, may influence litter fall and thus phenology and health of the system. The vulnerability of the Tudor Creek mangroves to climate change may be ranked high due to low production (20%

This study is intended to provide early access to recent findings on the formation of the successive cambia of Avicennia marina (Forssk.) Vierh. in Kenya. The non-annual character of the growth layers was demonstrated by using three trees from a cambial marking experiment and three trees from a plantation of known age. The respective number of growth layers produced during one year was on average a half and three. Considering 28 stem disks of trees at three study sites, differing in local site conditions, growth layer development was shown to be strongly correlated with stem diameter (R2=0.84, p

In response to widespread global degradation of mangrove forests, many initiatives have been undertaken to reforest degraded sites. However, many of these replantings are mono- specific, raising questions regarding habitat change and reduced ecological functions in mangrove plantations compared to natural mixed mangrove forests. The main objective of this study was to determine whether colonising mangrove juveniles can be recruited into the adult tree layer and thus enhance the structural complexity of previously reforested monospecific stands. Vegetation structure of originally monospecific replanted mangrove stands (Sonneratia alba and Rhizophora mucronata) that were 8 yr old was assessed. Instantaneous juvenile (seedling/sapling) diversity and abundance were determined. Adjacent natural stands were used as reference sites. The R. mucronata stand had the same species richness as its natural reference and thus had a higher Complexity Index due to recruitment of non-planted species into the adult tree population than in a previous assessment when it was monospecific. Juvenile species richness and diversity were similar between the R. mucronata stands (reforested and natural); however, the total juvenile density was significantly higher (p < 0.05) in the natural stand (7390 ± 660 juveniles ha -1 ) than in the reforested stand (2048 ± 667 juveniles ha -1 ). In contrast, the adult vegetation layer of the S. alba reforested stand remained monospecific, suggesting 100% mortality of previously observed non-planted mangrove juveniles. Many replanted mangroves around the globe are monocultures and are thus likely to have low thresholds to pertur- bations, as they do not benefit from the 'portfolio effect' provided in mixed species stands. Successful recruitment of non-planted species into replanted monospecific mangroves stands may therefore enhance ecosystem productivity and stability. However, more research needs to be conducted on traits of different mangrove species and their contribution to ecosystem productivity and sensitivities to environmental perturbations.

Long-term decadal retrospection in spatio-temporal imagery analyses can only be carried out using aerial photographs, which are still the most detailed remotely sensed data available. Visual interpretation of such imagery is most efficient and inexpensive in the light of ecosystem monitoring research in developing countries, which are often unable to cope with the development or the cost of acquisition of commercial space-borne imaging (e.g. IKONOS, Quickbird). In this light, the present paper explicitly analyses the methodological use of image attributes of air-borne imagery from mangrove forests, and investigates the consistency and constraints of mangrove image attributes in visually interpreted air-borne imagery. Six image attributes are analysed, and their application is illustrated using various mangrove sites in Kenya and Sri Lanka. Comparison of identification keys reveals that minor attributes such as 'ecological position' are informative, and that image attributes for a particular species or genus are apparently less plastic and more widely applicable than formerly assumed. Emphasis on compulsory fieldwork is made and constraints related to reflection and interference, amongst others, are discussed.

The main objective of this study was to assess how mangrove reforestation has influenced litter degradation and concomitant nutrient dynamics in previously deforested plantations. Dynamics of nutrients (carbon, nitrogen and C:N ratios) in decomposing leaves of conspecific species were investigated with litterbags in Sonneratia alba and Rhizophora mucronata reforested treatments using appropriate bare and natural less disturbed treatments as controls. Bare treatments had the lowest decay rates (Kd-1) and thus the highest t50 values (when 50% of the original weight had been decomposed) for both species. The contrary was true for natural treatments, while both parameters were intermediate in reforested treatments, suggesting that other than direct litter input, reforestation has modified site conditions which have enhanced organic matter decomposition. There were significant seasonal differences in decay rates for treatments within the R. mucronata species, with rates being higher during the wet season with accompanying lower t50 values. Decay rates were overall higher (P S. alba species and as a result no litter was retrieved from its natural treatment by the 5th week. Higher amphipod colonisation was observed in reforested and natural treatments than bare treatments, which may have contributed to higher decay rates in the former. There were significant differences (P

Recolonisation by crab species and sediment-infauna taxa (at class level) in artificially regenerated mangrove stands of Avicennia marina, Rhizophora mucronata and Sonneratia alba (5 yr old) were studied using respective bare sites (open without mangroves or denuded) and natural sites (relatively undisturbed) as controls. The controls were chosen based on site history, physical proximity and tidal inundation class in reference to the particular reforested mangrove stand and samples randomly taken. A number of environmental variables were measured; interstitial water salinity and temperature (measured at low tide) were lower, whereas sediment organic matter content was higher in the areas with mangrove cover, with the natural sites having the highest content. The bare sites were generally sandier, whereas the areas with mangrove cover had higher proportions of clay and silt. Generally, there was a higher crab density in the reforested sites than in the bare sites, whereas crab species diversity (Shannon diversity index) did not vary from one site to another for any of the mangrove species. In terms of crab species composition, the reforested sites were more similar (Sørensen similarity coefficient) to the natural sites and less to the bare controls. For sediment-infauna, the reforested sites had a significantly higher density than the respective bare controls, while the natural sites had the highest density. The number of sediment-infauna taxa in both the reforested and natural sites of all the mangrove species was similar and higher than in the comparable bare sites. The results suggest that the reforested sites are supporting more faunal recolonisation, and therefore becoming more akin to the natural mangrove sites in terms of the investigated functional indicators. The findings seem to support the use of artificial mangrove regeneration (in areas where natural regeneration has been impeded by physical conditions or otherwise) as an effective management tool in the restoration and conservation of the functional integrity of degraded mangrove habitats.

Mangrove forests are under global pressure. Habitat destruction and degradation persist despite longstanding recognition of the important ecological functions of mangroves. Hence new approaches are needed to help stakeholders and policy-makers achieve sound management that is informed by the best science. Here we explore how the new policy concept of Climate Compatible Development (CCD) can be applied to achieve better outcomes. We use economic valuation approaches to combine socio-economic data, projections of forest cover based on quantitative risk mapping and storyline scenario building exercises to articulate the economic consequences of plausible alternative future scenarios for the mangrove forests of the South Kenya coast, as a case study of relevance to many other areas. Using data from 645 household surveys, 10 focus groups and 74 interviews conducted across four mangrove sites, and combining these with information on fish catches taken at three landing sites, a mangrove carbon trading project and published data allowed us to make a thorough (although still partial) economic valuation of the forests. This gave a current value of the South Coast mangroves of USD 6.5 million, or USD 1166 ha(-1), with 59% of this value on average derived from regulating services. Quantitative risk mapping, projecting recent trends over the next twenty years, suggests a 43% loss of forest cover over that time with 100% loss at the most vulnerable sites. Much of the forest lost between 1992 and 2012 has not been replaced by high value alternative land uses hence restoration of these areas is feasible and may not involve large opportunity costs. We invited thirty eight stakeholders to develop plausible storyline scenarios reflecting Business as Usual (BAU) and CCD - which emphasises sustainable forest conservation and management - in twenty years time, drawing on local and regional expert knowledge of relevant policy, social trends and cultures. Combining these scenarios with the quantitative projections and economic baseline allowed the modelling of likely value added and costs avoided under the CCD scenario. This suggests a net present value of more than US$20 million of adoption of CCD rather than BAU. This work adds to the economic evidence for mangrove conservation and helps to underline the importance of new real and emerging markets, such as for REDD + projects, in making this case for carbon-rich coastal habitats. It demonstrates a policy tool - CCD - that can be used to engage stakeholders and help to co-ordinate policy across different sectors towards mangrove conservation.

Despite earlier efforts to understand the role played by grapsid crabs in mangroves, their importance in the structuring and functioning of such systems is fully appreciated, particularly with regard to small-scale studies. The present study provides some new data on the interaction between mangroves and crabs, namely the link between the distribution of particular mangrove tree species and the distribution of certain crab species at the assemblage level. Floristic and faunistic releves were made in Gazi Bay (2 sites) and Mida Creek (3 sites), 140 km apart on the Kenyan coast, along five transects in a series of quadrats covering the width of the mangrove belts. Zonation of both mangrove vegetation and brachyuran fauna was described and height above datum and distance to the mainland (limit of non-flooded area) measured. The relationship between the presence and the absence of crabs and trees was analysed using detrended correspondence analysis. Summarized, the mangrove tree zonation pattern contains four assemblages with a particular dominant species: first a landward Avicennia marina zone, followed by a mixed zone with Ceriops tagal, Rhizophora mucronata and Bruguiera gymnorrhiza, and finally a R. mucronata zone and a Sonneratia alba zone, both of which can mix with seaward A. marina. Ordination results show that the distribution of Neosarmatium meinerti and Sesarma ortmanni is linked to the landward A. marina zone, that of Neosarmatium smithii, Sesarma guttatum and Sesarma leptosoma corresponds to the R. mucronata zone and that of Metopograpsus thukuhar and Sesarma elongatum to the seaward A. marina and S. alba zone. There appears to be one major underlying factor in the zonation of both crabs and trees, with most likely a complex multiple causality. In certain cases the association between crabs and trees are causal, whereas in other cases it can be the result of an independent restriction to the same zones by a common cause.

The status of mangroves within and adjacent to Kiunga Marine Protected Area (MPA) were assessed by means of aerial photographs and intensive ground truthing. Vegetation maps (1 : 25,000) were produced on GIS environment making it possible to store, retrieve and analyze various types of information very quickly. The maps together with the digitized information provide important tools to the management of mangroves of Kiunga MPA since various proposed treatments can now be entered and summarized thus providing useful overviews for planning, implementation and monitoring. The present inventory revealed that the existing mangrove forests within and adjacent to Kiunga MPA have a net standing volume of 2,354,004.85 m3 in 16,035.94 ha. There are eight species of mangrove trees, of which Rhizophora mucronata and Ceriops tagal are dominant. The standing volume ranges between 6.85 to 710.0 m3 ha−1 for stem with diameter above 5.0 cm. The average volume of the entire study area was 145.88 m3 ha−1, which corresponds to a stocking rate of 1736 stems per ha. Given its high potential productivity and regeneration, mangroves within and adjacent to Kiunga MPA have excellent prospects for sustainable exploitation.

Vegetated marine habitats are globally important carbon sinks, making a significant contribution towards mitigating climate change, and they provide a wide range of other ecosystem services. However, large gaps in knowledge remain, particularly for seagrass meadows in Africa. The present study estimated biomass and sediment organic carbon (Corg) stocks of four dominant seagrass species in Gazi Bay, Kenya. It compared sediment Corg between seagrass areas in vegetated and un-vegetated 'controls', using the naturally patchy occurence of seagrass at this site to test the impacts of seagrass growth on sediment Corg. It also explored relationships between the sediment and above-ground Corg, as well as between the total biomass and above-ground parameters. Sediment Corg was significantly different between species, range: 160.7-233.8 Mg C ha-1 (compared to the global range of 115.3 to 829.2 Mg C ha-1). Vegetated areas in all species had significantly higher sediment Corg compared with un-vegetated controls; the presence of seagrass increased Corg by 4-6 times. Biomass carbon differed significantly between species with means ranging between 4.8-7.1 Mg C ha-1 compared to the global range of 2.5-7.3 Mg C ha-1. To our knowledge, these are among the first results on seagrass sediment Corg to be reported from African seagrass beds; and contribute towards our understanding of the role of seagrass in global carbon dynamics.

Sedimentation results in the creation of new mudflats for mangroves to colonize among other benefits. However, large sediment input in mangrove areas may be detrimental to these forests. The dynamics of phenological events of three mangrove tree species (Avicennia marina, Ceriops tagal, and Rhizophora mucronata) were evaluated under experimental sediment burial simulating sedimentation levels of 15, 30, and 45 cm. While there was generally no shift in timing of phenological events with sedimentation, the three mangrove tree species each responded differently to the treatments. Partially buried A. marina trees produced more leaves than the controls during the wet season and less during the dry season. Ceriops tagal on the other hand had higher leaf loss and low replacement rates in the partially buried trees during the first 6 months of the experiment but adapted with time, resulting in either equal or higher leaf emergence rates than the controls. Rhizophora mucronata maintained leaf emergence and loss patterns as the unaffected controls but had a higher fecundity and productivity in the 15-cm sedimentation level. The results suggest that under incidences of large sedimentation events (which could be witnessed as a result of climate change impacts coupled with anthropogenic disturbances), mangrove trees may capitalize on "advantages" associated with terrestrial sediment brought into the biotope, thus maintaining the pattern of phenological events. © 2014 The Authors., SCOPUS: ar.j, info:eu-repo/semantics/published

In this review paper, we aim to describe the potential for, and the key challenges to, applying PES projects to mangroves. By adopting a “carbocentric approach,” we show that mangrove forests are strong candidates for PES projects. They are particularly well suited to the generation of carbon credits because of their unrivaled potential as carbon sinks, their resistance and resilience to natural hazards, and their extensive provision of Ecosystem Services other than carbon sequestration, primarily nursery areas for fish, water purification and coastal protection, to the benefit of local communities as well as to the global population. The voluntary carbon market provides opportunities for the development of appropriate protocols and good practice case studies for mangroves at a small scale, and these may influence larger compliance schemes in the future. Mangrove habitats are mostly located in developing countries on communally or state-owned land. This means that issues of national and local governance, land ownership and management, and environmental justice are the main challenges that require careful planning at the early stages of mangrove PES projects to ensure successful outcomes and equitable benefit sharing within local communities. Electronic supplementary material The online version of this article (doi:10.1007/s13280-014-0530-y) contains supplementary material, which is available to authorized users.

The assessment of mangrove litter productivity by litter-traps for the year 1996–97 was obtained from three dominant mangrove stands in Mida Creek: Rhizophora mucronata (L.), Ceriops tagal (Perr.) C. B. Robinson and Avicennia marina (Forsks). Two Monsoon-related climatic conditions occur in the area: wet period (Southeast monsoons, March-July) and dry season (Northeast monsoons, October-January). The three stands showed variations in productions between morphological parts and between seasons. Community average total production during the period was 4.36g dry m −2 day −1 with 6.57 and 2.65g dry m −2 day −1 produced in wet and dry periods respectively. Species average total productions for the period were 4.49, 6.22 and 2.35g dry m −2 day −1 for Rhizophora, Ceriops and Avicennia stands respectively. Species average seasonal productions were 6.13, 11.00, and 2.55g dry m −2 day −1 for wet periods, and 2.91, 2.80 and 2.25g dry m −2 day −1 for dry periods for Rhizophora, Ceriops and Avicennia stands respectively. Peak litterfall in Rhizophora and Ceriops occurred during the wet season, while peak litterfall for Avicennia occurred during the dry season. Leaves dominated outflow throughout the observation period, with staggered peaks for the different species and seasons. The reproductive units also showed staggered peaks between the different species and seasons. The staggered production pattern in litter quality and quantity amongst the different species is discussed in relation with their phenological spreads and prevailing unique hydrological conditions.

Mangroves form important ecosystems in Kenya's coastal areas. They produce goods and services that are of environmental, ecological and economic importance to human society. However, mangroves are under continuing pressure from anthropogenic disturbances. A particular concern has been the clearing of mangrove areas to reclaim land for other uses such as aquaculture, salt manufacture, agriculture and housing. About 10 000 ha of mangrove areas have been cleared for salt manufacture between Ngomeni and Karawa, while in Lamu, close to 100 ha of mangrove forest was killed by dredged-up sediment that was deposited during the construction of the Mokowe sea jet. 100 ha of mangrove area have been converted for aquaculture at Ngomeni. At Gazi Bay, about 100 ha of mangrove forests was cleared for fuelwood and in Makupa Creek, Mombasa, 10 ha of mangroves died due to oil pollution. The total area lost is therefore 10 310 ha which represents about 20% of the total mangrove forest.