Effective monitoring of seagrass is essential for the conservation of this critical marine ecosystem. The choice of monitoring method depends on balancing accuracy, efficiency, cost and accessibility, especially in contexts requiring community engagement and ownership. This study evaluates and compares three seagrass monitoring methods, including video, quadrat and point count, at a field site in Kenya to assess their suitability for community-led monitoring in resource-limited settings. The video method, used as a benchmark, demonstrated high precision with moderate resource demands, requiring 18 samples to detect a 20% change in cover with 80% statistical power. However, its technical complexity and initial setup costs could limit community adoption. Quadrat sampling, while labour-intensive, provided reliable estimates of species richness and total cover, although it required a larger sample size (36) than the video method to achieve the same power. Point count, the least resource-intensive method, was time-efficient but consistently overestimated seagrass cover. These results support the widely used SeagrassNet and Seagrass-Watch sampling methods. These accessible methods can both supply accurate data and help to foster local ownership and capacity. The findings highlight trade-offs between the methods, suggesting that combining technical training with simplified tools such as automated analyses and accessible data interpretation frameworks could enhance the applicability of advanced techniques like the video method in community settings. While accessible technological advancements might improve accuracy and efficiency, such benefits need to be balanced against the wider community engagement in monitoring and conservation. Nevertheless, quadrat sampling emerges as the most suitable method for immediate community use, given its reliability and accessibility, while the integration of video methods could be pursued where resources and training permit.

Africa's 'blue carbon ecosystems' are increasingly recognised for their role in climate change mitigation, biodiversity conservation and sustainable livelihoods, with existing carbon offset projects showcasing their potential to sequester carbon and support community livelihoods. Despite this promise, blue carbon (BC) projects remain scarce across Africa. Understanding the barriers to BC implementation is therefore critical for unlocking their potential across the continent. Through a horizon scan and expert solicitation involving 41 participants from 20 countries, this study identified 13 major barriers spanning social, technical, economic, environmental, and policy domains. Governance obstacles, such as weak law enforcement, complex land tenure, and unclear carbon rights, emerged as the most significant reflecting Africa's diverse regulatory landscapes and often unstable political contexts. Socio-economic challenges, such as few sustainable livelihood options for those involved in/impacted by BC projects, further constrain progress. Economic barriers, particularly limited funding for project design, monitoring, and delivery, also featured prominently. Technical and environmental factors, including low scientific capacity, fragmented ecosystem distribution, and climate-driven impacts, further complicate project design and scalability. The barriers identified varied significantly across regions and ecosystem types. To overcome them, we propose targeted policy reforms, innovative financing, capacity building, and integrated management approaches that align local priorities with national climate goals. Collectively, these strategies can unlock Africa's BC potential, delivering substantial climate, biodiversity and socio-economic benefits.

1. Seagrass ecosystems are crucial for supporting biodiversity and serve as vital fishing grounds. Unfortunately, their cover is declining globally. In Kenya, seagrass cover is falling by similar to 1.6% annually but the causes are unknown. This study investigated the possible anthropogenic drivers of seagrass decline along the Kenyan coastline. 2. Satellite and large-scale geographic data on population growth, chlorophyll alpha trends, housing, and road density were used to explore their effects on seagrass cover loss along the whole coastline. Direct investigations were conducted into the effects of seine netting and basket trapping within seagrasses. 3. There was an average loss of 1.9 km(2) per 25 km(2) seagrass cover between 2000 and 2016 and a weak but significant relationship between population growth and seagrass decline, with losses concentrated in areas with the highest population density. In contrast with studies elsewhere, there was no evidence implicating eutrophication, supporting the suggestion that declines are linked to direct anthropogenic impacts such as fishing. A field experiment showed that a single instance of seine netting caused a significant loss of seagrass cover of 8.3% within the area fished, while no significant changes were observed with basket traps. 4. These findings support the evidence that declines in seagrass in Kenya and in other African countries are anthropogenic and are linked with fishing pressure and endorse existing efforts to restrict use of seine netting within seagrasses. 5. Understanding the status, changes, and drivers of change in seagrass ecosystems in Africa is crucial for developing effective national and local seagrass conservation plans, and for compliance with international commitments on seagrass conservation.

The recognition of the benefits that seagrasses contribute has enhanced the research interest in these marine ecosystems. Seagrasses provide critical goods and services and support the livelihoods of millions of people. Despite this, they are declining around the globe. To conserve these ecosystems, it is necessary to understand their extent and the drivers leading to their loss. However, global seagrass cover estimates are highly uncertain and there are large regional data gaps, especially in the African continent. This work reviewed all available data on the extent of seagrass cover, evidence of changes in cover and drivers of this change in Africa, to inform management and conservation approaches across the continent and identify gaps in knowledge. Using a systematic review and expert consultation, 43 relevant articles were identified. Of the 41 African countries with a coastline, 27% had no data on seagrass cover. For 44%, data were available for some parts of their coastline, while 29% had data for their entire coastline. Quantitative information on trends in seagrass cover change was only available from three countries. The study identified 32 suggested drivers of seagrass cover loss, with impacts from fishing mentioned most frequently. Direct anthropogenic drivers accounted for 66.7% of the mentions, while climate and biologically induced drivers accounted for 22.7% and 10.6%, respectively. This study demonstrates the need for better estimates of seagrass extent, in at least 70% of relevant African nations, and major gaps in our understanding of the drivers of seagrass decline in Africa.

Mangroves offer a range of globally acknowledged advantages, yet they continue to be lost and degraded. Efforts to restore lost mangroves using conventional techniques in high-energy areas result in low success rates due to the removal of seedlings via wave action. We assessed the efficacy of using modified Riley Encasement Methods in the restoration of mangroves in high-energy areas in Gazi Bay, Kenya. Vegetation and soil baseline data were collected in 49 square plots of 100 m2, which were established along belt transects perpendicular to the shoreline. The following mangrove vegetation data was collected: species composition, tree height (m), and stem diameter (cm). From these, the importance value index (IV), basal area, and standing density (stems/ha) were derived. Sediment cores were made in the center of each square plot for carbon and grain size analysis. Mangrove (Rhizophora mucronata) planting adopted a randomized complete block design (RCBD) in which the planting area was divided into three blocks (A, B, C). Within each block, treatments (bamboo and different-sized PVC pipes) were randomly assigned locations. The results of the study reveal significant variations in survival and growth rates among treatments. Higher survival rates were recorded for seedlings grown within PVC encasements (43%), surpassing bamboo (1%) and control groups (4%). Our findings suggest that PVC pipes were efficient in supporting and protecting seedlings from external forces. We expound on the implications of the results and highlight potential enhancements for the effectiveness of encasement technique in mangrove restoration.

Sustainable management of mangrove resources requires monitoring of status and conditions of the forest over time. This study assessed structure and regeneration of mangroves across five mangrove management blocks in Lamu, Kenya. Using stratified random sampling strategy, mangroves were sampled in 152 square plots of 400 m(2) along belt transects established perpendicular to the shoreline. Linear regeneration sampling (LRS) was employed to assess composition and patterns of natural regeneration. Six mangrove species were encountered during this study. Based on importance value index, the dominant mangrove species in Lamu are Rhizophora mucronata and Ceriops tagal. At least 42% of the forest is stocked with low-quality poles, an indicator of prolonged human pressure. However, natural regeneration rate of 7,342 +/- 450 juveniles ha(-1) observed in the forest is considered adequate to support forest recovery after disturbance. The findings of the study have direct applications in the development of harvest plans for mangroves in Lamu.

Mangrove forests provide harvestable wood and non-wood resources to human society globally. The current study evaluated value chain of mangrove wood products from Lamu, Kenya, and how these impacts on resources’ sustainability. Results show that, exploitation of mangrove wood products in Kenya involves several actors, including national regulator, licensees, cutters, transporters, stockists and the consumers. Based on the differences between allowable and harvest data, Lamu mangroves can be said to be under-exploited. For the 1992–2018 period, an average of 223.5 scores ha−1yr−1 of mangrove poles were target for harvesting from Lamu. During the same period, the harvest data indicate an average of 6.2 scores ha−1yr−1 of mangrove poles were removed. However, based on stand level data generated as part of this study, mangroves in Lamu are over-exploited and stocked with non-merchantable poles. There are differentiated net income among various actors in mangrove trade in Kenya. Mangrove cutters are among the ‘losers’ in mangrove trade value chain earning a monthly net income of USD118.6 ± 17.9. Winners in mangrove trade is the Kenya Forest Service, Licensees, transporters, and mangrove dealers (or stockists) in urban centers. The findings of this study are critical in development of the harvesting plan for Lamu mangroves. The results will provide insights toward streamlining mangrove trade for community development, revenue generation and environmental sustainability.

Our knowledge of the factors that can influence the stock of organic carbon (OC) that is stored in the soil of seagrass meadows is evolving, and several causal effects have been used to explain the variation of stocks observed at local to national scales. To gain a global‐scale appreciation of the drivers that cause variation in soil OC stocks, we compiled data on published species‐specific traits and OC stocks from monospecific and mixed meadows at multiple geomorphological settings. Species identity was recognized as an influential driver of soil OC stocks, despite their large intraspecific variation. The most important seagrass species traits associated with OC stocks were the number of leaves per seagrass shoot, belowground biomass, leaf lifespan, aboveground biomass, leaf lignin, leaf breaking force and leaf OC plus the coastal geomorphology of the area, particularly for lagoon environments. A revised estimate of the global average soil OC stock to 20 cm depth of 15.4 Mg C ha−1 is lower than previously reported. The largest stocks were still recorded in Mediterranean seagrass meadows. Our results specifically identify Posidonia oceanica from the Mediterranean and, more generally, large and persistent species as key in providing climate regulation services, and as priority species for conservation for this specific ecosystem service.

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 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.

Abstract. 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.

Seagrass and associated blue carbon ecosystems are important carbon sinks, and hence understanding their spatial and temporal variability is vital in appreciating their potential roles in climate change mitigation and adaptation. The Indo-Pacific region has the highest seagrass biodiversity, yet little focus has been made to compare seagrass habitat extent and carbon dynamics with their temperate counterparts. The present study assessed habitat characteristics and seagrass species distribution, diversity, and carbon storage in Eastern (marine) and Western (estuarine) mangrove-fringed creeks of Gazi Bay, Kenya. Data on species composition, canopy cover, biomass, and sediment organic carbon were collected in 80 plots of 0.25 × 0.25 m laid along transects established perpendicular to the waterline. Five species formation, viz., Thalassia hemprichii, Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, and Thalassidendron ciliatum, were encountered as either single or mixed stands. There was a significant difference in total seagrass biomass between creeks (p < 0.01), with the Eastern creek recording a mean of 10.2 ± 0.6 Mg C ha–1 while the Western creek recording 4.3 ± 0.3 Mg C ha–1. In addition, sediment carbon to 1-m depth varied significantly (p < 0.01) between species in the two creeks and ranged from 98 to 302 Mg C ha–1, with the Eastern and Western creeks recording means of 258 ± 90 and 107 ± 21 Mg C ha–1, respectively. The total carbon stock from 50 ha of seagrasses in the Eastern creek was 13,420 Mg C, whereas in the 70 ha of the Western creek it was 7,769 Mg C. The study shows that seagrass community attributes such as species composition and productivity can vary dramatically over a small spatial extent due to differences in biophysical conditions and caution estimations of site-specific carbon stocks using generalized global values.

Seagrass meadows are important carbon sinks, thus understanding this role and their conservation provides opportunities for their applications in climate change mitigation and adaptation. This study aimed at understanding seagrass contribution to ecosystem carbon at Gazi Bay; by comparing carbon stocks in seagrass beds in two mangroves fringed creeks of the bay. Specifically, the objectives included assessing the distribution and abundance of seagrass in the fringed creeks, estimating above and below-ground biomass and assessing sediment carbon in vegetated and un-vegetated sites of the creeks. Results obtained would be added to the mangrove and open bay carbon in estimating total ecosystem carbon of Gazi bay.

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 50cm. 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 elevation, harvested plots were eroded (7.6 ± 0.4 and -15.8 ± 0.5 mm yr-1 respectively, mean ± 95% C.I). Carbon concentration in the surface sediments was significantly reduced with a mean carbon loss of 1.13 Mg C ha-1 in the top 5cm. Because sediment was lost from harvested plots, with a mean difference in elevation of 3cm, an additional carbon loss of up to 22.9 ± 2.4 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 towards 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 lead to rapid changes in sediment dynamics and chemistry driven in part by significant alterations in the faunal community.

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 tropics have focused on coral reef fisheries, with little attention to seagrass meadows and mangroves. Using creel survey and in-depth interviews, this study assessed species composition, abundance and exploitation methods of fisheries from the seagrass meadows of Gazi Bay, Kenya. Eighty-five species were recorded with 8 species accounting for 75.7% of the total catch dominated by Leptoscarus vaigiensis, accounting for 30.9% of the total catch. Five dominant gears were observed: basket traps, hook and stick, handlines, nets and spear-guns. Basket traps were the most dominant accounting for 75.1% of the total catch by volume. These results underscore the value of the seagrass meadows to supporting fisheries. Gear management measures should be implemented for sustainability of the seagrass habitat and associated fisheries.

Purpose of Review We use the 'seascape' concept to explore how interactions between mangrove forests, tidal marshes and seagrass influence the storage of carbon in these ecosystems. Mangrove forests, with the other two 'blue carbon' habitats, are exceptionally powerful carbon sinks. Maintaining and enhancing these sinks is an emerging priority in climate change mitigation. However, managing any one ecosystem on its own risks is ignoring important contextual drivers of carbon storage emerging from its place in the seascape. We consider how interactions between these coastal habitats directly or indirectly affect the amounts of carbon they can store. Recent Findings The export of carbon from seagrasses may occur over hundreds or thousands of kilometres, much further than reported for mangroves or tidal marshes. Seagrasses may buffer mangroves from wave impacts, assisting forest regeneration. Trophic cascades supported by contiguous blue carbon habitat may limit excessive herbivory and bioturbation in them but evidence is limited. Summary Direct transfers of carbon between blue carbon habitats are common and are likely to enhance total carbon storage, but our understanding of their contribution to carbon stocks at the seascape level is elementary. There is evidence for indirect enhancement of carbon storage at the seascape by close association of habitats, mostly through the creation and maintenance of propitious conditions by one ecosystem for another. Protection from waves of mangroves by seagrass and protection from excess nutrients and sediment of seagrass by mangroves and tidal marsh are key mechanisms. There is little evidence or theory suggesting negative effects on carbon storage of one blue carbon habitat on another.

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 (C-org) 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 C-org. It also explored relationships between the sediment and above-ground C-org, 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 C-org compared with un-vegetated controls; the presence of seagrass increased C-org 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.

Seagrass meadows provide numerous ecosystem services and their rapid global loss may reduce human welfare as well as ecological integrity. In common with the other 'blue carbon' habitats (mangroves and tidal marshes) seagrasses are thought to provide coastal defence and encourage sediment stabilisation and surface elevation. A sophisticated understanding of sediment elevation dynamics in mangroves and tidal marshes has been gained by monitoring a wide range of different sites, located in varying hydrogeomorphological conditions over long periods. In contrast, similar evidence for seagrasses is sparse; the present study is a contribution towards filling this gap. Surface elevation change pins were deployed in four locations, Scotland, Kenya, Tanzania and Saudi Arabia, in both seagrass and unvegetated control plots in the low intertidal and shallow subtidal zone. The presence of seagrass had a highly significant, positive impact on surface elevation at all sites. Combined data from the current work and the literature show an average difference of 31 mm per year in elevation rates between vegetated and unvegetated areas, which emphasizes the important contribution of seagrass in facilitating sediment surface elevation and reducing erosion. This paper presents the first multi-site study for sediment surface elevation in seagrasses in different settings and species.

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.