Browsing by Author "Githaiga, Michael N."
Now showing 1 - 12 of 12
Results Per Page
Sort Options
Item Biomass and productivity of seagrasses in Africa(De Gruyter, 2016-05) Githaiga, Michael N.; Gilpin, Linda; Kairo, James G.; Huxham, Mark: 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.Item The Contribution of Subtidal Seagrass Meadows to the Total Carbon Stocks of Gazi Bay, Kenya(Diversity, 2022-08-11) Wang’ondu, Virginia W.; Githaiga, Michael N.; Gorman, Daniel; Kairo, James G.; Omollo, Derrick J.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.Item Estimation of Sedge Biomass around the dams at University of Embu, Kenya(University of Embu, 2019) Simiyu, Enos; Githaiga, Michael N.The role of vegetation as natural carbon sinks is widely acknowledged with many researchers focusing on understanding the carbon capture and storage in vegetation types and species. Wetlands are among the major carbon sinks and recent research reveal that they play important role in climate change mitigation. Despite this awareness, no research has focused on biomass estimation for the sedges in Embu County. This study aimed at estimating variation of biomass across sedges around the dams within the University of Embu. It evaluated variation in above ground and below ground biomass of the sedge vegetation, and the relationship between the two. Above ground biomass was obtained through harvesting shoot canopies while the below ground biomass was obtained by coring. One way ANOVA was used to compare the total biomasses across the sites. The mean values for the total biomass around dams 1, 2, 3, 4 and 5 were 4305.3, 4421.6, 3343.2, 3222.8 and 2702.4 gm 2 respectively. The mean values for above ground biomass around dams 1, 2, 3, 4 and 5 were 830.62, 796.74, 654.76, 628.75 and 207.50 -2 gm respectively. The mean values for below ground biomass around dams 1, 2, 3, 4 and 5 were 3468.9, 3624.9, 2690.5, 2554 and 2494.9 gm -2 respectively. There were significant differences in total biomass, above ground and below ground biomass accumulation across the zones (F (4, 24), = 14.13; P = 0.001), (F (4, 24) = 57.55; P = 0.001) and (F (4, 24) = 7.21; P = 0.001) respectively. There was a strong positive correlation between above ground and below ground biomass R=0.755. These findings are important as they enhance our knowledge on the contribution of wetland vegetation in carbon capture and storage and hence their role in climate change mitigation.Item Measuring the role of seagrasses in regulating sediment surface elevation(Scientific Reports, 2017-09) Potouroglou, Maria; Bull, James C.; Krauss, Ken W.; Kennedy, Hilary A.; Fusi, Marco; Dafonchio, Daniele; Mangora, Mwita M.; Githaiga, Michael N.; Diele, Karen; Huxham, MarkSeagrass 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 diferent sites, located in varying hydrogeomorphological conditions over long periods. In contrast, similar evidence for seagrasses is sparse; the present study is a contribution towards flling 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 signifcant, positive impact on surface elevation at all sites. Combined data from the current work and the literature show an average diference of 31mm 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 frst multi-site study for sediment surface elevation in seagrasses in diferent settings and species.Item The Role of Seagrass Meadows in Gazi Bay, Kenya as Carbon Sinks(Edinburgh Napier University, 2017-04) Githaiga, Michael N.Ongoing work on the ‘blue carbon’ has established that vegetated coastal ecosystems – mangroves, seagrasses and tidal marshes – are exceptionally powerful natural carbon sinks. Hence, there are important applied arguments for understanding the role of these ecosystems in climate change mitigation. Many gaps in knowledge remain, with seagrasses in particular being poorly understood. The overall aim of the present study was to understand the role of seagrass meadows of Gazi Bay, Kenya as carbon sinks. The specific objectives of the study were: (i) Carry out a comprehensive review on biomass and productivity studies of seagrasses in Africa. (ii) Estimate the carbon storage in the seagrass meadows of the bay (iii) Investigate the impact of seagrass canopy removal on sediment dynamics and on the benthic faunal communities (iv) Investigate productivity of the dominant seagrass species of the bay. (v) Highlight the implication of the knowledge and how it could be useful in the bundling of the ecosystem services of the seagrass meadows with that of adjacent mangrove ecosystem under the payment for ecosystem services (PES). The review work encountered 32 papers and 8 theses/reports on seagrass biomass and productivity at African sites, with the majority of the studies having been done along the E. African coast; however, there were no published reports of sedimentary Corg from Africa, revealing a major gap in knowledge. Results of carbon storage of the seagrass meadows of Gazi, Bay on biomass and sediment organic carbon (Corg) for the four dominant species, Thalassia hemprichii, Thalasodendron ciliatum, Syringodium isoetifolium and Enhalus acoroides, indicated that sediment organic carbon was highly 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 areas and revealed a surprising degree of spatial consistency and longevity in relatively small patches of seagrass meadows and bare areas thus demonstrating an exceptionally powerful effect of seagrass on C sequestration. Through a seagrass removal experiment that simulated the impact of seagrass loss on biodiversity and ecosystem functions the study recorded positive elevation change of the sediment in the controls and negative elevation in the treatments with significant effect of treatment and time on surface elevation change. Similarly, there were significant weight losses on clod cards in seagrass removed areas compared to the controls, an indication of the role of seagrasses in the reduction of the speed of water current. Carbon density in surface sediment was significantly higher in the control areas as compared to the treatments while higher litter decay rates were observed in seagrass removed areas than in the controls. Seagrass removal areas had significant decline on the fauna. Productivity estimates of the dominant seagrass species of the bay through a combination of the leaf plastochrone, and ingrowth cores, showed inter-species variability with Thalassia hemprichii recording the highest above and below-ground productivity at 188.6±34.8 g DW m-2 yr-1 and 197.4±108.7 g DW m-2 yr-1 respectively. Knowledge on the role of seagrasses of the bay as carbon sinks is likely to open opportunities for bundling seagrass ecosystem services with that of the contiguous mangrove ecosystem as part of Payment for Ecosystem Services (PES); an approach that makes economic and ecological sense, given the strong connections between the two ecosystems, and could provide a useful buffer against environmental shocks such as sea level rise and increasing storm surges.Item Seagrass Loss and Sub-Surface Carbon Fate: Insights from a Long-Term Experimental Removal in Gazi Bay, Kenya(Jupiter Publishers, 2021-08) Cadier, Charles; Githaiga, Michael N.Seagrass meadows are considered as global hotspots of blue carbon stocks. However, they suffer global cover loss mainly due to anthropogenic activities. Few is known on the impact of seagrass loss on their blue carbon stocks. This study investigates the impact of seagrass removal on soil organic carbon stocks two years after initial perturbation, and the potential bioturbation activity of co-existing burrowing shrimps in Gazi Bay, Kenya. Seagrass aboveground biomass was removed for a period of 18 months and organic carbon samples were taken 24 months after the first harvested at three depth layers (0-5cm, 5-10cm, 10-15cm). Results indicated that organic carbon was significantly lower in the 15cm depth profile sampled in harvested seagrass meadows. The sediment turnover rate of Callianassidae present in the bay was estimated at 948 ± 342 (SE) g.DW.d -1 . This bioturbation activity is assumed to play an important role in the potential release of sediment organic carbon stock from harvested plots. This study demonstrates the significant sub-surface organic carbon loss after seagrass removal, and the potential for burrowing shrimp to enhance organic carbon remineralisation. Further studies on tropical seagrass meadows organic carbon fate after seagrass loss to account for blue carbon budget.Item Seagrass Removal Leads to Rapid Changes in Fauna and Loss of Carbon(Frontiers, 2019-03) Githaiga, Michael N.; Frouws, Anna M.; Kairo, James G.; Huxham, MarkSeagrass 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 ± 0.5mm yr−1 respectively, mean ± 95% CI). Carbon concentration in the surface sediments was significantly reduced with a mean carbon loss of 2.21Mg 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 2.54Mg 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.Item Species composition, abundance and fishing methods of small-scale fisheries in the seagrass meadows of Gazi Bay, Kenya(Routledge, 2019-05) Musembi, Peter; Fulanda, Bernerd; Kairo, James; Githaiga, Michael N.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 indepth 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.Item Staff Profile: Dr. Michael Njoroge Githaiga(University of Embu, 2017-09) Githaiga, Michael N.Michael N Githaiga is a lecturer at University of Embu, department of biological sciences. He earned his PhD in Marine Ecology from Edinburgh Napier University, UK. He holds a BEd Science degree from Kenyatta University and Msc Plant Ecology from the same university. Previously he worked with Kenya Marine and Fisheries Research Institute. He has a wide experience in the management of coastal ecosystems particularly mangroves and seagrasses.Item Structure and Biomass Accumulation of Natural Mangrove Forest at Gazi Bay, Kenya(Kenyatta University, 2013-08) Githaiga, Michael N.Mangroves occupy only 0.4% of forested areas globally but are among the most productive ecosystems on earth. They account for about 11% of the total input of terrestrial carbon into the oceans. The above ground carbon stock in mangroves in some parts of the World has been estimated to be as high as 8 kg C m -2 ; with a similar amount reported for below ground components. Although a lot of research has been done on estimates of mangrove biomass in Kenya, there is no information on biomass accumulation across the zones. The present study aimed at determining the forest structure and estimating above and below ground biomass accumulation in Gazi Bay mangrove forest. Forest structure was determined in the western, middle and eastern forest blocks of the Gazi Bay mangrove forest while biomass accumulation studies were done in the western forest block. In-growth cores of 80 cm long × 20 cm wide and 60 cm-depth were used to estimate below ground biomass accumulation. Data on tree height and stem diameter at breast height (DBH-130) were used to estimate above ground biomass accumulation. Shoots were tagged for monitoring leaf phenology. Periodic measurements of environmental variables across four mangrove species zones were done at the beginning, thereafter every four months for a year. Composition and distribution pattern of natural regeneration was obtained using the method of linear regeneration sampling (LRS). Among the soil environment properties investigated, salinity had a significant negative correlation with above ground biomass accumulation. Comparing the four forest zones, Sonneratia alba had the highest biomass accumulation rate of 10.5 ± 1.9 t ha-1 yr -1 . This was followed by 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 ). There were significant differences in above ground and below ground biomass accumulation across zones (F (3, 8) = 5.42, p = 0.025) and (F (3, 8) = 16.03, p = 0 001) respectively. Total biomass accumulation was significantly different across zones (F (3, 8) =15.56, p = 0.001). A root: shoot biomass accumulation ratio of 2:5 was computed for the whole forest. The finding of this study gives better estimates of mangrove carbon capture and storage which can be used in negotiations for carbon credits in the evolving carbon market.Item Value chain and sustainability of mangrove wood harvesting in Lamu, Kenya(Elsevier, 2022-08) Riungu, Purity M.; Nyaga, Justine M.; Githaiga, Michael N.; Kairo, James G.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 of mangrove poles were target for harvesting from Lamu. During the same period, the harvest data indicate an average of 6.2 scores ha 1 1 yr 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.Item Variation in Seagrass Carbon Stocks Between Tropical Estuarine and Marine Mangrove-Fringed Creeks(Frontiers in Marine Science, 2020-08) Juma, Gabriel A.; Magana, Adiel M.; Githaiga, Michael N.; Kairo, James G.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