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In Richards Bay Harbour, the mangrove Avicennia marina exhibits a distinct natural productivity gradient. The fringe site, which is regularly inundated twice daily by tides, supports luxuriant adult A. marina trees that are 6-10 m tall and which form a dense, well-developed canopy. The landward site which is only inundated during high spring tides, supports diminutive or dwarf A. marina that are less than 1.5 m in height. In this study we compared leaves from fringe and dwarf sites with respect to morphology, ultrastructure and ecophysiology. Alterations in leaf morphology, ultrastructure and physiology of A. marina were compared at the fringe site (35 ‰) and dwarf site (60 ‰) using morphometric measurements, light (LM), transmission (TEM) and scanning microscopy (SEM). SEM and light microscopy revealed that multicellular salt glands were located on the thick, cutinised adaxial surface from leaves of both sites. The glands appeared to be scattered and protruding from individual crypts in fringe mangrove leaves whilst they appeared sunken and occluded by cuticular material in dwarf mangrove leaves. The salt glands on the abaxial surface were not sunken but obscured by the indumentum of peltate trichomes. Ultrastructural changes observed in dwarf mangrove leaves were associated with cuticle, cell walls, chloroplasts, mitochondria of mesophyll tissue and salt glands. Fringe mangrove leaves had chloroplasts with typical well-developed grana and stroma. Ultrastructural changes of chloroplasts were evident in dwarf mangrove leaves and included swelling and separation of thylakoids, disintegration of granal stacking and integranal lamellae, as well as loss of the integrity of the chloroplast envelope. Multivesicular structures were commonly found in vacuoles and associated with chloroplasts and mitochondria in both leaf types. In fringe mangrove leaves, mitochondria appeared spherical to tubular with a relatively smooth outer membrane and a highly convoluted inner membrane. Swelling and vacuolation of mitochondrial membranes, cristae and mitochondrial clustering in the cytoplasm around the chloroplasts were evident in dwarf mangrove leaves. Extensive lipid accumulation in the form of large, dense plastoglobuli occurred in the chloroplasts of dwarf mangrove leaves. There were characteristic differences in salt gland morphology of fringe and dwarf mangrove leaves, namely in the cell walls, vacuoles, and vesicle formation. In salt glands of dwarf mangrove leaves, a distinct withdrawal of the cytoplasm from the cell wall was observed. This feature was not observed in salt glands of fringe mangrove leaves. Numerous large vacuoles were observed in the secretory cells of glands of dwarf mangrove leaves compared to those of fringe plants. Multivesicular structures, vesicles and mitochondria were common features in both leaf types. Physiological studies involved a comparison of osmotic and ionic relations as well as whole plant responses in fringe and dwarf mangrove leaves. Relative leaf water content decreased by 7.8 % and specific leaf area by 17 % in dwarf compared to those of fringe mangroves. Dwarf mangrove leaves were 27.6 % thicker and leaf cuticle thickness 37.4 % higher than those from fringe mangroves. Fringe mangrove leaves displayed higher total chlorophyll contents by 27 %, with chlorophylls a and b being 22 % and 39.6 % higher, respectively than those of dwarf mangroves. Salt gland frequencies were higher in the apex, mid-lamina and base of fringe than dwarf mangrove leaves by 36 %, 45 % and 51 %, respectively. The concentration of glycinebetaine, a compatible, N-containing osmolyte was significantly higher by 40 % in dwarf than in fringe mangrove leaves. Concentrations of proline were 27 % lower in dwarf than in fringe mangrove leaves. The predominant inorganic ion detected in mature leaves was Na+, which was 19 % higher in dwarf than fringe mangrove leaves. Phosphorus was an element that appeared deficient in dwarf mangrove leaves, being 50 % lower compared to fringe mangrove leaves. The results of this investigation indicated that there were cytomorphological alterations as well as differences in physiological responses in leaves of A. marina at fringe and dwarf sites. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2007.

Heavy metal contamination of mangroves is of critical concern due to its accumulative and adverse effects in aquatic ecosystems. This study was undertaken to investigate the effects of mercury (Hg ), lead (Pb ), copper (Cu ) and zinc (Zn ) on plant responses, specifically growth and productivity, in Avicennia marina (Forssk.) Vierh. A. marina plants were grown for twelve months in pots contaminated with Hg +, Pb +, Cu2+ and Zn2+ at concentrations of 0, 40, 80, 120 and 160 ppm (1 ppm = 1 (agmf1). Accumulation and distribution of the heavy metals in shoot and root tissues were determined using atomic absorption spectroscopy (Perkin-Elmer Model 303) while secretion of the heavy metals from leaves was studied using scanning electron microscopy and energy dispersive X-ray microanalysis. I hypothesized that heavy metals have deleterious effects on plant growth and that they are absorbed by roots and secreted from salt glands present on the leaves. SEM X-ray microanalyses confirmed secretion of Cu + and Zn + ions as well as salt (NaCl) from glandular structures on both the adaxial and abaxial surfaces of leaves; however Hg2+ and Pb2+ were not detected in the secretion. Ion concentrations were significantly higher in plant roots than in shoots, particularly at 160 ligml"1 for all heavy metals. In addition, toxic levels of Hg and Pb were detected in the shoot tissue; however, Cu2+ and Zn2+ were within the normal ion concentration in the shoots. Plant height, number of leaves, biomass accumulation and chlorophyll content were significantly lower at 160 ugml" than the control values for all heavy metals. Carbon dioxide exchange, transpiration and leaf conductance generally decreased with increasing metal concentration. CO2 exchange at a concentration of 160 (J-gmf1 was significantly lower than the control for all metals. CO2 exchange at 160 ugml"1 for Hg2+, Pb2+, Cu2+ and Zn were 49.6 %, 55 %, 47.6 % and 63.6 % respectively lower than the control values. Photosystem II (PS II) quantum yield, photochemical efficiency of PSII (Fv/Fm) and electron transport rate (ETR) through PS II generally decreased with increasing concentration for all heavy metals. XV This study has shown that A. marina experiences dose-dependent stress responses to Cu2+, Zn2+, Hg2+ and Pb2+ in shoot and root tissue at a concentration of 160 lagmi"1, evidenced by decreases in growth and photosynthetic performance. The results also ~)A- "7-1- 9-1- "J-\-indicate that CuZT, Znz\ HgZT and PbZT are taken up by roots and transported to shoots. In addition, only Cu and Zn are secreted via the glands while Hg and Pb accumulate within the shoots. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2008.

To meet ambitious net-zero greenhouse gas emission targets by 2050, large-scale CO₂ reduction and removal are required. Nature-based solutions have been proposed as a potential aid to this process. Mangrove ecosystems, as well as their conservation and restoration, have the potential to make significant contributions in Saudi Arabia and other coastal regions. While field measurements of carbon assimilation rate and leaf area index (LAI) in mangroves provide important insights into carbon fluxes, they are time-consuming, labor-intensive, and limited when covering large areas. To address this issue, multispectral images captured by unmanned aerial vehicles (UAV) are used to generate spectral vegetation indices, which can then be used to build regression models for estimating mangrove LAI and carbon capture capabilities. The carbon assimilation rate measurements in the field for studying both diurnal and sub-seasonal fluxes revealed that Avicennia marina has a high carbon assimilation rate peak in the morning, which decreases thereafter, and a smaller peak in the afternoon. Furthermore, comparing all the studied sites, the KAM site (June) had the highest morning overall carbon assimilation rate values, ranging from 15- 20 μmol CO₂ m⁻² s⁻¹, followed by Island (October) ranging from 10- 17 μmol CO₂ m⁻² s⁻¹, and finally Rheem (February) ranging from 5- 15 μmol CO₂ m⁻² s⁻¹. Moreover, the acquired multispectral images were used to generate spectral vegetation indices, which were then used as input to build a random forest algorithm for estimating the LAI of mangroves. Following an evaluation of each mangrove site, the Rheem site dataset yielded the best Random forest algorithm (R²= 0.88 and RMSE= 0.39), so this model was used to create high resolution spatially distributed LAI-based maps for all of the mangrove sites studied. Knowing the carbon uptake per leaf area as well as the total leaf area (based on UAV-derived LAI estimates) within a mangrove site enabled us to create carbon capture maps (kg C yr⁻¹ per pixel) for all of the sites studied. To enable a more complete carbon accounting of mangrove ecosystems, future research should explore remote sensing approaches for inferring carbon assimilation in both belowground biomass and soils.

Mangrove plants are a productive ecosystem that provide several benefits for marine organisms and industry. They are considered to be a food source and habitat for many organisms. However, mangrove growth is limited by nutrient availability. According to some recent studies, the dwarfism of the mangrove plants is due to the limitation of nitrogen in the environment. Biological nitrogen fixation is the process by which atmospheric nitrogen is fixed into ammonium. Then, this fixed nitrogen can be uptaken by plants. Hence, biological nitrogen fixation increases the input of nitrogen in the mangrove ecosystem. In this project, we focus on measuring the rates of nitrogen fixation on Red Sea mangrove (Avicennia marina) located at Thuwal, Saudi Arabia. The nitrogen fixation rates are calculated by the acetylene reduction assay. The experimental setup will allow us to analyze the effect of crab bioturbation on nitrogen fixing rates. This study will help to better understand the nitrogen dynamics in mangrove ecosystems in Saudi Arabia. Furthermore, this study points out the importance of the sediment microbial community in mangrove trees development. Finally, the role of nitrogen fixing bacteria should be taken in account for future restoration activities.

[ES] A través de la fitosociología se ha estudiado las agrupaciones de plantas, sus interrelaciones y su dependencia con el medio ambiente en la costa del golfo Arabe en los Emiratos Arabes Unidos (EAU). La vegetacion de los Emiratos se caracteriza por la presencia del manglar paleotropical propio de las zonas intertidales en clima subtropical, acompañado por halofitas de desierto. Se han identificado 9 grupos de vegetación: (I) Asoc. Avicennietum marinae Chapman, J. 1970, (II) Asoc. Salicornietum fruticosi Br. Bl. 1928, (III) Asoc. Arthrocnemum machostachi- Halocnemetum strobiliaci Associatio nova Leandro, P. 2018, (IV) Asoc. Suaedetum verae (fruticosae) Br. Bl. ex O. Bolós & Molinier 1958. (V) Asoc. Tetraena qatarensis Associatio nova Leandro, P. 2018 (VI) Com. Calotropis procera (VII) Com. Heliotropium bacciferum (VIII) Com. Prosopis cineraria en orden deacuerdo al transecto que va dese la primera linea de costa al interior, y las comunidades nuevas como consecuencia de alteraciones en el entorno (IXa) Com. Avicennio marinae y Sesuvietum portulacastri y (IXb) Com. Avicenium y Salicornietum fruticosi. Se ha utilizado el programa TWINSPAN para la confirmacion de las mismas. Mediante los analisis de ACC se observa que las comunidades de Avicennia marina se correlacionan positivamente con la conductividad / salinidad del suelo, la alcalinidad o el pH y con las concentraciones de cationes. Se ha observado que las alteraciones antrópicas de la costa causan diferencias en la distribución normal de las poblaciones y este estudio propone medidas de restauración para garantizar la adaptación y la viabilidad de un proyecto futuro de revegetación costera a través del conocimiento geobotánico adquirido. / [CA] A través de la fitosociologia s'ha estudiat les agrupacions de plantes, les seues interrelacions i la seua dependència amb el medi ambient en la costa del golf Arabe als Emirats Arabs Units (EAU). La vegetacio dels Emirats es caracteritza per la presència del manglar paleotropical propi de les zones intertidales en clima subtropical, acompanyat per halofites de desert. S'han identificat 9 grups de vegetació: (I) Assoc. Avicennietum marinae Chapman, J. 1970, (II) Assoc. Salicornietum fruticosi Br. Bl. 1928, (III) Assoc. Arthrocnemum machostachi- Halocnemetum strobiliaci Associatio nova Leandro, P. 2018, (IV) Assoc. Suaedetum verae ( fruticosae) Br. Bl. ex O. Bolós & Molinier 1958. (V) Assoc. Tetraena qatarensis Associatio nova Leandro, P. 2018 (VI) Com. Calotropis procera (VII) Com. Heliotropium bacciferum (VIII) Com. Prosopis cinerària en ordre d'acuerd al transecte que va desde la primera llínia de costa a l'interior, i les comunitats noves com a conseqüència d'alteracions a l'entorn ( IXa) Com. Avicennio marinae i Sesuvietum portulacastri i ( IXb) Com. Avicenium i Salicornietum fruticosi. S'ha utilitzat el programa TWINSPAN per a la confirmacion d'aquestes. Mitjançant els analisis de ACC s'observa que les comunitats de Avicennia marina es correlacionen positivament amb la conductivitat / salinitat del sòl, l'alcalinitat o el pH i amb les concentracions de cations. S'ha observat que les alteracions antròpiques de la costa causen diferències en la distribució normal de les poblacions i aquest estudi proposa mesures de restauració per a garantir l'adaptació i la viabilitat d'un projecte futur de revegetació costanera a través del coneixement geobotánic adquirit. / [EN] Through phytosociology, plant clusters, their interrelations and their dependence on the environment on the Arabian Gulf coast in the United Arab Emirates (UAE) have been studied. The vegetation of the Emirates is characterized by the presence of paleotropical mangroves typical of intertidal areas in subtropical climate, accompanied by desert halophytes. Nine vegetation groups have been identified: (I) Assoc. Avicennietum marinae Chapman, J. 1970., (II) Assoc. Salicornietum fruticosi Br. Bl. 1928, (III) Assoc. Arthrocnemum machostachi- Halocnemetum strobiliaci nova. Leandro, P. 2018, (IV) Assoc. Suaedetum verae (fruticosae) Br. Bl. ex O. Bolós & Molinier 1958. (V) Assoc. Tetraena qatarensis nova hoc loco (VI) Com. Calotropis procera (VII) Com. Heliotropium bacciferum (VIII) Com. Prosopis cineraria, in order according to the transect that goes from the first coastline to the interior, and the new communities originated by anthropic factors are (IXa) Com. Avicennio marinae-Sesuvietum portulacastri nova and (IXb) Com. Avicenium- Salicornietum fruticosi nova. The TWINSPAN program has been used to confirm them. Through the CCA analysis, the communities of Avicennia marina can be positively correlated with the conductivity / salinity of the soil, the alkalinity or the pH and with the concentrations of cations. It has been seen that the anthropic alterations of the coast cause differences in the normal distribution of the populations and this study proposes restoration measures for the adaptation and viability of the future coastal revegetation project through the acquired geobotanical knowledge. / Leandro Baladrón, P. (2021). Estudio de la vegetación costera de los Emiratos Árabes Unidos (EAU) (Golfo Arábigo). Análisis del estado actual [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167018 / TESIS

Diploma thesis is focused on establishment of forest nurseries and seedling production on Socotra Island where a natural regeneration of many endemic species is limited by overgrazing and has been moreover affected by cyclone that hit the island in 2015. Planting stock of Dracaena cinnabari, Boswellia elongata, Boswellia ameero, Boswellia dioscorides, Punica protopunica, Aloe perryi and mangrove Avicennia marina was planned to be propagated in nurseries located in three areas of interest – Firmihin, Homhil and Niyt. Therefore data about the species seed germination or growth rate were gathered and mentioned in the literature section. The species selection was always firstly preceded by dendrological survey of the area. Individual pilot areas were also described together with climatic data and moreover, soil samples were analysed as the substrate for the seedling production comes from local sources. Finally, the projects for forest nurseries establishment were created and according to them were individual nurseries established.