Seagrasses are marine flowering plants found in both temperate and tropical coastal environments, that offer vital ecosystem services and adaptations. However, due to their proximity to the shore, they are heavily impacted by human activities and climate change, endangering seagrasses and their services. To manage seagrass meadows effectively and sustainably, detailed monitoring and data on distribution and extent are essential. Unfortunately, past under-prioritization of reliable baseline data impedes understanding of ecosystem dynamics and rapid response to declines. This study employs satellite imagery, coupled with ground truthing, to comprehensively report seagrass coverage along Tanzania's mainland coast and Zanzibar islands. By utilizing machine-learning technologies, the study achieves 84.2% accuracy, and found that Tanzania has 2817 km2 of seagrass coverage, which is five times higher than previously reported. In addition, the results also provide coverage of additional benthic habitats, such as corals, rocks/rubble, and sand. This study provides the first comprehensive overview of seagrass coverage in Tanzania and will function as a valuable tool and baseline for understanding and managing these habitats. The findings suggest that seagrasses in Tanzania are still relatively abundant, but due to a number of threats, including pollution, coastal development, and climate change, these habitats require improvement in management strategies including regular monitoring to understand their status and trends in their area coverage. The study highlights the significance of remote sensing and machine learning in mapping and monitoring coastal habitats across extensive geographical areas. We aspire for the presented results to be utilized among stakeholders and researchers to develop more effective conservation measures for seagrasses in Tanzania and the Western Indian Ocean.

Abstract Stagnating capture fisheries and increasing fish protein demand necessitate aquaculture production to bridge the gap. Lake Victoria is a potential water body for increasing fish production through cage farming. The sustainability of Lake Victoria for cage farming depends on timely and holistic site selection. However, current site selection methods involve complex, resource‐intensive field surveys that lack a holistic approach to integrate multiple factors. Accordingly, information regarding suitable sites for sustainable fish cage farming in Lake Victoria remains scarce. In this study, a transparent geographic information systems (GIS) and multicriteria evaluation (MCE) here after reffered to as GIS‐MCE was used to reveal potential sites to be permitted or avoided during cage aquaculture development in the Mwanza Gulf of Lake Victoria (Tanzania). Our analysis involved weighting and integration of sub‐models representing ecologically sensitive areas, physical environment, and socio‐economic and water quality variables into a single spatial model portraying different site suitability levels in the Mwanza Gulf. The results indicated that the sub‐models identified relatively larger suitable and most suitable sites compared to the overall model. No site maintained its status across all sub‐models. The overall model designated a small area (5.10 km2 or 1.52%) as the most suitable site, with 24.20 km2 (7.44%) as suitable, 64.47 km2 (19.82%) as less suitable, and 42.63 km2 (13.12%) as unsuitable for cage fish farming. The remaining area (188.84 km2 or 58.06%) was a constrained site to be avoided during cage aquaculture development. Taken together, the individual sub‐models are ineffective in designating potential sites for fish cage culture and thus should not be used solely. The GIS‐MCE general model provides a fast and timely method for identifying potential sites for cage farming in Lake Victoria. Fish farmers and managers should use the GIS‐MCE overall model in inland waters to facilitate site selection for complying with licensing requirements and decrease field extensive surveys.

Estimating bathymetric information is vital for aquaculture and navigation applications. Free, high-resolution satellite imagery provides a cost-effective solution for routine bathymetric measurements. We tested six algorithms to retrieve water depth in the Mwanza Gulf of Lake Victoria using Sentinel-2 satellite imagery: the conventional Stumpf method, Random Forest (RF), Gradient Boosting Machine (GBM), Extreme Gradient Boosting (XGB), Neural Network (NNET), and Support Vector Machine (SVM). In-situ depth points collected via echo sounders were used to train and validate the algorithms. Performance evaluation metrics included coefficient of determination (R2), mean absolute error (MAE), root-mean-square error (RMSE), and spatial autocorrelation of residuals. Among the algorithms tested, the Stumpf model exhibited moderate performance with an R2 of 0.441, higher MAE (2.078 m), and RMSE (2.964 m) values. The RF algorithm improved performance with an R2 of 0.957, lower MAE (0.476 m), and RMSE (0.823 m). The GBM and XGB algorithms achieved R2 values of 0.960 and 0.956, respectively, with low MAE (0.484 m for GBM, 0.482 m for XGB) and RMSE (0.795 m for GBM, 0.830 m for XGB) values. The NNET algorithm outperformed the GBM and XGB models, obtaining an R2 of 0.963, the lowest MAE (0.438 m), and RMSE (0.761 m). The SVM algorithm demonstrated the best performance with an R2 of 0.965, the lowest MAE (0.403 m), and RMSE (0.745 m), implying the highest accuracy in depth estimation. SVM also showed stable generalization across different locations with insignificant spatial autocorrelation of residuals. Therefore, SVM is recommended for repetitive bathymetry calculations.

Lake Bunyonyi ecosystem plays vital roles in water resource conservancy and tourism. Nevertheless, the rapid increase in human population and the unrelenting human activities are threatening the values, functions, and ecological integrity of the lake. In this study, the public perceptions of drinking water quality and its health implications in the Lake Bunyonyi Sub-catchment, Western Uganda are presented. A closed-ended questionnaire was administered to 267 respondents living within one Kilometre away from the lake shores. Besides, observation and interview methods were used to complement data collected by the questionnaire method. Results indicate that the prominent activities around the lake are peasantry and small-scale businesses attributed to soil fertility and rural tourism. Despite the lake being a popular source of drinking water in the sub-catchment, the quality of its water suffers from diffuse pollution and little has been done to avert it. This study recommends regular surveillance and water quality testing to increase people’s awareness of water quality. Besides, the local authorities should train people the alternative environmentally-friendly farming practices like afforestation with correct tree species and agro-forestry practices to increase vegetation cover and reduce soil erosion debris washed into the lake system. Environmental-friendly household water treatment methods (biosand filtration and solar disinfection) should be promoted to improve the quality of drinking water.

The study was conducted to assess the spatial and temporal variations of the trophic state condition of Lake Bunyonyi between October 2019 and September 2020. Secchi depth (SD), total phosphorus (TP) and chlorophyll- a (Chl- a ) concentration were measured to aid the quantification of trophic state condition of the lake using Carlson trophic state index (CTSI). The trophic state index (TSI) values based on SD, TP and Chl- a values were 60.82 ± 5.35, 68.99 ± 11.04 and 61.74 ± 7.51, respectively. March 2020 recorded the highest mean CSTI value (70.14 ± 4.04), while in September 2020, the lowest mean value (58.03 ± 6.22) was obtained. Based on CTSI values, the lake was eutrophic in both dry and wet seasons albeit with differences in the values. The eutrophic state of the lake is possibly attributed to nutrients inflow into the lake via runoff and drainage from farmlands. The negative value of TSI-Chl- a –TSI-TP deviation pointed out that the lake is not phosphorus limited, while the positive TSI-Chl- a –TSI-SD mean deviation value revealed the effect of Chl- a and TP on the lake’s transparency. The study recommends the necessity to develop guidelines for the trophic status monitoring of Lake Bunyonyi since results suggest the deteriorating lake condition.

The purpose of this study was to examine the spatial and temporal variations of phytoplankton species composition and biomass in Lake Bunyonyi, South-Western Uganda. Samples were collected monthly from nine fixed stations in the lake from October 2019 to September 2020. Based on the morphological characterization, 52 different species of phytoplankton were recorded. These were dominated by cyanobacteria (21 species) and chlorophytes (15 species) followed by diatoms (10 species), euglenophytes (4 species), dinoflagellates (2 species), and cryptophytes (1 species). The biomass (Chl-a concentration) ranged from 0.019 ± 0.009 mg/L at Heissesero station to 0.045 ± 0.013 mg/L obtained at Nyombe station. On a temporal basis, the highest mean Chl-a concentration of 0.044 ± 0.03 mg/L was recorded in March 2020 while the least concentration of 0.015 ± 0.011 mg/L was obtained in September 2020. Significant differences existed in the Chl-a concentration values between stations and across sampling months. Chl-a concentration was significantly positively correlated with dissolved oxygen (DO), turbidity but negatively correlated with temperature. The Shannon–Wiener index and evenness put it clear that the distribution of phytoplankton species in the lake is inequitable. Besides, 94.2% of the phytoplankton species revealed had never been reported by the previous studies in the study area. The dominance of species cyanobacteria (such as Microcystis spp., Cylindrospermopsis raciborskii, Anabaenopsis sp., and Anabaena sp.) presents potential future challenges to water quality management. Therefore, the establishment of a strong and committed committee dubbed “Lake Bunyonyi Water Management Committee” to oversee the activities and avert potential water quality challenges is strongly recommended. The existence of some toxic phytoplankton species calls for regular monitoring and careful use of the lake and its food products.

Lake Bunyonyi is one of the major resources of social-economic potential in the districts of Rubanda and Kabale, South-Western Uganda. The lake’s sub-catchment faces environmental problems because of intensive agriculture, settlement, business and tourism activities, which consequently cause pollution of water in the lake’s system. This study, therefore, intended to determine the processes that govern nitrogen dynamism using a numerical model that takes into account various processes in the system using STELLA® 8.1.1 software. From the model simulation, it was found that mineralization, microbial uptake and nitrification were the major processes governing nitrogen transformation in the water phase, accounting for 47.8% (0.49 g/d m −2 ), 44.2% (0.45 g/d m −2 ), and 7.8% (0.05 g/d m −2 ), respectively. The developed model predicted reasonably well the behaviour of the lake evidenced by the validation results of observed and simulated data that showed good linear regression coefficients ( R 2 ) of organic nitrogen (0.48), ammonia–nitrogen (0.68), and nitrate–nitrogen (0.61). The model has proven suitable for application on lakes with characteristics similar to that of Lake Bunyonyi. The study recommended that a compressive investigation that puts into consideration all the possible sources of nutrient and water inflow into the lake system be done on Lake Bunyonyi.

Although seagrass restorations have been conducted in many regions globally, restorations in high-energy wave environments are less explored. With accelerating losses of seagrass meadows globally, we also lose valuable ecosystem-based adaptations and ecosystem services, where the Western Indian Ocean is not an exception. The coast of Tanzania has only a few island shelters, creating an open exposed coast with a long wind fetch, generating strong wave exposure on the coastline. Still, seagrass meadows are present but have similar to global trends declined due to e.g. warmer ocean temperatures, coastal developments and destructive fishing methods. In view of the above challenges, there is a strong need for restoring seagrass meadows along the coast of Tanzania and the Western Indian Ocean (WIO) at large. However, restoration studies in the WIO are scarce and generally lacking in Tanzania. Studies elsewhere have shown that the success of a seagrass restoration varies significantly among trials and is to a large extent subject to the choice of a planting technique. Thus, in order to initiate the best practice for seagrass restoration in the Western Indian Ocean Region, for high-energy wave intertidal en-vironments, we contrasted two restoration techniques, the plug and the sprig methods. We further explored different anchoring techniques and how various physical environmental factors influenced the growth and survival rates of seagrass shoots and rhizomes. We found that Syringodium isoetifolium transplants survived poorly in the sprig method (median = 0%), while the plug method demonstrated a much higher survival (median = 33.3%) for the 7 cm plug, and 66.7% for the 10 cm plug. The study also revealed a strong effect of water depth, where survival and growth parameters decreased with increased water depth. Finally, the study found a number of significant correlations, both positive and negative, between growth parameters and the measured environ-mental factors - and revealed that most of the measured environmental parameters were influenced by the local weather conditions and the monsoon seasonal cycling. The study illustrates that the restoration technique is strongly related to restoration success, providing clear guidance for future seagrass restorations in high-energy coasts in the Western Indian Ocean.

The current study was carried out to examine the spatial and temporal variations of physicochemical water quality parameters of Lake Bunyonyi. The observations were made on the surface water of Lake Bunyonyi for 1 year to determine the water quality. The basic 12 variables used to determine the quality of water were measured monthly at nine stations. Water temperature, dissolved oxygen (DO), turbidity, electric conductivity (EC), pH and Secchi depth (SD) were measured in the field, while parameters like total nitrogen (TN), total phosphorus (TP), nitrite-nitrogen (NO 2 -N), nitrate-nitrogen (NO 3 -N), soluble reactive phosphorus (SRP) were determined following APHA 2017 standard guidelines for physicochemical analysis. Taking into account standard guidelines for drinking water by the Uganda National Bureau of Standards (UNBS) and the World Health Organization (WHO), the water quality index (WQI) was used to determine the water quality. Temperature, DO, pH, turbidity and EC did not differ significantly among the study stations ( p > 0.05) but showed significant temporal variations among the study months ( p < 0.05). Likewise, TN, TP, NO 2 -N, NO 3 -N and SRP did not differ significantly among the study stations ( p > 0.05) but showed significant temporal variations among the study months ( p < 0.05). The WQI values ranged from 28.36 to 49 across and from 28.2 to 56.2 between study months with an overall mean value of 36.9. The measured water quality variables did not exceed the UNBS and WHO standards for drinking water in all months and at all stations. According to these values, the water quality of Lake Bunyonyi generally belongs to the ‘good’ class in terms of drinking water quality based on the WQI classification. The study findings are fundamentally important for policy makers in setting guidelines for effective lake management.

Background Microbial water quality serves to indicate health risks associated with the consumption of contaminated water. Nevertheless, little is known about the microbiological characteristics of water in Lake Bunyonyi. This study was therefore undertaken to examine the spatial and temporal variations of faecal indicator bacteria (FIB) in relation to physicochemical parameters in Lake Bunyonyi. Result The FIB concentration was consistently measured during sampling months and correlated with each other showing the presumed human faecal pollution in the lake. The highest concentration values for E. coli (64.7 ± 47.3 CFU/100 mL) and enterococci (24.6 ± 32.4 CFU/100 mL were obtained in the station close to the Mugyera trading centre. On a temporal basis, the maximum values were recorded during the rainy season in October 2019 (70.7 ± 56.5 CFU/100 mL for E. coli and 38.44 ± 31.8 CFU/100 mL for enterococci. FIB did not differ significantly among the study stations (p > 0.05) but showed significant temporal variations among the months (p < 0.05) with concentrations being significantly high in wet season than dry season (U = 794, p < 0.0001 for E. coli; U = 993.5, p = 0.008 for enterococci). Spearman’s rank correlation revealed that FIB concentrations were significantly positively correlated with turbidity and DO concentration levels (p < 0.05). Approximately 97.2% of the water samples had E. coli and enterococci concentrations levels below USEPA threshold for recreational waters. Likewise, 98.1 and 90.7% of samples recorded E. coli and enterococci counts exceeding the UNBS, APHA, WHO and EU threshold values for drinking water. Conclusion The FIB counts show that the Lake Bunyonyi water is bacteriologically unsuitable for drinking unless it is treated since the FIB pose health risks to consumers. Besides, the water can be used for recreational purposes.

Plastic pollution is a growing problem, not at least in areas where poor waste management results in direct pollution of coastal zones, such as South Asia and regions in Africa. In addition to the effect on ecosystems and their related services, plastic pollution may also affect human health indirectly as vectors for infectious disease. As plastic offers a suitable surface for the attachment of biofilm forming bacteria, it may contribute to disease outbreaks and antimicrobial resistance. To investigate the role of plastic litter as potential vectors for pathogenic bacteria, we collected plastic litter from four rural sites in Zanzibar, and isolated adhered bacteria. Isolates were short-read sequenced for further molecular analysis. This revealed that collected plastic litter was associated with diverse bacterial species, including human pathogens Citrobacter freundii, Klebsiella pneumoniae and Vibrio cholerae. Furthermore, most isolates were found to be multidrug resistant. Our findings confirm that plastic litter, serve as novel reservoir for human multidrug resistant pathogenic bacteria that combined with poor sanitation and waste handling, may lead to transmission of infectious diseases and antimicrobial resistance. These findings add a new level to the environmental challenges with plastic pollution; the potential health risk associated with exposure to plastic litter.

Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophylla, chlorophyllband total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.

The function of mangrove-fringed estuarine ecosystems are considered to be affected by mangrove degradation, high fishing pressure and fresh water abstraction for multi-uses including damming and irrigation activities in the upstream. The present study aimed at describing the food web structure and trophic interactions for the Pangani estuarine ecosystem using Ecopath modeling tool. The study compared Pangani estuarine model outputs with other 6 available tropical estuarine Ecopath models in order to provide a broader picture of the variations in structure and functioning of tropical estuaries. The model was built based on the pre-defined 27 functional groups including commercially important individual fish species or groups of species, shrimps and crabs. Despite the high mean trophic transfer efficiency for the entire ecosystem (15%) relative to the theoretical value (10%), the overall Pangani model reliability indicators were generally within the acceptable range. Fishery catches were dominated by the pre-adult predatory fish positioned at trophic level III and the ecosystem was predominantly relying on phytoplankton and microphytobenthos food web pathways. The keystone index and mixed trophic impact analyzed showed that Mudskipper and Arius africanus were the key biological groups with high impact in the estuarine food web. Although the ecosystem structural and functional indices of the model were significantly similar to other tropical estuarine indices (PERMANOVA, pseudo-F=1.5; p > 0.05), Pangani estuary indicated less complex food web. Like other estuarine ecosystem models, the ecosystem maturity indices proved that Pangani estuarine ecosystem was still developing. These observations call upon effective management practices for maintaining the health and productive estuarine ecosystem. Preferred Mode of Presentation: Poster

The present study was formulated with the aim of using MIKE 21 software in studying the hydrodynamic regime of the Pangani estuary. Water level, river discharge and wind drag force were used as hydrodynamic forcing factors during the model set up. The data set for the model (i.e. water level, tidal current winds and river discharge) were collected in Pangani estuary during the field campaigns conducted from December 2010 and August 2011. The results indicated that the tidal currents were relatively sluggish (0-0.05 m/s) in the beginning of model simulation. The ebb currents were established from 2 to 7 hours; originating from the inner part of the estuary tended to flow radially (Eastwards, Northwards and Southwards) soon after reaching the river mouth. The radial flow pattern of the ebb tidal currents seemed to be influenced by the funnel shape of the estuary. The flood tidal currents were established after 7 hours. The flood tidal phase started earlier on the southern part of the river mouth compared to the northern and tended to become more intensive on the northern part than on the southern part of the estuary. The currents pattern observed were influencing the transport and deposition of Suspended Particulate Matter (SPM). The maximum deposition of SPM preferentially occurred about 3 km north and south of the estuary mouth and the minimum deposition occurred in the middle of the estuary mouth. The deposition of SPM was highest during the southeast monsoon relative to the northeast monsoon. Approximately 872.6 kg/m(2)/year of SPM were brought into the estuary. This implies that, in the long term, the SPM deposition along the river mouth will significantly change the Pangani hydrodynamic regime, from its present condition. Also infilling of navigational channel and alteration of the ecosystems is imminent. Urgent actions are required to minimize the generation of SPM within the Pangani river basin.