Browsing by Author "Chauka, Leonard"

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Climate change impacts outweigh conservation efforts in coral reefs that are highly exposed to thermal stresses in Zanzibar, Tanzania
(Elsevier, 2023-05-01) Chauka, Leonard; Nyangoko, Baraka
With a greater range of management practices and so many threats to coral reefs, assessing coral reef resilience using social-ecological approaches is an important way towards understanding the climatic and non-climatic impacts, and proper conservation efforts in coral reefs. In this study, six reefs (Changuu, Chapwani, Chumbe, Kizimkazi, Mnemba East and Mnemba West) were selected as case study sites to explore resilience potential of coral reefs in Zanzibar in relation to contrasting conservation strategies. Data were collected through household surveys, key informant interviews and biological survey (line-intercept transect and direct observations). Results showed that, Chumbe reefs was perceived to be highly protected followed by Kizimkazi reefs, while Changuu and Chapwani were considered to be less protected. Fishing pressure, climate change, inadequate management and pollution were regarded as the most critical drivers of coral reefs degradation. Coral bleaching was identified to be a main cause of coral reef damage by communities in Chumbe and Mnemba East, whereas inadequate management, pollution and uncontrolled tourisms were identified as the major driver by those in Changuu and Chapwani. Overall, reefs from Kizimkazi was found to have the highest resilience potential as it is under community-based conservation compared to other reefs. We conclude that coral reef resilience is context-specific and influenced by multiple factors, and although conservation efforts have a positive impact on coral reef health, climate change effects outweigh conservation efforts in reefs that are highly exposed to thermal stresses, such as the Chumbe and Mnemba East reefs. We recommend further promotion of viable alternative livelihood activities to reef reliant communities and collaborative management for the improvement of corals' resilience and conservation in the study area.
Mitochondrial DNA revealed a single stock structure of the Spotted sardinella Amblygaster sirm (Walbaum, 1792) (Teleostei; Clupeidae) in Tanzanian coastal waters
(Springer Berlin Heidelberg, 2023-06-12) Fabiani, Godfrey; Mtonga, Cretus; Chauka, Leonard; Rumisha, Cyrus; Muhando, Christopher
The Spotted sardinella Amblygaster sirm are small pelagic fish that are important protein source to coastal communities in the Indo-West Pacific. In this study, a cytochrome c oxidase subunit 1 (COI) gene of A. sirm from Tanzania was amplified to assess the species’ genetic structure and demographic history. All individuals collected were identified using both morphological examination and genetic barcoding as A. sirm. A total of 19 haplotypes were found in the dataset, with low overall nucleotide (π = 0.13 ± 0.001) and moderate haplotype diversities (h = 0.45 ± 0.07). AMOVA revealed a very low and non-significant genetic differentiation in the dataset (Fst = 0.002, Фst = −0.004, p > 0.05), indicating a lack of population structure. The minimum spanning haplotype network revealed additional evidence for the lack of population structure, which grouped all the sampled haplotypes into one cluster, regardless of their geographical regions. The Tajima’s D, Fu’s Fs tests, and mismatch distribution analyses supported a hypothesis of recent demographic expansion. The lack of population structure identified suggests that the fishery should be treated as a single-stock management unit, consistent with the existing management regime for the species in Mainland Tanzania that currently does not consider genetic structure in managing the fishery. The lack of population structure suggests that populations with low genetic diversity, such as Dar es Salaam, can rebuild by recruiting from other sites if regulations against unsustainable fishing are strictly enforced.
Stakeholders' perspectives on seagrass ecosystem services and their threats vary across Zanzibar archipelago, Tanzania
(ELSEVIER, 2025) Nyangoko, Baraka; Chauka, Leonard; Meysick, Lukas; Rohde, Sven; Adams, Janine; Schupp, Peter
Recognizing the ecosystem functions and services provided by seagrass meadows and their vulnerability to different environmental and anthropogenic stressors is crucial for effective decision-making, especially in resource-dependent regions. This study explored how stakeholders (local communities) living in proximity to three distinct seagrass meadows in Zanzibar (Chwaka, Jambiani, and Stone Town) perceive and rely on seagrass ecosystem services (SES), their threats and factors influencing on their perception. Data were collected through a combination of methods, including participatory rural appraisal, household questionnaire surveys and field observations. Results revealed that local communities across these sites had mixed perceptions regarding SES. Provisioning services (e.g., fish provision) were the mostly identified SES, followed by regulating services (e.g., coastal protection), supporting services (e.g., fish nursery grounds), and cultural services (e.g., ecotourism). Fish provision, nursery habitats, and coastal protection were ranked as the most important SES for sustaining local well-being. Among all predictors analyzed, proximity to the shore, the main occupation of respondents, and residence time were significant factors that influenced the local communities' awareness of all SES. Unregulated fishing practices, overgrazing by sea urchins, and seaweed farming were perceived as the primary causes of seagrass loss in Chwaka and Jambiani, while in Stone Town, seagrass degradation was attributed to increased wave activity and changing tidal regimes, unregulated tourism (boat anchoring), and pollution. The study concludes that the perceived importance of SES and the drivers impacting seagrass ecosystems vary depending on context-specific factors. This strongly emphasizes the need for conservation actors to increase awareness of the multiple benefits generated by seagrasses, restore degraded areas, and devise solutions tailored to specific threats for sustainable management of seagrass meadows.