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A phenoregion approach to understanding chlorophyll‐a seasonal cycles and interannual variability in the South‐West Indian Ocean

2026-03-30T00:00:00Z

Title: A phenoregion approach to understanding chlorophyll‐a seasonal cycles and interannual variability in the South‐West Indian Ocean Authors: Arens, Aline; Penven, Pierrick; Chenillat, Fanny; Pous, Stephane; Nehama, Fialho P.J.; Malauene, Bernardino S. Abstract: The South-West Indian Ocean (SWIO) displays marked spatial variations in physical forcings, driving in turn distinct seasonal biogeochemical regimes. Mesoscale eddies in the Mozambique Channel drive large-scale redistribution of nutrients and plankton, while eastern Madagascar waters are highly oligotrophic. However, the spatial organization and diversity of biogeochemical seasonal cycles across the SWIO remain insufficiently characterized on the basin scale. This study examines the seasonal and interannual variability of surface chlorophyll-a (Chl-a), used as a proxy for primary production. A phenoregion approach is employed, involving the grouping of areas exhibiting similar Chl-a phenology, that is, bloom timing (austral winter and/or summer) and the number of blooms per year (0, 1, or 2). 22-year of weekly satellite-derived Chl-a from the OC-CCI data set was used to generate normalized climatological seasonal cycles, which were subsequently clustered using a k-means algorithm. This approach identifies six distinct Chl-a phenoregions across the SWIO. Winter blooms dominate the basin and are likely associated with mixed-layer deepening and enhanced vertical nutrient supply, leading to temporally stable phenoregions. In contrast, summer blooms are restricted to coastal regions and south-eastern Madagascar, coinciding with enhanced terrestrial nutrient inputs during the wet season. In the Mozambique Channel, Chl-a exhibits limited seasonal variability, likely reflecting strong eddy-driven exchanges between coastal and offshore waters. Interannual analysis reveals stable phenoregion cores with consistent seasonality, while their boundaries exhibit variability, highlighting contrasts between persistent and highly intermittent biogeochemical regimes. The results obtained provide a basin-scale framework for linking physical dynamics to ecosystem variability in the SWIO.

Efeito dos fertilizantes inorgânicos no desempenho zootécnica de alevinos de Tilapia Moçambicana (Oreochromis mossambicus - Peters, 1852) cultivados em tanques rede

2025-04-01T00:00:00Z

Title: Efeito dos fertilizantes inorgânicos no desempenho zootécnica de alevinos de Tilapia Moçambicana (Oreochromis mossambicus - Peters, 1852) cultivados em tanques rede Authors: Conceição, Helton Fernando Dias da Abstract: O presente trabalho tem como objectivo avaliar a resposta zootécnica de alevinos de Tilapia Moçambicana (Oreochromis mossambicus) cultivados em tanques rede sob efeito de fertilizante inorgânico. O estudo foi realizado na unidade piscícola da Escola Superior de Ciências Marinhas e Costeiras, localizado no distrito de Quelimane, Província da Zambézia, por um período de 90 dias, compreendidos de 12 de Dezembro a 24 de Abril de 2016. Um total de 180 juvenis foram utilizados no ensaio, tendo um peso médio inicial de 3±1.04g, povoados em tanques rede (hapas) inseridas em dois tanques terra de 162m2, sendo um com aplicação de fertilizantes inorgânico (Tratamento 1) e outro sem fertilização e com alimentação a base de ração comercial da marca LFL (Tratamento 2). O estudo esteve assente em um tanque escavado com dois tratamentos e três repetições cada, perfazendo 6 unidades experimentais, povoadas com 30 peixes cada. Foram feitas biometrias quinzenais a 40% da amostra, sendo que o cultivo esteve acompanhado com o monitoramento diário de parâmetros de qualidade de água, medidos duas vezes ao dia (manhas e tardes) as 6:30h e 15:30h. Posteriormente, foram determinados os Índices de desempenho zootécnico de Crescimento Diário em Peso (CPD), Taxa Específica de Crescimento (TEC), Taxa de Sobrevivência Final (TSF), Factor de Conversão Alimentar (FCA) e Biomassa Total Produzida (BTP). Os resultados obtidos indicaram diferenças significativas (p <0.05) entre os tratamentos. As Tilápias alimentadas com a ração comercial obtiveram valores de peso medio (76.6±2g) superior em relação a biomassa dos peixes criados sobe efeito de fertilizantes inorgânicos (52.6±2.03g), sendo que o inverso foi observado para a taxa específica de crescimento diário (1.4±0.9%) contra e 1.2±0.8%. Conclui-se que a tilápia teve o melhor desempenho zootécnico quando alimentada com ração comercial, sendo que o T1 apresentou ganho de peso menor e, consequente menor peso final e ganho em biomassa também menor em relação ao T2 (ração comercial). Estes resultados sugerem que o uso de fertilizantes inorgânicos Apesar das diferenças estatísticas nos índices zootécnicos calculados este este método pode ser usado.

Impacto socioeconómico da produção aquícola em Moçambique: caso de estudo- Província da Zambézia

2025-04-08T00:00:00Z

Title: Impacto socioeconómico da produção aquícola em Moçambique: caso de estudo- Província da Zambézia Authors: Ferreira, Lucinda Verónica Cuamba Abstract: Fish farming has become an excellent business and area of research, providing important economic and nutritional benefits for the population, where tilapia farming, in particular, has expanded significantly throughout the country, with an emphasis on Zambézia province. The aim of the study was to analyse the socio-economic impact of aquaculture production in Mozambique. 49 fish farmers were surveyed in the districts of Quelimane, Nicoadala, Pebane and Milange. The descriptive analysis showed that most of the fish farmers were men, aged between 35 and 55, with secondary education, living in medium-sized families where 1 or 2 people contribute to the monthly income. They produce in an area of less than 500 square metres, with one pond and use a semi-intensive system for tilapia production. Production is destined for commercialisation and is sold locally. Production aspects limit the development of fish farming and feed was identified as the main obstacle. Variables such as production area, number of ponds, construction cost, production cycles, cost of fry and revenue have a direct impact on productivity and profitability. Tilapia production is considered profitable, although fish farmers are unaware of the profits made at the end of each cycle. To do this, fish farmers need to know the production costs and understand cost accounting in order to be able to estimate the profits from the activity. They also need to undergo technical training in economic viability. Aspects such as the availability of inputs, technical training, extension services and access to finance must be taken into account in order to increase productivity and profitability

Efeito do ambiente e o método de cultivo sobre o crescimento da macroalga Eucheuma denticulatum na região norte de Moçambique

2024-08-02T00:00:00Z

Title: Efeito do ambiente e o método de cultivo sobre o crescimento da macroalga Eucheuma denticulatum na região norte de Moçambique Authors: Madeira, Ana Domingos Abstract: Macroalgae cultivation plays an important role in several tropical and equatorial regions, contributing to local and global economic development. In Mozambique, the potential for the cultivation of macroalgae E. denticulatum and other species is estimated at around 10,600 hectares, but the record of large-scale production is low. In this context, this study aimed to evaluate the influence of the environment on the cultivation of the alga E. denticulatum in the northern region of Mozambique. Cultivation was carried out in the Palma and Mossuril regions for 9 months, using two cultivation techniques called "tie-tie" and tubular net. Samples were taken every two weeks to record the biomass, observe the quality of the vegetative parts and monitor the physico-chemical parameters at the site. The other environmental data parameters used to correlate with biomass as well as the relative growth rate (RGR) were obtained from My Ocean Copernicus. The generalized additive model (GAM) was applied to determine the influence of the environment on biomass accumulation and TCR throughout cultivation. The comparison between cultivation methods was made using the independent samples t-test. All statistical analyses were carried out using R software. The results indicated that there were no significant differences in biomass accumulation between the two cultivation techniques (t = -1.40, df = 392, p-value = 0.16), although the tubular net technique showed higher biomass values (12.16 ± 11.34 kg). Regarding to TCR, the tubular net method had a higher relative growth rate (16.44 ± 18.48 kg) compared to the tie-tie method (5.45 ± 7.48 kg), and these differences were confirmed by the test (t = -7.01, df = 179.45, p-value <0.05). The biomass model explained ~97% of the total variation, while the growth rate model explained ~90%, both with significant levels of the high selected variables (p-value < 0.001). The variables that most influenced the variation in biomass were tidal height (F-statistic ~175), pH (F-statistic ~125), sea surface temperature (SST, F-statistic ~44), dissolved inorganic carbon (DIC, F-statistic ~37) and nitrate (NO3-, F-statistic ~32). For growth rate variation, the most influential variables were nitrate (NO3-, F-statistic ~89), sea surface temperature (SST, F-statistic ~39) and wave energy (SWH, F-statistic ~12). These results highlight the importance of monitoring environmental variables during the cultivation of E. denticulatum in order to optimize production and can help guide the selection of sites for the establishment of macroalgae aquaculture enterprises for ecosystem recovery as well as for socio-economic purposes.