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

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.