Desempenho das macroalgas marinhas Kappaphycus alvarezii e Eucheuma denticulatum cultivadas em substrato com e sem ervas marinhas, na Ilha de Inhaca

Abstract

Seaweeds play an important role in the marine environment for the coastal population and for a long time were collected in natural areas for use in various branches of the industry. Currently, they are growing in various regions to meet market demand, with applications ranging from the food and cosmetics industries to pharmacology and biotechnology. Mozambique has a high potential for cultivating seaweeds, there are interest in maximizing production and also cultivating them in the southern region. However, there is a need to choose a substrate that meets appropriate environmental conditions for their success. This study aimed to evaluate the performance of the seaweed Kappaphycus alvarezii and Eucheuma denticulatum cultivated on substrates with and without seagrass. The research was conducted in Maputo Bay, on the limits of Inhaca Island, at Ponta Torres beach. The experimental cultivation was carried out over 45 days using the off-bottom method, with 6mm thick and 5m long ropes, each with 17 seedlings, in six replicas during hot and cold seasons. Throughout the cultivation period, analyses of temperature, dissolved oxygen, salinity, pH, nutrients, phytoplankton, biomass, and the nutritional composition of the seaweed were performed. The relative growth rate was determined to compare the daily growth of the seaweed. The average temperature during the warm season ranged from 27.5°C to 31.5°C, while during the cold season it ranged from 21.5°C to 25.5°C. The highest daily growth rate was observed in Eucheuma denticulatum cultivated on the substrate without seagrass during the hot season with an average of 7.2±0.1%day-1, with a net biomass of 10713.3±205.1g, +700%. Conversely, on the substrate with seagrass during the hot season, Eucheuma denticulatum obtained negative values for the average daily growth rate, of -0.1±0.2%day-1 and a negative biomass of -178.3±147g, -12%, likely as a result of herbivory and bleaching. Kappaphycus alvarezii showed positive growth in all experiments with its highest daily growth rate on the substrate without seagrass during the hot season, with an average of 6.4 ± 0.2%day-1 and a net biomass of 8798.3±407.7g, +500%. The results indicate that the substrate without seagrass showed better performance in the cultivation seaweed in the off-bottom system and the best time for cultivation is the hot season.