Abstract:Microalgae use photosynthesis to convert solar energy into chemical energy, such as lipid and they can be a replacement for oil-based fuels. They are among the fastest growing plants in the world, and about 50% of their weight is oil. This lipid oil can be used to make biodiesel. Unfortunately, there are only some of potential strains isolated from Indonesia and most of the biodiesel productions are usually using a single strain. Then, although they are rich of oils, their biomass productivity is still low. Salinity treatment can be used to increase their biomass as well as their lipid content. Therefore, the research aim was to study the effect of salinity on the growth, dry weight and lipid content of mixed microalgae isolated from Glagah, Yogyakarta. The mixed microalgae were cultured in 3NBBM medium with different salinities or types of water (sea water, brackish water, and fresh water). The cultures were incubated at light intensity 3,000 lux under dark:light exposure of 12:12 h for 7 days. The number of cells was counted every 24 h with a Haemocytometer, and the biomass was calculated based on the dry weight. The lipid content was measured on days 0, 3, and 7 using NR (Nile Red) staining, and then the amount of lipid was analyzed using a fluorescence microscope and measured with CellProfiler 2.0 software. The highest dry weight and lipid content were found in seawater medium, they accounted for 3.42 mg/mL and 13.58% at day 7, respectively. Whereas, the highest number of cells was found in freshwater medium, this was 9.8 × 10 6 cells/mL.

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Ela-ela beach has wide seagrass ecosystem with sandy substrate. Sea grass is a habitat of various invertebrates including mollusks. Some mollusks live by burrowing in substrate and attaching to seagrass leaves. A study of mollusks diversity of Ela-ela Beach, Sekotong Lombok Barat regency NTB was conducted on July 2012. The objective of this study was to estimate the abundance and diversity of mollusks. Parallel quadrate transect was applied as the sampling methods. Ninety two individuals were collected and identified, consisting of Gastropods (29 species), Bivalves (6 species). The most abundant species in this studied area were Trachycardium rugosum (18 individuals) and Pyrene scripta (17 individuals). The Diversity Index (H') was 2.99, the Pielou Index (J) was 0.84, and the Margalef Index (d) was 17.31. Based on Odum (1994), the Diversity Index is moderate.

Microalgae is one organism that can be used as raw material for bioethanol production. Growth and composition of microalgae cells affected by strain and environmental conditions, including temperature, pH and nutrients. Nutrients are used for the growth of one of silica, except that the silica used to form frustule on diatoms. This study aimed to determine the effect of silica on growth, dry weight, and carbohydrate produced from mixed cultures Phaeodactylum sp. and Chlorella sp. Cultivation is carried out for 21 days on a laboratory scale using a medium F / 2. Culture growth was measured by counting cell density. The dry weight is calculated every 7 days to obtain a biomass productivity. Carbohydrate content was measured by the phenol-sulfuric method. samples were taken on days 0, 7, 14 and 21. It could be concluded that the highest quota of carbohydrate per cell was obtained on Si 90 ppm, accounted for 0.03977 mg / cell. Furthermore, total carbohydrate content and the highest percentage in the mixed culture Phaeodactylum sp. and Chlorella sp. were found in treatment of 30 ppm and 6 ppm, amount of 289.93 mg / L and 40.45%, respectively. Thus the mixed culture was prospective as bioethanol feedstock.