Serangan Island was a costal area located in the Serangan village, South Denpasar district, near with Sanur and Nusa Dua tourism area. Serangan beach has a biodiversity such as natural macroalgae. This study was conducted in January 2017 at the seaweed cultivation area with the aims of research were to know the variety and density of macroalgae. The method used was a 1x1 m quadrat transect. Sampling was carried out during low tide. Macroalgae found in the area, consist of 12 species namely Ulva lactuca, Chaetomorpha linum. Chaetomorpha aera, Padina australis, Sargassum fluitans, Turbinaria ornate, Gelidium sp., Hypnea cornuta, Hypnea spicifera, Gracilaria salicornia, Acanthophora spicifera, Halimeda opuntia. Those species were belonging to 3 divisi namely Chlorophyta, Phaeophyta, Rhodophyta. The highest density of macroalgae was Padina australis while the lowest density was Chaetomorpha linum. Type of dominated macroalgae was from a group of Phaeophyta (brown algae) with highest dominance from the species of Padina australis. Water quality namely acidity (pH) was in the range of 7.54 to 7.75, salinity of 31.33-32.00 ppt, the water temperature was 26.50-27.30? C, which all was categorized as the optimal parameters for the growth of macroalgae. Assosiation of biota found were 9 species namely fish of larva, Cypraea lynx (Molusca), Emerita sp., Halodule sp., Synapta maculate, Enhalus acoroides, Cymodocea serrulata, Hermit crab, Ophiuroidea sp. The conditions coastal waters substrate was varied from white sand stone type to stony type by coral pieces.

Fiddler crabs (Uca spp.) are one of the mangrove fauna that has an important role of food chain within the scope of mangrove, which is as a deposit eater. The mangrove area in Kampoeng Kepiting has been damaged due to reclamation for Bali Mandara toll road construction, which can interfere the survival/existence of Fiddler crabs. Therefore, it is necessary to do a research concerning the abundance of Fiddler Crabs in Kampoeng Kepiting mangrove area. The aim of this study is to determine the type and abundance of Fiddler crabs and to discover the coherency among Fiddler Crabs abundance in the manner of c-organic matter content in Kampoeng Kepiting area. Fiddler crabs samples were carried out using 1×1 meter quadrant transect by digging as deep as 30 cm. The abundance of Fiddler crabs was analyzed under the Krebs equation. The results from this study indicate Fiddler crabs were found in Kampoeng Kepiting area ,i.e. Uca demani, Uca coarctata, Uca dussumieri, Uca bellator, Uca lactea perplexa, Uca tetragonon, Uca chlorophthalmus crassipes, Uca lactea annulipes, Uca triangularis, and Uca vocans. The highest Fiddler crabs abundance were found at station 4 which is 72±4,2 ind/m2, whilst the abundance of Fiddler crabs (Uca spp.) at station 5 is (33±1,2 ind/m2). The c-organic matter content has a strong relationship with the abundance of Fiddler crabs in Kampoeng Kepiting mangrove area (r = 0,91). This study shows that mangrove conditions in Kampoeng Kepiting are still able to support Fiddler Crabs (Uca spp.) existence.

Macroalgae is a type of flora known as seaweed and is classified into low-level plants, where roots, stems, and leaves are relatively difficult to distinguish. This study aims to determine the differences of habitat characteristics, number of species, biomass, and macroalgae community structure in Geger Beach and Mengening Beach. This quadrant transect method was used to collect the data. The results show that Geger Beach has sandy substrate, while Mengening Beach has substrate consisting of coral rock. The water quality in both locations are still suitable for macroalgae growth. The results of the study found 8 types of macroalgae in Geger Beach and 10 types of macroalgae in Mengening Beach. The highest macroalgae biomass at Geger Beach was found in Gracilaria hayi with the weight ranging from 72.08-73.18 g/m2, while at Mengening Beach was found in the Valonia aegagropila, ranging from 181.31-190.40 g/m2. The diversity index of macroalgae in Geger Beach was between 1.93-1.99, while at Mengening Beach was between 1.79-2.07, therefore categorized as medium. The dominance index of macroalgae at Geger Beach was between 0.15-0.17, while at Mengening Beach was between 0.17-0.25, therefore the dominance index at both site was categorized low. The evenness index at Geger Beach was between 0.93-0.96, while at Mengening Beach was between 0.78-0.90, which categorized as stable conditions.

Seaweed is one of Indonesia's fishery commodities with great potential to be cultivated, the condition of seaweed produced in Indonesia is not optimal yet. This can be seen from the low productivity of seaweed in Indonesia which is caused by the low growth rate. The growth rate of seaweed can be supported by proper planting techniques and cultivation methods. Seaweed farmers generally use planting techniques and traditional cultivation methods called the monoculture system, which is planting one type of plant in an area. As the cultivation systems developed, a new cultivation system was found that supports increased growth of seaweed, namely the co-cultivation. This system is sustainable and environmentally friendly which combines species from various trophic in one system. This research was conducted for 6 weeks from December 2019 to January 2020 in the coastal area of Pandawa Beach, Bali. The data was analysed in Completely Randomized design with three treatments and three replications. The monoculture cultivation system which contain 100 gr of seaweed in a bag was treated as control and co-culture systems were added with 10 and 30 individuals of abalones. The results showed that the growth rate pattern as a measure of weight increased during the time of study. The weight of seaweed was highest in co-cultured treatment with 10 individual abalones. The highest specific growth rate of seaweed occurred in the co-culture system up to 4%/day compared to the monoculture cultivation system only 3.4%/day.

Seaweed farmers on Kutuh Beach experienced problems in seaweed cultivation activities, namely that seaweed cannot grow well. This is due to the large number of predators that ate seaweed in the cultivated area. One method that can be used to overcome this problem was using bags in seaweed cultivation. The purpose of the research that was carried out in July-October 2018 was to determine the effect of using bags on seaweed cultivation in Kutuh Beach waters. The method used in this research was experimental using two treatments (planting seaweed using bags and without bags) and three replications. Water quality parameters measured as supporting data ware DO, pH, salinity, temperature, nitrate, and phosphate. The result of this study was the growth of seaweed cultivated using bags is better than the growth of seaweed cultivated without bags.