Judul: Implications of changes in nutrient availability for phytoplankton rapid growth (blooming) at Jakarta Bay Waters
Abstrak: The main inorganic nutrients are necessary for phytoplankton to grow and develop are nitrogen, phosphorus, and silica. If the input of nutrients in marine waters beyond the optimal growth of phytoplankton, it will lead to rapid growth (blooming) of certain types of phytoplankton. This study aimed to analyze and determine the concentration and ratio of N : P as well as changes in nutrient availability to the population explosion and change the structure of phytoplankton communities in Jakarta Bay, to set the amount of nutrient preparations leading to population explosions of certain phytoplankton in the Jakarta Bay, as well as to examine the relationship between increased production phytoplankton biomass with nutrient availability in the dry season and rainy season and transitional season. The experiment was conducted in Jakarta Bay in August 2009 to May 2010. Sampling was performed six times at nine stations. Phytoplankton enumeration was performed by the method of deposition. Nutrient samples were analyzed using a spectrophotometer. Canonical correspondence analysis was used to determine the relationship between phytoplankton with physico-chemical parameters of water. The results showed that the spatially and temporally there were found 47 genera of phytoplankton from four classes : Bacillariophyceae (26 genera), Chlorophyceae (8 genera), Cyanophyceae (7 genera), and Dinophyceae (6 genera). Concentration of major nutrients (N, P, and Si) was high and the ratio of N : P was less than 16 resulted in very rapid growth (blooming) of certain types of phytoplankton in Jakarta Bay waters. Very rapid growth of phytoplankton occured in the range of concentrations of nutrients, namely nitrate: 0.0105-0.0829 mg.L-1, orthophosphate : 0.0114-0.3010 mg.L-1, and silica : 0.2787-5.9946 mg.L-1. Genera of phytoplankton that were experiencing rapid growth (blooming) in the dry season were Skeletonema and Rhizosolenia, while those of phytoplankton in the transitional season were Skeletonema, Chaetoceros, Rhizosolenia, and Noctiluca. How ever, in the rainy season there was no genus of phytoplankton that grew very rapidly. Physico-chemical parameters contributing to the blooming of Skeletonema were silica, nitrate, orthophosphate, and temperature. Parameters that contributing to the blooming of Chaetoceros were pH and silica. pH also played a role in the rapid growth of the genus Rhizosolenia.
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Judul: Relationship of phytoplankton productivity with nutrient availability streaming derived from the river and the sea in Inner Ambon Bay
Abstrak: The development of increasingly rapid development resulted in bay conditions, particularly in Ambon bay gets heavy pressure, resulting in changes in the aquatic environment. These changes further affect marine organisms that live in it. One of the marine organisms playing an important role for productivity is a water plankton community. Plankton community plays great role in marine ecosystems, particularly because phytoplankton are the foundation of the food chain so called primary producers. As primary producers, phytoplankton can form organic matter from inorganic matter through photosynthesis which in turn can be used directly by other living organisms. The purposes of this study were 1) to analyze seasonal changes in the distribution of temperature, salinity and density in the water; 2) to analyze the inter-relationship between the light intensity and the level of turbidity water; 3) to analyze the load level of nutrients in water derived from river and sea; 4) to analyze the spatial and temporal distribution of phytoplankton composition and abundance in the water; 5) to analyze seasonal changes in the level of productivity of phytoplankton in the water; and 6) to examine the inter-relationship between the succession of phytoplankton to changes in N:P ratio in the water of the Ambon bay. The results of this study indicate that temperature, salinity and density were low in East Season. In the Bay of Ambon there was stratification in temperature and salinity, while mixing was not occur either from surface to bottom water. Season were great influence on the distribution of nutrients in the water, again the average ammonia concentration was higher in East Season that indicate domestic sewage polluted water. Average NO3-N concentration of the lowest in the Western season (0.05 μm) and high in East Season (0.55 μm). Average concentration of nitrate in the East Season in Zone-1 was low and Zone-2 was high. In East Season high phosphate concentrations, so that phosphate stimulates rapid growth (blooming) Trichodesmium in water. Average concentration of silica in the East, Transition II, Western and Transition I Season highly significant, with the lowest concentrations in Transition Season I (1.29 μm) and high in East Season (35.61 μm). At the moment there was a high concentration of silica Bacillariophyceae low abundance in the eastern season. In the Transition II, the West, and the Transition I Season occurred increased abundance of Bacillariophyceae, along with decrease in the concentration of silica. Input nitrate and phosphate in East Season was very large from outside Ambon Bay compared to from river. Spatial and temporal waters in the Inner Ambon Bay were found oligotrofik and mesotrofik state. Flushing time were occured in Ambon Bay within 14 days. The average of chlorophyll-a concentration in the East, Transition II, West and Transition I Season were highly significant, the lowest concentration at West season (0.44 μg/l) and high in East season (0.94 μg/l). In the East Season, there was an increase of chlorophyll-a, but the low abundance of phytoplankton. In the East Season, chlorophyll-a negative correlation revealed in nitrate and nitrite, this is due to an increase in chlorophyll-a caused by decrease in nitrate and
Keyword: primary productivity, phytoplankton, nutrients, succession, Inner Ambon Bay

Judul: Truncated Stop Loss as a Optimal Solution of Reinsurance Agreement in One-Period Model
Abstrak: Reinsurance is one of risk management efforts of an insurance company, which is called the cedent. Similar with insurance, reinsurance constitutes the cedent to pay the premium. We consider one-period reinsurance model and derive a rule which minimizes the ruin probability of the cedent for a fixed reinsurance premium. Therefore, it is needed to construct an optimal reinsurance agreement for the cedent. The premium is calculated according to four different principles, i.e. economic, generalized zero-utility, Esscher, and mean-variance principles. Stop loss is a reinsurance contract which protect the insurance company for losses that exceed a certain amount. The result of this research shows that a truncated stop loss is an optimal agreement in the class of all reinsurance contracts with various premiums calculated using above mentioned principles.
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