Judul: Analysis of Periphyton Presence Related to Physical Chemical Parameter and the Characteristic of Seagrass beds in Pari Island
Abstrak: Seagrasses represent one of the important and highly productive ecosystems of the world, which provides critical habitat for many animals and plants including periphyton. The characteristics of seagrass beds are acutely responsive to density and distribution of assosiated periphyton due to physical chemical factors and community structure of the seagrass itself. The aims of this research were to investigate composition and density of periphyton taxa between mixed vegetation and monospesific seagrasses beds and to study the physics chemical parameters that influence the community structure of periphyton on seagrass leaves and the density of seagrass community. The results showed that the highest density of seagrasses and periphyton occured in station II with mixed vegetation and consists of four species of seagrasses. PCA analysis indicated that the most influenced of physical chemical factors were current, nitrate and phosphate, while the presence and density of periphyton weree affected by seagrass densities.
Keyword: physical chemical factors, periphyton, characteristic of seagrass bed.

Judul: Asosiasi ikan dengan padang lamun di perairan karang lebar, kepulauan seribu, Jakarta
Abstrak: Seagrass is a complex aquatic ecosystem in trophics area with high productivity and biodiversity. This ecosystem play role of physics, chemistry, and biology. Biologically, seagrass used as spawning, feeding, and nursery ground for aquatic biota, especially fish. Seagrass is part of the coastal region where there are many human activities, such as coastal development, overfishing, boat traffic, and sand mining. One of the seagrass areas with high human activity around is Karang Lebar shallow waters, Kepulauan Seribu, Jakarta. Types of data taken in this research is primary data, including environmental parameters, condition of seagrass and fishes that live in it. Fishes caught by gill net with mesh size from 0.5 – 3 cm. Sampling conducted in day and night, started from March until May 2011 with the arrest period twice a month. Observations were made at three stations of seagrass beds with different covering conditions (healthy, less healthy, and poor). Sorensen similarity index, constancy index, and fidelity index were used to determine the relationship of fish associated with seagrasses. In addition, it also used statistical tests such as Pearson correlation, biplot analysis, and Two Way ANOVA as a tool to test the truth of descriptive analysis results based on the facts as represented by data. Three seagrass species found in the observation area include Thalassia hemprichii, Cymodocea rotundata, and Halophila ovalis. The highest cover obtained from Cymodocea rotundata. Value of total cover ranged between 26.5 % - 82.13 %. The highest INP of the species obtained from Cymodocea rotundata, indicate that these organisms have a great influence to the ecosystem. Fish were caught consist of 37 species and 22 genera. Total abundance was found in all three observation stations for 2287 individuals (healthy seagrass), 547 individuals (less healthy seagrass), and 889 individuals (poor seagrass). Pre-adult fish dominate at each station. While the most commonly species found are Hypoatherina temmincki, Gerres oyena, and Scolopsis lineatus. The catch composition on day and night differ in terms of abundance, type and size of the species. Adult fish were more common at night, although abundance in day were more than in the night. Based on size and species composition, healthy seagrass and less healthy seagrass functioning as nursery ground and feeding ground, while poor seagrass tend to play a role as feeding ground, especially for carnivorous fish. Change of the diversity and dominance value in the day and night allegedly due to the activity or movement of fish, which is not a permanent resident in seagrass. Referring Tomascik et al. (1997), permanent resident fish found in the observation area is Apogon margaritiphorus. Based on Sorensen similarity index, the fishes were divided into six groups of species. Constancy index ranging from 0-1, while fidelity index ranges from 0-3. Group of species 1 has a high preference on healthy and poor seagrasses, and low preference in unhealthy seagrasses. Healthy seagrass also preferred by group 6, which include Apogon kallopterus, Apogon margaritiphorus, Hemirhapus far, Chrysiptera hemicyanea, and Syngnathoides biaculeatus. Groups of species that have a high preference towards less healthy habitat is group 4, with Stethojulis balteata, and Chaetodon
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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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