Judul: Bioecological Study of Eightband butterflyfish (Chaetodon octofasciatus, Bloch 1787) to Detect Condition of Coral Reef Ecosystem in East Petondan Island, Seribu Islands, Jakarta
Abstrak: Monitoring the changes of coral reefs is an important task considering many of the world’s coral reefs have been destroyed or severely degraded. There are reliable ways to indirectly assess the changes of a coral reef and monitor it through time: certain members of an easily identifiable conspicuous family of fish, Chaetodontidae, have been considered to be reliable indicators of reef health. Data of Chaetodon octofasciatus are based on field observation using SCUBA set on the reef slope (3 and 10 meter) and food and feeding habit analysis conduct in the laboratory. The percent coverage of living corals was estimated on the reef slope (3 and 10 meter) at all sites. A 50 m line transect were laid at each site and depth. By using belt transect the abundance of C. octofasciatus and the occurrence of each coral genus were counted and recorded in data sheets. Feeding rates were calculated by observing randomly selected species at study area. Ivlev’s electivity index was used to measure feeding selectivity, comparing the utilization of food with respect to its availability. The feeding bites to be larger in rich reef corals with high percentage of live coral. The feeding rates in south, west and north site which have high percentage of live coral is highest comparing to east site which have low percentage of live coral. Based on food and feeding analysis, the fish stomach contain 94,1% coral nematocysts and 0,59% periphytic algae, which indicated C. octofasciatus as an obligate coralivores.
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Judul: Coral Reef Health Condition based on Herbivorous Fish Density in Pulau Tiga Subdistrict, Natuna District
Abstrak: The research was conducted in Pulau Tiga Subdistrict, Natuna District, Riau islands Province from April to August 2009. Pulau Tiga is an area dominated by a sea area with marine resource potential, particularly coral reefs. Around the area of coral reefs, fishing activities have been carried out intensively by fishermen using explosives (bombs) and toxic (potassium). Consequently, aquatic ecosystems have been exploited, take time to make a natural recovery in order to maintain and restore the quality and quantity of available resources. Especially for coral reef ecosystem, one of the factors that influence the resilience rate is the availability of hard substrate in a bottom waters as a settlement for coral larvae. Herbivorous animal has a major influence in determining the rate of coral reef animal larval settlement on a substrate because it can prevent the occurrence of a macro-algae excessive closure of hard substrate. This study was aimed to know the relationship between the conditions of the abundance of herbivorous fish with coral reef recovery rate. The methods used were the square transect for determining the condition of coral reefs, growth of juvenile corals and algae cover (DCA), whereas for the determination of herbivorous fish community structure using modification of Line Intercept Transect (LIT), Quadrat Method (QM) and Underwater Fish Visual Census (UVC). The analysis used was standard ecological analysis, correlation test, linier regression and multivariate analysis to find the relationship between the abundance of herbivorous fish, algae (DCA) and coral reefs. The results showed that coral reefs ecosystem in the area are still in good condition with live coral cover average of 63.17%, and shown an indication of an increase in the percentage of coral cover which previously <25%. The result of multivariate analysis can be stated that the higher the abundance of herbivorous fish, then live coral cover and growth of juvenile corals increasing, and decreasing algae cover on coral reef ecosystems. The results of correlation test, multivariate analysis and linear regression (t-Student test), show that from 24 species of herbivorous fish recorded then obtained three species of herbivorous fish that play a role in herbivory in stabilizing coral reefs ecosystem in Pulau Tiga Subdistrict, they are Chlorurus microrhinos, Scarus rivulatus and Siganus doliatus.
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Judul: Konstruksi aritmetika kurva eliptik F(2m) supersingular dan non-supersingular untuk skema kunci publik ElGamal
Abstrak: Algoritme ElGamal adalah salah satu algoritme kunci publik dengan aritmetik modular p yang mempunyai struktur grip siklik Z(p). Tingkat keanaman algoritme ini terletak pada pemecahan masalah logaritme diskret dari Z(p). Akan tetapi, tingkat keamanan tadi tahun ke tahun semakin menurun yang disebabkan kemampuan pemecahan algoritme diskret semakin meningkat. Untuk memenuhi tingkat keamanan yang memadai dibutuhkan p yang cukup besar yang menyebabkan proses enkripsi dan dekripsi menjadi lambat.
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