Judul: Plankton community structure as an indicator of fertility in mangrove ecosystem waters and surrounding Pejarakan, Bali, Indonesia
Abstrak: Desa pejarakan merupakan desa yang memiliki wilayah pertambakan yang berdekatan dengan ekosistem mangrove. Limbah yang dihasilkan pertambakan dapat menyebabkan resiko bagi perairan sekitar. Penelitian ini bertujuan menganalisis struktur komunitas plankton di wilayah perairan ekosistem mangrove dan sekitar di Pejarakan, Bali. Penelitian dilakukan pada Bulan September 2022, Januari 2023, September 2023, Januari 2024 pada 6 stasiun pengambilan data. Analisis data meliputi kelimpahan, indeks keanekaragaman, keseragaman, dominansi, regresi linear sederhana dan berganda, indeks similaritas, dan principal component analysis. Hasil penelitian menunjukkan bahwa fitoplankton didominasi oleh Bacillariophyceae dan Dinophyceae, sedangkan zooplankton didominasi oleh Malacostraca dan Ciliata. Kelimpahan fitoplankton berkisar antara 96.388–316.852 sel/L, sedangkan zooplankton berkisar antara 15.539–35.284 ind/L. Plankton memiliki indeks keanekaragaman sedang, indeks keseragaman sedang ke tinggi, dan tidak terjadi dominansi. Struktur komunitas plankton menunjukkan bahwa perairan ini memiliki kategori tingkat keseburan yang tinggi.
Keyword: pejarakan, plankton, structure community

Judul: Macrozoobenthic Community Structure in the Mangrove Aquatic Ecosystem of Pejarakan Village, Bali
Abstrak: Struktur komunitas makrozoobentos yang menurun biasanya menjadi indikator adanya gangguan ekosistem di perairan tersebut, hal ini disebabkan makrozoobentos mobilitas rendah serta siklus hidup relatif panjang, sehingga mampu merespon dengan segera gangguan di lingkungan secara kontinyu. Penelitian ini bertujuan menganalisis struktur komunitas makrozoobentos, yang mencakup komposisi jenis, kepadatan, indeks keanekaragaman, indeks keseragaman, dan indeks dominansi pada lingkungan perairan mangrove dan sekitarnya di Desa Pejarakan, Bali. Penelitian ini dilakukan pada bulan September 2022, Januari 2023, September 2023 dan Januari 2024 dengan enam titik stasiun pengamatan, yang mewakili inlet tambak, outlet tambak dan area mangrove. Sampel bentos diambil menggunakan Van Veen Grab serta dilakukan pengukuran kualitas air secara insitu. Data dianalisis menggunakan struktur komunitas, PCA, indeks similaritas Bray-Curtis, serta AMBI dan M-AMBI. Makrozoobentos di lokasi penelitian tersusun atas lima filum. Kepadatan tertinggi pada Januari 2024 yaitu 289 ind/m2. Indeks keanekaragaman (H’) rendah-sedang (1,99 3,17), keseragaman (E) tinggi (0,69-0,96), dominanasi (C) rendah-sedang (0,13-0,38). Analisis PCA menunjukkan persebaran makrozoobentos dipengaruhi oleh parameter kekeruhan dan TSS. Analisis AMBI menunjukkan dominan makrozoobentos bersifat umum dengan nilai AMBI berkisar 0,62-1,29., Decreased macrozoobenthic community structure is usually an indicator of ecosystem disturbance in these waters, this is due to macrozoobenthic low mobility and a relatively longlife cycle, so that it is able to respond immediately to continuous disturbances in the environment. This research aims to analyze macrozoobenthic community structure, which includes genera composition, density, diversity index, evenness index, and dominance index in the mangrove ecosystem waters and its surroundings in Pejarakan Village, Bali. This research was conducted in September 2022, January 2023, September 2023 and January 2024 with six observation stations representing shrimp pond inlet, outlet, and mangrove area. Benthos samples were taken using a VanVeen Grab and water quality measurements were carried out in-situ. Data were analyzed using community structure, PCA, Bray-Curtis similarity index, and AMBI and M-AMBI. The macrozoobenthos at the research location is composed of five phyla. The highest density will be in January 2024, (289 ind/m2). Diversity index (H') is low-medium (1.99-3.17), uniformity (E) is high (0,69-0,96), dominance (C) is low medium (0,13-0,38). PCA analysis shows that the distribution of macrozoobenthos is influenced by turbidity and TSS parameters. AMBI analysis shows that the dominant macrozoobenthos is general with AMBI values ranging from 0,62-1,29.
Keyword: struktur komunitas, makrozoobentos, Desa Pejarakan, community structure, macrozoobenthos, Pejarakan Village

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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