ABSTRAKMangrove merupakan salah satu ekosistem penting di kawasan pesisir. Pemanfaatan yang berlebihan dapat menurunkan kuantitas dan kualitas ekosistem mangrove. Tujuan penelitian ini adalah mengetahui kondisi ekosistem mangrove berdasarkan struktur komunitas. Pengambilan contoh mangrove, dilakukan dengan menggunakan metode transect quadrant dan "spot check" (Bengen, 2004). Berdasarkan hasil penelitian ditemukan 12 spesis mangrove yang berasal dari 5 famili. Struktur vegetasi hutan mangrove menunjukan nilai tertinggi untuk kategori kerapatan terdapat pada stasiun I yakni dengan nilai 9,50 ind/ m 2 dan diikuti oleh stasiun II dengan nilai 6,78 ind/ m 2 serta nilai terendah terdapat pada stasiun III yaitu 6,56 ind/m 2 . Struktur komunitas hutan mangrove di Teluk Dodinga berdasarkan indeks ekologi (nilai kerapatan, frekuensi jenis, tutupan dan nilai penting) cukup baik, sedangkan keanekaragaman spesies mangrove termasuk dalam kategori sedang. Secara umum kondisi lingkungan masih sesuai dengan kriteria habibat mangrove. Kata kunci: Struktur komunitas, ekosistem, mangrove, Teluk Dodinga. ABSTRACTMangroves is important ecosysytem in coastal area. The high exploration could reduce the quality and quantity of mangrove ecosystem. The objective of this study was to known the structure community of mangrove in Dodinga Bay, North Halmahera. Transect quadrant and spot check method were used in this study. The results found 12 specieses from 5 families of mangroves. The higest density of mangrove was founded in station ( 9,50 ind/ m 2 ). The density of mangrove in station II was 6,78 ind/ m 2 , and the lowest density of mangrove was in station III (6,56 ind/m 2 ). The stucture comunity of mangrove based on ecology factors (density, frequency, persent cover and value significant) were chategoryzed into moderate condition, whereas mangrove biodiversity was chategoryzed into medium. The ecology conditions in area study were support for mangrove.

Seagrass ecosystems are located between mangrove ecosystems and coral reefs. Seagrass ecosystems are habitats and foraging area for many marine organisms. Eco-biological cycles in seagrass ecosystems are important for maintaining populations of many organisms. Seagrass at Hiri Island is distributed horizontally along the coast. This island is also a location where Dugong dugon is found North Maluku. Dugong dugon is a vurneable species that has been included in the IUCN and Appendix I Cites. This study aimed to identify species, density of seagrass and existence of Dugong dugong. The survey method used quadratic transect method to collect seagrass data. The Results found 6 species of seagrass at Hiri Island. Five species of those seagrass (Cymodocea serrulata, Cymodecea rotundata, Halodule uninervis, Halodule pinifolia, Halophila spinulosa) are known as food of Dugong dugon. The highest species density was shown by Halodule uninervis. The presence of Dugong dugon and its feeding trail was found during field survey. Information on seagrass species and Dugong dugon sightings location can be used for endangered species conservation policies. Management and conservation efforts need to be done to maintain seagrass ecosystem and Dugong dugon potential habitat at Hiri Island.

Catfish (Clarias sp.) is one of the fresh water fish commodities widely cultivated and very popular in community for being simple in breeding and fast in growth. The demand of people for catfish has led to the increase of production in meeting the demand. This study aimed to analyze the values of SR, RPS, MT and MTD of catfish using the challenge test with bacterium A. hydrophila and given the fatty acid compounds of A. planci. The results of this study showed that the highest average value of SR was found in the treatment with 0.7 mg/kg BBI (26-76%), the highest average of RPS was found in the treatment with 0,7 mg/kg BBI (65%), the lowest average values of MR was found in the treatment with 0,7 mg/kg BBI (23,33%), and the average values of MTD were in the range of 94,24 to 142,67%. Meanwhile, the water quality parameter in the range of the optimum value of DO on day 1 was in the range of 5 to 6,8, on day 7 it was in the range of 5,2 to 6,8, and on day 15, it was in the range of 5,5 to 6. The level of oxygen was at 4 ppm and the water temperature was in the range of 26 to 28°C. The results of the identification towards the fatty acid compounds with GS-MS showed two fatty acid compounds; those are Hexadecanoic acid and 13-Octadecenoic acid. From this study, it can be concluded that there was an effect of giving the injection doses of A. planci compound on the analyses of SR, RPS, MR and MTD in the challenge test with the bacterium Aeromonas hydrophila in comparison to the fish not given with fatty acid compounds of A. planci.

Study on the percentage of coral cover four small islands of Oba Sub-district, Halmahera Island of North Maluku Utara Province was carried out in April 2021.The four small islands of Oba Sub-district studied are Woda Island, Raja Island, Tamin Island, and Guratu Island. The study applied systematic sampling method that included collecting coral reef data using UPT (Underwater Photo Transect) method and coral fish data collection using visual census method. Study results showed that live coral coverage of reefs on the four small islands of Oba Sub-district had the highest value of 5.415% and the lowest value of 4.29%. There was positive relationship between coral growth form diversity and fish diversity. High diversity of coral growth forms was significantly related to high diversity of target reef fish.