Aida Sartimbul

VARIASI KOMUNITAS PLANKTON DAN PARAMETER OSEANOGRAFI DI DAERAH PENANGKAPAN IKAN PELAGIS DI PERAIRAN MALANG SELATAN, JAWA TIMUR

Abstract Perairan Malang Selatan merupakan daerah yang potensial sebagai daerah penangkapan ikan. Keberadaan berbagai jenis ikan pelagis kecil terutama ikan planktivor secara langsung dipengaruhi oleh pertumbuhan fitoplankton dan zooplankton. Fitoplankton mempunyai peran penting sebagai dasar rantai makanan dalam ekosistem perairan, sedangkan zooplankton merupakan herbivor pemangsanya. Pertumbuhan fitoplankton dan zooplankton dipengaruhi oleh faktor oseanografinya. Penelitian ini bertujuan untuk mengetahui variasi komunitas plankton dan hubungannya dengan parameter oseanografinya, serta distribusi spasial plankton di daerah penangkapan ikan di Perairan Malang Selatan, Jawa Timur. Metode purposive sampling dengan teknik zigzag pada 10 titik sampling digunakan dalam pengambilan data pada penelitian ini. Sedwicgk rafter counting cell digunakan dalam metode penghitungan plankton. Sampel plankton diambil secara horizontal dan vertikal pada kedalaman 1 dan 15 m dengan jaring plankton bermata jaring 20 µm, sedangkan parameter oseanografi secara in situ diukur menggunakan aqua quality sensor tipe AAQ 1183 C. Hasil penelitian menunjukkan bahwa kelimpahan fitoplankton sebesar 49.764 sel/m3, didominasi oleh genus Chaetoceros. (Bacillariophyceae), dan kelimpahan zooplankton sebesar 894 ind/m3, didominasi oleh genus Nauplius. (Copepoda). Indeks keanekaragaman dan keseragaman fitoplankton dan zooplankton dapat dikategorikan sedang, berturut-turut sebesar 1,77–1,85 dan 1,70–1,77; 0,58–0,59 dan 0,77–0,79, sedangkan indeks dominansinya masuk dalam kategori rendah yaitu berturut-turut 0,27–0,28 dan 0,24–0,27. Analisis Principal Component Analysis (PCA) menunjukkan bahwa parameter oseanografi utama yang paling berpengaruh pada variasi komunitas plankton adalah turbiditas, klorofil-a, oksigen terlarut dan fosfat. Hasil uji T menunjukkan bahwa distribusi spasial kelimpahan fitoplankton dan zooplankton pada kedalaman 1 m dan 15 m berbeda nyata. Studi ini memberikan informasi penting tentang kelimpahan plankton dan faktor oseanografi yang berpengaruh di daerah penangkapan di Perairan Malang Selatan. Kata Kunci: komunitas plankton, parameter oseanografi, fishing ground, Perairan Malang Selatan Abstract The South Malang water is a potential area as a fishing ground. The existence of various species of small pelagic fishes such as planktivores fishes are directly influenced by the growth of phytoplankton and zooplankton. Phytoplankton has an important role as the basis of the food chain in aquatic ecosystems, whereas zooplankton is its predator. The growth of phytoplankton and zooplankton is influenced by oceanography factors. This study aims to determine the variation of the plankton community and its relationship with oceanographic parameters, as well as the spatial distribution of plankton in the fishing ground at South Malang water. The purposive sampling method with zigzag technique at 10 sampling sites was used in data collection in this research. Sedwicgk rafter counting cells were used in plankton counting methods. The plankton samples were taken horizontally and vertically at depths of 1 and 15 m with a 20 μm planktonnet, while in situ oceanographic parameters were measured using aqua quality sensor AAQ type 1183 C. The results showed that phytoplankton abundance was 49.764 cells / m3, dominated by the genus Chaetoceros (Bacillariophyceae), and zooplankton abundance of 894 ind / m3, dominated by the genus Nauplius (Copepoda). The diversity index and uniformity index of phytoplankton and zooplankton could be categorized as the middle as 1.77-1.85 and 1.70-1.77; 0.58-0.59 and 0.77-0.79, respectively, while the dominance index was included in the low category that was 0.27-0.28 and 0.24-0,27, respectively. Principal Component Analysis (PCA) analysis showed that the most important major oceanographic parameters for plankton community variation were turbidity, chlorophyll-a, dissolved oxygen and phosphate. T test results show that the spatial distribution of phytoplankton abundance and zooplankton at depth of 1 m and 15 m are significantly different. This study provides important information on the plankton abundance and oceanography factors affected at fishing ground of South Malang water. Keywords: Plankton community, oceanography parameters, fishing ground, South Malang Water

CHANGE IN SPECIES COMPOSITION AND ITS IMPLICATION ON CLIMATE VARIATION IN BALI STRAIT: CASE STUDY IN 2006 AND 2010

Sardinella lemuru is a dominant small pelagic fish (80-90%) caught by purse seiner in Bali Strait, while the remaining 10-20% consist Decapterus spp., Euthynus affinis, and others. This composition typically varies seasonally, whereas Southeast monsoon season was dominated by S. lemuru, while Northwest monsoon season replaced by Decapterus spp. and Euthynus affinis. Fishing trend in the last 14 years indicated regime shift with the shifting in species composition by a seasonal into the inter-annual due to global climate change, such as El Niño and La Niña. 2006 was indicated a cold period of water temperature, which is triggered by the El Nino and positive Indian Ocean Dipole (pIOD). In this cold period, the S. lemuru reached peak of fishing, otherwise this fish disappear when warm period (strong La Niña) in 2010. When S. lemuru disappeared during warm period, it was substituted by Decapterus spp. Furthermore, as predatory fish of both small pelagic fishes, Euthynnus affinis always appear throughout the year. Understanding the species composition trend from seasonal to longer period is important for better strategy to manage fisheries of Bali Bali Strait in climate change era.

Remote sensing application for Sardinella lemuru assessment: a case study of the south waters of Malang Regency, East Java, Indonesia

The assessment of lemuru fish (Sardinella lemuru) using remote sensing and Geographical Information System (GIS) has provided preliminary information on the habitat of lemuru fish at the South waters of Malang Regency, Indonesia. Lemuru fish catch data, mangrove mapping, Sea Surface Temperature (SST) and chlorophyll-a concentration derived from MODIS/Aqua images have been used in this study. The average of SST during the study was 26.1 °C, the highest average was on December and August was the lowest. The average of chlorophyll-a concentration was 0.55 mg/m3, July was the highest and the lowest concentration of chlorophyll-a was on March. Most of the lemuru fish migrated to the west part of Malang waters during northwest monsoon (December-February), and moved toward eastern part during transitional (March-April-May). In contrast, on the southeast monsoon (June-August), lemuru spread across Malang waters. Habitat suitability of lemuru around coastal waters of Malang Regency related to their migration has different criteria for each month depend on the oceanographic factors and primary productivity. Based on the levels of habitat suitability, lemuru predicted to spawn on June. Sumbermanjing area was the most suitable area (72.39%). Lemuru moved away from Malang waters during transitional until the beginning of northwest monsoon. Primary productivity in coastal waters around Sumbermanjing increased in the southeast monsoon. It represented by January (0.7 mg/m3) in the northwest monsoon and increased reaches 3 mg/m3 in the southeast monsoon on July. It was followed by the increasing of lemuru catch.