Karangkates Reservoir is a reservoir formed due to the damming of the flow of the Brantas River and the supply of rainwater, has various benefits as a flood prevention, power plant, water supply for agricultural irrigation needs, for fisheries activities. This reservoir is also utilized by local fishermen for fisheries activities, both capture fisheries and aquaculture activities. This study aims to determine the structure of the fish community which includes diversity, uniformity, dominance and water quality of Karangkates reservoir. This study used a survey method with a sampling technique of "purposive sampling" at four different station locations, which were considered to represent the Karangkates Reservoir. There were 8 species of fish from 3 families, red lohan fish (Amphilophus labiatus) was found the most, diversity index (H') throughout the station ranged from 1.04 - 1.62 with low category, uniformity index (E) 0.75 - 0.83 in high category, and dominance index throughout the station 0.26 - 0.44 in low category. Water quality conditions based on PP No. 22 of 2021 concerning the Implementation of Environmental Protection and Management, in the waters of the Karangkates Reservoir at station II (tourism area) the value of dissolved oxygen does not meet class III water quality standards.

Phytoplankton has been known to play its role as an indicator of water quality. In the intensive cultivation system of Pacific White Shrimp (Litopenaeus vannamei), phytoplankton can respond to water quality dynamics simultaneously. However, the impact of weather differences on community structure and phytoplankton diversity has not been further investigated. Here we analyze water quality and phytoplankton diversity in ponds, including uniformity and dominance. The results showed that 12 genera of phytoplankton were found in sunny weather, whereas 9 genera were found in rainy weather. Phytoplankton diversity in sunny weather is greater. The diversity index (H') value when it rains and shines is in the medium category with a stable community structure and low polluted water conditions. The uniformity value (E') is moderate. No plankton dominance was found (C ≤ 0.5) with the highest important index value during rain being Rhizosolenia sp. and Chlorella sp. when it's sunny. Water quality in general does not differ and meets quality standards except for the nitrate and phosphate values. Nitrate and phosphate values in both weather conditions exceeded standard standards. Differences in the types of phytoplankton present in different weather can be caused by the brightness that enters the water. Apart from that, the volume of water and the dilution and mixing effect of rainwater can cause differences in the amount. The source of growth nutrients is a supporting factor for phytoplankton growth.

The fishing ground of the floating lift net fishing fleet in each season in the TPK Kei Kecil conservation area has different economic value because the number of catches, fleet income, and operational costs of the fleet operating in the fishing ground of Ngaf-Ohoiew Island, Sepuluh Island, and Lima Island in each season is different. This study aims to analyze the economic fishing ground of the floating lift net fishing fleet in each season in the region. The locations of this research are Ohoi Namar, Ohoi Selayar, Ohoi Ohoililir, and Ohoi Dian Island, and it will be carried out in May – Oktober 2023. Data was collected using the survey method; respondents were determined using purposive sampling. The data that has been collected includes fishing ground, catches, fleet revenues, and fleet operational costs, then analyzed descriptively, qualitatively, and quantitatively, then presented in the form of pictures. The study recommends that the economical floating lift net fishing fleet fishing area in the TPK Kei Kecil conservation area in transition season 1 and 2 is a fishing ground located in the waters of Ngaf-Ohoiew Island because it has a high income from operational costs of Rp 136,059,000 in transition season 1 and Rp 126,420,000 in transition season 2, respectively while in the eastern season is the fishing ground in the waters of Pulau Lima because the average income is Rp 157,669,000.

Seaweed is a superior commodity for aquaculture and is a raw material for export. Sustainability of exports requires sustainable seaweed production to ensure the sustainability of raw materials to fulfil market demand from buyers and consumers. In this regard, this research aims to analyze the supply chain, margins and marketing efficiency of Kappaphycus alvarezii seaweed cultivated by the community in Nunukan District, North Kalimantan. This research is classified as a quantitative type of research with a survey method using an interview method through the distribution of questionnaires to seaweed business actors. The results of the research show that information was obtained about the Kappaphycus alvarezii seaweed supply chain through three marketing channels, namely (1) channels from seaweed farmers to collectors and consumers, (2) channels from seaweed farmers to consumers and (3) channels from collectors to consumers . Seaweed production produced by farmers does not have a minimum production quantity standard so that the seaweed produced can be sold at any time to collectors according to a predetermined price agreement. Meanwhile, there are differences in seaweed marketing margins between respondents in the marketing network, and price differences at the collector level cause price differences at the consumer level. The resulting marketing efficiency is at an efficient level (≤ 50%). Seaweed marketing in Nunukan is classified as efficient because the share received by seaweed farmers as producers is below 50%. The efficiency of seaweed marketing depends on the level of marketing margin and the share received by seaweed farmers.

Analysis of the relationship between carrageenan content of seaweed (Kappaphycus alvarezii Doty, 1986) with water quality in the Makassar Strait) Kappaphycus alvarezii seaweed is experiencing high demand and supply as an industrial raw material, so it is important to analyze its carrageenan content. This study aims to analyze the carrageenan content of Kappaphycus alvarezii seaweed cultivated in estuaries, around corals and the open sea. This research is classified as a type of quantitative research with observation methods. The research was conducted from September to October 2022 in the waters of the Makassar Strait. The results showed that the carrageenan content of red seaweed Kappaphycus alvarezii as a whole ranged from 53.05 to 58.37% (55.84 ± 1.57%) with details of 55.52 ± 0.242% for carrageenan content in samples from the estuary, 55.57 ± 2.671% for the area around the reef and 56.43 ± 1.388% for the open sea. The highest carrageenan content of Kappaphycus alvarezii seaweed was obtained in the high seas cultivation areas.