Arsad S, Putra KT, Latifah N, Kadim MK, Musa M. 2021. Epiphytic microalgae community as aquatic bioindicator in Brantas River, East Java, Indonesia. Biodiversitas 22: 2961-2971. One way to monitor water quality is by using biological indicators, namely epiphytic microalgae (periphyton). This study aims to analyze the epiphytic periphyton community structure and analyze the river health status using a saprobic index. The research location was in the Brantas River, Blitar District, East Java, Indonesia. The method used was a survey with sampling at three sites based on the purposive sampling technique. Periphyton samples were taken using the quadrant transect (5x5 cm²) method and then identified using the Lackey Drop Micro transect Counting Method. The results show that the periphyton community structure is in balance, and there are six divisions of 59 different genera. The six divisions found are Bacillariophyta, Cyanophyta, Chlorophyta, Charophyta, Ochrophyta, and Rhodophyta. The most identified genus is from the Bacillariophyta Division with 28 genera, while the least identified genus is the Rhodophyta division with 1 genus. The abundance ??ranges from 242,800-1,229,174 cells. cm-2, the relative abundance index ??of periphyton ranges from 3-60% (site 1), 9-57% (site 2), 1-62% (site 3), the diversity index ranges from 1.212-2.617 (moderate), the uniformity index ranges from 0.307-2.151 (high), the dominance index ranges from 0.105-0.549 (moderate), and the saprobic index ranges from-0.18 to 0.55. Moreover, supporting water quality parameters are still optimal, except for ammonia and total organic matter parameters that exceed the quality standard. Based on the saprobic value obtained, the water quality of the Brantas River in Tawangrejo Village can be classified into the category of ?/?-mesosaprobic to ?-mesosaprobic saprobic levels with mild to moderate levels of pollution.

Research focusing on seagrass ecosystems as carbon storage has been conducted in various Indonesian waters. However, an essential aspect that remains unexplored is the simultaneous analysis of blue carbon storage in seagrass alongside carbon dioxide (CO₂) flux values, particularly within Karimunjawa waters. This study aims to assess the organic carbon stock and sea–air CO₂ flux in seagrass ecosystems in Karimunjawa. Our hypothesis posits that although seagrass ecosystems release CO₂ into the water, their role as blue carbon ecosystems enables them to absorb and accumulate organic carbon within seagrass biomass and sediments. This investigation took place in Karimunjawa waters, encompassing both vegetated (seagrass meadows) and unvegetated (non-seagrass meadows) areas during August 2019, 2020, and 2022. Over this period, the organic carbon stock in seagrass and sediment displayed an increase, rising from 28.90 to 35.70 gC_org m⁻² in 2019 and from 37.80 to 45.25 gC_org m⁻² in 2022. Notably, the expanse of seagrass meadows in Karimunjawa dwindled by 328.33 ha from 2019 to 2022, resulting in a total carbon stock reduction of the seagrass meadows of 452.39 tC to 218.78 tC. Sediment emerges as a pivotal element in the storage of blue carbon in seagrass, with sedimentary organic carbon outweighing seagrass biomass in storage capacity. The conditions in Karimunjawa, including a high A:B ratio, low dry bulk density, and elevated water content, foster a favorable environment for sediment carbon absorption and storage, facilitated by the waters’ CO₂ emission during the southeast monsoon season. Notably, our findings reveal that CO₂ release within vegetated areas is lower compared to unvegetated areas. This outcome underscores how seagrass ecosystems can mitigate CO₂ release through their adeptness at storing organic carbon within biomass and sediment. However, the presence of inorganic carbon in the form of calcium carbonate introduces a nuanced dynamic. This external source, stemming from allochthonous origins like mangroves, brown algae like Padina pavonica, and calcareous epiphytes, leads to an increase in sedimentary organic carbon stock of 53.2 ± 6.82 gC_org m⁻². Moreover, it triggers the release of CO₂ into the atmosphere, quantified at 83.4 ± 18.26 mmol CO₂ m⁻² d⁻¹.

Sea urchins are one of the key species for coral reef communities because have the capability for controlling populations of microalgae. The existence of sea urchins in an waters ecosystem influenced by abiotic and biotic environmental factors such as intraspecific or intraspecific interactions. This study aims to determine the relationship between the abundance of Sea Urchins, Macroalga on massive coral, and coral cover on Cemara Kecil Island by PCA analysis. The study was conducted in May 2017 in Cemara Kecil Island. Method of research with Haphazard sampling technique. The results indicate that numbers of sea urchins found ranges from 78-130 ind/m², an abundance of macroalgae found are Sargassum sp 1.36%, Caulerpa sp.7.43% and Padina sp 91.21%. The results of substrate cover are living coral 47,21%, dead coral 23.33%, other fauna 2.85% and abiotic element 26,61%. Based on the results of PCA analysis that Sea Urchin abundance has a positive correlation with the closure of Coral Reef and Caulerpa sp. While the Padina sp and Sargassum sp have a positive correlation as well as abiotic factors, dead coral, and other fauna.