The emission of greenhouse gases, including high CO2 and other materials, initiates global warming and climate change. Atmospheric CO2 that affects the carbonate system of seawater causes ocean acidification (OA). OA affects marine organisms directly, as well as humans economically and ecologically. Considering the high impact of OA and following the United Nations' Sustainable Development Goals, systematic research and monitoring of OA is necessary in Indonesia, whose seas play an important role in this emerging phenomenon. This review discusses the urgency of OA monitoring systems and suggests carbonate system monitoring, as well as carbon biogeochemistry. OA significantly affects marine production and alters ecosystem services, and it is likely to have an impact on habitats shifting from calcified to non-calcified and reducing benthic complexity. Its effect on calcifying organisms can also be found, i.e., coral calcification and/or dissolution of CaCO3 of calcifying organisms. Acidity (pH), as well as the carbonate system variables of seawater, fluctuate, especially with variations in space and time. Coastal ecosystems that are directly affected by terrestrial input will have carbonate system variables that fluctuate more. The annual rate of decreasing seawater pH, especially over an open and large spatial scale, may indicate OA. Therefore, a monitoring system must be implemented to obtain systematic and comprehensive information on OA. Here, we also introduce a biogeochemical monitoring initiative for OA in Lombok with the established protocols. Improvement of many aspects, including analysis instruments, analysis methods, sample treatment, and sampling frequency will provide new insight into further research and monitoring of OA.

<strong>Physical and Chemical Properties of Waters in Java – Ambang Dewakang Sea</strong>.The Java Sea is a region of important pelagic fish production in Indonesia. The distribution of abundance of fish is affected by changes in water physical and chemical properties. The important chemical property that can affect the abundance of the fish is the availability of nutrients. Nutrients are the basic compounds of marine biogeochemical cycles that play important role in increasing aquatic productivity through growth of the phytoplankton. The purposes of this study are to know recent condition of chemical and physical characteristics of the sea water within the region Java Sea ‒ Ambang Dewakang and to investigate relationships among these parameters. This research was conducted in November 2014 at 7 stations in the region. The observed parameters were physical (temperature, salinity, turbidity, density) and chemical such as nutrients (DIN, PO₄-P, SiO₃-Si), pH, and DO. CTD (<em>Conductivity-Temperature-Depth</em>) SBE (<em>Sea Bird Electronics</em>) 911 Plus was used to measure water physical properties. Water sample was collected using Rosette sampler, while analysis of nutrients concentration employed methods from Strickland and Parsons 1972. The result showed that temperatures in the Java Sea ranged from 13.06 – 30.33 °C with an average of 25.29 °C, whereas salinity ranged between 33.07 – 34.74 psu with an average of 34.41 psu. Variations within temperature and salinity showed a homogeneous condition due to the influence of mixing processes. Concentration range of DIN (NO₃-N+NO₂-N+NH₄-N), PO₄-P, SiO₃-Si were from 0.070 to 0.180 mg/L, from 0.004 to 0.022 mg/L and from 0.082 to 0.361 mg/L, with an average of 0.096 mg/L, 0.010 mg/L, and 0.159 mg/L respectively. The ratio DIN/DIP of 13.24 showed that the waters quality of Java Sea was in the moderate category.

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Pulau Bintan di Provinsi Kepulauan Riau merupakan wilayah perairan yang diandalkan sebagai penghasil bahan tambang bauksit, penghasil komoditas perikanan dan sebagai daerah wisata yang banyak dikunjungi oleh wisata baik lokal ataupun mancanegara. Wilayah pesisir dan sumber daya yang dimiliki Pulau Bintan merupakan kontributor penting untuk pembangunan ekonomi dan kualitas hidup sehingga perlu dikelola dengan baik. Penelitian ini bertujuan untuk mengetahui kondisi perairan Bintan ditinjau dari kandungan nitrat, fosfat, dan silikat pada dua musim yang berbeda yang nantinya dapat digunakan oleh pemerintahan setempat dan instansi terkait dalam mengembangkan dan mengelola perairan kawasan perairan Pulau Bintan. Pengambilan sampel untuk penelitian nutrien (nitrat, fosfat, dan silikat) di perairan timur Kepulauan Bintan telah dilakukan di 27 titik lokasi pada April dan Agustus 2014. Konsentrasi nutrien berfluktuasi pada April dan Agustus. Nilai rata-rata kosentrasi nitrat, fosfat, dan silikat pada April berturut-turut yaitu 0,0510 ± 0,0014 mg/L, 0,0050 ± 0,0026 mg/L dan 0,2660 ± 0,1655 mg/L. Konsentrasi rata-rata nitrat, fosfat, dan silikat pada Agustus berturut-turut yaitu 0,0260 ± 0,0104 mg/L, 0,0160 ± 0,0091 mg/L dan 0,057 ± 0,035 mg/L. Konsentrasi nitrat, fosfat, dan silikat di perairan Bintan termasuk dalam kategori rendah.

<strong>Effects of Nutrients Concentration on Phytoplankton Abundance in The Halmahera-Molucca Sea.</strong> The availability of nutrients in the ocean is essential for the growth and accumulation of phytoplankton biomass. The input nutrients can then changes its ratio which may affect the species composition of phytoplankton communities and higher trophic level biotas. The effects of nutrients on phytoplankton abundance are very important to be studied due to its role as limiting factors for phytoplankton growth. Besides that, these two variables are most important factors in measuring aquatic productivity. This study aims to analyzed composition and abundance of phytoplankton and its relationship with dissolved inorganic nutrients in the Halmahera-Molucca Sea. This research was conducted in November 2015 covering 8 sampling station within the Halmahera-Molucca Sea. Water quality parameters, such as pH was measured using potentiometic method, dissolved oxygen (DO was measured using titrimetric method), and nitrate, nitrite, ammonium, phosphate and silicate, were measured using the colorimetric method. The water samples were taken using Rosette sampler and then filtered using hand net plankton with size 20 μm to obtain the phytoplankton. Plankton composition and abundance were then determined by microscopic analysis. The result showed that ammonium positively correlated with phytoplankton abundance (r=0.9133 at p&lt;0.01). The correlation between nutrients and phytoplankton show that each genus has a preference for different nutrients. The presence of ammonium significantly increase the phytoplankton abundance from genus <em>Chaetoceros, Nitzchia, Climacodium, Ceratium, Eucampia, Lauderia, Protoperidinium</em>, and <em>Rhizosolenia</em>. On the other hand, phosphates increase the phytoplankton abundance from genus Coscinodiscus although not significantly. Besides, silicates increase the phytoplankton abundance from genus <em>Thalassiothrix, Bacteriastrum, Skletonema</em>, and <em>Hemiaulus</em> while nitrates increase the phytoplankton abundance from genus <em>Alexandrium</em>.