Recent studies have highlighted the valuable role played by mangrove forests in carbon sequestration and storage. Although Indonesia accounts for a large proportion of global mangrove area, knowledge on the carbon stock and sources in the Indonesian mangrove is still limited. In this study, we quantified the ecosystem organic carbon (OC) stock and its spatial variation at an oceanic mangrove in Wori, North Sulawesi, Indonesia. The sources of soil OC were also investigated. The results showed that the mangrove soil had a substantial OC stock containing 15.4 kg/m² (calculated by carbon) in the top 50 cm soil, and represented the majority of the ecosystem OC stock at the Wori mangrove. The mangrove biomass and ecosystem OC stock were 8.3 kg/m² and 23.7 kg/m², respectively. There was no significantly difference in the soil OC stock among the stations with difference distances offshore, while the highest mangrove biomass OC stock was found at the seaward station. Isotope mixing calculations showed that the rich OC in mangrove soils was attributed to the accumulated autochthonous mangrove source while the suspended organic matter in tidal water and the mangrove-adjacent seagrass contributed less than 20% to the soil OC. The results further demonstrated the importances of the oceanic mangrove in carbon storage and the mangrove plants in contributing OC to their soils.

Mangrove ecosystems are sites with high biodiversity of benthic fauna, and fiddler crabs (genus Uca) are common benthic fauna in mangroves. The North Sulawesi in Indonesia has a good condition of mangrove while the information of the fiddler crabs is still limited. Manual samplings were conducted in wet, dry and transient seasons at a mangrove in Kema, North Sulawesi to investigate the species composition, density and distribution pattern of fiddler crabs. A total of 168 individuals, subjected to eight species of genus Uca crabs were collected at the mangrove, with U. triangularis having the highest abundance and U. annulipes having the lowest abundance. The densities of fiddle crabs were 27.56 ind./m², 32.89 ind./m² and 14.22 ind./m² at the seaward, middle and landward zones, respectively, and the density was higher in dry and wet seasons than in transient season.

Three specimens of the serranid fish (Serranidae), Plectranthias kamii Randall, 1980 were collected from fish market, Bitung, North Sulawesi on May and June 2010. Some morphological characters P. kamii is closely related to P. sheni, P. megalophthalmus, P. retrofasciatus, P. rubrifasciatus, P. knappi, P. helenae, P. pelicieri, P. jothyi, P. retrofasciatus and P. randalli in sharing of body width, upper jaw length, pelvic spine length and orbit diameter. Meristic count characters of P. kamii differ from P. sheni, P. pilicieri, P. megalophthalmus, P. retrofasciatus and P. rubrifasciatus in having more numerous dorsal spine (18 vs. 15-17) and below lateral line (33-34 vs. 29-33) and differ from P. megalophthalmus and P. rubrifasciatus in having more numerous pored scales in lateral line (13 vs. 14-15) and shorter of anal spine. The present anthiine fish collected from Bitung, Indonesia was described as new record and bringing the total number of species of this genus known in Indonesia to seven.

A three-dimensional (3-D) finite volume coastal ocean model (FVCOM) was used for the study of water circulation and seawater exchange in the Benoa Bay, Bali Island. The M₂ tidal component was forced in open boundary and discharge from six rivers was included in the numerical calculation. The M₂ tidal elevation produced by the FVCOM has a good agreement with the observation data. The M₂ tidal current is also successfully calculated under the ebb tide and flood tide conditions. The non-linear M₂ tidal residual current was produced by the coastline geometry, especially surrounding the narrow strait between the Serangan Island and the Benoa Peninsula. The tidal residual current also generated two small eddies within the bay and one small eddy in the bay mouth. The salinity distribution influenced by river discharge could be successfully calculated, where the numerical calculation and the observation results have a good correlation (r2) of 0.75. Finally in order to examine the seawater exchange in the Benoa Bay, the Lagrangian particle tracking method and calculation of residence time are applied. The mechanism of particle transport to the flushing of seawater is depicted clearly by both methods.

Based on oceanographic survey data in June 2012 in the Lembeh Strait, the zooplankton ecological characteristics such as species composition, individual abundance, dominant species and distribution were analyzed. The results showed that 183 species (including 4 sp.) had been recognized, most of them belonged to copepoda. Cnidaria followed with 43 species (including 1 sp.) were identified. The average abundance of zooplankton was (150.47±58.91) ind./m³. As to the horizontal distribution, the abundance of the zooplankton was higher in the southern waters than in the northern waters. The dominant species in the study area were Lensia subtiloides, Sagitta enflata, Lucifer intermedius, Oikopleura rufescens, Diphyes chamissoni, Creseis acicula, Subeucalanus subcrassus, Temora discaudata, Aglaura hemistoma, Doliolum denticulatum, Canthocalanus pauper, Oikopleura longicauda and Nanomia bijuga. Zooplankton biodiversity indexes were higher in study area than previous study in the other regions. The findings from this study provide important baseline information for future research and monitoring programs.

Two field observations were conducted around the Lembeh Strait in September 2015 and 2016, respectively. Evidences indicate that seawater around the Lembeh Strait is consisted of North Pacific Tropical Water (NPTW), North Pacific Intermediate Water (NPIW), North Pacific Tropical Intermediate Water (NPTIW) and Antarctic Intermediate Water (AAIW). Around the Lembeh Strait, there exist some north-south differences in terms of water mass properties. NPTIW is only found in the southern Lembeh Strait. Water mass with the salinity of 34.6 is only detected at 200-240 m between NPTW and NPTIW in the southern Lembeh Strait, and results from the process of mixing between the saltier water transported from the South Pacific Ocean and the lighter water from the North Pacific Ocean and Sulawesi Sea. According to the analysis on mixing layer depth, it is indicated that there exists an onshore surface current in the northern Lembeh Strait and the surface current in the Lembeh Strait is southward. These dramatic differences of water masses demonstrate that the less water exchange has been occurred between the north and south of Lembeh Strait. In 2015, the positive wind stress curl covering the northern Lembeh Strait induces the shoaling of thermocline and deepening of NPIW, which show that the north-south difference of air-sea system is possible of inducing north-south differences of seawater properties.

Anthropogenic impacts and natural disturbances have been intense recently in the global scale, affecting the composition of coral reef benthic communities from coral to algal dominated reefs. However, this condition does not always occur considering corals are able to recover when the stressors falter. This study aims to investigate the change in coral reef benthic communities and the relationship among benthic categories. The study was carried out in 2014 and 2016 at five sites, three sites in the Lembeh Strait and two sites in Likupang, North Sulawesi Province. Underwater Photo Transect (UPT) was used at depth of around 4-6 m in slope areas. The result indicated that the benthic communities were slightly changing: the percent covers of hard corals, sponges, soft corals, macroalgae and substrate categories were not significantly different between the years but category of others, particularly seasonally growing hydroid, increased significantly, occupying the available substrates and overtopping other benthos surrounding. The study also found that there was a significant relationship between the change in benthic gradient and the number of hard coral colonies: when the composition becomes less complex, the number of colony declines. In contrast, the hard coral diversity remained unchanged, suggesting the coral reefs apparently have an ecological resilience (sustainable species diversity) against the change although ecological complexity declines. In addition, the hard coral cover was significantly correlated with soft coral and sponge covers, which did not change significantly among the years. In general, the coral reefs in North Sulawesi might experience a temporary blip due to the increasing percent cover of others, and be predicted to recover as there was no indication of soft corals and sponges to increase significantly. However, it is necessary to investigate the dynamic of benthic communities in different depth gradients to gain a comprehensive understanding as the communities respond differently to the light intensity.

Bacterial diseases affecting corals pose an enormous threat to the health of coral reefs. The relationship between certain bacterial species and coral diseases remain largely unknown. Pigment abnormalities are common in Porites lutea. Here we used Illumina 16S rRNA gene sequencing to analyze the bacterial communities associated with healthy P. lutea and P. lutea with pigment abnormalities. We observed an increase of alpha diversity of the bacterial community of P. lutea with pigment abnormalities, relative to healthy corals. We then identified changes in the abundance of individual operational taxonomic units (OTUs) between pigmented and healthy corals. We were able to identify eight OTUs associated with pigment abnormalities, which are possibly the causative agents of pigment abnormalities.

Phytoplankton species composition and abundance in the Lembeh Strait waters was studied in four cruises of April 2013, May 2014, June 2012 and October 2015, during the period of monsoon transition time of SE monsoon. With data obtained the seasonal alternations of phytoplankton community structures and its driving factors were discussed. A total of 416 taxa belonging to 5 classes of phytoplankton were recorded in the four month surveys. Phytoplankton density was averaged 2 348 cell/L and diatoms and dinoflagellates had the most diversified species. Cyanobacterium was characterized by its low species numbers but high abundance in the waters of Lembeh Strait. Total phytoplankton abundance occurred low in April and October in the monsoon transition period and it raised high in May and June during the SE monsoon. Frequently occurred species were pelagic diatoms in addition to cyanobacterium Trichodesmium. Abundance and diversity of phytoplankton significantly differed seasonally. The diatoms Thalassionema and Pseudo-nitzschia, and cyanobacterium Trichodesmium contributed most to the community dissimilarities. Due to potentially higher nutrient supply in the south of Lembeh Strait, diatoms and dinoflagellates showed higher densities in the south than in the north of the strait. Though, cyanobacterium preferred distributing much evenly in all waters, it had higher density in the southern Lembeh Strait. Total phytoplankton abundance is quite low compared with the Jakarta Bay and some bays in China. Analysis showed that nutrients from upwelling forced by SE monsoon are the key factor varying the monthly phytoplankton abundances. Due to its primitive nature state, Lembeh water can be an ideal location for the study of pelagic ecosystem under merely the influence of macro environment changes with lower background noise from human activities.

The community structure of zooplankton has been conducted in the Lembeh Strait in Bitung and Wori Beach in Manado, North Sulawesi in October 2015. Sampling of this research was conducted in 22 sampling sites along the strait. Zooplankton samples were collected from 22 stations, by NORPAC 300 μm net that was vertically hauled from maximum 10 m depth up to the surface water. The samples were poured into the bottle with formalin of 4% as preservative. The results showed that there were 43 taxa of zooplankton. The abundance of zooplankton was between 21.216-4 193.776 ind./m³. The dominant taxa were copepod, especially Calanoida. The composition of zooplankton was relatively similar in all stations. We showed the abundance, dominance, composition and distribution of zooplankton at this research. More extensive studies concerning zooplankton is required to understand zooplankton biodiversity as a whole especially on the geographical and spatial distribution to describe population and community dynamic in the Lembeh Strait and Wori Beach.