Wijaya A, Zakiyah U, Sambah AB, Setyohadi D. 2020. Spatio-temporal variability of temperature and chlorophyll-a concentration of sea surface in Bali Strait, Indonesia. Biodiversitas 21: 5283-5290. The Bali Strait is influenced by seasonal and inter-annual systems. El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are climate variabilities that affect water conditions. The knowledge about influence of ENSO and IOD variations on the fertility of waters in the Bali Strait is still lacking. The purpose of this study was to determine the effect of seasonal and inter-annual variability on the variability of Sea Surface Temperature (SST) and Sea Surface Chlorophyll-a (SSC) in the Bali Strait. This study applied SST and SSC data collected from the Aqua/Terra MODIS satellite, as well as the ENSO and IOD indices during March 2000-December 2019. The results described that the effect of ENSO on SST and SSC was low and IOD on SST and SSC was quite high. The effect was quite high between IOD and SST anomaly of-0.401. Seasonal variations indicate the abundance of high SSC and low SST in the southeast monsoon (JJA) which characterizes upwelling. Meanwhile, in the northwest monsoon (DJF), SSC was low and SST was high which characterizes downwelling. This condition cannot separate from the monsoonal process that occurred in the Bali Strait. The inter-annual variation showed that in the strong El Nino period and IOD (+) triggers a negative SST anomaly and a positive SSC results in strong upwelling, while in the strong La Nina period and strong IOD (-) triggers a positive SST anomaly and a negative SSC results in downwelling. The inter-annual variability of SSC influenced by IOD rather than ENSO. This condition indicates that the ENSO/IOD event changes the period of SSC concentration.

Understanding the impact of Indian Ocean Dipole (IOD) on fishery around Indonesia is important as the fishery resources are small compared to the demand. In this study, we analyzed the effect of positive and negative phases of IOD on chlorophyll-a concentration and the catch of Sardinella lemuru in the Bali Strait. Data are based on field surveys in the Bali Strait during the positive and negative phase of IOD and Sea Surface Temperature (SST) and Sea Surface Chlorophyll (SSC) obtained from the analysis of satellite images. The results suggest that SSC concentration in the strait significantly correlates with the positive and negative phase of IOD, possibly through a change of upwelling and downwelling there. It is suggested that the change of phytoplankton biomass due to positive IOD would result in an increase of Sardinella lemuru in the Bali Strait. This research has direct implications as important information for the government in planning lemuru fisheries management in the Bali Strait based on oceanographic studies and climate phenomena.

The existence of pelagic fish resources is greatly influenced by the condition of the waters which are described through its relationship with the oceanographic parameters. As a dominant species in Bali Strait, lemuru fish (Sardinella lemuru) have catch dynamics that vary each year. Oceanographic factor influence the number of fish catch in Bali Strait, in which global phenomena such as ENSO and IOD also have a role in influencing the migration of marine resources. This research aims to analysis annual variation of Sea Surface Temperature (SST) and Sea Surface Chlorophyll-a (SSC) in Bali Strait, and its effect on fish catch. The method applied a quantitative descriptive with correlation analysis and spatial analysis using Geographical Information System approach. The analysis described a significant impact of oceanographic parameters on pelagic fish catch. SSC has a significant impact on the number of fish catch which describes a positive correlation, and it illustrated a time interval between the highest concentration of SSC and the period of fishing peak season. It also impacts the fishing trip and the distribution of fishing ground that spread along the area of the Indian Ocean to Bali Strait. SSC has a significant impact on the number of fish catch which describes a positive correlation, and it illustrated a time interval between the highest concentration of SSC and the period of fishing peak season. It also impacts the fishing trip and the distribution of fishing ground that spread along the area of the Indian Ocean to Bali Strait

ENSO and IOD are oceanographic phenomena that occur in the tropical Pacific Ocean and Indian Ocean, due to the interaction between the sea and the atmosphere. The study aims to determine the impact of ENSO and IOD on the abundance of Sea Surface Chlorophyll (SSC) and Sea Surface Temperature (SST) in the Bali Strait. The data used are Ocean Nino Index (ONI), Dipole Mode Index (DMI), Sea Surface Chlorophyll (SSC) and Sea Surface Temperature (SST). The method applied the SSC and SST anomaly analysis during the ENSO and IOD periods from March 2000 to July 2020. The results showed that during the ENSO and IOD periods in the eastern monsoon, there was an increase in SSC concentrations and a decrease in SST in the Bali Strait. In the ENSO period, there were La Nina and El Nino phases, while IOD had positive and negative phases. During the observation, it was known that the mean range of SSC was 0.49 - 1.91 mg m-3 and 25.32 - 29.30 °C for SST. SSC anomaly during the observation period was between -0.04 - 0.62 and SST was -0.66 - 1.47. Therefore, it was known that the period that causes an increase in high SSC and a decrease in SST in the waters of the Bali Strait was during the El Niño period along with positive IOD phases in 2006, 2015, 2018, and 2019.

This article describes a new approach to the study of the environmental conditions that relate to the Sardinella lemuru habitat in the Bali Strait, through remote sensing data and fish catch data using the generalized additive model. Data that are acquired daily and then compiled into monthly data for sea surface temperature, sea surface chlorophyll-a concentration, photosynthetically available radiation, and sea surface depth (SSD) were used for the years 2008–2010. The objectives of the study are to describe the variability of the environmental conditions in the Bali Strait, to analyze a combination model of environmental factors in estimating the Sardinella lemuru habitat, and to map potential Sardinella lemuru fishing areas. We illustrate the proposed method by constructing seven generalized additive models with catches of Sardinella lemuru as a variable response and use sea surface temperature, sea surface chlorophyll-a concentration, photosynthetically available radiation, and SSD as covariant models for assessing the environmental characteristics of the abundance of Sardinella lemuru. Predicted values were validated using a linear model. Based on the three model parameters, habitat selection for Sardinella lemuru was significantly (P < 0.0001) influenced by photosynthetically available radiation (50–55 Einstein m-2 d-1), sea surface chlorophyll-a concentration (0.2–2.0 mgm-3), sea surface temperature (28.95–29.64 °C), and SSD (60–150 m). Catch predictions show a consistent trend toward environmental conditions and water depth. Our method allows for improvement with the validation of catch predictions that were observed and collected monthly, and the result was significant (P < 0.001, r2 = 0.816). Photosynthetically available radiation explains the highest deviation in continued generalized additive models; therefore, it was considered to be the best predictor of habitat, followed by sea surface chlorophyll-a concentration, sea surface temperature, and then SSD. New research results supplement several previous studies that relate to the analysis of environmental parameters in estimating the fish habitat and can be used in mapping the distribution of potential Sardinella lemuru fishing areas in spatial and temporal scales.