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Upwelling Impact on Sardinella Lemuru During the Indian Ocean Dipole in the Bali Strait, Indonesia

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Upwelling Impact on Sardinella Lemuru During the Indian Ocean Dipole in the Bali Strait, Indonesia fishes Article Upwelling Impact on Sardinella lemuru during the Indian Ocean Dipole in the Bali Strait, Indonesia Daduk Setyohadi 1,*, Umi Zakiyah 1, Abu Bakar Sambah 1 and Adi Wijaya 2,3 1 Faculty of Fisheries and Marine Science, Brawijaya University, Jalan Veteran No.1 Malang, Jawa Timur 65145, Indonesia; [email protected] (U.Z.); [email protected] (A.B.S.) 2 Institute for Marine Research and Observation, Ministry of Marine Affairs and Fisheries, Jalan Baru Perancak Negara Jembrana Bali, Jakarta Pusat 10110, Indonesia; [email protected] 3 Graduate School of Doctoral Programs, Fisheries Science and Marine, Faculty of Fisheries and Marine Science, Brawijaya University, Jalan Veteran No.1 Malang, Jawa Timur 65145, Indonesia * Correspondence: [email protected]; Tel.: +62-857-5574-4008 Abstract: 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. Keywords: Bali Strait; Indian Ocean Dipole; sea surfaces temperature; sea surface chlorophyll; Citation: Setyohadi, D.; Zakiyah, U.; Sardinella lemuru Sambah, A.B.; Wijaya, A. Upwelling Impact on Sardinella lemuru during the Indian Ocean Dipole in the Bali Strait, Indonesia. Fishes 2021, 6, 8. 1. Introduction https://doi.org/10.3390/ The Indian Ocean is the center of the occurrence of the Indian Ocean Dipole (IOD) fishes6010008 phenomenon [1–3]. During the positive IOD period, the incidence of upwelling along the South Coast of Java increased due to the strengthening of the southeasterly winds along Received: 31 December 2020 the coast, as a result of which there was a significant increase in chlorophyll-a concentra- Accepted: 13 March 2021 Published: 16 March 2021 tion [4,5]. Conversely, during the negative IOD period, the southeasterly wind along the southern coast of Java weakened and caused low chlorophyll-a concentrations [4,6]. Publisher’s Note: MDPI stays neutral The Bali Strait connects water masses from the Indian Ocean to the Bali Sea and vice with regard to jurisdictional claims in versa [7,8] with a shallow, narrow and steep bathymetry facing the Indian Ocean, producing published maps and institutional affil- high surface inlet and outflow current velocities [8]. Recent velocity results in dynamic iations. exchange of water masses [5,7,9–12]. The waters of the Bali Strait are also indirectly affected by the IOD phenomenon, in which primary productivity fluctuations occur in the surface layer due to the upwelling process that occurs in the Indian Ocean [12–16]. This condition affects the dynamics of Sardinella lemuru caught in the Bali Strait. Positive IOD was associated with strong El-Nino Southern Oscillation (ENSO) during 2006 and early Copyright: © 2021 by the authors. Sardinella lemuru Licensee MDPI, Basel, Switzerland. 2007, causing fluctuations in [7,17]. This article is an open access article The IOD period has an impact on the intensity of the upwelling that occurs. This distributed under the terms and condition affects the variability of chlorophyll-a concentration and sea surface temperature conditions of the Creative Commons and affects the production of Sardinella lemuru in the Bali Strait. This study aims to analyze Attribution (CC BY) license (https:// the upwelling phenomenon when positive IOD occurs in the Bali Strait. The discussion creativecommons.org/licenses/by/ focuses on the spatial and temporal variation of oceanographic parameters on the upwelling 4.0/). phenomenon during the IOD event, and its effect on Sardinella lemuru in the Bali Strait. Fishes 2021, 6, 8. https://doi.org/10.3390/fishes6010008 https://www.mdpi.com/journal/fishes Fishes 2021, 6, x FOR PEER REVIEW 2 of 9 aims to analyze the upwelling phenomenon when positive IOD occurs in the Bali Strait. The discussion focuses on the spatial and temporal variation of oceanographic parameters Fishes 2021, 6, 8 on the upwelling phenomenon during the IOD event, and its effect on Sardinella lemuru2 of in 9 the Bali Strait. 2. Results 2. Results 2.1.2.1. Variability of Sea Surface Temperature (SST)(SST) and and Sea Sea Surface Surface Chlorophyll Chlorophyll (SSC) (SSC) TheThe SSTSST andand SSCSSC verticalvertical profilesprofiles inin thethe BaliBali StraitStrait duringduring thethe IODIOD (+)(+) yearsyears werewere significantlysignificantly different (Figure(Figure1 1).). The The average average of of SST SST was was very very low low (24 (24 ◦°C)C) atat thethe peakpeak ofof thethe IODIOD (+)(+) phase, whereas at thethe endend ofof thethe IODIOD (+)(+) phasephase itit waswas veryvery highhigh (29(29 ◦°C),C), soso therethere waswas aa veryvery highhigh SSTSST differencedifference betweenbetween thethe peakpeak andand thethe endend ofof the the IOD IOD (+) (+) phasephase whichwhich waswas closeclose toto 55 ◦°C.C. AtAt aa depthdepth ofof 2020 toto 4040 m,m, thethe temperaturetemperature differencedifference waswas higherhigher thanthan thethe surfacesurface temperature,temperature, about 4 ◦°C.C. The thermocline layer rose up toto 1010 mm inin thethe IODIOD (+)(+) phase. Moreover, Moreover, the the average average of of SSC SSC during during the the peak peak of of the the IOD IOD (+) (+) phase phase was was 3 3mg/m mg/m3, and3, and at atthe the end end of ofthe the IOD IOD (+) (+) it reached it reached <1 <1mg/m mg/m3. The3. The SSC SSC difference difference between between the thepeak peak and and the the end end of ofthe the IOD IOD (+) (+) phase phase was was relatively highhigh (2(2 mg/m mg/m33). The verticalvertical distributiondistribution ofof SSTSST andand SSCSSC showed extremeextreme upwellingupwelling duringduring IOD IOD (+)(+) in the year of 2012. FigureFigure 1.1. DepthDepth profileprofile observedobserved onon JulyJuly 2012;2012; ((aa)) SeaSea SurfaceSurface TemperatureTemperature (SST) (SST) ((°C)◦C) duringduring IndianIndian OceanOcean DipoleDipole (IOD)(IOD) (+);(+); ((bb)) SSCSSC duringduring IODIOD (+); (+); andand observedobserved on on August August 2013; 2013; ( c(c)) SST SST ( ◦(°C)C) during during IOD IOD ( −(‐); ( d) Sea Surface Chlorophyll (SSC)(SSC) duringduring IODIOD ((−‐)) in in the the Bali Bali Strait. Strait. TheThe averageaverage SSC SSC at at the the peak peak of of the the IOD IOD (+) (+) phase phase in thein the Bali Bali Strait Strait was was 1.91 1.91 mg/m mg/m3, an3, increasean increase compared compared to the to end the of end the IODof the (+) IOD phase (+) of phase 0.92 mg/m of 0.923. Themg/m high3. The SSC high supports SSC thesupports physical the processes physical processes that show that very show strong very upwelling strong upwelling in the Bali in Strait the Bali during Strait the during IOD (+)the phase. IOD (+) We phase. used theWe Hovmöllerused the Hovmöller diagram to diagram see the variabilityto see the variability of SST and of SSC SST during and SSC the IODduring (+) the and IOD IOD (+) (− and) phases IOD from(‐) phases 2000–2019 from (Figure2000–20192). This (Figure pattern 2). This occurs pattern in the occurs eastern in monsoonthe eastern from monsoon June to from October, June andto October, the opposite and the occurs opposite in the occurs west monsoon in the west period. monsoon The effectperiod. of The the season effect of can the be season seen from can the be changeseen from in SST the at change each season in SST shift at each towards season the shift east season.towards The the transition east season. of seasons The transition was characterized of seasons bywas the characterized changes of warm by the temperatures changes of describedwarm temperatures in red to cold described temperatures in red to in cold blue. temperatures During the in 2000–2019 blue. During observation the 2000–2019 years, thereobservation was a similarity years, there in the was pattern a similarity of warm in the temperatures pattern of (Figurewarm 2temperatures) in the west monsoon(Figure 2) (DJF)in the towardswest monsoon transition (DJF) I (MAM),towards andtransition cold temperatures I (MAM), and in cold the temperatures east monsoon in (JJA)the east to transitionmonsoon (JJA) II (SON). to transition The upwelling II (SON). intensity The upwelling was affected intensity during was affected the IOD during phase, the where IOD the IOD (+) intensity was higher than the IOD (−) and neutral conditions. It follows a seasonal pattern. Fishes 2021, 6, x FOR PEER REVIEW 3 of 9 phase, where the IOD (+) intensity was higher than the IOD (‐) and neutral conditions. It follows a seasonal pattern. High SSC concentration during IOD (+) explains the extreme upwelling which indicates nutrient‐rich waters. The richness of nutrients in these waters causes the surface water level in the Bali Strait to have high primary productivity [8,18]. The IOD period has changed the trophodynamics of the Sardinella lemuru zone in the Bali Strait due to a significant increase in phytoplankton abundance and biomass. The monthly catch of Sardinella lemuru over 20 years is shown in Figure 2. During the IOD (+) phase in 2006, 2011, 2012, 2015, 2017, 2018 and 2019, SSC anomalies tended to increase, whereas SST anomalies tended to be low. This phenomenon can be used as an indicator of an increase in phytoplankton biomass which is followed by an increase in the production of Sardinella lemuru.
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