Physical Oceanography Physical Oceanography 1573-160X 20260308 Analysis of observations and methods of calculating Hydrophysical fields in the ocean Research Article Phytoplankton Blooms in the Open Black Sea: Review of Satellite Studies https://orcid.org/0000-0001-6307-1322 8324-7686 Yunev O. A.
Russian Federation
yunevoleg@gmail.com https://orcid.org/0000-0002-8627-7603 B-4994-2017 1681-7926 Suslin V. V.
Russian Federation
slava.suslin@mhi-ras.ru https://orcid.org/0000-0003-4699-9588 5697-5700 Belokopytov V. N.
Russian Federation
v.belokopytov@gmail.com https://orcid.org/0000-0003-0016-6118 Carstensen J.
Denmark
jac@ecos.au.dk Marine Hydrophysical Institute of RAS Sevastopol Russia Aarhus University Roskilde Denmark 28 02 2026 33 3 482 500 27 10 2025 04 12 2025 16 03 2026 Copyright ©; 2026, O. A. Yunev, V. V. Suslin, V. N. Belokopytov, J. Carstensen 2026 O. A. Yunev, V. V. Suslin, V. N. Belokopytov, J. Carstensen https://creativecommons.org/licenses/by-nc/4.0/ https://physical-oceanography.ru/repository/issues/2026/03/08/

Purpose. The purpose of the article is to analyze the studies of phytoplankton blooms in the deep-open Black Sea based on satellite bio-optical data obtained using various algorithms. Satellite data are used due to the lack of in situ monitoring programs for studying the spatiotemporal variations of phytoplankton blooms in this region, and the use of different algorithms results in conflicting conclusions. The presented analysis summarizes the available results.

Methods and Results. The examined publications have demonstrated the evolution of research on phytoplankton blooms in the deep-open Black Sea from the application of satellite-derived chlorophyll a concentration Chlsat to the use of satellite-derived phytoplankton biomass in carbon units Csat. Csat is obtained from Chlsat concentration data and in situ seasonal changes in the carbon-to-chlorophyll a ratio C:Chla. Determination of Chlsat concentration in the Black Sea using standard NASA algorithms (OC2 and OC4) results in errors of up to 500% and requires the development of regional algorithms, which take into account the specificity of bio-optical parameters in the given basin. The iterative statistical algorithm identifies the blooms as biomass outliers exceeding the 99th percentile of the base seasonal values. The C:Chla ratio varies from 46 (February) to 195 (September). The seasonal maximum shifts from December–January, typical of Chlsat concentration, to September–November, typical of Csat biomass, i.e., to the actual timing of phytoplankton bloom in the deep-open Black Sea. Bloom thresholds vary by month: 90 (August), 120 (September), and 105 mg C · m−3 (October–November). During the post-eutrophication period (since the mid-1990s), the phytoplankton biomass decreased, and winter-spring blooms disappeared.

Conclusions. The significant difference in the seasonal dynamics of Chlsat concentration and Csat biomass indicates that satellite-derived chlorophyll a concentration corresponding to the period of operation of the SeaWiFS and MODIS-Aqua/Terra ocean color satellite scanners (the post-eutrophication period) is not an acceptable indicator of biomass and cannot be used for studying the patterns of phytoplankton bloom and their mechanisms. One of the solutions to this problem consists in recalculating Chlsat concentration into Csat biomass using the C:Chla ratio and the algorithm with iterative bloom event extraction.

 subject field overview chlorophyll a concentration phytoplankton biomass seasonal changes interannual changes long-term changes phytoplankton bloom iterative algorithm Black Sea regional bio-optical algorithms satellite methods The authors are grateful to two anonymous reviewers for their constructive comments. The work was carried out within the framework of state assignments of FSBSI FRC MHI FNNN-2024-0012 "Analysis, diagnosis and forecast of the state of hydrophysical and hydrochemical fields of marine water areas based on mathematical modeling using the data from remote and contact measurement methods" and FNNN-2024-0014 "Fundamental studies of interaction processes in the sea-air system that form the physical state variability of the marine environment at various spatial and temporal scales". J. Carstensen received funding through the Horizon Europe project OBAMA-NEXT (Grant No. 101091642).

Article text not included.

REFERENCES BianchiT.S. EngelhauptE. WestmanP. AndrénT. RolffC. ElmgrenR. Cyanobacterial Blooms in the Baltic Sea: Natural or Human-Induced Limnology and Oceanography 2000 45 3 716 726 10.4319/lo.2000.45.3.0716 BehrenfeldM.J. Abandoning Sverdrup's Critical Depth Hypothesis on Phytoplankton Blooms Ecology 2010 91 4 977 989 10.1890/09-1207.1 PetranuA. ApasM. BodeanuN. BolognaA.S. DumitracheC. MoldoveanuM. RaduG. TiganusV. Status and Evolution of the Romanian Black Sea Coastal Ecosystem Environmental Degradation of the Black Sea: Challenges and Remedies 1999 Dordrecht Springer 175 195 10.1007/978-94-011-4568-8_11 ZaitsevYu.P. AlexandrovB.G. MinichevaG.G. North-Western Part of the Black Sea: Biology and Ecology Kyiv Naukova Dumka 2006 702 (in Russian) BodeanuN. Algal Blooms and Development of Main Phytoplankton Species at the Romanian Black Sea Littoral under Eutrophication Conditions Cercetari Marine 1989 22 107 125 BodeanuN. Microalgal Blooms in the Romanian Area of the Black Sea and Contemporary Eutrophication Conditions Toxic Phytoplankton Blooms in the Sea: Proceedings of the Fifth International Conference on Toxic Marine Phytoplankton, Newport, Rhode Island, U.S.A., 28 October – 1 November 1991 1993 Amsterdam Elsevier 203 209 BodeanuN. MonchevaS. RutaG. PopaL. Long-Term Evolution of the Algal Blooms in Romanian and Bulgarian Black Sea Waters Cercetari Marine 1998 31 37 55 MonchevaS. Gotsis-SkretasO. PagouK. KrastevA. Phytoplankton Blooms in the Black Sea and Mediterranean Coastal Ecosystem Subjected to Anthropogenic Eutrophication: Similarities and Differences Estuarine, Coastal and Shelf Science 2001 53 3 281 295 10.1006/ECSS.2001.0767 VelikovaV. Long-Term Study of Red Tides in the Western Part of the Black Sea and Their Ecological Modeling Harmful Algae 1998 Xunta de Galicia Intergovernmental Oceanographic Commission of UNESCO 261 265 VelikovaV. MonchevaS. PetrovaD. Phytoplankton Dynamics and Red Tides (1987–1997) in the Bulgarian Black Sea Water Science and Technology 1999 39 8 27 36 10.2166/wst.1999.0378 MonchevaS. Petrova-KaradjovaV. PalasovA. Harmful Algal Blooms along the Bulgarian Black Sea Coast and Possible Patterns of Fish and Zoobenthic Mortalities Harmful Marine Algal Blooms: Proceedings of the Sixth International Conference on Toxic Marine Phytoplankton, October 18–22, 1993, Nantes, France 1995 Paris Lavoisier Publishing Inc. 193 198 VinogradovK.A. On the Biology of the Northwestern Part of the Black Sea Zoologicheskii Zhurnal 1956 35 4 492 500 (in Russian) IvanovA.I. On the Use of Aeromethods for Phytoplankton Research in Estuarine Areas of the Northwestern Black Sea Botanicheskii Zhurnal 1956 41 11 1617 1619 (in Russian) ZaitsevYu.P. Odessa Biological Station of the Academy of Sciences of Ukraine: Foundation, Tasks, First Achievements (Memoirs of a Contemporary) Ecology of the Sea 2003 63 12 16 (in Russian) DuleninA.A. DuleninaP.A. KotsyukD.V. SviridovV.V. Experience and Perspectives of Small Unmanned Aerial Vehicles Application for Marine Coastal Biological Studies Trudy VNIRO 2021 185 134 151 10.36038/2307-3497-2021-185-134-151 (in Russian) SukhanovaI.N. Phytoplankton of the Open Black Sea in the Late Spring Period Current State of the Black Sea Ecosystem 1987 Moscow Nauka 86 97 (in Russian) MikaelyanA.S. NesterovaD.A. GeorgievaL.V. Winter Bloom of Nitzschia Delicatula on the Open Waters of the Black Sea Winter State of the Open Black Sea Ecosystem 1992 Moscow IO RAS 58 72 (in Russian) LeeZ.-P. Remote Sensing of Inherent Optical Properties: Fundamentals, Tests of Algorithms, and Applications 2006 Dartmouth, Canada IOCCG 122 Reports of the International Ocean-Colour Coordinating Group, vol. 5 SiegelD.A. BehrenfeldM.J. MaritorenaS. McClainC.R. AntoineD. BaileyS.W. BontempiP.S. BossE.S. DierssenH.M. Regional to Global Assessments of Phytoplankton Dynamics from the SeaWiFS Mission Remote Sensing of Environment 2013 135 77 91 10.1016/j.rse.2013.03.025 ReidP.C. RobinsonG.A. HuntH.G. Spatial and Temporal Patterns of Marine Blooms in the Northeastern Atlantic and North Sea from the Continuous Plankton Recorder Survey Rapports et Procès-Verbaux des Réunions 1987 187 27 37 RichardsonK. Algal Blooms in the North Sea: the Good, the Bad and the Ugly Dana 1989 8 83 93 SmaydaT.J. What is a Bloom. A Commentary Limnology and Oceanography 1997 42 5, part 2 1132 1136 10.4319/lo.1997.42.5_part_2.1132 TettP. The Ecophysiology of Exceptional Blooms Rapports et Procès-Verbaux des Réunions 1987 187 47 60 CarstensenJ. HenriksenP. HeiskanenA.-S. Summer Algal Blooms in Shallow Estuaries: Definition, Mechanisms, and Link to Eutrophication Limnology and Oceanography 2007 52 1 370 384 10.4319/lo.2007.52.1.0370 ParkerM. Exceptional Plankton Blooms Conclusion of Discussions: Convener's Report Rapports et Procès-Verbaux des Réunions 1987 187 108 114 CarstensenJ. ConleyD.J. Frequency, Composition, and Causes of Summer Phytoplankton Blooms in a Shallow Coastal Ecosystem, the Kattegat Limnology and Oceanography 2004 49 1 191 201 10.4319/lo.2004.49.1.0191 CarstensenJ. KlaisR. CloernJ.E. Phytoplankton Blooms in Estuarine and Coastal Waters: Seasonal Patterns and Key Species Estuarine, Coastal and Shelf Science 2015 162 98 109 10.1016/j.ecss.2015.05.005 SuslinV.V. ChurilovaT.Ja. SosikH.M. The SeaWiFS Algorithm of Chlorophyll a in the Black Sea Marine Ecological Journal 2008 7 2 24 42 (in Russian) SuslinV. ChurilovaT. A Regional Algorithm for Separating Light Absorption by Chlorophyll-a and Coloured Detrital Matter in the Black Sea, Using 480–560 nm Bands from Ocean Colour Scanners International Journal of Remote Sensing 2016 37 18 4380 4400 10.1080/01431161.2016.1211350 KopelevichO.V. BurenkovV.I. SheberstovS.V. VazyulyaS.V. ZavialovS.P. Bio-Optical Characteristics of the Russian Seas from Satellite Ocean Color Data of 1998–2010 Proceedings of VI International Conference "Current problems in Optics of Natural Waters (ONW 2011)" 2011 Saint Petersburg Nauka 181 182 KopelevichO.V. BurenkovV.I. SheberstovS.V. Development and Use of Regional Algorithms for Calculating Bio-Optical Characteristics of the Russian Seas from Satellite Ocean Color Data Sovremennye Problemy Distantsionnogo Zondirovaniya Zemli iz Kosmosa 2006 3 2 99 105 (in Russian) YunevO.A. CarstensenJ. StelmakhL.V. BelokopytovV.N. SuslinV.V. Reconsideration of the Phytoplankton Seasonality in the Open Black Sea Limnology and Oceanography Letters 2021 6 1 51 59 10.1002/lol2.10178 YunevO. CarstensenJ. SuslinV. BelokopytovV. StelmakhL. ZhukE. Temporal Variability of Phytoplankton Biomass and Algae Blooms in the Open Black Sea Progress in Oceanography 2025 237 103541 10.1016/j.pocean.2025.103541 NezlinN.P. Seasonal Variation of Surface Pigment Distribution in the Black Sea on CZCS Data Sensitivity to Change: Black Sea, Baltic Sea and North Sea 1997 Dordrecht Springer 131 138 10.1007/978-94-011-5758-2_11 NezlinN.P. DyakonovV.Yu. Seasonal and Interannual Variations of Surface Chlorophyll Concentrations in the Black Sea on CZCS Data Ecosystem Modeling as a Management Tool for the Black Sea 1998 Dordrecht Kluwer Academic Publishers 1 137 150 NezlinN.P. KostianoyA.G. GregoireM. Patterns of Seasonal and Interannual Changes of Surface Chlorophyll Concentration in the Black Sea Revealed from the Remote Sensed Data Remote Sensing of Environment 1999 69 1 43 55 10.1016/S0034-4257(99)00007-3 McClainC.R. EsaiasW.E. BarnesW. GuentherB. EndresD. MitchellB.G. BarnesR. SeaWiFS Calibration and Validation Plan 1992 Greenbelt, MD NASA 41 NASA Technical Memorandum, 104566; SeaWiFS Technical Report Series, vol. 3 MikaelyanA.S. Winter Bloom of the Diatom Nitzschia Delicatula in the Open Waters of the Black Sea Marine Ecology Progress Series 1995 129 241 251 10.3354/meps129241 O'ReillyJ.E. MaritorenaS. MitchellB.G. SiegelD.A. CarderK.L. GarverS.A. KahruM. McClainC. Ocean Color Chlorophyll Algorithms for SeaWiFS Journal of Geophysical Research: Oceans 1998 103 C11 24937 24953 10.1029/98JC02160 O'ReillyJ.E. MaritorenaS. O'BrienM.C. SiegelD.A. TooleD. MenziesD. SmithR.C. MuellerJ.L. MitchellB.G. SeaWiFS Postlaunch Calibration and Validation Analyses 2000 Greenbelt, Maryland Goddard Space Flight Centre 49 NASA Technical Memorandum 2000-206892, vol. 11, part 3 NezlinN.P. Unusual Phytoplankton Bloom in the Black Sea during 1998–1999: Analysis of Remotely Sensed Data Oceanology 2001 41 3 375 380 BersenevaG.P. ChurilovaT.Ya. GeorgievaL.V. Seasonal Variability of the Chlorophyll and Phytoplankton Biomass in the Western Part of the Black Sea Oceanology 2004 44 3 362 371 SuetinV.S. KorolevS.N. SuslinV.V. KucheryavyiA.A. Improved Interpretation of the Data of Observations of the Black Sea by a SeaWiFS Satellite Instrument in Autumn 1998 Physical Oceanography 2008 18 2 106 115 10.1007/s11110-008-9011-9 NezlinN.P. Remote-Sensing Studies of Seasonal Variations of Surface Chlorophyll-a Concentration in the Black Sea Satellites, Oceanography and Society 2000 Amsterdam Elsevier 267 277 OguzT. DeshpandeA.G. Malanotte-RizzoliP. The Role of Mesoscale Processes Controlling Biological Variability in the Black Sea Coastal Waters: Inferences from SeaWIFS-Derived Surface Chlorophyll Field Continental Shelf Research 2002 22 10 1477 1492 10.1016/S0278-4343(02)00018-3 KubryakovaE.A. KubryakovA.A. StanichnyS.V. Impact of Winter Cooling on Water Vertical Entrainment and Intensity of Phytoplankton Bloom in the Black Sea Physical Oceanography 2018 25 3 191 206 10.22449/1573-160X-2018-3-191-206 NezlinN.P. Seasonal and Interannual Variability of Remotely Sensed Chlorophyll The Black Sea Environment 2006 Berlin, Heidelberg Springer 333 349 10.1007/698_5_063 KubryakovA.A. ZatsepinA.G. StanichnyS.V. Anomalous Summer-Autumn Phytoplankton Bloom in 2015 in the Black Sea Caused by Several Strong Wind Events Journal of Marine Systems 2019 194 11 24 10.1016/j.jmarsys.2019.02.004 VostokovS.V. LobkovskiyL.I. VostokovaA.S. Solov'evD.M. Seasonal and Interannual Variability of Phytoplankton in the Black Sea on the Basis of Remote Sensing Data and In Situ Measurements of Chlorophyll-a Doklady Earth Sciences 2019 485 1 293 297 10.1134/S1028334X19030097 MikaelyanA.S. ZatsepinA.G. KubryakovA.A. Effect of Mesoscale Eddy Dynamics on Bioproduction of the Marine Ecosystems (Review) Physical Oceanography 2020 27 6 590 618 10.22449/1573-160X-2020-6-590-618 YunevO.A. KonovalovS.K. VelikovaV. Anthropogenic Eutrophication in the Black Sea Pelagic Zone: Long-Term Trends, Mechanisms, Consequences Moscow GEOS 2019 164 10.34756/GEOS/2019.16.37827 YunevO.A. VedernikovV.I. BasturkO. YilmazA. KideysA.E. MonchevaS. KonovalovS.K. Long-Term Variations of Surface Chlorophyll a and Primary Production in the Open Black Sea Marine Ecology Progress Series 2002 230 11 28 10.3354/meps230011 YunevO.A. CarstensenJ. MonchevaS. KhaliulinA. ArtebjergG. NixonS. Nutrient and Phytoplankton Trends on the Western Black Sea Shelf in Response to Cultural Eutrophication and Climate Changes Estuarine, Coastal and Shelf Science 2007 74 1–2 63 76 10.1016/j.ecss.2007.03.030 BurenkovV.I. KopelevichO.V. SheberstovS.V. ErshovaS.V. EvdoshenkoM.A. Bio-Optical Characteristics of the Aegean Sea Retrieved from Satellite Ocean Color Data The Eastern Mediterranean as a Laboratory Basin for the Assessment of Contrasting Ecosystems 1999 Dordrecht Springer 313 326 10.1007/978-94-011-4796-5_21 SancakS. BesiktepeS.T. YilmazA. LeeM. FrouinR. Evaluation of SeaWiFS Chlorophyll-a in the Black and Mediterranean Seas International Journal of Remote Sensing 2005 26 10 2045 2060 10.1080/01431160512331337853 SuetinV.S. SuslinV.V. KorolevS.N. KuchevyavyiA.A. Analysis of the Variability of the Optical Properties of Water in the Black Sea in Summer 1998 According to the Data of a SeaWiFS Satellite Instrument Physical Oceanography 2002 12 6 331 340 10.1023/A:1021729229168 YunevO.A. SuetinV. SuslinV. MonchevaS. Long-Term Changes in the Black Sea Surface Chlorophyll a According to in Situ and Modern Satellite Data Building the European Capacity in Operational Oceanography 2003 Elsevier 168 173 10.1016/S0422-9894(03)80028-4 IOCCG Ocean-Colour Data Merging 2007 Dartmouth, Canada IOCCG 72 Reports of the International Ocean-Colour Coordinating Group, No. 6 IOCCG Phytoplankton Functional Types from Space 2014 Dartmouth, Canada IOCCG 164 Reports of the International Ocean-Colour Coordinating Group, No. 15 KopelevichO.V. SheberstovS.V. YunevO. BasturkO. FinenkoZ.Z. NikonovS. VedernikovV.I. Surface Chlorophyll in the Black Sea over 1978–1986 Derived from Satellite and In Situ Data Journal of Marine Systems 2002 36 3–4 145 160 10.1016/S0924-7963(02)00184-7 FinenkoZ.Z. SuslinV.V. KovalevaI.V. Seasonal and Long-Term Dynamics of the Chlorophyll Concentration in the Black Sea According to Satellite Observations Oceanology 2014 54 5 596 605 10.1134/S0001437014050063 MikaelyanA.S. ChasovnikovV.K. KubryakovA.A. StanichnyS.V. Phenology and Drivers of the Winter-Spring Phytoplankton Bloom in the Open Black Sea: The Application of Sverdrup's Hypothesis and Its Refinements Progress in Oceanography 2017 151 163 176 10.1016/j.pocean.2016.12.006 MikaelyanA.S. ShapiroG.I. ChasovnikovV.K. WobusF. ZanacchiM. Drivers of the Autumn Phytoplankton Development in the Open Black Sea Journal of Marine Systems 2017 174 1 11 10.1016/j.jmarsys.2017.05.006 BellaciccoM. VolpeG. ColellaS. PitarchJ. SantoleriR. Influence of Photoacclimation on the Phytoplankton Seasonal Cycle in the Mediterranean Sea as Seen by Satellite Remote Sensing of Environment 2016 184 595 604 10.1016/j.rse.2016.08.004 JakobsenH.H. MarkagerS.S. Carbon-to-Chlorophyll Ratio for Phytoplankton in Temperate Coastal Waters: Seasonal Patterns and Relationship to Nutrients Limnology and Oceanography 2016 61 5 1853 1868 10.1002/ln.10338 MikaelyanA.S. KubryakovA.A. SilkinV.A. PautovaL.A. ChasovnikovV.K. Regional Climate and Patterns of Phytoplankton Annual Succession in the Open Waters of the Black Sea Deep Sea Research Part I: Oceanographic Research Papers 2018 142 44 57 10.1016/j.dsr.2018.08.001 StelmakhL.V. GorbunovaT.I. Carbon-to-Chlorophyll-a Ratio in the Phytoplankton of the Black Sea Surface Layer: Variability and Regulatory Factors Ecologica Montenergina 2018 17 60 73 10.37828/em.2018.17.8 Alvarez-FernandezS. RiegmanR. Chlorophyll in North Sea Coastal and Offshore Waters Does not Reflect Long Term Trends of Phytoplankton Biomass Journal of Sea Research 2014 91 35 44 10.1016/j.seares.2014.04.005 WinnC.D. CampbellL. ChristianJ.R. LetelierR.M. HebelD.V. DoreJ.E. FujiekiL. KarlD.M. Seasonal Variability in the Phytoplankton Community of the North Pacific Subtropical Gyre Global Biogeochemical Cycles 1995 9 4 605 620 10.1029/95GB02149 YunevO. CarstensenJ. StelmakhL. BelokopytovV. SuslinV. Temporal Changes of Phytoplankton Biomass in the Western Black Sea Shelf Waters: Evaluation by Satellite Data (1998–2018) Estuarine, Coastal and Shelf Science 2022 271 107865 10.1016/j.ecss.2022.107865 IvanovL.I. BesiktepeS. OzsoyE. Physical Oceanography Variability in the Black Sea Pycnocline Sensitivity to Change: Black Sea, Baltic Sea and North Sea 1997 Dordrecht Springer 265 274 10.1007/978-94-011-5758-2_21 KonovalovS.K. EremeevV.N. SuvorovA.M. KhaliulinA.Kh. GodinE.A. Climatic and Anthropogenic Variations in the Sulfide Distribution in the Black Sea Aquatic Geochemistry 1999 5 1 13 27 10.1023/A:1009655502787 KonovalovS.K. IvanovL.I. MurrayJ.W. EremeevaL.V. Eutrophication: A Plausible Cause for Changes in Hydrochemical Structure of the Black Sea Anoxic Layer Environmental Degradation of the Black Sea: Challenges and Remedies 1999 Dordrecht Springer 61 74 10.1007/978-94-011-4568-8_5 KonovalovS. IvanovL. SamodurovA. Oxygen, Nitrogen and Sulphide Fluxes in the Black Sea Mediterranean Marine Science 2000 1 2 41 59 10.12681/mms.289 KonovalovS.K. MurrayJ.W. Variations in the Chemistry of the Black Sea on a Time Scale of Decades (1960–1995) Journal of Marine Systems 2001 31 1–3 217 243 10.1016/S0924-7963(01)00054-9 YunevO.A. MonchevaS. CarstensenJ. Long-Term Variability of Vertical Chlorophyll a and Nitrate Profiles in the Open Black Sea: Eutrophication and Climate Change Marine Ecology Progress Series 2005 294 95 107 10.3354/meps294095