Oceanologia No. 61 (1 / 19)


Original research article

Short communications

Original research article

Distributions of photosynthetic and photoprotecting pigment concentrations in the water column in the Baltic Sea: an improved mathematical description
Oceanologia 2019, 61(1), 1-16

Joanna Stoń-Egiert1,*, Roman Majchrowski2, Mirosława Ostrowska1
1Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: aston@iopan.gda.pl
*corresponding author
2Institute of Physics, Pomeranian University in Słupsk, Słupsk, Poland;

keywords: Phytoplankton pigments, Marine photosynthesis, Baltic

Received 30 January 2018, Accepted 20 August 2018, Available online 12 September 2018.


Mathematical formulas are given to describe the changes with depth of concentrations of chlorophylls b, c, and photosynthetic and photoprotecting carotenoids in Baltic phytoplankton resulting from the adaptation of algal cells to ambient conditions. They take into account the spectral variability and differences in intensity, characteristic of the Baltic, in the irradiance penetrating the water, and also the spectral similarities among the spectra of different groups of phytoplankton pigments. The formulas were derived and validated on the basis of an extensive set of empirical data acquired from different parts of the Baltic Sea in 1999–2016. The standard error factor x of these formulas ranges from 1.32 to 1.73. These values are lower than those obtained for formulas derived for ocean waters, in which the influence of allogenic constituents on optical properties is negligibly small: 1.44 and 1.52 respectively in the case of chlorophyll c, and 1.32 and 1.47 respectively for photoprotecting carotenoids. With these formulas, overall levels of the main groups of pigments can be calculated from known irradiance conditions and chlorophyll a concentrations at any depth in a layer equal to one and a half thicknesses of the euphotic layer (i.e. to an optical depth of τ = 7) in the Baltic. The accuracy of these approximations is close to that of estimates of other bio-optical characteristics in this sea. This was confirmed by a validation based on an independent dataset (x from 1.27 to 1.84).
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Influence of environmental factors on the population dynamics of key zooplankton species in the Gulf of Gdańsk (southern Baltic Sea)
Oceanologia 2019, 61(1), 17-25

Maja Musialik-Koszarowska1, Lidia Dzierzbicka Głowacka2,*, Agata Weydmann2
1Institute of Oceanography, University of Gdańsk, Gdynia, Poland;
*corresponding author
2Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: dzierzb@iopan.gda.pl

keywords: Copepoda, Environmental factors, Acartia spp., Temora longicornis, Pseudocalanus sp., Biomass

Received 16 November 2017, Accepted 4 June 2018, Available online 30 June 2018.


We studied the influence of abiotic environmental factors on the seasonal population dynamics’ of Acartia spp., Temora longicornis and Pseudocalanus sp. in the southern Baltic Sea in the period of 2006–2007 and 2010–2012. Zooplankton samples were being collected monthly at 6 stations located in the western part of the Gulf of Gdańsk with a WP2 net (100 µm mesh sizes) and then analyzed according to the HELCOM guidelines. Although the sampling stations did not significantly differ from each other in the terms of variability of abiotic environmental factors, the biomass of copepods developmental stages differed between them, apart from the shallow stations in both, Gulf of Gdańsk and in its inner part – Puck Bay. According to redundancy analysis, 26.1% of the total variability observed in the biomass of the copepod species has been explained by water temperature, salinity, air temperature, cloudiness, wind speed and direction and station's depth, with the first variable having the greatest power, alone explaining 13.7%. ANOSIM revealed that sampling stations in the Gulf of Gdańsk were significantly different from one another in terms of copepods’ biomasses. Generalized Additive Models fitted for water temperature and salinity were significant for all ontogenetic stages of Acartia spp. and Temora longicornis and for the majority of stages of Pseudocalanus sp. (apart from the C1 for both and the males for salinity).
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Role of macrophytes in structuring littoral habitats in the Vistula Lagoon (southern Baltic Sea)
Oceanologia 2019, 61(1), 26-37

Krzysztof Pawlikowski*, Ryszard Kornijów
Department of Fisheries Oceanography and Marine Ecology, National Marine Fisheries Research Institute, Kołłątaja Str. 1, 81-332 Gdynia, Poland;
e-mail: k.pawlikowski@mir.gdynia.pl
*corresponding author

keywords: Submerged and emergent vegetation, Oxygenation, Temperature, Insulation, Sediments

Received 10 January 2018, Accepted 26 May 2018, Available online 18 June 2018.


The objective of the research conducted in the years 2011–2014 in the near-shore zone of the Vistula Lagoon was the verification of the hypothesis that in the coastal lagoon, similarly as in inland waters, habitat conditions can be substantially modified by macrophytic vegetation, depending on the represented life form and its abundance. The research was conducted in the zone of emergent plants (reed rush composed of Phragmites australis) and in the zone of submerged plants occurring as scattered patches of Potamogeton perfoliatus and Stuckenia pectinata. The hypothesis was supported only in the case of the reed rush which substantially modified water insolation, temperature, and oxygenation, as well as the grain size composition of sediments, and concentration of organic matter contained in the sediments. Patches of submerged vegetation had insufficient surface area and were too scarcely overgrown by plants to considerably affect the habitat conditions and weaken the strong mechanical effect of waves and rate of water exchange between the littoral and open water zone.
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Effects of atmospheric circulation on water temperature along the southern Baltic Sea coast
Oceanologia 2019, 61(1), 38-49

Józef Piotr Girjatowicz*, MałgorzataŚwiątek*
Unit of Hydrology and Water Management, Faculty of Geosciences, University of Szczecin, Szczecin, Poland;
e-mail: jozef.girjatowicz@usz.edu.pl, malgorzata.swiatek@usz.edu.pl
*corresponding author

keywords: Circulation patterns, Water temperature, Correlation, Regression, Relationship, Coastal zone

Received 11 May 2017, Accepted 5 June 2018, Available online 10 July 2018.


The relationships between atmospheric circulation patterns and water surface temperature along the coast of the southern Baltic Sea were studied. Seasonal water temperature values for Świnoujście, Międzyzdroje, Kołobrzeg, Władysławowo, Hel and Gdynia stations measured during the period of 1951–2010 were used. The methods of correlation and regression were applied to determine the relationships between water temperature and the number of days of atmospheric circulation patterns.
It was demonstrated that the strongest relationships occur in winter, chiefly on account of intense atmospheric circulation activity and weaker effects of solar radiation. The relationships with western circulation are slightly stronger than that associated with the eastern circulation. During the remaining seasons, those dependencies are clearly weaker. Asynchronous relationships between water temperature and atmospheric circulation are less pronounced than the synchronous ones. Despite being weaker, the asynchronous relations are still statistically significant, mainly in the spring season and as such, they may have a prognostic significance.
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Driving forces of sandy sediment transport beyond the surf zone
Oceanologia 2019, 61(1), 50-59

Magdalena Stella1,*, Rafał Ostrowski1, Piotr Szmytkiewicz1, Jarosław Kapiński2, Tomasz Marcinkowski2
1Institute of Hydro-Engineering, Polish Academy of Sciences (IBW PAN), Gdańsk, Poland;
e-mail: m.stella@ibwpan.gda.pl
2Maritime Institute in Gdańsk, Gdańsk, Poland
*corresponding author

keywords: Wind-induced current, Wave–current interactions, Apparent roughness, Sediment transport rates

Received 2 November 2017, Accepted 12 June 2018, Available online 2 July 2018.


The paper deals with experimental and theoretical investigations of forces that drive sediment motion beyond the surf zone of the southern Baltic Sea. The study site is located in the sandy coastal zone at Lubiatowo (Poland). Field surveys were carried out by the Institute of Hydro-Engineering of the Polish Academy of Sciences (IBW PAN) and the Maritime Institute in Gdańsk (IMG). The measurements comprise parameters of wind, waves and currents. The wind velocities and directions were recorded at the IBW PAN Coastal Research Station (CRS) in Lubiatowo, while the wave and current data were collected near CRS Lubiatowo, ca. 1.5 Nm from the shoreline, at a depth of 17 m. Theoretical investigations concern wind-induced currents, nearbed wave-induced oscillatory velocities and wave-current interactions. The concept of the apparent roughness related to the wave bed boundary layer is used in the description of wind-induced steady flow. A theoretical model of the wind-induced current is proposed in two variants, depending on the predominance of wave or current impact. The wind-induced flow model is successfully verified using measured current velocity profiles. Previously developed at IBW PAN, a three-layer sediment transport model is adapted to the study site and applied in calculations of sediment transport rates.
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Impact of artificial coastal protection structures on Ascidians settlement along the Tamil Nadu coast, India
Oceanologia 2019, 61(1), 60-67

Jebarathanam Prince Prakash Jebakumar1,*, Ganesan Nandhagopal1, Bose Rajan Babu1, Shunmugavel Ragumaran1, Chokalingam Muthiah Ramakritinan2, Abdul Jaffar Ali3, Mohammed Kaleem Arshan3, Vijaya Ravichandran1
1Coastal Environmental Engineering Division, National Institute of Ocean Technology, Pallikaranai, Chennai, India;
e-mail: prince@niot.res.in
2Department of Marine and Coastal Studies, Madurai Kamaraj University, Madurai, India
3Department of Biotechnology, Islamiah College, Vaniyambadi, India
*corresponding author

keywords: Artificial structures, Novel niche, Ascidian, Native, Introduced, Cryptogenic

Received 5 February 2018, Accepted 18 June 2018, Available online 6 July 2018.


Ascidians are one of the dominant marine sedentary filter feeders recorded more frequently as introduced species than other taxa. It is renowned that artificial structures offer novel niches to the non-native species. A yearlong investigation was carried out to understand the role of ascidian colonization on various artificial structures located along 84 stations stretched on the 1076 km long Tamil Nadu coast of South India. It revealed the occurrence of 26 ascidian species, among these18 specimens were identified to species level, 8 were identified to genus level based on morphological characters. As on origin and nativity, out of the total 26, 3 species were classified as introduced, 8 species were classified as native and 15 as cryptogenic species. Interestingly, Polyclinum isipingense and Diplosoma variostigmatum were reported first time in Indian waters. The cryptogenic and colonial forms of ascidians are dominant in the artificial structures. There were significant differences observed between artificial structure type, geographic locations (p = 0.0071) and between ascidians forms as well as geographic areas (p = 0.00375). This study also confirms the artificial structures offer new niches for non-native ascidian colonization. The influence of the substrate (structure type) as well as geographic locations on the biotic assemblage was also observed.
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Surface layer desalination of the bays on the east coast of Novaya Zemlya identified by shipboard and satellite data
Oceanologia 2019, 61(1), 68-77

Dmitry I. Glukhovets1,2,*, Yury A. Goldin2
1Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia;
e-mail: glukhovets@ocean.ru
2Moscow Institute of Physics and Technology, Moscow Region, Russia
*corresponding author

keywords: Surface layer, Continental runoff, High-resolution satellite data, Salinity, Fluorescence

Received 16 February 2018, Accepted 3 July 2018, Available online 17 July 2018.


This study examined the influences of continental and island river runoff as well as glacial meltwater runoff on the water surface layers of the Kara Sea in different bays on the eastern coast of Novaya Zemlya, an archipelago off the coast of Russia. High-resolution satellite and shipboard data obtained in 2015 were used to determine the sources of desalination (glacial meltwaters and river waters), which can be distinguished by the type of correlation (positive, negative, or none) seen between salinity and the coloured dissolved organic matter fluorescence intensity. Examples of the various situations that can occur in the bays are provided and discussed.
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Canthaxanthin in recent sediments as an indicator of heterocystous cyanobacteria in coastal waters
Oceanologia 2019, 61(1), 78-88

Magdalena Krajewska1,*, Małgorzata Szymczak-Żyła1,*, Justyna Kobos2,*, Małgorzata Witak3,*, Grażyna Kowalewska1,*
1Institute of Oceanology PAN, Marine Pollution Laboratory, Sopot, Poland;
e-mail: mkrajewska@iopan.pl, szymczak@iopan.gda.pl, Kowalewska@iopan.pl
2University of Gdańsk, Faculty of Oceanography and Geography, Division of Marine Biotechnology Gdynia, Poland;
e-mail: justyna.kobos@ug.edu.pl
3University of Gdańsk, Faculty of Oceanography and Geography, Division of Marine Geology, Gdynia, Poland;
e-mail: ocemaw@univ.gda.pl
*corresponding author

keywords: Cyanobacteria, Carotenoids, Canthaxanthin, Gulf of Gdańsk (southern Baltic), Oslofjord

Received 15 May 2018, Accepted 10 July 2018, Available online 31 July 2018.


The mean share of heterocystous cyanobacteria in total chlorophyll-a production in coastal waters, based on cyanobacterial marker carotenoid and chloropigments preserved in recent sediments (0–5 cm, ca 30 years), has been studied in the Gulf of Gdańsk (southern Baltic) and for comparison in the Oslofjord/Drammensfjord (southern Norway). First of all, Baltic cyanobacteria, both from laboratory cultures and field samples, were analysed to select marker heterocysteous cyanobacteria carotenoids for sediments. The pigment relation to diatom percentages of different salinity preferences has been tested, to confirm origin of cyanobacteria. The results indicate that canthaxanthin is the best marker of heterocystous cyanobacteria in the southern Baltic Sea. These filamentous cyanobacteria inflow to the Gulf of Gdańsk from the open sea and their abundance has increased in the last thirty years, in comparison with previous time. In that period they made up ca 4.6% of the total chlorophyll-a production in the Gulf of Gdańsk. The estimate for Oslofjord, at the same assumptions, suggests that heterocystous cyanobacteria occurred there also (up to 5.8% of the total chlorophyll-a production), were of marine origin, but their abundance has decreased during the last thirty years. Such an estimate may be used in environmental modelling and can be applied to other coastal areas, once the marker pigments of the main cyanobacteria species have been identified, and the percentage of total chlorophyll-a produced in a basin, preserved in sediments, has been determined for such area.
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Spectral structure of surface waves and its influence on sediment dynamics
Oceanologia 2019, 61(1), 89-102

Boris V. Divinsky*, Ruben D. Kosyan
*corresponding author
Shirshov Institute of Oceanology RAS, Moscow, Russia;
e-mail: divin@ocean.ru
*corresponding author

keywords: Sand bottom dynamics, JONSWAP spectra, Acoustic backscatter measurements, Concentration profiles, Frequency domain

Received 9 April 2018, Accepted 11 July 2018, Available online 28 August 2018.


Analysis of the influence of wave energy frequency distribution on the dynamics of suspension over the sea-bottom is the main objective of this study. We revealed the differences between the response of the eroded sea-bottom to external disturbances represented by irregular surface waves with permanent integral characteristics (significant wave height and frequency of the spectrum peak) and variable frequency of the wave energy distribution.
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Mixing characteristics of the subarctic front in the Kuroshio-Oyashio confluence region
Oceanologia 2019, 61(1), 103-113

Zhu Ke-Lan1,*, Chen Xi2, Mao Ke-Feng2,*, Hu Dong3, Hong Sen4, Li Yan2
1Army of PLA, Beijing, China;
e-mail: 503068020@qq.com
2College of Meteorology and Oceanography, National University of Defense Technology, Nanjing, China;
e-mail: oceanlgdx@163.com
3Army of PLA, Beijing, China
4Army of PLA, Beihai, China
*corresponding author

keywords: Kuroshio–Oyashio confluence region, Subarctic front, Mixing, Turbulent eddy diffusivity, Thermal diffusivity

Received 17 October 2017, Accepted 23 July 2018, Available online 11 August 2018.


This paper analyzes the mixing characteristics of the Subarctic Front (SAF) in the Kuroshio-Oyashio Confluence Region based on temperature, salinity, and current data obtained from surveys and remote sensing in June 2016. The frontal zone of the observed area is at 145°–151°E, 38°–41°N. The front is distributed between 25.5–26.7 σθ in a band pattern inclined from north to south and is deeper in the south. The region shallower than 200 m and distributed along the isopycnal of 25.9–26.1 σθ has the strongest horizontal temperature and salinity gradients, and the largest of the former can reach over 0.7°C/km. Diapycnal mixing of the SAF is mainly turbulent; it is stronger in the north than in the south. The region with stronger turbulence (Kρ > 10−3.5 m2/s) is distributed mainly in water layers within and under the front (26.1–26.7 σθ), showing that the SAF is shallower in the north and deeper in the south along the front. Symmetric instability may be the main factor causing strong turbulent mixing in the frontal zone. Double diffusion mixing is stronger in the south than in the north; the region with stronger double diffusion (Kθ > 10−4.5 m2/s) is distributed mainly in water layers within and above the front (25–26.5 σθ) on the southern side of the SAF. These water layers are dominated mainly by "salt-fingering" double diffusion, with only a few water layers dominated by "diffusive layering" double diffusion mixing in middle and lower waters deeper than 300 m.
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Annual cycle of phytoplankton community through the water column: Study applied to the implementation of bivalve offshore aquaculture in the southeastern Bay of Biscay
Oceanologia 2019, 61(1), 114-130

Oihane Muñiz1,*, Marta Revilla1, José Germán Rodríguez1, Aitor Laza-Martínez2, Almudena Fontán1
1AZTI-Tecnalia, Marine Research Division, Pasaia, Spain;
e-mail: omuniz@azti.es
2Department of Plant Biology and Ecology, Faculty of Science and Technology, University of the Basque Country, UPV/EHU, Leioa, Spain
*corresponding author

keywords: Phytoplankton abundance, Taxonomic composition, Biomass, Size-fractionated chlorophyll, Environmental variables

Received 14 March 2018, Accepted 2 August 2018, Available online 28 August 2018.


This study describes, for the first time, the annual variability of phytoplankton community in different layers of the water column in open waters off the Basque coast (southeastern Bay of Biscay). Phytoplankton composition, abundance and biomass, together with size-fractionated chlorophyll a, nutrients, and optical and hydrographic conditions were measured in an experimental bivalve culture area from May 2014 to June 2015. Water column conditions showed the typical dynamics previously described for temperate areas, characterised by winter homogeneity and summer stratification. Phytoplankton temporal variability was studied at depths of 3, 17 and 33 m, and was found to be related to those processes. In particular, temperature and nutrients (mostly nitrate and silicate) were the environmental variables which significantly explained most of the variability of chlorophyll concentration, whereas river flow was the main driver of abundance variability. Total chlorophyll was generally low (0.6 µg L−1 on average). Of the 194 registered taxa, 47.4% belonged to dinoflagellates and 35.1% to diatoms. In addition, diatoms showed the highest biomass values, and haptophytes represented the greatest contribution to cell-abundance. This fact, despite the low chlorophyll values indicating low phytoplankton biomass, could favour mussel growth given the high fatty acid content reported for diatoms and haptophytes.
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Random forest assessment of correlation between environmental factors and genetic differentiation of populations: Case of marine mussels Mytilus
Oceanologia 2019, 61(1), 131-142

Tomasz Kijewski1, Małgorzata Zbawicka1, Jakob Strand2, Hans Kautsky3, Jonne Kotta4, Merli Rätsep4, Roman Wenne1,*
*corresponding author
1Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: rwenne@iopan.gda.pl
2Arctic Research Centre, Department of Bioscience, Aarhus University, Aarhus, Denmark
3Department of Ecology, Environment and Plant Sciences, Stockholm University, Sweden
4Estonian Marine Institute, University of Tartu, Tallinn, Estonia
*corresponding author

keywords: Marine environment, Spatial distribution, Seascape genetics, Nuclear DNA markers EFbis, Glu-5′, ITS, M7 and Single Nucleotide Polymorphism, Baltic Sea

Received 29 April 2018, Accepted 15 August 2018, Available online 30 August 2018.


The novel machine learning technique Random Forest (RF) was used to test if the genetic differentiation of populations of marine species may be related to any of the key environmental variables known to shape species distributions. The study was performed in North and Baltic Sea characterized by strong gradients of environmental factors and almost continuous distributions of Mytilus mussel populations. Assessment of the species identity was performed using four nuclear DNA markers, and previously published single nucleotide polymorphism (SNP) data. A general pattern of cline variation was observed with increasing Mytilus trossulus share towards the eastern Baltic Sea. Average allele share rose to 61% in Höga Kusten, Gulf of Bothnia. All Baltic Sea samples revealed a strong introgression of Mytilus edulis and a limited introgression of M. trossulus through the Danish Straits.
The studied environmental variables described 67 and 68% of the variability in the allele frequencies of M. edulis and M. trossulus. Salinity defined over 50% of the variability in the gene frequencies of the studied Mytilus spp. populations. Changes along this environmental gradient were not gradual but instead a significant shift from gene dominance was found at a salinity of 12 PSU. Water temperature and the trophic status of the sea area had only moderate association with the gene frequencies. The obtained results showed that the novel machine learning technique can be successfully used for finding correlations between genetic differentiation of populations and environmental variables and for defining the functional form of these linkages.
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Average nutrient and chlorophyll distributions in the western Mediterranean: RADMED project
Oceanologia 2019, 61(1), 143-169

María del Carmen García-Martínez1,*, Manuel Vargas-Yáñez1, Francina Moya1, Rocío Santiago2, María Muñoz3, Andreas Reul3, Teodoro Ramírez1, Rosa Balbín2
1Instituto Español de Oceanografía, C.O. Málaga (Fuengirola), Spain;
e-mail: mcarmen.garcia@ieo.es
2Instituto Español de Oceanografía, C.O. Baleares, Spain
3Universidad de Málaga. Departamento de Ecología, Spain
*corresponding author

keywords: Inorganic nutrients, Chlorophyll, Western Mediterranean, Climatological values, Time series, Climate change

Received 31 May 2018, Accepted 16 August 2018, Available online 2 September 2018.


Because of its reduced dimensions and its location, surrounded by three continents, the Mediterranean Sea could be especially vulnerable to climate change effects. An increase of the water column stratification could inhibit winter mixing and reduce the frequency and intensity of convection processes which inject nutrients into the photic layer and are responsible for the ventilation of deep waters. In this context, the long-term monitoring of the Mediterranean waters is a basic task. The RADMED project is a monitoring program that covers the waters from the eastern side of the Gibraltar Strait to the Catalan and Balearic Seas. This project was initiated in 2007, merging some previous programs, some of them initiated in 1992. The main objective of this project is to establish average distributions, ranges of variability and long-term trends for physical, and biochemical variables which could be considered as indicative of the environmental state of the sea. The present work analyses nutrient, chlorophyll and oxygen time series from 2007 to 2015 in some cases and from 1992 in other cases. The current analyses show a clear trophic gradient in the RADMED area. Nutrient and chlorophyll concentrations and the intensity of the deep chlorophyll maximum decrease northeastward. The deep chlorophyll maximum depth increases to the northeast. The Balearic and Catalan Seas show a clear seasonal pattern with maximum surface concentrations for nutrients and chlorophyll in winter/spring, associated with winter mixing. On the contrary, the Alboran Sea does not show such a clear seasonal cycle, probably because of the existence of permanent upwelling processes acting along the whole year. The Atlantic Water occupying the upper part of the water column shows a Redfield N:P ratio close to or lower than 16, indicating no phosphorus limitation. Finally, chlorophyll concentrations seem to have increased from 1992 to 2015 in the Alboran Sea, while no long-term changes could be established for the rest of the variables and geographical areas.
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Short communications

Spatiotemporal variation of alkaline phosphatase activity in coastal waters off Trivandrum
Oceanologia 2019, 61(1), 170-177

Mamatha S. Shivaramu*, Amruta K. Randive, Ritu Kumari, Manguesh Gauns, LokaBharathi A. Ponnapakkam
Biological Oceanography Division, CSIR-National Institute of Oceanography, Goa, India;
e-mail: mamatha@nio.org
*corresponding author

keywords: Phosphorus, Alkaline phosphatase activity, Chlorophyll, Phytoplankton, Bacteria

Received 16 February 2018, Accepted 13 June 2018, Available online 3 July 2018.


Phosphatase is an extracellular enzyme which releases inorganic phosphate (Pi) from dissolved organic phosphate and indirectly organic carbon as nutrients for aquatic communities. Here, we have examined spatiotemporal variation in total alkaline phosphatase activity (APA) over a short period off Trivandrum, SW India. Sampling was at 50 m water depth at 5, 15, 25 and 45 m for 5 consecutive days at 6 h intervals during post-monsoon season. Total APA and phosphatase producing bacteria (PPB) were estimated along with pertinent environmental parameters. APA increased with depth up to 3.98 µM P h−1 at 45 m. Increase in pigment concentration with depth is responsible for an increase in APA and Pi uptake. There is a marginal increase in APA towards 18–24 h suggesting feeding activities of secondary producers. On the whole, chlorophyll and phaeophytin were responsible for nearly 45 and 55% variation in APA (p < 0.01, p < 0.001, n = 16), respectively. Total bacterial count (TBC) was responsible for 32% (p < 0.05, n = 16) and total viable direct counts-aerobic (TVCa) for 24% (p < 0.05, n = 16) APA variation. About 38% (p < 0.01, n = 20) variation of APA was linked to chlorophyll at noon and 22% (p < 0.001, n = 20) to PPB at dawn. Thus, it is possible that bacteria and chlorophyll/phytoplankton could be responsible for variation in APA, with the latter contribution greater than the former at noon. Such studies would help to profile the fertility of coastal waters in terms of bioavailable Pi. Laboratory experiments are underway to help us discern the extent of light-dependent contribution of chlorophyll/phytoplankton to APA and light independent participation of bacteria to the process.
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