During the June 2010 survey of phytoplankton and physicochemical parameters in the Krka River estuary (eastern Adriatic Sea), a cryptophyte bloom was observed. High abundance of cryptophytes (maximum 7.9×106 cells l–1) and high concentrations of the class-specific biomarker pigment alloxanthine (maximum 2312 ng l–1) were detected in the surface layer and at the halocline in the lower reach of the estuary. Taxonomical analysis revealed that the blooming species was
Se observó una proliferación de una criptófita durante el estudio del fitoplancton y de los parámetros fisicoquímicos en el estuario del río Krka (Adriático) en junio de 2010. La abundancia más alta de criptofitas (máximo 7.9×106 células l–1) y las mayores concentraciones del pigmento marcador específico de la clase, la aloxantina (máximo 2312 ng l–1), fueron detectados en la capa superficial y en la haloclina en el tramo inferior de la ría. El análisis taxonómico reveló que la especie que proliferó fue
Nanoplanktonic cryptophyte flagellates (Phylum Cryptophyta, Class Cryptophyceae) are widely distributed in most aquatic habitats (
Reports of cryptophyte blooms and cryptophyte-dominated communities in oceanic (
Here we present the new report on the cryptophyte bloom in the Mediterranean Sea dominated by
The highly stratified Krka River estuary is situated in the central part of the eastern Adriatic Sea (
The sampling was performed in June 2010 along the lower reach of the Krka River estuary (stations E3, E4a and E5) and at the marine station (C1) near Zlarin island (
Standard colorimetric methods were used to determine orthophosphate (
Samples for the light microscopy (LM) analysis of phytoplankton abundance were fixed in situ in 1.4% hexamine-buffered formaldehyde (Kemika, Zagreb, Croatia) and cells were counted under the Zeiss Axiovert 200 inverted microscope (Carl Zeiss, Oberkochen, Germany) using the
For the scanning electron microscopy (SEM) analysis of field samples, 30 mL of 1.4% hexamine-buffered formaldehyde fixed sample from the 1-m depth of station E4a was gravity filtered on a 1- to 3-µm pore size Nucleopore polycarbonate filter (Nucleopore, Pleasanton, CA). The filter was rinsed three times with 20 ml dH2O and dehydrated in a series of ethanol dilutions (25, 35, 50, 75, 80, 90 and 100%). After that, the filtered material was dried in a series of ethanol : hexamethyldisilazane (HMDS, Sigma-Aldrich, Seelze, Germany) dilutions (3:1, 1:1, 1:3 and 100% HMDS). Finally, filters were air dried for 1 hour at 60°C, sputter-coated with gold-palladium and observed using JEOL JSM-6500F (JEOL-USA Inc., Peabody, MA, USA) and Mira II FE LMU (Tescan, Brno, Chech republic) scanning electron microscopes. The cryptophyte
Samples of 1-L volume for the high performance liquid chromatography (HPLC) analysis of phytoplankton pigments were filtered in situ on 0.7-µm pore HPLC following the protocol of
Principal component analysis (PCA) of the environmental data with the subsequent overlay of alloxanthine concentration data was performed in Primer 6 software (
The sharp halocline was detected at station E3 in the 1.5- to 3-m layer and at station E4a in the 1- to 2-m layer (
Temperature (°C) | Salinity | TIN (µM l–1) | NO3- (µM l–1) | NO22– (µM l–1) | NH4+ (µM l–1) | PO43– (µM l–1) | SiO44+ (µM l–1) | Redfield ratio (TIN/PO4) | Chlorophyll |
Cryptophytes (cells l–1) | |
---|---|---|---|---|---|---|---|---|---|---|---|
Minimum | 14.71 | 2.29 | 1.07 | 0.18 | 0.03 | 0.86 | 0.01 | 1.86 | 21.71 | 112.61 | 8.5×103 |
Maximum | 24.17 | 37.93 | 35.04 | 11.70 | 0.37 | 2.48 | 0.30 | 44.31 | 1317.73 | 5028.75 | 7.9×106 |
Arithmetic mean | 15.69 | 29.08 | 6.61 | 2.67 | 0.14 | 1.56 | 0.07 | 15.93 | 153.33 | 1070.00 | 8.98×105 |
Standard deviation | 2.98 | 12.78 | 7.76 | 3.14 | 0.11 | 0.51 | 0.08 | 15.15 | 256.34 | 1307.88 | 2.1×106 |
Pearson’s correlation | 0.395 | –0.296 | 0.242 | 0.182 | 0.557 | 0.490 | 0.950 | 0.376 | –0.218 | 0.968 | 0.991 |
Chlorophyll
Concentrations of total inorganic nitrogen (TIN = size Whatman Glass Fibre Filters (GF/F) and preserved NH4+ + NO22– + NO3–) and orthosilicates decreased in –80°C liquid nitrogen until the analysis. The extraction in 4 ml of cold 90% acetone was performed by sonication, and the extract was clarified by centrifugation. Pigments were separated by reversed phase along the estuary, from stations E3 to E5. Concentrations were higher in the surface layer and at the halocline (
High concentrations of alloxanthine were detected in the sub-surface layer of station E4a, with peak values between 1 and 2 m depth (1434-2311 ng l–1,
The PCA of environmental parameters was conducted to link the distribution of alloxanthine concentrations with the physicochemical parameters. The first two principal components accounted for 98% of the variance, and were both primarily defined by orthosilicates, nitrites, ammonium and salinity (
Variable | PC1 | PC2 |
---|---|---|
NH4+ | –0.122 | –0.088 |
NO22– | –0.059 | –0.012 |
NO3+ | –0.522 | –0.152 |
PO43– | –0.030 | –0.041 |
SiO44+ | –0.681 | –0.476 |
Temperature | –0.074 | –0.053 |
Salinity | 0.489 | –0.859 |
Along with cryptophytes, the samples were rich in green flagellates, the most abundant group at station C1 (maximum 8.6×105 cells l–1 at 2 m depth) and co-dominant at station E4a, and in diatoms, which dominated stations E3 and E5, and were very abundant (5.4×106 cells l–1) below the halocline of station E4a (
Cryptophytes were identified at the class level during LM counts, and no quantitative taxonomic composition was determined. However, most of the cells counted throughout the estuary represented a distinct morphotype (
Although the riverine inflow determined the depth of the halocline, vertical distribution of temperature was regulated by the solar radiation. Distribution of orthosilicates was defined by the river inflow, while high concentrations of TIN and orthophosphates at station E4a (Šibenik harbour) probably originated from both anthropogenic input and microbial regeneration. Nutrient enrichment, slower river flow and the increased temperature supported the cryptophyte-dominated bloom.
Cryptophyte blooms are rarely reported in marine and estuarine phytoplankton communities of the Mediterranean Sea. As a result, detailed ecological data linked with particular species are scarce. Furthermore, a high degree of species-specific and strain-specific seasonality in cryptophytes further complicates research on their ecological preferences and possible triggers of blooms. Available reports on the ecology of
Statistical analysis suggests that the cryptophyte bloom at station E4a was linked to the higher concentration of orthophosphates at the halocline. The main sources of orthophosphates in Šibenik harbour are anthropogenic eutrophication and bacterial regeneration of the organic matter (
Investigations conducted in other anthropogenically-influenced estuaries have detected a shift in the dominant communities due to increased levels of ammonium. High concentrations of ammonium (usually higher than 4 µM l–1) inhibit the uptake of nitrate, thus limiting the growth of larger diatoms and favouring smaller primary producers such as cryptophytes and green flagellates (
Previous investigations of the phytoplankton in the Krka estuary (
High abundance of cryptophytes may affect the mariculture production. Although cryptophytes are considered a “high-quality” food, lacking hard exoskeleton structures or toxic metabolic products (
The field work was supported by the Croatian Ministry of Science, Education and Sports through the project 119-1191189-1228. We would like to thank Professor Marijan Ahel from the Ruđer Bošković Institute in Zagreb for providing HPLC instrumentation. We are grateful to Dario Omanović, Zdeslav Zovko and Zvonko Roman from the same institution for their help during the field sampling. We would also like to thank Illiam Jackson from Uppsala University for valuable comments on the English language.