Spatial and temporal distribution of phytoplankton in a highly stratified estuary (Zrmanja, Adriatic Sea)

Abstract

The karstic Zrmanja River discharges into the eastern Adriatic Sea, forming a highly stratified estuary with a sharp halocline that divides upper brackish and lower marine layers. Low orthophosphate concentrations and high Redfield ratios indicate that phosphorus limits phytoplankton growth. In addition, high transparency (avg 6.7 m) and oxygen saturation (avg 98.78%) indicate oligotrophy. Maximum phytoplankton abundance reached 3.4 × 106 cells·l−1 in early spring, a period when the community was composed mainly of diatoms. Dinoflagellates and nanoplanktonic phytoplankton dominated in summer; coccolithophorids and silicoflagellates characterized autumn. Stable conditions in the middle and lower estuary provided a suitable setting for development of microphytoplanktonic diatoms, whereas unstable conditions (frequent salinity variations) at the head of the estuary favored nanophytoplankton. Canonical correspondence analysis identified salinity, temperature, and river inflow as the main factors influencing phytoplankton development. Nutrients strongly limited phytoplankton growth in summer when the river discharge was a minimum.

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“…Negative significant correlation between nitrate and silicate on one side and salinity on other indicates an influence of river runoff during periods of high precipitation. The same correlation was noticed in other Adriatic estuaries (Burić et al, 2007;Aubry, Berton, Bastianini, Socal, & Acri, 2004), while in previous study of the Bay correlation was positive (Drakulović et al, 2012).…”

“…The same situation was noticed in the coastal north-western Mediterranean (Cermeno et al, 2006) and in the eastern Adriatic Sea (Buzančić, Ninčević-Gladan, Marasović, Kušpilić, & Grbec, 2016) where chl a increases in the autumn-winter period. The present result is slightly different from the results recorded in the Zrmanja estuary (Burić et al, 2007) and in the south-eastern Adriatic (Krivokapić et al, 2011), where a chlorophyll a peak was noticed in late winter and spring when the water column is rich with regenerated nutrients and solar radiation is increasing. The chlorophyll a values in this study were significantly lower than those in the previous study of Boka Kotorska Bay (Drakulović et al, 2012).…”

“…(Drakulović, Pestorić, Cvijan, Krivokapić, & Vuksanović, 2012). Generally, in the Adriatic Sea (Burić et al, 2007;Viličić et al, 2008), limited nutrient is phosphate almost throughout the year, while nitrogen availability is sporadically limited in the summer. Negative significant correlation between nitrate and silicate on one side and salinity on other indicates an influence of river runoff during periods of high precipitation.…”

Longitudinal patterns of phytoplankton distribution in a tributary bay under reservoir operation

“…The responses of phytoplankton to physical and chemical factors in the surrounding environment affect the structure and function of the entire planktonic community (Buric et al, 2007). The longitudinal pattern of phytoplankton is more complex because the dynamics of phytoplankton are altered by human activities and hydrological dynamics of the reservoir when the systems are highly regulated (Sabater et al, 2008).…”

Taxonomic survey of benthic diatoms in Neum Bay, southeastern Adriatic

“…On the other hand, to the best of our knowledge, the structure and taxonomic composition of benthic diatoms have been only rarely taken into consideration in the eastern Adriatic Sea (Burić et al, 2004;Miho & Witkowski, 2005;Caput et al, 2008;Levkov et al, 2010;Car et al, 2012;Nenadović et al, 2015;Mejandžić et al, 2015). Diatoms were investigated synoptically and mostly related to estuaries or coastal wetlands.…”