Marina Carić

PSEUDO-NITZSCHIA BLOOMS IN THE ZRMANJA RIVER ESTUARY (EASTERN ADRIATIC SEA)

The spatial and temporal distribution of the diatom genus Pseudo-nitzschia was investigated in the small, highly stratified Zrmanja River estuary (eastern Adriatic Sea) from 1998 to 2004. During this period, Pseudo-nitzschia spp. mostly dominated the phytoplankton assemblages (abundance close to 1.3 × 106 cells L−1, appeared in 51% of the samples). The maximum abundance of Pseudo-nitzschia spp. was during mid-winter (February 1999), when it contributed up to 85% of the total diatom abundance. Pseudo-nitzschia bloom was significantly correlated with phosphorous concentration and temperature, whereas there was no significant correlation with total inorganic nitrogen, silicate and salinity. The very broad range of environmental factors over which Pseudo-nitzschia spp. were observed suggests there was more than one Pseudo-nitzschia species in the diatom assemblage. Morphological analysis has shown that the dominating Pseudo-nitzschia species corresponded to Pseudo-nitzschia calliantha. Two other species were encountered; one identified as Pseudo-nitzschia heimii, while other has yet to be identified. This study was the first to find P. heimii in the Adriatic Sea and the first to record the presence of a potentially toxic diatom P. calliantha in an Adriatic estuary.

The occurrence and ecology of the centric diatom Cyclotella choctawhatcheeana Prasad in a Croatian estuary

The centric diatom Cyclotella choctawhatcheeana Prasad has been found for the first time in the Adriatic Sea. It develops dense populations in the highly stratified, oligotrophic, karstic estuary of the Zrmanja River (eastern Adriatic Sea, Croatia). Cyclotella choctawhacheeana contributed to the phytoplankton community in the estuary with high abundance of up to 2 x 10(6) cells L-1. Maximum abundance was found in the marine layer, below the halocline, at a salinity range between 13-28, but it was able to develop over a very wide salinity range. The maximum development appeared in the temperature range of 8-18 degrees C. It was present in 52% of samples throughout the year. The significant negative correlation with silica, nitrates and total inorganic nitrogen showed its preference for a marine, oligotrophic environment. We consider C. choctawhacheeana to be a significant constituent of the phytoplankton of the east Adriatic coast. It can be assumed that its succes is based on species wide tolerance to fluctuations of environmental factors.

Diatoms in a poor fen of Bijambare protected landscape, Bosnia & Herzegovina

Diatom populations of five microhabitats of a poor (Sphagnum) fen in Bijambare Protected Landscape area were studied. The fen is situated at an altitude 930 m a.s.l., on a slope of Mt. Zvijezda near Sarajevo. The major part of the fen is covered with Sphagnum recurvum and Sphagnum subsecundum, while at the outer borders communities are dominated by Carex spp. Samples were taken in May, July and October 2007 and May 2008, in vegetationally different microhabitats by squeezing water from mosses and taking material from pools. The diatom flora was studied under LM and SEM. The part of the fen that is characterized by Sphagnum species has a very poor diatom assemblage dominated by acidobiontic and acidophilous species such as Eunotia exigua, E. glacialis, E. paludosa and Pinnularia rhombarea. In the border area of the fen, diatom assemblages become richer with Nitzschia acidoclinata, Eolimna minima and Eunotia bilunaris as dominating species. According to published data, 45 taxa are recorded here for the first time for Bosnia and Herzegovina such as: Chamaepinnularia mediocris, Navicula digitulus, Navicula medioconvexa and Placoneis hambergii. Sellaphora bosniaca and Sellaphora hafnerae are described here as a new species.

Plankton and hydrography in a moderately eastern Adratic bay (Gruž Bay)

Gruž Bay (south-eastern Adriatic) is moderately eutrophicated, mostly by discharge from the karst river Ombla. Input of inorganic nitrogen might be attributed to enrichment from the open sea during strong and continuous north winds in winter 1988/89. Annual succession of primary producers, herbivores and decomposers was defined by seven stages and induced by specific physical-chemical characteristics. In the period April–August, biological production was mostly due to small size fractions of phytoplankton and zooplankton. Recycling of planktonic biomass occurred in September, of allochtonous organic matter in February and March.

Hydrography, nutrients, and plankton along the longitudinal section of the Ombla Estuary (south-eastern Adriatic)

Abundance and structure of phytoplankton and zooplankton, along with their relationship to hydrographic conditions were determined in the highly stratified estuary of the karstic Ombla River, south-eastern Adriatic. Sampling was carried out during 17 cruises within a one year period. River discharge lowered surface salinity and enriched the estuary with NO 3 and SiO 4 . Nutrient ratios suggested that PO 4 was the most likely limiting nutrient for phytoplankton growth in the estuary. Diatoms were present in low numbers and dominated the winter-early spring period. Dinoflagellates dominated from the end of May to August. Phytoplankton and zooplankton were composed mostly of marine species and their abundance decreased in seaward direction. Planktonic populations are controlled by the river runoff, temperature, salinity, nutrient concentrations and grazing. The results were consistent with the hypothesis that no algal blooms have been recorded due to short renewal time.

Diatoms in an extreme euxinic environment (Rogoznica Lake, eastern Adriatic coast)

Abstract The Rogoznica Lake marine system is a small, karstic, naturally eutrophic and euxinic marine environment. Abundance and temporal distribution of phytoplankton was investigated in relation to environmental conditions in the period from 1998 to 2013. The 36 determined diatoms contributed 90% of the total phytoplankton abundance. The diatom composition is characterized by low species diversity and high single species abundance (up to 107 cells L-1). There were, on average, 2.6 diatom species per sample (maximum 14 diatom species per sample) reflecting extreme environmental conditions. Dominant diatoms Thalassionema nitzschioides, Cyclotella choctawhatcheeana, Dactyliosolen fragilissimus and Chaetoceros curvisetus occurred repeatedly and were alternately dominant in the lake during the whole research period. Some diatoms were dominant only in limited period, like Cyclotella choctawhatcheeana (evident since 2001), and Pseudo-nitzschia spp. (evident in the period 2002 to 2009). It appears that the interplay of environmental conditions such as variability in thermohaline and redox conditions, nutrient and reduced sulphur concentration influence the phytoplankton development and abundance in the lake.

Ecological characteristics of plant species and associations along two Dinaric karstic rivers (Bosnia and Herzegovina, the Balkans)

This paper describes the plant communities of two oligotrophic karstic rivers with a slight anthropogenic influence — the Trebižat and the Lištica — in South Bosnia and Herzegovina, their sinecology, and the relationship between vegetation and plant species and environmental parameters. According to 87 relevés, a total of 26 plant associations, using Braun-Blanquet methods, were found in the rivers and nearby surveyed area. Only nine associations were common to both rivers. Eight associations were recorded for the territory of Bosnia and Herzegovina for the first time. Associations from both rivers differed according to following parameters measured at the sampling site: water temperature, distance from the mouth (river kilometers), river width, water depth, flow, pH and slope. There were no differences in nutrient concentrations among the associations. According to Canonical Correspondence Analysis (CCA), three environmental variables out of the 11 initially considered were retained as being related to plant distribution. The first two axes explained 56.8% and 35.2% of variance of species-environment relationship in the Trebižat and Lištica rivers, respectively. Water depth in the Trebižat River, and pH and river kilometers in the Lištica River were found to be the most influential, while nutrients and other physico-chemical parameters were not significant in either river. Water depth vector was identified as an underlying environmental factor determining distribution of Potamogeton lucens and Myriophyllum verticillatum (Potamion), and Nymphaea alba (Nymphaeion albae). According to in situ measurements of light intensity, the highest coefficients of light attenuation, radiance and reflection were found at a station with dense populations of Potamogeton lucens and Nuphar luteum (Potametum lucentis). The vegetation and floristic value of the rivers is discussed as a basis for biodiversity conservation programmes and evaluating the state of these ecosystems in the future.

Rogoznica Lake (Croatia), a Unique Euxinic Seawater System on the Adriatic Coast

The characteristics outlines above (a well- studied hydrography-since 1994 ; a stable and constant oxic/anoxic interface ; and a stratified system that has persisted long enough to produce steady-state conditions relative to alkalinity and sulfide concentrations) make Rogoznica lake ideal sites to examine the processes that control the biogeochemistry of anoxic environments. The small size and physically stable nature of the lake allows researchers to examine small scale spatial and temporal variability as well as longer term processes. All our data show how particular sequences of meteorological events, some of which can be regarded as extreme, have affected the internal processes in the Lake. An integration of all results (since 1994 up to now) reveals an interesting possibility that this environment may well potentially serve as valuable sentinels of climate change