Protected Freshwater Ecosystem with Incessant Cyanobacterial Blooming Awaiting a Resolution

Abstract

For 50 years persistent cyanobacterial blooms have been observed in Lake Ludoš (Serbia), a wetland area of international significance listed as a Ramsar site. Cyanobacteria and cyanotoxins can affect many organisms, including valuable flora and fauna, such as rare and endangered bird species living or visiting the lake. The aim was to carry out monitoring, estimate the current status of the lake, and discuss potential resolutions. Results obtained showed: (a) the poor chemical state of the lake; (b) the presence of potentially toxic (genera Dolichospermum, Microcystis, Planktothrix, Chroococcus, Oscillatoria, Woronichinia and dominant species Limnothrix redekei and Pseudanabaena limnetica) and invasive cyanobacterial species Raphidiopsis raciborskii; (c) the detection of microcystin (MC) and saxitoxin (STX) coding genes in biomass samples; (d) the detection of several microcystin variants (MC-LR, MC-dmLR, MC-RR, MC-dmRR, MC-LF) in water samples; (e) histopathological alterations in fish liver, kidney and gills. The potential health risk to all organisms in the ecosystem and the ecosystem itself is thus still real and present. Although there is still no resolution in sight, urgent remediation measures are needed to alleviate the incessant cyanobacterial problem in Lake Ludoš to break this ecosystem out of the perpetual state of limbo in which it has been trapped for quite some time.

Past studies and potential measures for rehabilitation of the shallow lake (Lake Ludas)

“…Subtropical cyanobacterium R. raciborskii was discovered in Serbia for the first time in 2003 in the Ponjavica River (Karadžić et al, 2013). Shortly after, new published findings started to appear, mostly connected with carp ponds and reservoirs (Ćirić, Marković, Dulić, & Subakov-Simić, 2010;Simić, Mišćević, Đorđević, & Popović, 2011;Svirčev, Tokodi, & Drobac, 2017;Tokodi et al, 2020). This species has been regularly recorded in Lake Ludaš since 2013.…”

“…Two aeolian lakes in northern Serbia, Lake Palić and Lake Ludaš, are probably the most investigated shallow water bodies in the country. Studies dealing with Lake Ludaš include various topics: water and sediment quality, changes and modeling of its hydrological regime, microbiological community and phytoplankton dynamics, cyanobacterial bloom and their toxic effect on other aquatic organisms (Ćirić et al, 2019;Gavrilović et al, 2020;Grabić, Đurić, Ćirić, & Benka, 2018;Grba et al, 2017;Pamer et al, 2011;Raicevic et al, 2013;Rudic et al, 2018;Rudić, Vujović, Božić, Arizanović, & Raičević, 2018;Rudić, Vujović, Božić, & Raičević, 2015;Seleši, 1981Seleši, , 2006Svirčev et al, 2013;Tokodi, 2016;Tokodi et al, 2018;Tokodi et al, 2020).…”

“…Apart from its ability to influence nitrogen cycle in aquatic ecosystems, some R. raciborskii strains can produce different cyanotoxins. In Lake Ludaš, microcystins (MC) and saxitoxin (STX) were detected (Gavrilović et al, 2020;Simeunovic, Svircev, Karaman, Knezević, & Melar, 2010;Tokodi et al, 2020), but it is still unclear whether R. raciborskii is a potential STX producer in this lake.…”

“…In addition to the two invasive microorganisms, there is one important allochthonous vertebrate species, the Prussian carp (also silver Prussian carp or Gibel carp) Carassius gibelio Block, 1782(before 2003. This fish is dominant in the lake and feeds on zooplankton and macro-vegetation thus disturbing the food chains and contributing to the excessive phytoplankton growth (Plan for the Improvement, 2014;Pujin & Budakov, 1979;Tokodi et al, 2020).…”

Advancing Knowledge on Cyanobacterial Blooms in Freshwaters

“…In this direction, a deeper understanding of the mechanisms that determine cyanobacterial bloom structure and toxin production become a target for managing practices [5,6]. This Special Issue, entitled "Advancing Knowledge on Cyanobacterial Blooms in Freshwaters", includes 11 research papers [9][10][11][12][13][14][15][16][17][18][19] and aims to bring together the recent research of multiand interdisciplinary approaches from the field to the laboratory and back again, driven by working hypotheses based on any aspect from ecological theory to applied research on mitigating cyanobacterial blooms.…”