Polysiphonia subtilissima is originally a marine macroalga with a wide tolerance for salinity and therefore present on nearly all the coastlines of the planet. However, the transition of P. subtilissima toward freshwater ecosystems has been noticed worldwide, with numerous authors recording oligohaline and intertidal populations of notable size, although only three localities (Florida, Jamaica and Spain) with truly freshwater populations have been registered to date. This paper reports large populations of P. subtilissima in transitional, oligohaline and freshwater ecosystems of the Adriatic Sea Basin (Croatia, Southeast Europe). The alga was recorded in salinity ranging from 0.42 to 4.59 in the waters of the Neretva River Valley, and at 18.2 in transitional waters in the Zrmanja River. Along with P. subtilissima, the freshwater tropical red alga Compsopogon caeruleus has been recorded in the Neretva River Valley, being the first record of this species for Croatia and SE Europe. This particular combination of species has previously been recorded in freshwater localities only in Florida, Jamaica and Spain. Measured environmental parameters and species composition were analysed using canonical correspondence analysis and Gaussian response model, which showed that both species prefer waters with temperatures above 20 °C, high water conductivity, pH values above 7.5, and elevated water turbidity.
Two new sites with benthic freshwater alga Hydrurus foetidus (Villars) Trevisan have been discovered in Dinaric Ecoregion of Croatia. The sites are located in two karst watercourses: Kupa River and Slušnica River. Both sites are non-shadowed aquatic habitats, with developed vegetation characteristic for clear, running waters. The alga was found during summer months at its disintegration stage, and during autumn at the beginning of its growing stage. In the Kupa River, incrusted calcium carbonate was found within the thalli of H. foetidus. After the first known record in Bijela Rijeka River from 2015, our findings represent the second and the third known localities of this species in Croatia. Even though the vegetation composition indicates high ecological status of the sites, future anthropogenic impacts and climatic changes could become a threat to this underexplored species in Croatia. Dva nova nalaza bentičke slatkovodne alge Hydrurus foetidus (Villars) Trevisan zabilježena su u dinarskoj ekoregiji u Hrvatskoj. Nalazi su locirani u dva krška vodotoka: rijeka Kupa i Slušnica. Na oba istražena nalazišta alga raste na nezasjenjenim staništima s vodenom vegetacijom makrofita karakterističnom za čiste tekuće vode. Alga je uočena tijekom ljeta u fazi raspadanja talusa te tijekom jeseni u početnoj fazi rasta. Na talusu jedinki iz rijeke Kupe primijećen je inkrustat kalcijevog karbonata. Nakon nalaza u Bijeloj rijeci 2015. godine, ovi nalazi predstavljaju drugi i treći nalaz ove rijetke vrste u Hrvatskoj. Iako sastav vegetacije ukazuje na vrlo dobro ekološko stanje na oba nalazišta, mogući antropogeni pritisci i klimatske promjene u budućnosti mogli bi ugroziti ovu nedovoljno istraže-nu vrstu u Hrvatskoj.
As many as 963 herbarium sheets featuring 76 aquatic plant taxa from the ZA collection were digitised and published online through the Virtual Herbarium. Aquatic plants have been collected over a period of 176 years, with three peaks (second decade of the 20th century, in the 1940s and 1950s, and in the current decade). Most of the specimens were collected in Croatia and a smaller number in neighbouring and geographically close countries. The importance of the collection is expressed through the specimens of many rare and threatened species, because it represents the only evidence of their presence in Croatia (the regionally extinct Caldessia parnassifolia, as well as Luronium natans, Callitriche platycarpa, C. truncata, C. hermaphroditica, Potamogeton alpinus, P. compressus, P. polygonifolius, Nuphar × spenneriana and Sparganium minimum). The collection in ZA is a valuable source of data about the historical and recent distribution of aquatic plants that constitute a foundation for the estimation of distribution changes, threat assessment and conservation policies.
A small population of the circumholoarctic species Glaux maritima L. (Primulaceae) was discovered in the Mediterranean part of Croatia, on the bank of the River Zrmanja. This is the first record of G. maritima in SE Europe, and the third record in the Mediterranean, apart from in Spain and the Asian part of Turkey. It was found on the open riverbank within sub-halophytic vegetation, forming a small population of several dozen erect stems, most probably clonally propagated. The site is characterized by a periodic intrusion of seawater. We propose to classify this species as critically endangered (CR) on a national level due to the small population size and the fragile habitat, which requires active protection and conservation.
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