The development of epilithic cyanobacteria communities in a Mediterranean calcareous stream in the province of Murcia (SE Spain) was studied during the course of one year in an attempt to clarify the environmental variables that influence the production of microcystins. The predominant cyanobacteria were species of Rivularia, which formed conspicuous colonies throughout the year. Seasonally, other species were abundant: Schizothrix fasciculata, Tolypothrix distorta and Phormidium splendidum. All the species collected produced microcystins to a varying degree (up to five varieties), while the benthic community as a whole produced concentrations as high as 20.45 mg m −2 . At the same time, the presence of microcystins dissolved in water was confirmed. Among environmental variables, air temperature and silicate content were positively and strongly correlated with total microcystins, while nitrite, nitrate, orthophosphate, calcium and flow were negatively correlated with them. Dissolved microcystins were negatively correlated with microcystin LR, P.A.R. and total phosphorus and positively with rainfall. The production of microcystin YR seems to be regulated by different factors from those regulating the other main varieties (microcystin LR and microcystin RR). The data obtained indicate that all the tested benthic cyanobacteria produced microcystins in this shallow calcareous stream, which may contribute to their predominance in the prevailing conditions. The accumulation of microcystins in mucilaginous colonies of other groups of algae poses new questions concerning the possible ecological function of these compounds and needs further study.

Microcystins (MCs) are potent hepatotoxins, and their presence in water bodies poses a threat to wildlife and human populations. Most of the available information refers to plankton, and much less is known about microcystins in other habitats. To broaden our understanding of the presence and environmental distribution of this group of toxins, we conducted extensive sampling throughout Spain, under a range of conditions and in distinct aquatic and terrestrial habitats. More than half of the tested strains were toxic; concentrations of the hepatotoxin were low compared with planktic communities, and the number of toxic variants identified in each sample of the Spanish strains ranged from 1–3. The presence of microcystins LF and LY (MC-LF and MC-LY) in the tested samples was significant, and ranged from 21.4% to 100% of the total microcystins per strain. These strains were only detected in cyanobacteria Oscillatoriales and Nostocales. We can report, for the first time, seven new species of microcystin producers in high mountain rivers and chasmoendolithic communities. This is the first report of these species in Geitlerinema and the confirmation of Anatoxin-a in Phormidium uncinatum. Our findings show that microcystins are widespread in all habitat types, including both aerophytic and endolithic peat bogs and that it is necessary to identify all the variants of microcystins in aquatic bodies as the commonest toxins sometimes represent a very low proportion of the total.

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As part of an extensive study of the caves in the Province of Alicante (SE Spain), the distribution of cyanobacteria and physical data for the Gelada Cave are presented. This cave is 9.4 m deep, 0.9 to 5.0 m high, 1.2 m wide, and is located in a karst region. Photon flux density, relative humidity, and temperature were measured, and the environmental ranges of conditions where growth occurred fluctuated between 0.0008-0.06 mE.m 22 s 21 , 55.0-95.0% and 5.4-18.0 uC, respectively. All the microorganisms determined from the Gelada Cave were cyanobacteria. Other frequently observed groups in caves, such as Bacillariophyta and Chlorophyta, were not detected because the cave was too weakly illuminated and dry. Cyanobacteria were found to be grouped as blue, brown, green, or gray patina according to the sampling sites and their constituent organisms. The primary common stress factor on the distribution of algal communities in the Gelada Cave is light shortage, followed by humidity, lack of nutrients, and temperature. Twenty-two epilithic cyanobacteria were identified, ten of which have not been previously reported in caves. The species studied are included in the Chroococcales order (77.30%), followed by the Oscillatoriales order (13.60%) and by the Nostocales (4.55%) and Stigonematales (4.55%) orders. The extreme values of the environmental parameters are presented for each taxon in this cave. RESULTS AND DISCUSSION The mean relative humidity in the Gelada Cave was 81.0% in both summer and winter. Values ranging between A. Martínez and A.D. Asencio-Distribution of cyanobacteria at the Gelada Cave (Spain) by physical parameters.

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