The dominance of cyanobacteria in Mediterranean hypereutrophic lagoons: a case study of Cabras Lagoon (Sardinia, Italy)

Abstract

SUMMARY: An intense proliferation of cyanobacteria in Cabras Lagoon was investigated over a period of two years (July 2007 to June 2009. The influence of environmental and meteorological parameters in the lagoon on temporal variations in cyanobacteria orders was assessed. For 17 months, Chroococcales was the only cyanobacterial order observed in the lagoon. Cyanobium-type cells (Reynolds functional group Z) were the most abundant phytoplankton taxon during this period. In the following months, drastic changes in the cyanobacteria assemblages occurred simultaneously with constant, intense rainfall that led to a sudden drop in the lagoon's salinity. The succession of autumn-winter Oscillatoriales (Planktothrix sp. and Pseudanabaena catenata; Reynolds functional group S1) and late spring growth of Nostocales (Aphanizomenon gracile, Aphanizomenon aphanizomenoides, and Anabaenopsis circularis; Reynolds functional group H1) was monitored. Canonical Correspondence Analysis was carried out to quantify the influence of environmental variables, and indicated strong relationships between Chroococcales and salinity, Oscillatoriales and higher values of SRP and the DIN/SRP ratio, and Nostocales and lower nutrient concentrations, the DIN/SRP ratio and salinity.Keywords: cyanobacteria, phytoplankton, coastal lagoons, eutrophication, Sardinia, Mediterranean Sea. RESUMEN: Dominancia de las cianobacterias en lagunas mediterráneas hipertróficas: el caso de la laguna de Cabras (Cerdeña, Italia). -Durante dos años (julio 2007-junio 2009) se monitoreó una proliferación intensa de cianobacterias en la laguna de Cabras, así como los parámetros ambientales y climáticos que determinaron sus variaciones temporales. Durante 17 meses, Chroococcales fue el único orden de cianobacterias en la laguna, del cual células similares a Cyanobium (grupo funcional Z según Reynolds) fueron las más importantes en cuanto a abundancia. En los meses siguientes, las cianobacterias sufrieron cambios drásticos, que ocurrieron simultáneamente con lluvia constante e intensa que dio lugar a una caída brusca de la salinidad de la laguna. Se monitoreó también la sucesión de Oscillatoriales en otoño-invierno (Planktothrix sp. and Pseudanabaena catenata; grupo funcional S1 según Reynolds) y el crecimiento en primavera de Nostocales (Aphanizomenon gracile, Aphanizomenon aphanizomenoides, y Anabaenopsis circularis; grupo funcional H1 según Reynolds). Análisis de Correspondencia Canónica permitieron cuantificar la influencia de las variables ambientales, indicando una estrecha relación entre Chroococcales y salinidad, Oscillatoriales y altos niveles de SRP y proporción DIN/ SRP, y Nostocales y bajos niveles de nutrientes, proporción DIN/SRP y salinidad.

Long-term phytoplankton dynamics in a Mediterranean eutrophic lagoon (Cabras Lagoon, Italy)

“…From 2007, the greater stability of these parameters for more than a year permitted the persistence of some species of Cyanophyceae, which are well adapted to those lagoon conditions (salinity 415%; N/P59; DIN 57 mmol N L -1 ; RP 51.16 mmol P L -1 ). Only in the autumn of 2008, when the strong rainfall began, the phytoplankton composition become more variable, with an increase in biodiversity, in the context of a sudden decline in salinity and a strong increase in nutrients (Pulina et al 2011). The stability of environmental conditions appears essential in controlling Cyanophyceae development in a large number of cases (Sorokin et al 1996;Scheffer et al 1997;Chomérat et al 2007).…”

“…Moreover, our data regard only a decade (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009), which is a long study period in respect to the majority of Mediterranean lagoons but that may be not enough to assess the tendencies of In the light of this consideration, and despite this, at least some trends can be highlighted, especially for the biotic component: the shift in the peak cellular density from the summer-autumn season, observed from 1999 to 2002, to the winter-spring season in the following years; the contemporaneous reductions in the Chl a concentration and phytoplanktonic cell sizes from 1999 to 2008; and the changes in the structure of the phytoplankton assemblage from a more differentiated class composition in 1999-2002 to the subsequent dominance of the Cyanophyceae. During 2009, immediately after a period of strong and persistent rainfall that deeply altered the ecological framework of the lagoon, all these tendencies were interrupted (Pulina et al 2011). In Sardinia, the autumn of 2008 was the wettest for 40 years (http://www.regione.sardegna.it/j/v/491?s¼11 5820&v¼2&c¼1489&t¼1).…”

“…In Cabras Lagoon, phytoplankton is the main primary producer, and anthropogenic disturbances and meteoclimatic factors appear to play important roles in controlling the phytoplankton assemblages and abundances in individual years (Sechi et al 2006;Padedda et al 2010;Pulina et al 2011). To achieve our objective, data for phytoplankton and environmental parameters were considered across several years, from 1999 to 2009.…”

“…In relation to the muddy and sandy sediments at the bottom of the lagoon, the macroalgae and seagrass components are very scarce and phytoplankton is absolutely the main primary producer (Sechi et al 2006;Magni et al 2008;Pulina et al 2011).…”

Cyanobacterial dynamics and toxins concentrations in Lake Alto Flumendosa, Sardinia, Italy

“…Indeed, cyanobacteria have become dominant in many reservoirs over time Lugliè, 1992, 1996;Aktan et al, 2009;Pulina et al, 2011). However, only a few studies have assessed the presence of CTX, namely MCs (Messineo et al, 2009;Sulis et al, 2014;Mariani et al, 2015).…”