Effects of increases in salinity on phytoplankton in the Broadwater of the Myall Lakes, NSW, Australia

Abstract

The Broadwater of the Myall Lakes system is highly susceptible to cyanobacterial bloom formation after heavy rain events. During prolonged low flow periods, saline intrusion from the lower Myall River increases salinity levels and effectively controls some bloom forming algal taxa. To assess the effect of low-to-moderate increases in salinity (up to 4 ppt) on phytoplankton chlorophyll a, cell abundance, diversity and assemblage structure, salinity enhancement experiments were conducted on Broadwater samples collected in June 2005 (salinity 1.5 ppt), October 2005 (4 ppt) and January 2006 (12 ppt). Natural phytoplankton assemblages were incubated in the laboratory for 10 days, under different treatments of salinity (no addition, +2 ppt, + 4 ppt) and nutrient conditions (no addition, excess N+P). The greatest impact of salinity enhancement in N+P enriched samples was observed in June (1.5-5.5 ppt); chlorophyll a was significantly reduced in samples with the highest salinity treatment, and the taxon most negatively affected by an elevation in salinity to 5.5 ppt was Anabaena circinalis. Taxonomic richness and diversity (Shannon-Wiener index) were unexpectedly significantly higher at 5.5 ppt than at 1.5 ppt. This result, in part, explains the observed significant differences in phytoplankton assemblage structure over this salinity range. In October, the main effect of elevating salinity levels from 4 ppt to 8 ppt was a reduction in the abundance of chlorophytes, particularly Scenedesmus. Phytoplankton samples that were collected when the lake salinity level was 12 ppt were little affected by salinity increases of 2 ppt and 4 ppt, most likely because field samples were already relatively high in salt content. We suggest that further investigations focus on phytoplankton responses to salinity under a range of nutrient regimes that are common to coastal lakes.

Resilience of estuarine phytoplankton and their temporal variability along salinity gradients during drought and hypersalinity

“…6, CCA) whereas DIN:DIP added little to the explained variability. This confirms a suggestion made by Redden and Rukminasari (2008), that enriched treatments of different DIN:DIP ratios do not lead to different taxonomic diversity, however, different salinity treatments result in variations in taxonomic diversity. In our study, an increase in salinity had a stronger effect on the algal community composition than nutrients (N and P).…”

Temporal and spatial variability in the phytoplankton community of Myall Lakes, Australia, and influences of salinity

“…Only a few eukaryotic taxa, including the chlorophyte genera Oocystis and Cosmarium, the diatom Thalassiosira and the dinoflagellate Gymondinium, tended to persist above an electrical conductivity of 5 mS cm -1 , although at reduced abundances. Redden & Rukminasari (2008) also report a reduction in chlorophyte abundance in Bombah Broadwater phytoplankton communities after salinity was increased from 4 to 8 g l -1 . Salinity has been used to explain the greatest variation in diatom species composition and abundance in the Murray River (Tibby & Reid, 2004), and negative correlations between salinity and diatom richness have been shown for Victorian and West Australian inland waters (Blinn & Bailey, 2001;Blinn et al, 2004).…”

“…Winder & Cheng (1995) found that salinities of 5-7 g l -1 (7-10 mS cm -1 ) inhibited the growth of Anabaena circinalis, whilst Otsuka et al (1999) reported net growth of Microcystis aeruginosa at salinities up to 7 g l -1 or about 10 mS cm -1 . Redden & Rukminasari (2008) also found that Anabaena circinalis from Bombah Broadwater were negatively affected by increased salinity. Only a few eukaryotic taxa, including the chlorophyte genera Oocystis and Cosmarium, the diatom Thalassiosira and the dinoflagellate Gymondinium, tended to persist above an electrical conductivity of 5 mS cm -1 , although at reduced abundances.…”

Interactions between plankton and cyanobacterium Anabaena with focus on salinity, growth and toxin production

“…Anabaena occurs both in freshwater and brackish water, but in our study the growth of Anabaena was higher in Reposaari, the freshwater area. Redden and Rukminasari (2008) showed that a slight increase in salinity (2%) had a strong negative effect on cell numbers of Anabaena. The differences between sites highlight the importance of repeating experiments in different locations in order to make general conclusions.…”