Abstract
Coastal California experiences large-scale blooms of Synechococcus cyanobacteria, which are predicted to become more prevalent by the end of the 21st century as a result of global climate change. This study investigated whether exposure to bloom-like concentrations of two Synechococcus strains, CC9311 and CC9902, alters fish behaviour. Black perch (Embiotoca jacksoni) were exposed to Synechococcus strain CC9311 or CC9902 (1.5 × 10(6) cells ml(-1)) or to control seawater in experimental aquaria for 3 days. Fish movement inside a testing arena was then recorded and analysed using video camera-based motion-tracking software. Compared with control fish, fish exposed to CC9311 demonstrated a significant preference for the dark zone of the tank in the light-dark test, which is an indication of increased anxiety. Furthermore, fish exposed to CC9311 also had a statistically significant decrease in velocity and increase in immobility and they meandered more in comparison to control fish. There was a similar trend in velocity, immobility and meandering in fish exposed to CC9902, but there were no significant differences in behaviour or locomotion between this group and control fish. Identical results were obtained with a second batch of fish. Additionally, in this second trial we also investigated whether fish would recover after a 3 day period in seawater without cyanobacteria. Indeed, there were no longer any significant differences in behaviour among treatments, demonstrating that the sp. CC9311-induced alteration of behaviour is reversible. These results demonstrate that blooms of specific marine Synechococcus strains can induce differential sublethal effects in fish, namely alterations light-dark preference behaviour and motility.
Highlights
Phytoplanktonic organisms are major primary producers that are essential components of aquatic ecosystems
Other toxins produced by phytoplanktonic organisms are domoic acid, saxitoxin and microcystins
None of the variables analysed were significantly different between the two experimental sets of fish (ES1 and ES2) for any of the three treatments; data from ES1 and ES2 were pooled for subsequent analyses
Summary
Phytoplanktonic organisms are major primary producers that are essential components of aquatic ecosystems. In certain environmental conditions, including anthropogenic pollution, certain species of phytoplankton can achieve dense populations that may be harmful for other aquatic life due to their production of toxic secondary metabolites and/or generation of hypoxic or anoxic conditions. These phenomena, known as harmful algal blooms, can be caused by many diverse. Other toxins produced by phytoplanktonic organisms are domoic acid (a neurotoxin produced by some diatoms of the genus Pseudo-nitzschia), saxitoxin (a neurotoxin produced by some marine dinoflagellates and freshwater cyanobacterial strains) and microcystins (hepatotoxins produced almost exclusively by some freshwater cyanobacterial strains; Landsberg, 2002; Salierno et al, 2006; Bakke and Horsberg, 2007; O’Neil et al, 2012; Hackett et al, 2013). As toxin-producing phytoplanktonic species can be very abundant in certain marine environments, they have the potential to affect marine life negatively
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