Variability of planktonic and epiphytic vibrios in a coastal environment affected by Ostreopsis blooms

Abstract

Vibrios include several pathogenic bacteria that occur in aquatic environments. The presence of Vibrio has been assessed in many ecosystems by culture-based techniques. However, little is known on the contribution of Vibrios in the sea, especially in areas subject to harmful algal blooms. A preliminary study in Sant Andreu de Llavaneres beach (NW Mediterranean) showed the presence of some Vibrio species during a recurrent bloom of the harmful benthic dinoflagellate Ostreopsis cf. ovata. In order to establish the importance of Vibrios in a coastal area of the NW Mediterranean and to study the association with the dinoflagellate, we conducted a sampling monitoring for one year to quantify the concentration of Vibrios both in the water (free-living and attached to particles) and in the epiphytic community of macroalgae. The aims were 1) to evaluate the relative abundance of Vibrio in the epiphytic and in the planktonic bacterial community, 2) to assess the percentage of free-living and attached Vibrios in the planktonic community, and 3) to determine whether the presence of Vibrios is associated with the blooms of the toxic dinoflagellate Ostreopsis or with other environmental parameters. For this purpose, a CARD-FISH molecular probe was applied for the specific detection of bacteria belonging to the genus Vibrio. Cells were quantified and the abundance of both particles and bacteria attached to particles were assessed. The maximum Vibrio concentration (1.3x104 cells ml^–1 and 1.4x10⁶ cells g^–1 FW, for planktonic and epiphytic samples, respectively) was detected in September. Free-living Vibrios contributed 0.38±0.24% to the total free-living planktonic community and 1.12±0.28% to the epiphytic bacterial community. However, their contribution was particularly high in the planktonic community attached to particles (17.37±20.49%). Although in the planktonic community Vibrio was found preferentially free-living (82.63±20.01%), particles are a niche for Vibrios, since in particles Vibrios may represent up to 72% of the total attached bacterial community. Abundance of planktonic Vibrio was correlated with Ostreopsis concentration and it is likely that they play a role in the wound infections suffered by beach users during the bloom.