AME 81:137-148 (2018)  -  DOI: https://doi.org/10.3354/ame01870

ABSTRACT: In the northern coastal area of the Alboran Sea (the most western basin of the Mediterranean Sea), the distribution of plankton at the surface follows complex patterns corresponding to the variability of abiotic (environmental) and biotic factors, including virus-host interactions. To assess these interactions, we measured the abundances of virus-like particles (VLPs) and different microbial virus hosts of the plankton community, including heterotrophic bacteria (HB), cyanobacteria and autotrophic eukaryote pico-, nano- and microplankton (APP, ANP and AMP, respectively). Samplings were carried out in the euphotic zone during 2 contrasting seasonal periods (autumn and spring), in 3 coastal areas of the Alboran basin. Virioplankton abundance varied, ranging from 8.5 × 10⁵ to 2.2 × 10⁷ VLPs ml^-1, covering almost the whole range of variability described for the Mediterranean Sea. The mean VLP to microbial ratio (VMR) was 13.6 and the median was 10.5, although the VMR varied substantially from 1.3 to 44. In autumn, the abundance of VLPs did not correlate with HB, although it correlated positively with Prochlorococcus and Synechococcus and negatively with APP and AMP. In contrast, in spring, VLPs correlated positively with HB and APP and negatively with Synechococcus. These abundance data suggest that not only bacteria but also cyanobacteria could play a relevant role as virus hosts in the Alboran Sea, at least in autumn. The changes in abiotic factors that favor the growth of cyanobacteria vs. HB or vice versa and their possible role in regulating cyanophage to bacteriophage dynamics are further discussed.

KEY WORDS: Virus-like particles · Bacteria · Phytoplankton · Pelagic ecosystem · Mediterranean Sea · Phosphate