Viral Control of Phytoplankton Populations—a Review¹

Abstract

Phytoplankton population dynamics are the result of imbalances between reproduction and losses. Losses include grazing, sinking, and natural mortality. As the importance of microbes in aquatic ecology has been recognized, so has the potential significance of viruses as mortality agents for phytoplankton. The field of algal virus ecology is steadily changing and advancing as new viruses are isolated and new methods are developed for quantifying the impact of viruses on phytoplankton dynamics and diversity. With this development, evidence is accumulating that viruses can control phytoplankton dynamics through reduction of host populations, or by preventing algal host populations from reaching high levels. The identification of highly specific host ranges of viruses is changing our understanding of population dynamics. Viral-mediated mortality may not only affect algal species succession, but may also affect intraspecies succession. Through cellular lysis, viruses indirectly affect the fluxes of energy, nutrients, and organic matter, especially during algal bloom events when biomass is high. Although the importance of viruses is presently recognized, it is apparent that many aspects of viral-mediated mortality of phytoplankton are still poorly understood. It is imperative that future research addresses the mechanisms that regulate virus infectivity, host resistance, genotype richness, abundance, and the fate of viruses over time and space.

Isolation and Characterization of a Novel Single-Stranded RNA Virus Infectious to a Marine Fungoid Protist, Schizochytrium sp. (Thraustochytriaceae, Labyrinthulea)

“…Viruses and virus-like particles (VLPs) have been discovered in a variety of phytoplankton and bacteria (48,54,64) and have been recognized as important agents in controlling bacterial and algal biomass (4,41,48) and nutrient cycling (17,66) and in maintaining the biodiversity of bacteria and microalgae (5,10,12). So far, more than 13 viruses infecting marine microalgae have been isolated and characterized (5).…”

“…Viruses and virus-like particles (VLPs) have been discovered in a variety of phytoplankton and bacteria (48,54,64) and have been recognized as important agents in controlling bacterial and algal biomass (4,41,48) and nutrient cycling (17,66) and in maintaining the biodiversity of bacteria and microalgae (5,10,12). So far, more than 13 viruses infecting marine microalgae have been isolated and characterized (5). The majority of these viruses are large (100-to 200-nm) double-stranded DNA viruses, and they are either included in the family Phycodnaviridae (5,58,65) or considered most likely to belong to this family based on some characteristics (7,16,23,43,57,62).…”

“…So far, more than 13 viruses infecting marine microalgae have been isolated and characterized (5). The majority of these viruses are large (100-to 200-nm) double-stranded DNA viruses, and they are either included in the family Phycodnaviridae (5,58,65) or considered most likely to belong to this family based on some characteristics (7,16,23,43,57,62).…”

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

“…Especially, coccolithophores are a prominent feature of the late spring bloom, and this has been attributed to their tolerance for high irradiances, lower nutrient requirements and/or ability to utilise organic nitrogen or phosphorus sources (Palenik and Henson, 1997;Leblanc et al, 2009 and references therein). Bloom termination follows when nutrient depletion depresses primary productivity and grazing and viral control catch up with algal growth (Brussaard, 2004;Calbet and Landry, 2004;Behrenfeld, 2010). In reality, this general NE Atlantic spring bloom scenario can be more or less scrambled due to local weather conditions and physical phenomena (Ji et al, 2010), both in the open ocean, where movements of eddies and other water masses can reset succession events (Smythe-Wright et al, 2010), and along continental margins, where vertical mixing resulting from internal tides can bring nutrient-rich deeper water into the euphotic zone (Sharples et al, 2007).…”

Analysis of phytoplankton distribution and community structure in the German Bight with respect to the different size classes

“…This needs time series data where the development of both parameters can be tracked over a longer period, or modeling approaches (e.g., Baretta et al, 1995). Of course, also other parameters like light availability (Loebl et al, 2009), zooplankton grazing (e.g., Calbet and Landry, 2004), or degradation by viruses (Brussaard, 2004;Rhodes et al, 2008) influence phytoplankton biomass development and have to be taken into account.…”