Impact of phytoplankton bloom magnitude on a pelagic microbial food web

Abstract

ABSTRACT-The impact of phytoplankton bloom magnitude on the microbial food web of the Dutch pelagic coastal zone (Southern Bight of the North Sea) was studied during spring 1993. Data were compared to a study carried out in 1992 at the same location. Light availability and temperature were the key factors for the timing of the diatom spring bloom. Specific algal cell lysis rates during the diatom bloom were always <0.1 d-' Due to sinking of the diatoms no effect of the difference in bloom magnitude between the 2 years on the pelagic microbial food web was detected. A high onset level of nitrate (55 PM) resulted in a dense bloom of the colonial Phaeocystis, with maximum cell numbers of 1.8 X 1 0 ' cells I-'. During the development of the bloom, the pH of the seawater increased from 7.9 to 8.7. The bloom of Phaeocystis declined through cell lysis (up to 0.3 d-'). Due to the enhanced biomass of Phaeocystls the amounts of released algal cellular carbon were high (up to 400 pg C 1-' d-'). Differences in Phaeocystjs bloom magnitude were, as a consequence of algal cell lysls, reflected in bacterial production (up to 90 pg C 1" d-' in 1993) and grazing activity of members of the m~crobial food web. The elevated importance of the microbial food web resulted in a high standing stock of microzooplankton (850 pg C I-') and accumulation of regenerated inorganic nutrients. Calculations on both carbon and nitrogen budgets indicate that most of the Phaeocystis bloom was mineralized within the water column.

Is Ocean Acidification an Open-Ocean Syndrome? Understanding Anthropogenic Impacts on Seawater pH

“…Metabolic-intense ecosystems, such as seagrass meadows, mangroves, salt marshes, coral reefs and macroalgal beds, can support diel changes in pH as high as 1.0 unit (Table 2). Coastal phytoplankton blooms can also modify water column pH significantly, with pH increasing to 8.6-9.0 during phytoplankton blooms (Brussaard et al 1996;Spilling 2007;Dai et al 2008). Conversely, the collapse and subsequent remineralization of phytoplankton blooms can lead to substantial drops in pH, such as a seasonal decline in pH of 0.3-0.4 units reported in bottom waters at Seto Inland Sea, Japan (Taguchi and Fujiwara 2010), and Bohai Sea, China (Zhai et al 2012).…”

Viral lysis of Phaeocystis pouchetii: Implications for algal population dynamics and heterotrophic C, N and P cycling

“…This coupling between algal lysis and bacterial and HNF abundances demonstrated a direct and efficient transfer of organic matter from the algae to bacteria and HNF through viral lysis. Such energy transfer in the microbial food web through viral lysis of phytoplankton has been documented in various studies (for example, Brussaard et al, 1995Brussaard et al, , 1996aBrussaard et al, , 2005aGobler et al, 1997;Bratbak et al, 1998b), and confirms that viral lysates may divert organic matter away from the classical grazer food chain, and rather contribute to sustaining heterotrophic activities in the microbial food web (Fuhrman, 1992).…”

“…Following viral lysis, labile cell contents are released as dissolved organic matter, which may be utilized with high efficiency by heterotrophic bacteria and thus stimulate heterotrophic growth and nutrient cycling (Fuhrman, 1992;Gobler et al, 1997;Bratbak et al, 1998a;Middelboe et al, 2003;Brussaard et al, 1996aBrussaard et al, , 2005aBrussaard et al, , 2007. During decomposition of algal lysates in the microbial food web, N and P and other nutrients in the lysates may become mineralized and released as inorganic forms.…”

Arctic microbial community dynamics influenced by elevated CO&lt;sub&gt;2&lt;/sub&gt; levels

“…Potential restructuring of the phytoplankton community (classes, species and cell size; Falkowski et al, 1998;Boyd and Doney, 2002) as a result of ocean acidification will have direct consequences for grazer communities and organic carbon flow. It may also influence the dominance of grazing over other loss processes such as viral lysis, and consequently the cycling of energy and biogeochemically relevant elements, the ratio of production and respiration of the ocean and the efficiency of the biological pump (Brussaard et al, 1996Ruardij et al, 2005;Suttle, 2007). Phytoplankton that are consumed by grazers are channeled to higher trophic levels, whereas viral lysis directly forces the food web towards a more regenerative pathway Suttle, 2007).…”