Microscopic agents of death

Marine microbes are subject to attack by a range of organisms with voracious appetites and a variety of feeding strategies, but many are also consumers.

Viruses

Microscopic viruses are the most abundant biological agents in antarctic waters, with numbers up to four million per millilitre. They inject their DNA or RNA and take over the cell metabolism of the host resulting in viral multiplication and eventual cell rupture. In temperate marine food webs, viruses have been shown to be major agents of death for bacteria and phytoplankton.

Protozoa

  • Puncturers — Many dinoflagellates and ciliates pierce the prey cell with a peduncle, digesting and absorbing its contents.
  • Engulfers — cover prey cells with their cytoplasm and digest them. This is the prime strategy for amoeboid cells but some other cells, notably dinoflagellates, can project a veil of cytoplasm (pallium) externally through their cell wall to enclose prey. They can sometimes successfully engulf cells larger than themselves.
  • Ingesters — feeding currents created by cilia or flagella draw prey cells to the predator where they are captured and ingested e.g. ciliates and choanoflagellates.

Mesoplankton

  • Biters — copepods
  • Swallowers — salps
  • Crushers — krill

Microbes have evolved various strategies for avoiding or resisting these modes of attack, giving them a competitive advantage.

(based on a talk by V. Smetacek)