Mortality in the oceans: Causes and consequences

Jennifer R. Brum, J. Jeffrey Morris, Moira Décima, and Michael R. Stukel

Full Citation: Brum, Jennifer R., J. Jeffrey Morris, Moira Décima, and Michael R. Stukel. 2014. Mortality in the oceans: Causes and consequences p. 16-48. In P.F. Kemp [ed.], Eco-DAS IX Symposium Proceedings. ASLO. [doi: 10.4319/ecodas.2014.978-0-9845591-3-8.16]

ABSTRACT: Microorganisms dominate the oceans and exert considerable control over fluxes of nutrients, organic matter, and energy. This control is intimately related to the life cycles of these organisms, and whereas we know much about their modes and rates of reproduction, comparably little is known about how they die. The method of death for a microorganism is a primary factor controlling the fate of the nutrients and organic matter in the cell, e.g., whether they are incorporated into higher trophic levels, sink out of the water column, or are recycled within the microbial loop. This review addresses the different sources of mortality for marine microbes including grazing, viral lysis, programmed cell death, and necrosis. We describe each mode of death, the methods used to quantify them, what is known of their relative importance in the ocean, and how these vectors of mortality differentially affect the flow of organic matter in the open ocean. We then conclude with an assessment of how these forms of mortality are incorporated into current numerical ecosystem models and suggest future avenues of research to increase our understanding of the effects of death processes in oceanic food webs.