Planktonic marine copepods and harmful algae

• Planktonic copepods are major grazers of harmful algae (HA) in the sea.
• Copepods are major entry points for vectorial intoxication of pelagic food webs with HA toxins.
• This paper reviews copepod:HA grazing studies primarily over the last decade.
• It examines the extent to which HA toxins are copepod grazing deterrents, selective feeding on HA, impact of grazing on HA bloom development, and other issues.
• The review also focuses on biogeographic aspects of copepod:HA grazer interactions.

Marine planktonic copepods are important grazers on harmful algae (HA) species of phytoplankton, and copepods are major entry points for vectorial intoxication of pelagic food webs with HA toxins. Previous reviews (Turner and Tester, 1997, Turner et al., 1998a and Turner, 2006) summarized information on HA interactions with zooplankton grazers, and vectorial intoxication of pelagic food webs, up through approximately 2005. Accordingly, this review will address primarily studies published during the last decade. It will concentrate on generic issues in the developing field of HA:grazer interactions, such as the extent to which HA toxins serve as copepod grazing deterrents, induction of HA grazing deterrents by exposure to copepods, copepod selective feeding to avoid ingesting HA taxa versus non-selective feeding on HA taxa, possible biogeographic aspects of the effects of HA toxins on copepods, impact of copepod grazing on HA bloom development and termination, the role of copepods as entry points for vectorial intoxication of pelagic food webs with HA toxins, and possible reasons and remedies for the highly-variable and conflicting results reported for many studies of copepod grazing on various HA species.