Harmful Algae Interactions with Marine Planktonic Grazers

Abstract

Toxins from harmful algae (HA) can cause shellfish toxicity and become accumulated in and transported through benthic and pelagic marine food webs by trophic interactions. In pelagic food webs, this often causes harmful effects on upper-trophic-level consumers such as marine mammals, seabirds and humans (Turner and Tester 1997; Turner et al. 1998). Effects of HA toxins on their primary grazers, zooplankton and planktivorous fish are variable, in some cases causing deleterious effects on grazers, but in others having little or no obvious effects. Such variability likely relates to different concentrations of different toxins having different effects on different grazers. Just because some phytoplankters are toxic does not mean that toxins necessarily evolved to repel grazers. The numerous documented cases where phycotoxins have minimal effects on grazers suggest that toxicity may be coincidental, or that these chemicals may have evolved for other reasons, such as nitrogen storage, bioluminescence, chromosome structural organization, pheromones for induction of sexuality, or they may be vestigial remnants of archaic pathways for nucleic acid biosynthesis (Cembella 2003). Previous reviews (Turner and Tester 1997; Turner et al. 1998) summarized information on interactions between toxic phytoplankton and their zooplanktonic grazers published prior to about the mid 1990s. Also, Turner et al. (2002) reviewed information on grazer interactions with Phaeocystis, published prior to 2002. Most previous information on HA grazer interactions dealt with copepods. There have been considerable advances within the last decade on grazer interactions with harmful algae, including not only copepods and other mesozooplankton (metazoans >200 μm in longest dimension), but also microzooplankton (mostly protists <200 μm in longest dimension). This recent information will be the focus of the present review, with citation of the aforementioned reviews for most studies published prior to