Marine microalgae attack and feed on metazoans

Abstract

Free-living microalgae from the dinoflagellate genus Karlodinium are known to form massive blooms in eutrophic coastal waters worldwide and are often associated with fish kills. Natural bloom populations, recently shown to consist of the two mixotrophic and toxic species Karlodinium armiger and Karlodinium veneficum have caused fast paralysis and mortality of finfish and copepods in the laboratory, and have been associated with reduced metazooplankton biomass in-situ. Here we show that a strain of K. armiger (K-0688) immobilises the common marine copepod Acartia tonsa in a densitydependent manner and collectively ingests the grazer to promote its own growth rate. In contrast, four strains of K. veneficum did not attack or affect the motility and survival of the copepods. Copepod immobilisation by the K. armiger strain was fast (within 15 min) and caused by attacks of swarming cells, likely through the transfer and action of a highly potent but uncharacterised neurotoxin. The copepods grazed and reproduced on a diet of K. armiger at densities below 1000 cells ml, but above 3500 cells ml À 1 the mixotrophic dinoflagellates immobilised, fed on and killed the copepods. Switching the trophic role of the microalgae from prey to predator of copepods couples population growth to reduced grazing pressure, promoting the persistence of blooms at high densities. K. armiger also fed on three other metazoan organisms offered, suggesting that active predation by mixotrophic dinoflagellates may be directly involved in causing mortalities at several trophic levels in the marine food web.

Ichthyotoxic Karlodinium veneficum (Ballantine) J Larsen in the Upper Swan River Estuary (Western Australia): Ecological conditions leading to a fish kill

“…A number of Karlodinium species have recently been described from Australia (de Salas et al, 2005,2008), but hemolytic karlotoxins were only present in K. veneficum (Mooney et al, 2009). However, immobilization and ingestion of copepods by K. armiger suggests uncharacterized toxins may be present in other species of the Karlodinium genus (Berge et al, 2012). …”

Dinoflagellates: Ecological Approaches and Spatial Distributions in Malaysia Waters

“…These dinoflagellates are armored with peduncle that helps their attachment to fish organs like gills and fins where ingestion happens gradually. Unfortunately, this can be lethal when toxic microalgae attack speeds up the toxin release upon contact with the ruptured gills [71]. Recent cases of fish killing were documented in Tanjung Kupang, Johor that involved economical loss to 250 fishermen and fish farmers due to Karlodinium australe [53,72].…”

Assembling the protist puzzle

“…Intriguingly, mixotrophs can sometimes utilize organisms much larger than themselves for their nutrition. Indeed, working together in groups, some dinoflagellates can even attack and consume copepods (Berge et al 2012); while other dinoflagellates have been shown to be detrital feeders using copepod fecal pellets as a food source (Poulsen et al 2011).…”

“…Indeed, working together in groups, some dinoflagellates can even attack and consume copepods (Berge et al. ); while other dinoflagellates have been shown to be detrital feeders using copepod fecal pellets as a food source (Poulsen et al. ).…”