Feeding of Fragilidium cf. duplocampanaeforme and F. subglobosum on four Dinophysis species: prey specificity, local adaptation and fate of toxins

Abstract

We studied the feeding behaviour of 2 Fragilidium species—F. cf. duplocampanaeforme (strains VGO1120 and VGO692 from NW Iberia and the Mediterranean Sea, respectively), and F. subglobosum (IO97-01, W Iberia)—on Dinophysis acuminata, D. acuta, D. caudata and D. tripos from NW Iberia. Only the Atlantic strain of F. cf. duplocampanaeforme fed upon D. acuminata (2.52 ± 0.48 cells Fragilidium-1 d-1) and D. caudata (0.58 ± 0.32 cells Fragilidium-1 d-1); furthermore, this strain fed weakly on D. tripos (<0.10 cells Fragilidium-1 d-1) and not at all on D. acuta. Neither the Mediterranean F. duplocampanaeforme nor F. subglobosum were observed to ingest Atlantic strains of Dinophysis species. Deleterious effects caused by Fragilidium, namely cell immobilization or even death, were observed in some cases (the D. acuminata and D. caudata cultures). The Atlantic F. cf. duplocampanaeforme that had previously fed on D. acuminata and D. caudata showed low intracellular toxin levels at the end of the exponential growth phase (based on LC-MS). However, extracellular toxin levels were higher in the Dinophysis cultures exposed to the Atlantic F. cf. duplocampanaeforme than in those without Fragilidium (the contrary being true for the toxin amount per cell). Our results indicate that (1) Fragilidium cf. duplocampanaeforme feeds differentially on certain Dinophysis species (in particular D. acuminata and D. caudata), (2) inter-specific and intraspecific differences exist in Fragilidium-Dinophysis predator-prey interactions, (3) the amount of extracellular Dinophysis toxins is enhanced by the presence of Fragilidium, and (4) decreased final yields and higher frequencies of small cells of Fragilidium in mixotrophic cultures.