| In this paper, we confirmed that Alexandrium species might be capable ofproducing toxins, other than PSP, by the investigation of the effects of 11 strains ofAlexandrium species: A. lusitanicum,A. minutum,A. catenella and A. tamarense(ATHK, AT5-1, AT5-3, ATCI02, ATCI03, AT-6), on egg hatching success of A.irradians and the population of B. plicatilis. Our study showed that the egg hatching success of A. irradians was inhibitedsignificantly exposed to 8 strains of Alexandrium species: A. lusitanicum,A.minutum,A. catenella and A. tamarense (ATHK, AT5-1, AT5-3, ATCI02, ATCI03),with a likewise inhibition exposed to non-PSP producers: A. sp1 and A. sp2. Thedissolved PSP toxins standard (STX) had no such inhibition on egg hatching success.The A. tamarense (ATHK) was chosen as an assay strain to further study. Theresults indicated that the inhibition was density-dependent. Observation by anoptical microscope and transmission electron microscope (TEM), we found thatexposing the eggs to A. tamarense strain ATHK, at the stage of gastrulae, the embryocavity was not able to present in time; some cells in embryo swelled up, the organellesuch as mitochondrion lysed and multi-nucleus cell observed. The ATHK cells alsodecreasing the survival of the embryos of A. irradians, and induced malformation. Itwas likely that some toxic substance might change the osmosis of cell membrane inembryo resulting in the cell swelling up and the abnormal metabolism. Exposing rotifer populations to each of 11 Alexandrium strains as the same aboverevealed that the (non-PSP) A. tamarense (AT-6) and two other PSP-producing algae: IA. lusitanicum, A. minutum, did not appear to adversely impact rotifer populations.Rotifers exposed to these three strains were able to maintain their population numbers,and in some cases, increase them. In contrast, the remaining 8 algal strains (A.catenella, A. tamarense strains ATHK, AT5-1, ATCI02, ATCI03; also non-PSPproducers: A. sp1, A. sp2) all had adverse effects on the rotifers. The respectivemean LT50 for rotifers populations exposed to these 8 strains at the density of2000cells/ml was significantly longer than that to non-exposed "starvation group".Experiments to determine ingestion rates for the rotifers, based on changes in theirChlorophyll a content, showed that the rotifers could feed on A. lusitanicum, A.minutum and A. tamarense (AT-6), but could graze to little or no extent upon algalcells of the other 8 strains. The effects on rotifers exposed to different cell densities,fractions, and growth phases of algal culture of A. tamarense were respectivelycompared. It was found that only the whole algal cells had lethal effects, withstrongest impact being shown by the early exponential growth phase of A. tamarense.The results indicated that some toxic mechanism(s), other than PSP, present in wholealgal cells, might be responsible for the adverse effects of the exposed rotifers. Exposing eggs of A. irradians to the other algal species: P. donghaiense, P. globosa,P. micans and H. akashiwo on the egg hatching success, revealed that H. akashiwohad also an inhibition on the egg hatching success. Observation under an opticalmicroscope and TEM, it indicated that the toxic mechanism significantly differedfrom that of A. tamarense. The H. akashiwo cells attached to the membrane of thetrochophore larvae preventing them from swimming freely. The attachment andadherence between algal cells and embryos might stimulate the release or transfer ofsome toxic substances. The effects on other early development of A. irradiansexposed to the alga H. akashiwo were also performed. It was found that the algalcells could inhibit the swimming activity of D-shaped larvae and decreased thesurvival of eye-spot larvae. Exposing rotifer populations to the other species as the same above showed that H.akashiwo appeare...
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