. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 208 M. S. DAVIES ET 0 * 0 08 0 m 03 80 I M A Otillty o iX -'i ! ?40 I 1 20 2 3 04 06 Log n+1 [Ca] (mM) Figure 12. Motility response of strain III,, (pre-incuhated at By = 0, B„ = 20 /jT for at least 3 months) to external [Ca] in EMF experi- ments in which electrical equipment was set to give ion cyclotron reso- nance conditions (By = 0, Bh = ^T, Bh,, = /jT peak-peak at 16 Hz), but the coils were not energized. Unfilled circles = EMF-ex- posed; filled circles = sham-exposed;
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 208 M. S. DAVIES ET 0 * 0 08 0 m 03 80 I M A Otillty o iX -'i ! ?40 I 1 20 2 3 04 06 Log n+1 [Ca] (mM) Figure 12. Motility response of strain III,, (pre-incuhated at By = 0, B„ = 20 /jT for at least 3 months) to external [Ca] in EMF experi- ments in which electrical equipment was set to give ion cyclotron reso- nance conditions (By = 0, Bh = ^T, Bh,, = /jT peak-peak at 16 Hz), but the coils were not energized. Unfilled circles = EMF-ex- posed; filled circles = sham-exposed; n = 3 in each case. cell density and position in the cell-cycle, and assessing the distance and direction moved by diatoms militates against the potential of diatoms as a useful model for EMF effects. However, the increase (compared to paired controls) in pop- ulation motility exhibited by a significant proportion of EMF-exposed diatoms (all strains) on agar at ion cyclotron resonance conditions indicates that diatoms are susceptible to the effects of EMFs, but only when they have experienced a defined EMF environment prior to experimentation. Sig- nificant increases in motility of EMF-exposed over sham- exposed diatoms were observed in single experiments (Figs. 8-10). although again only where diatoms had been ""pre- incubated" in specific EMFs. The abolition of the effect when the EMF-producing coils were disconnected (Fig. 12) gives clear evidence for the role of extraneous fields in producing the effect, and the abolition at even harmonics (Figs. 13 and 14) does not rule out the presence of a fre- quency window. Blackman el al. (1985, 1990) and Leal et al. (1986) reported EMF effects that were modulated by the intensity of the geomagnetic field. In our experiments we effectively modified the Earth's field to create defined condi- tions (Bh s Bh used in the experiments at ion cyclotron resonance conditions) during diatom growth, as originally suggested by Sm
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