Are the shells of Scrobicularia plana useful for monitoring trace metal pollution events?

The rupture of a mine dam in Aznalcóllar (SW Spain) in April 1998 entailed the contamination of Guadalquivir River and its estuary. To study the ability of bivalve shells to monitor the temporal changes on metal composition in the area, two year old Scrobicularia plana were obtained from two different locations of the estuary (Pantalan highly influenced and Pantoca less influenced) during the year 2000 and 2007. Co, Hg, Mo, Ni and Zn content was measured in shell and soft tissue of S. plana. Metal composition in shells sampled by micromilling and corresponding to the years 1999, 2000, 2006 and 2007 was higher in Pantalan (Co: 5.88 +/- 2.7 microg g(-1); Hg: 0.04 +/- 0.03 microg g(-1); Mo: 0.41 +/- 7.90 microg g(-1); Ni: 37.66 +/- 25.56 microg g(-1) and Zn: 9.19 +/- 8.88 microg g(-1)) than in Pantoca (Co: 3.64 +/- 0.50 microg g(-1); Hg: 0.02 +/- 0.02 microg g(-1); Mo: 4.70 +/- 1.20 microg g(-1); Ni: 7.21 +/- 13.60 microg g(-1) and Zn: 3.90 +/- 1.89 microg g(-1)). A marked temporal decrease was observed for all metals in Pantalan station with concentrations of Co, Hg, Mo, Ni and Zn varying respectively from 7.35 +/- 3.02, 0.05 +/- 0.03, 19.90 +/- 2.40, 70.58 +/- 21.94 and 18.04 +/- 0.98 microg g(-1), in 1999 to 3.07 +/- 1.08, 0.009 +/- 0.001, 2.40 +/- 1.43, 10.11 +/- 3.80 and 1.11 +/- 0.33 microg g(-1) in 2007, indicating that the effect of the mine accident had diminished significantly. Metal content in soft tissues did not follow the same decreasing trend indicating that soft tissues present a different capacity to accumulate metals from the environment. Our results confirm that micromilling shells are a suitable tool to assess bioaccumulation ofcontaminants during the entire life-span of bivalves.

INTERACTIVE EFFECTS OF SALINITY AND TEMPERATURE ON PLANOZYGOTE AND CYST FORMATION OF ALEXANDRIUM MINUTUM (DINOPHYCEAE) IN CULTURE(1).

The factors regulating dinoflagellate life-cycle transitions are poorly understood. However, their identification is essential to unravel the causes promoting the outbreaks of harmful algal blooms (HABs) because these blooms are often associated with the formation and germination of sexual cysts. Nevertheless, there is a lack of knowledge on the factors regulating planozygote-cyst transitions in dinoflagellates due to the difficulties of differentiating planozygotes from vegetative stages. In the present study, two different approaches were used to clarify the relevance of environmental factors on planozygote and cyst formation of the toxic dinoflagellate Alexandrium minutum Halim. First, the effects of changes in initial phosphate (P) and nitrate (N) concentrations in the medium on the percentage of planozygotes formed were examined using flow cytometry. Second, two factorial designs were used to determine how salinity (S), temperature (T), and the density of the initial cell inoculum (I) affect planozygote and resting-cyst formation. These experiments led to the following conclusions: 1. Low P/N ratios seem to induce gamete expression because the percentage of planozygotes recorded in the absence of added phosphate (-P) was significantly higher than that obtained in the absence of added nitrogen (-N), or when the concentrations of both nitrogen and phosphate were 20 times lower (N/20 + P/20). 2. Salinity (S) and temperature (T) strongly affected both planozygote and cyst formation, as sexuality in the population increased significantly as salinity decreased and temperatures increased. S, T combinations that resulted in no significant cyst formation were, however, favorable for vegetative growth, ruling out the possibility of negative effects on cell physiology. 3. The initial cell density is thought to be important for sexual cyst formation by determining the chances of gamete contact. However, the inoculum concentrations tested did not explain either planozygote formation or the appearance of resting cysts.