Feeding preferences of the endemic gastropod Astraea latispina in relation to chemical defenses of Brazilian tropical seaweeds

Seaweed preference by the Brazilian endemic gastropod Astraea latispina was examined in the laboratory to evaluate the role of secondary metabolites in determining food choice. Of three species of seaweeds examined, Plocamium brasiliense was highly preferred; less so were Sargassum furcatum and Dictyota cervicornis were preferred less. Extracts and/or pure major metabolites of the two potentially chemically-defended seaweeds (P. brasiliense and D. cervicornis) were tested as feeding deterrents against A. latispina. Algal extract assays demonstrated that three concentrations of crude organic extract of the red alga P. brasiliense (50%, 100%: natural concentration, and 200% of dry weight: dw) did not affect feeding of this gastropod. In contrast, the three concentrations of crude organic extract of the brown alga D. cervicornis (50%, 100% and 200% dw) inhibited feeding by A. latispina. The chemical deterrent property of D. cervicornis extract against the gastropod A. latispina occurred due to a mixture of the secodolastane diterpenes isolinearol/linearol (4:1--0.08% dry weight). This is the first report showing that Dictyota cervicornis produces a chemical defense against herbivores using secodolastane diterpenoid. In addition, these results widen the action spectrum of secondary metabolites found in seaweed belonging to this brown algal genus.

[Methylmercury human exposure in riverside villages of Tapajos basin, Pará State, Brazil]

Evaluation of total human exposure to mercury and methylmercury was effected in riverine villages along the Tapajos river and in the metropolitan area of Belem city, state of Para, Brazil, by using total mercury and methylmercury concentrations in hair samples in 1994 and 1995. It was observed that average concentrations of total mercury are in a range from 2 +/- 1 microg/g-1 to 20.5 +/- 12. 1 microg/g-1. While methylmercury average concentration varies from 1. 4 +/- 0.7 microg/g-1 to 18.5 +/- 11 microg/g-1. These results confirm mercury contamination in the Tapajos river and possible appearance of mercury intoxication symptoms, and recommends the monitoring of compounds in hair samples as well as the need for epidemiological and clinical studies for human health prevention and control of mercury intoxication.