Recruitment and colonization of colonial ascidians (Tunicata: Ascidiacea) on intertidal rocks in Northeastern Brazil

Recruitment and colonization of colonial ascidians, starting on natural scraped substratum, was observed throughout one year, in quadrats marked on sea- and continental-rock faces in the sublittoral fringe of an exposed beach in the Northeast of Brazil. The species of the Didemnidae, Didemnum duplicatum Monniot, 1983, D. psammathodes Sluiter, 1895, and Polysyncraton amethysteum Van Name, 1902, and an unidentified species of Polycitoridae, Eudistoma sp. 1, were recruited. Presenting continuous recruitment of all species, the density of living and dead recruits and colonies was similar on both faces of the rocks. The highest rainfall during winter, affected significantly the recruits density of D. duplicatum and D. psammathodes. Different permanence periods were observed for colonies of each species. The longest permanence periods were assigned to the colonies of P. amethysteum and D. psammathodes, extending up to four and five months, respectively.

Characterization and nutrient release from silicate rocks and influence on chemical changes in soil

The expansion of Brazilian agriculture has led to a heavy dependence on imported fertilizers to ensure the supply of the growing food demand. This fact has contributed to a growing interest in alternative nutrient sources, such as ground silicate rocks. It is necessary, however, to know the potential of nutrient release and changes these materials can cause in soils. The purpose of this study was to characterize six silicate rocks and evaluate their effects on the chemical properties of treated soil, assessed by chemical extractants after greenhouse incubation. The experimental design consisted of completely randomized plots, in a 3 x 6 factorial scheme, with four replications. The factors were potassium levels (0-control: without silicate rock application; 200; 400; 600 kg ha-1 of K2O), supplied as six silicate rock types (breccia, biotite schist, ultramafic rock, phlogopite schist and two types of mining waste). The chemical, physical and mineralogical properties of the alternative rock fertilizers were characterized. Treatments were applied to a dystrophic Red-Yellow Oxisol (Ferralsol), which was incubated for 100 days, at 70 % (w/w) moisture in 3.7 kg/pots. The soil was evaluated for pH; calcium and magnesium were extracted with KCl 1 mol L-1; potassium, phosphorus and sodium by Mehlich 1; nickel, copper and zinc with DTPA; and the saturation of the cation exchange capacity was calculated for aluminum, calcium, magnesium, potassium, and sodium, and overall base saturation. The alternative fertilizers affected soil chemical properties. Ultramafic rock and Chapada mining byproduct (CMB) were the silicate rocks that most influenced soil pH, while the mining byproduct (MB) led to high K levels. Zinc availability was highest in the treatments with mining byproduct and Cu in soil fertilized with Chapada and mining byproduct.