ALBERT

Notes: Succession of phytoplankton dominance was studied in shrimp culture ponds treated with commercial bacterial products. Diatoms were dominant and the cyanobacteria were absent in both treated and control ponds at the beginning of the culture period. After 34 days, the diatoms significantly decreased whereas cyanobacteria increased in both ponds. Chlorophyll a increased from a mean of 35.56 mg m−3 in the first phase to 186.00 mg m−3 in the final phase, and from 42.12 mg m−3 to 242.81 mg m−3 in the treated and control ponds respectively. Cyanobacteria were significantly higher in the control compared with the treated ponds during the final phase of the culture. Algal bioassay showed that the addition of nitrogen either alone or with silica to pond water significantly increased the specific growth rate of Chaetoceros calcitrans. The specific growth rate of Oscillatoria sp. significantly increased when a combination of nitrogen, phosphorus and carbon was added to the pond water. Addition of silica seemed to depress the growth rate of Oscillatoria sp. Nutrient enrichment should be minimized and the supply of nitrogen and silica should be adequate for promoting the growth of beneficial phytoplankton in aquaculture systems.

Notes: Abstract Penang Island represents the northwestern extension of the western magmatic belt of Peninsular Malaysia. Thirty-one samples of highly evolved biotite-and biotite-muscovite granites were used in an integrated study to unravel the complex magmatic, tectonic and cooling histories of these rocks. Highly distorted Rb−Sr whole-rock age patterns are evident. These are attributed to the partial post-magmatic Sr homogenization within the granite batholith which led to the rotation of isochrons towards younger ages and higher (87/86)Sr intercepts. The recognition of this mechanism allowed the establishment of a new Rb−Sr interpretation model. The intrusion ages of the granites can be extrapolated based on the evolutionary trend of the initial (87/86)Sr. Including the data of Bignell and Snelling, three episodes of granite emplacement at 307±8 Ma, 251±7 Ma and 211±2 Ma are suggested for Penang and the NW Main Range. The late-Triassic intrusive induced a hydrothermal conductive convection system which affected all the granites. It is considered to be responsible for the Rb−Sr whole-rock age distortion, the Rb−Sr and K−Ar biotite age resetting and the textural and mineralogical changes in the granites. The duration of the hydrothermal convections, deduced from the Rb−Sr whole rock ages, is about 6 Ma and 20 Ma in the northern and southern parts of Penang respectively. Fast regional cooling to 350±50°C within a time span of 1–3 Ma is recognized for the late-Triassic Feringgi intrusive from the mica ages, followed by a generally slow cooling rate of about 1°C/Ma. Fission track ages, in addition, indicate blockwise uplift along the N-S and NW-SE tending faults, thus resulting in the exposure of deeper crustal levels in southern and eastern Penang. A change in the tensional regime since Oligocene/Miocene, accompanied by a southwest tilting of the island, is indicated by the fission track apatite ages. Variable sometimes younger K−Ar, respectively Rb−Sr biotite ages mainly depend on the degree of hydrothermal overprint at different crustal levels. An increase of the reaction surface by grain size reduction influences Rb−Sr and K−Ar mica ages in similar ways, as has been demonstrated by experimental data.