Hypoxia, with dissolved oxygen levels < 1.4 ml L-1, is a recurring summer feature of Louisiana shelf bottom waters. Stable isotope characterization (delta^18O and delta D) of surface waters over the hypoxic zone shows a shift of dominant river influence from the Mississippi River during April to the Atchafalaya in July. Carbon isotopes of dissolved inorganic carbon (δ13CDIC) in bottom waters reveal the respiration of terrestrial organic carbon (OC) at inshore localities of 10 m depth and the respiration of marine OC at depths equal to and greater than 20 m. delat^18O and delta^13C profiles of Louisiana shelf Conus shells collected in 1972 show no evidence for summer hypoxia. Comparison with modern Conus records reveal a delta^13CDIC reduction during the last four decades associated with intrusion of ^13C-depleted fossil fuel CO2. Summer delta^13C reductions in Texas shelf Pteria shells may imply dissolved oxygen (DO) was reduced by ≈0.7 ml L-1, although this may be attributed to influence of Brazos River discharge on shell delta^18O and delta^13C. Foraminifera fauna measured in age-calibrated sediments from the Texas shelf reveal a low oxygen conditions on between 1960 and modern sediments. From 1950 to 1960, fauna indicate oxygenated bottom waters. Contemporaneous increases of foraminifera delta^13Cand delta^18O suggest this event is associated with severe drought (the Little Dust Bowl). The synchronicity of these data suggests a link between Brazos River discharge and shelf hypoxia.

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Transmission at an identified chemical synapse between two giant molluscan neurones, in the snail Achatina fulica, was sampled continuously from late embryogenesis to adulthood. The laboratory culture and reproductive life-cycle of the snail are described. The propagation of spontaneous excitatory postsynaptic potentials (Epsps) into the postsynaptic soma was documented throughout development. Short-term facilitation (Epsp(,2)/Epsp(,1)) was present at the identified synapse at all ages studied. Over a series of 100 trials, embryonic synapse showed a net synaptic depression; while, postembryonically, there was a progressive increase in frequency-facilitation with increasing age. A quantal analysis of transmission indicates that the amplitude of the quantal unit declines in parallel with the decrease in the postsynaptic input resistance. There is a progressive (20-fold) increase in quantal content from embryos to adults. The developmental increase in transmission at the synapse is primarily presynaptic in origin. Structural correlates for the electrophysiological findings were discussed.

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