Phagotrophic protists are major consumers of microbial biomass in aquatic ecosystems. However, biochemical mechanisms underlying prey recognition and phagocytosis by protists are not well understood. We investigated the potential roles of cell signaling mechanisms in chemosensory response to prey, and in capture of prey cells, by a marine ciliate (Uronema...
Recent data on seasonal variation in the concentration of atmospheric oxygen are independent evidence for a marked annual cycle in the production/respiration (P/R) ratio of the biotic community of the ocean in both the northern and southern hemispheres. Based on the oxygen data, the P/R ratio tends to be >1...
The Galapagos Islands, located off the coast of Ecuador, have a spatially diverse marine environment suitable for a variety of species with different climatic requirements. A year-long inventory program was carried out in 2000-2001 to provide baseline data on the abundances and distribution of coastal fish and macro-invertebrates. The purposes...
The Northern California Current (NCC) ecosystem exhibits extreme seasonal, interannual and interdecadal shifts in the abiotic environment and shifts in primary and higher production. This variability is also apparent in the spatial structure of the ecosystem with nearshore-shelf waters (<150 m isobath) being highly productive and having a different community...
Grazing by phagotrophic flagellates and ciliates is a major source of mortality for bacterioplankton in both
marine and freshwater systems. Recent studies have demonstrated a positive relationship between clearance
rate and prey size for bacterivorous protists. We tested the idea that, by selectively grazing the larger (more
actively growing or...
We evaluated whether bacteria with higher cell-specific nucleic acid content (HNA) or an active electron transport system, i.e., positive for reduction of 5-cyano-2,3-ditolyl tetrazolium chloride (CTC), were responsible for the bulk of bacterioplankton metabolic activity. We also examined whether the phylogenetic diversity of HNA and CTC-positive cells differed from the...
Under conditions of fixed N-limitation, as with most oligotrophic systems, the process of biological N₂ fixation (diazotrophy) is favored, provided the necessary trace elements and vitamins are sufficient. Despite the well understood contributions of N₂
fixation in oligotrophic regions, the nutritional and ecological controls of marine diazotrophs have not been...
Marine bacterioplankton play an important role in global elemental cycles because they return carbon dioxide and nutrients to the biosphere as they reduce organic matter. Furthermore, marine bacterioplankton are not uniformly active, and subpopulations of the in situ community may be more or less active at any given time. Defining...