APOPTOTIC RESPONSE Phenotypic changes that occur during programmed cell death in eukaryotic cells, for example, cell shrinkage.

AUTOTROPHY The acquisition of metabolic energy from the fixation of inorganic carbon, for example, by photo- or chemosynthesis.

BACTERIOPLANKTON Bacteria that inhabit the water column of lakes and oceans, either freely suspended or attached to particles.

BACTERIVOROUS NANOFLAGELLATES Small, flagellated protists that range in size from 3 to 15 mm and that can feed on bacteria.

BOTTOM-UP CONTROL Ecological scenario in which the abundance or biomass of organisms is mainly determined by a lack of resources and mortality owing to starvation.

CHEMOSPHERE Zone of elevated concentration of organic molecules that diffuse from the surface of a suspended particle.

CHEMOTAXIS Ability of microorganisms to follow a chemical gradient.

COMMUNITY EVENNESS Balance of the respective number of individuals in each species of a community.

DETRITAL PARTICLES Dead organic material suspended in the water column.

ECOPHYSIOLOGICAL APPROACHES Determination of protistan physiological properties under field conditions, for example, of feeding rates through uptake of surrogate particles.

EUPHOTIC ZONE Upper realms of the oceans that are penetrated by sufficient amounts of light for the growth of photosynthetic organisms.

EUTROPHIC Aquatic systems with high availability of dissolved organic matter from photosynthetic production or other sources. Examples include shallow lowland lakes and coastal estuaries.

FEAST OR FAMINE Growth strategy of microorganisms that rapidly proliferate if conditions are optimal and that can survive extended periods of starvation.

FILTER FEEDING Feeding mode that filters particles from the water by means of a sieving structure. Usually the prey is very small compared with the predator.

HERBIVORY The consumption of plants.

HETEROTROPHY The acquisition of metabolic energy by consumption of particulate or dissolved organic matter.

INTERCEPTION FEEDING The capture of individual bacteria or particles by direct random contact with a protistan cell. Usually the sizes of the predator and prey are similar.

MIXOTROPHS Organisms that are part autotrophic and part heterotrophic, for example, carnivorous plants.

MOLECULAR BIOLOGICAL APPROACHES Cultivation-independent identification of protists in environmental samples by sequencing of rRNA genes and fluorescence in situ hybridization with rRNA-targeted probes.

NUTRIENT REGENERATION Processes by which nutrients that are bound in organismic biomass are retransformed into their inorganic form.

OLIGOTROPHIC An aquatic environment that has low levels of nutrient and algal photosynthetic production (for example, high mountain lakes).

OMNIVORY Ability of animals to feed on different types of prey.

PELAGIC HABITAT The parts of a lake, river and ocean that make up the water column.

PHAGOTROPHY The uptake of particles by eukaryotic cells.

PHOTOTROPHS Organisms that fix inorganic carbon using light energy.

PICOPLANKTON Organisms suspended in the water column that are less than 2 mm in size.

PRIMARY PRODUCERS Organisms that are the original source of organic material in an ecosystem — plants, algae or chemosynthetic microorganisms.

QUORUM SENSING Bacterial communication system based on the secretion and detection of a quorum, which is a substance that increases with population density and that induces expression of specific genes in the population above a threshold concentration.

SPECIES RICHNESS Number of species that are present in a community.

TOP-DOWN CONTROL Ecological scenario in which the abundance or biomass of organisms is mainly determined by mortality owing to predation.

ULTRAMICROBACTERIA Bacteria that maintain cell volumes of <0.1 mm3 even during exponential growth on rich media.