salinity	This term, which describes the quantity of inorganic salts in a solution or water sample, is the subject of much confusion and extensive learned discourse. Traditionally, salt was defined as the weight in grams of the dissolved inorganic matter in one kg of water after all Br- and I- had been replaced by the equivalent quantity of Cl- and all HCO3 and CO3= converted to oxide. In this way, salinity scales were defined on a mass fraction basis (in theory, dimensionless in the SI system) and were expressed as "parts per thousand" (% or 10-3) indicating that the weight fraction was multiplied by a factor of 1000: standard sea water had a value of 35%.In recent years, a more robust definition of salinity has been sought. Absolute salinity (SA) is defined as the ratio of the mass of dissolved material in sea water to the mass of sea water. In practice, this quantity cannot be measured directly but a Practical Salinity (below) has been defined for the reporting of scientific observations.Practical Salinity (S), of a sample of sea water, is defined in terms of the ratio K 15 of the electrical conductivity of the sea water sample ( at 150C and one standard atmospheric pressure) to that of a potassium chloride (KC1) solution in which the mass fraction of KC1 is 32.4356 x 10 -3 at the same temperature and pressure. The K 15 value equal to 1 corresponds, by definition, to a value of 35 (= primary standard salinity) on the Practical Salinity Scale (PSS). In this definition, salinity is defined in terms of a conductivity ratio between a sample and standard sea water and is, therefore, a dimensionless value and not a strict unit/designator. On this basis, any oceanic water having a precisely known conductivity of near unity at 150C with the standard KC1 solution can be used as a secondary standard for the routine calibration of oceanographic equipment.
salt	A white powder or colourless crystalline solid, consisting mainly of sodium chloride
sand	Sediment having a particle size of between 0.0625 mm and 2 mm in diameter
satellite	1. A celestial body orbiting aroudn a planet or star : the Earth is a satellite of the Sun 2. A man-made device orbiting around the Earth, Moon or another planet; used for communication or for transmitting scientific information
scavenger	Can be considered a sub-category of carnivores. Feed on dead bodies or remnants of benthic or water column organisms
school (fish )	A shoal of fish
season	One of the four equal periods into which the year is divided by the equinoxes and solstices. These periods (spring, summer, autumn, winter) have characteristic weather conditions, and occur at opposite times of the year in the North and South hemispheres.
seawater	All the known elements are probably dissolved in the oceans. Thus natural seawater contains elements known to be essential to marine organisms in addition to many others that do not serve any known biological function. These elements can be classified into two groups according to concentration: (a) major and (b) trace.
secondary consumer	Organisms that occupy the third trophic level in the grazing food chain. These organisms are carnivores. Also known as a primary carnivore.
secondary metabolite (toxin)	A poison, especially one secreted by a microbe and causing some particular disease.
secondary treatment (sewage)	Liquid from the primary treatment stage is subjected to further biological treatment. It may be filtered through beds of rock, or coke, providing a large surface area for degradong bacteria. After treatment, supernatant is discharged to the receiving waters.
sediment	Inorganic or organic material which is fragmented from parent structures and deposited in horizontal strata. Sediments are typically defined by their principal constituents, place of origin, time of origin, method of deposit or grain size.
Selenium	Non- metallic element of sulphur-tellurium group, characterised by the fact that its electrical resistance varies with the intensity of illumination falling on it.
sex	Gender: being male, or female, or hermaphrodite.
shellfish	Aquatic invertebrates possessing a shell or exoskeleton, usually molluscs and/or crustaceans.
silt	Mineral particle with a size between 0.004 and 0.06 millimeters in diameter.
siphon	Inhalent and exhalent siphons: tubes of bivalves and cephalopods used for aeration and feeding
solar radiation	Energy from the sun in the form of electromagnetic waves.
somatic	Of or relating to the soma: somatic cells.
species	In systematics, a group of organisms of common ancestry that are able to reproduce only among themselves and which are usually geographically distinct. It constitutes the fundamental rank in the taxonomic hierarchy.
spring tide	The high tides of greatest amplitude caused by the Earth, Sun and Moon being almost co-linear. This causes the gravitational pulls of both the Sun and Moon to reinforce each other. The high tide is higher and low tide is lower than the average, and spring tides occur twice a month at the times of both new moon and full moon.
stability	The capacity to withstand changes.
standing crop	see: Biomass
stenohaline	Organisms capable of osmoregulating only in a relatively specific range of salinities.
stenotherm	Organisms which have very specific and narrow temperature demands.
stratification	Deposition of sediment in layers or strata. Layers within a sedimentary rock. Stratification may form in lake sediments because of the alteration of wet seasons and dry seasons.
substrate	1. Chemical substance that reacts with enzymes 2. Underground to live on
sun	The star that is the source of heat and light for the planets in the solar system.
suspension feeder	Suspension feeders have appendages covered by mucus to which suspended particles of the water column are attached. Have only limited mobility and live attached to the substrate; they prefer hard substrate and usually construct special hard cases or tubes into which they retreat when they sense danger.
swimbladder	Muscular, gas-filled organ (as in fishes) used to control depth. By constricting the bladder muscles, the contained gas (usually air and metabolic products) is compressed and the animal sinks in the water column. Relaxing the bladder de-compresses its contents, and this expansion provides buoyancy. Non-muscular gas vacuoles also provide buoyancy in some species of kelp synchronisation occurring, or recurring, or causing to occur at the same time or in unison.