Aquatic ecology

A fish is an aquatic, anamniotic, gill-bearing vertebrate animal with a tough cranium to protect the brain, but lacking limbs with digits. Fish can be grouped into the more basal jawless fish and the more common jawed fish, the latter including all living cartilaginous and bony fish, as well as the extinct placoderms and acanthodians. In a break from the long tradition of grouping all fish into a single class (Pisces), modern phylogenetics views fish as a paraphyletic group that includes all vertebrates except tetrapods. In English, the plural of "fish" is fish when referring to individuals an

thumb|upright=1.35|A pair of muddy Wellington boot|Wellington boots thumb|Gamo mud volcano in Tokamachi, Japan Mud (, or Middle Dutch) is loam, silt or clay mixed with water. Mud is usually formed after rainfall or near water sources. Ancient mud deposits hardened over geological time to form sedimentary rock such as shale or mudstone (generally called lutites). When geological deposits of mud are formed in estuaries, the resultant layers are termed bay muds. Mud has also been used for centuries as a construction resource for mostly houses and also used as a binder. An Old English word for it

landform that is formed at the mouth of a river

thumb|upright=1.5|The Earth captured in the [[Pacific Ocean side]]

thumb|upright=1.5| Part of the contents of one dip of a hand net. The image contains diverse planktonic organisms, ranging from [[photosynthetic cyanobacteria and diatoms to many different types of zooplankton, including both holoplankton (permanent residents of the plankton) and meroplankton (temporary residents of the plankton, e.g., fish eggs, crab larvae, worm larvae). 100 μm = one tenth of a mm.]]

thumb|upright=1.3|Mangroves are hardy shrubs and trees that thrive in salt water and have specialised adaptations so they can survive the volatile energies of intertidal zones along marine coasts.

thumb|Río de la Plata estuary thumb|Mattole River estuary

naturally occurring water with low concentrations of dissolved salts

portion of a continent that is submerged under an area of relatively shallow water known as a shelf sea

contamination of water bodies

thumb|upright=1.3|Lake Hāwea, New Zealand

thumb|upright=1.3|right|Annual mean sea surface salinity for the World Ocean. Data from the [[World Ocean Atlas 2009.]] thumb|upright|right|International Association for the Physical Sciences of the Oceans (IAPSO) standard seawater. Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰).

Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately of dissolved salts (predominantly sodium () and chloride () ions). The average density at the surface is 1.025 kg/L. Seawater is denser than both fresh water and pure water (density 1.0 kg/L at ) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentrati

water with salinity between freshwater and saline water

Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from Ancient Greek φυτόν (phutón), meaning "plant", and πλαγκτός (planktós), meaning "drifter, wanderer, roamer", and thus, "plant drifter".

thumb|313x313px|Eutrophication can cause harmful algal blooms like this one in a river near Chengdu, China.

ice formed from frozen seawater

part of a sea, lake or river that is close to the shore

rapid increase or accumulation in the population of algae

flat area on the ocean floor

flow of excess rainwater not infiltrating in the ground over its surface

layer of the pelagic zone of the ocean; the deeper part of the midnight zone which starts in the bathypelagic waters above, the area below the abyssal zone is the sparsely inhabited hadal zone

thumb|250px|right|Spartina alterniflora ([[cordgrass), a halophyte.]]

climate change-induced decline of pH levels in the ocean

sources of water that are useful or potentially useful

thumb|Horse [[feces and straw are forms of detritus, and are used as manure.]]

thumb|Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 1000 meters. The temperature is nearly constant after 1500 meters depth.

underwater areas with a high density of kelp

Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll a.

Nekton or necton (from the ) is any aquatic organism that can actively and persistently propel itself through a water column (i.e. swim) without touching the bottom. Nekton generally have powerful tails and appendages (e.g. fins, pleopods, flippers or jets) that make them strong enough swimmers to counter ocean currents, and have mechanisms for sufficient lift and/or buoyancy to prevent sinking. Examples of extant nekton include most fish (especially pelagic fish like tuna and sharks), marine mammals (cetaceans, sirenia and pinnipeds) and reptiles (specifically sea turtles), penguins, coleoid

ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers

area between tide marks

human-created waste that has deliberately or accidentally been released in a lake, sea, ocean or waterway

uppermost layer of water in a lake or ocean that is exposed to sunlight more than 1% of surface illumination

thumb|Turbidity standards of 5, 50, and 500 NTU

measure of the amount of oxygen that can be consumed by reactions in a solution

movement of fishes from one water body to another

portion of a lake or ocean where less than 1% of sunlight penetrates

degradation of water quality by any process that changes ambient water temperature

Animals that feed by straining food particles from water

thumb|388x388px|An example of a mountain lake ecosystem Hydrobiology is the science of life and life processes in water. Much of modern hydrobiology can be viewed as a sub-discipline of ecology but the sphere of hydrobiology includes taxonomy, economic and industrial biology, morphology, and physiology. The one distinguishing aspect is that all fields relate to aquatic organisms. Most work is related to limnology and can be divided into lotic system ecology (flowing waters) and lentic system ecology (still waters).

type of fish passage

water temperature close to the ocean's surface

part of the ocean

ocean floor area where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs

300px|thumb|upright=1.0| Nannochloropsis microalgae 300px|thumb|upright=1.0|Collection of microalgae cultures in CSIRO's lab

among the largest of Earth's aquatic ecosystems

A halocline (or salinity chemocline), from the Greek words hals (salt) and klinein (to slope), refers to a layer within a body of water (water column) where there is a sharp change in salinity (salt concentration) with depth.

ecosystem in a body of water

shower of mostly organic detritus falling from the upper layers of the water column

looks at how water moves in a closed system

intervals in the Earth's past

luminous phenomenon in the ocean in which large areas of seawater glow brightly enough at night to be seen by satellites orbiting Earth

right|thumb|upright=1.3|

A bioassay is an analytical method to determine the potency or effect of a substance by its effect on living animals or plants (in vivo), or on living cells or tissues (in vitro). A bioassay can be either quantal or quantitative, direct or indirect. If the measured response is binary, the assay is quantal; if not, it is quantitative.

thumb|Lakes are stratified into three separate sections: I. The Epilimnion II. The Thermocline|Metalimnion III. The [[Hypolimnion The scales are used to associate each section of the stratification to their corresponding depths and temperatures. The arrow is used to show the movement of wind over the surface of the water which initiates the turnover in the epilimnion and the hypolimnion.]]

relatively flat submarine region that rises well above the level of the ambient seabed

300px|thumb|Lakes are stratified into three separate sections: I. The Epilimnion II. The Metalimnion III. The Hypolimnion The scales are used to associate each section of the stratification to their corresponding depths and temperatures. The arrow is used to show the movement of wind over the surface of the water which initiates the turnover in the epilimnion and the hypolimnion.

alt=Walrus |thumb|upright=1.5 |Sediment on the left tusk of a walrus. Walrus bioturbations in Arctic benthic sediments have large-scale ecosystem effects.