Oceanic basin

Hydrologically, an oceanic basin may be anywhere on Earth that is covered by seawater, but geologically ocean basins are large geologic basins that are below sea level. Geologically, there are other undersea geomorphological features such as the continental shelves, the deep ocean trenches, and the undersea mountain ranges (for example, the mid-Atlantic ridge) which are not considered to be part of the ocean basins; while hydrologically, oceanic basins include the flanking continental shelves and shallow, epeiric seas.
Some consider the oceanic basins to be the complement to the continents, with erosion dominating the latter, and the sediments so derived ending up in the ocean basins. Others regard the ocean basins more as basaltic plains, than as sedimentary depositories, since most sedimentation occurs on the continental shelves and not in the geologically-defined ocean basins.
Hydrologically some geologic basins are both above and below sea level, such as the Maracaibo Basin in Venezuela, although geologically it is not considered an oceanic basin because it is on the continental shelf and underlain by continental crust.
Earth is the only planet with bimodal hypsography, reflecting the different kinds of crust, oceanic crust and continental crust. Oceans cover 70% of the Earth's surface. Because oceans lie lower than continents, the former serve as sedimentary basins that collect sediment eroded from the continents, known as clastic sediments, as well as precipitation sediments. Ocean basins also serve as repositories for the skeletons of carbonate- and silica-secreting organisms such as coral reefs, diatoms, radiolarians, and foraminifera.
Geologically, oceanic basins may be actively changing size or may be inactive, depending on whether there is a moving plate tectonic boundary associated with it. The elements of an active - and growing - oceanic basin include an elevated mid-ocean ridge, flanking abyssal hills leading down to abyssal plains. The elements of an active oceanic basin often include the oceanic trench associated with a subduction zone.
The Atlantic ocean and the Arctic ocean are good examples of active, growing oceanic basins, whereas the Mediterranean Sea is shrinking. The Pacific Ocean is also an active, shrinking oceanic basin, even though it has both spreading ridge and oceanic trenches. Perhaps the best example of an inactive oceanic basin is the Gulf of Mexico, which formed in Jurassic times and has been doing nothing but collecting sediments since then. The Sea of Japan and Bering Sea are also good examples of inactive oceanic basins.

Ecology

The intertidal region is an important model systems for the study of ecology, especially on wave-swept rocky shores. The region contains a high diversity of species, and the different zones caused by the physics of the tides causes species ranges to be compressed into very narrow bands. This makes it relatively simple to study species across their entire cross-shore range, something that can be extremely difficult in, for instance, terrestrial habitats that can stretch thousands of kilometers. Communities on wave-swept shores also have high turnover due to disturbance, so it is possible to watch ecological succession over years rather than decades.
Since the foreshore is alternately covered by the sea and exposed to the air, organisms living in this environment must have adaptions for both wet and dry conditions. Hazards include being smashed or carried away by rough waves, exposure to dangerously high temperatures, and desiccation. Typical inhabitants of the intertidal rocky shore include sea anemones, barnacles, chitons, crabs, isopods, mussels, seastars, and many marine gastropod mollusks such as limpets, whelks etc. Also see tide pool.

Intertidal ecology is the study of intertidal ecosystems, where organisms live between the low and high tide lines. At low tide, the intertidal is exposed (or ‘emersed’) whereas at high tide, the intertidal is underwater (or ‘immersed’). Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as between different species of intertidal organisms within a particular intertidal community. The most important environmental and species interactions may vary based on the type of intertidal community being studied, the broadest of classifications being based on substrates - rocky shore and soft bottom communities.
Organisms living in this zone have a highly variable and often hostile environment, and have evolved various adaptations to cope with and even exploit these conditions. One easily visible feature of intertidal communities is vertical zonation, where the community is divided into distinct vertical bands of specific species going up the shore. Species ability to cope with desiccation determines their upper limits, while competition with other species sets their lower limits.
Intertidal regions are utilized by humans for food and recreation, but anthropogenic actions also have major impacts, with overexploitation, invasive species and climate change being among the problems faced by intertidal communities. In some places Marine Protected Areas have been established to protect these areas and aid in scientific research.

Intertidal zone

The intertidal zone (also known as the foreshore and seashore and sometimes referred to as the littoral zone) is the area that is exposed to the air at low tide and underwater at high tide (for example, the area between tide marks). This area can include many different types of habitats, including steep rocky cliffs, sandy beaches, or wetlands (e.g., vast mudflats). The area can be a narrow strip, as in Pacific islands that have only a narrow tidal range, or can include many meters of shoreline where shallow beach slope interacts with high tidal excursion.
Organisms in the intertidal zone are adapted to an environment of harsh extremes. Water is available regularly with the tides but varies from fresh with rain to highly saline and dry salt with drying between tidal inundations. The action of waves can dislodge residents in the littoral zone. With the intertidal zone's high exposure to the sun the temperature range can be anything from very hot with full sun to near freezing in colder climates. Some microclimates in the littoral zone are ameliorated by local features and larger plants such as mangroves. Adaption in the littoral zone is for making use of nutrients supplied in high volume on a regular basis from the sea which is actively moved to the zone by tides. Edges of habitats, in this case land and sea, are themselves often significant ecologies, and the littoral zone is a prime example.
A typical rocky shore can be divided into a spray zone or splash zone (also known as the supratidal zone), which is above the spring high-tide line and is covered by water only during storms, and an intertidal zone, which lies between the high and low tidal extremes. Along most shores, the intertidal zone can be clearly separated into the following subzones: high tide zone, middle tide zone, and low tide zone.

Zonation

Marine biologists and others divide the intertidal region into three zones (low, middle, and high), based on the overall average exposure of the zone. The low intertidal zone, which borders on the shallow subtidal zone, is only exposed to air at the lowest of low tides and is primarily marine in character. The mid intertidal zone is regularly exposed and submerged by average tides. The high intertidal zone is only covered by the highest of the high tides, and spends much of its time as terrestrial habitat. The high intertidal zone borders on the swash zone (the region above the highest still-tide level, but which receives wave splash). On shores exposed to heavy wave action, the intertidal zone will be influenced by waves, as the spray from breaking waves will extend the intertidal region above the high tide line.
Depending on the substratum and topography of the shore, additional features may be noticed. On rocky shores, tide pools form at low tide when water is trapped in hollows. Under certain conditions, such as those at Morecambe Bay, quicksand may form.

Low tide zone (lower littoral)

This subregion is mostly submerged - it is only exposed at the point of low tide and for a longer period of time during extremely low tides. This area is teeming with life; the most notable difference with this subregion to the other three is that there is much more marine vegetation, especially seaweeds. There is also a great biodiversity. Organisms in this zone generally are not well adapted to periods of dryness and temperature extremes. Some of the organisms in this area are abalone, anemones, brown seaweed, chitons, crabs, green algae, hydroids, isopods, limpets, mussels, nudibranchs, sculpin, sea cucumber, sea lettuce, sea palms, sea stars, sea urchins, shrimp, snails, sponges, surf grass, tube worms, and whelks. Creatures in this area can grow to larger sizes because there is more available energy in the localised ecosystem and because marine vegetation can grow to much greater sizes than in the other three intertidal subregions due to the better water coverage: the water is shallow enough to allow plenty of light to reach the vegetation to allow substantial photosynthetic activity, and the salinity is at almost normal levels. This area is also protected from large predators such as large fish because of the wave action and the water still being relatively shallow.

Cetacea

The order Cetacea (pronounced /sɨˈteɪʃ(i)ə/, L. cetus, whale, from Greek) includes whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster". In Greek mythology the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus. Cetology is the branch of marine science associated with the study of cetaceans.
Cetaceans are the mammals best adapted to aquatic life. Their body is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated by a thick layer of blubber. As a group, they are noted for their high intelligence.
The order Cetacea contains about ninety species, all marine except for four species of freshwater dolphins. The order is divided into two suborders, Mysticeti (baleen whales) and Odontoceti (toothed whales, which includes dolphins and porpoises). The species range in size from Commerson's Dolphin, smaller than a human, to the Blue Whale, the largest animal known to have lived.

Respiration

As mammals, cetaceans need to breathe air. Because of this, they need to come to the water's surface to exhale carbon dioxide and inhale a fresh supply of oxygen. During diving, a muscular action closes the blowholes (nostrils), which remain closed until the cetacean next breaks the surface; when it surfaces, the muscles open the blowholes and warm air is exhaled.
Cetaceans' blowholes have evolved to a position on top of the head, allowing more time to expel stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled, it condenses as it meets the cold air outside. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'blow' or 'spout' and is different in terms of shape, angle and height, for each cetacean species. Cetaceans can be identified at a distance, using this characteristic, by experienced whalers or whale-watchers.
Cetaceans can go underwater for much longer periods of time than other mammals. Their duration under water varies greatly between species due to large physiological differences between many members of this Order. There are two studied advantages of cetacean physiology that let this Order (and other marine mammals) forage underwater for extended periods of time without breathing at the water surface.
Myoglobin concentrations in skeletal muscle of mammals have much variation. A New Zealand white rabbit has 0.08+/-0.06 g (in a 100 g Wet muscle) of myoglobin,whereas a Northern Bottlenose Whale has 6.34 g (in a 100 g Wet muscle) of myoglobin. Myoglobin, by nature, has a higher affinity to oxygen than hemoglobin. That is, myoglobin retains oxygen molecules better than hemoglobin. Therefore, it is useful to have higher concentrations of myoglobin when needed and there is no oxygen available for re-uptake. The higher the myoglobin concentration in cetacean skeletal muscle, the longer they can stay underwater and forage.
Increased body size is another way of elongating dive duration of large cetaceans. This is true because of two considered aspects. An increase in body size means that there is increase in muscle mass, therefore, increase in muscle oxygen stores. Another aspect is the universal correlation of mass and metabolic rate (Kleiber's law). In layman’s terms, Kleiber’s law states that the metabolic rate of a large animal is slower than a small animal per unit mass. From this we can conclude that larger animals will use up less oxygen than smaller animals

Vision, hearing and echolocation

Cetacean eyes are set well back and to either side of its head. This means that cetaceans with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward but others, with blunt heads (such as the Sperm Whale), can see either side but not directly ahead or directly behind. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. Cetaceans also have an almost spherical lens in their eyes, which is most efficient at focusing what little light there is in the deep waters. Cetaceans make up for their generally quite poor vision (with the exception of the dolphin) with excellent hearing.
As with the eyes, cetacean ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect airborne sound waves and focus them in order for them to become strong enough to hear well. However, water is a better conductor of sound than air, so the external ear was no longer needed: it is no more than a tiny hole in the skin, just behind the eye. The inner ear, however, has become so well developed that the cetacean can not only hear sounds dozens of miles away, but it can also discern from which direction the sound comes.
Some cetaceans are capable of echolocation. Many toothed whales emit clicks similar to those in echolocation, but it has not been demonstrated that they echolocate. Mysticeti have little need of echolocation, as they prey upon small fish that would be impractical to locate with echolocation. Some members of Odontoceti, such as dolphins and porpoises, do perform echolocation. These cetaceans use sound in the same way as bats—they emit a sound (called a click), which then bounces off an object and returns to them. From this, cetaceans can discern the size, shape, surface characteristics and movement of the object, as well as how far away it is. With this ability cetaceans can search for, chase and catch fast-swimming prey in total darkness. Echolocation is so advanced in most Odontoceti that they can distinguish between prey and non-prey (such as humans or boats); captive cetaceans can be trained to distinguish between, for example, balls of different sizes or shapes.
Cetaceans also use sound to communicate, whether it be groans, moans, whistles, clicks or the complex 'singing' of the Humpback Whale.

Oceanography

Oceanography (compound of the Greek words ωκεανός meaning "ocean" and γράφω meaning "to write"), also called oceanology or marine science, is the branch of Earth science that studies the ocean. It covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and fluxes of various chemical substances and physical properties within the ocean and across its boundaries. These diverse topics reflect multiple disciplines that oceanographers blend to further knowledge of the world ocean and understanding of processes within it: biology, chemistry, geology, meteorology, and physics.

Branches

The study of oceanography is divided into a number of branches:
Biological oceanography, or marine biology, is the study of the plants, animals and microbes of the oceans and their ecological interaction;
Chemical oceanography, or marine chemistry, is the study of the chemistry of the ocean and its chemical interaction with the atmosphere;
Geological oceanography, or marine geology, is the study of the geology of the ocean floor including plate tectonics;
Physical oceanography, or marine physics, studies the ocean's physical attributes including temperature-salinity structure, mixing, waves, internal waves, surface tides, internal tides, and currents. Of particular interest is the behavior of sound (acoustical oceanography), light (optical oceanography) and radio waves in the ocean.
These branches reflect the fact that many oceanographers are first trained in the exact sciences or mathematics and then focus on applying their interdisciplinary knowledge, skills and abilities to oceanography.Data derived from the work of Oceanographers is used in marine engineering, in the design and building of oil platforms, ships, harbours, and other structures that allow us to use the ocean safely.

Oceanographic data management is the discipline ensuring that oceanographic data both past and present are available to researchers.

Phytoplankton

Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτον ("phyton"), or "plant", and πλαγκτος ("planktos"), meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, they may appear as a green discoloration of the water due to the presence of chlorophyll within their cells (although the actual color may vary with the species of phytoplankton present due to varying levels of chlorophyll or the presence of accessory pigments such as phycobiliproteins, xanthophylls .

Phytoplankton obtain energy through the process of photosynthesis and must therefore live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, lake, or other body of water. Phytoplankton account for half of all photosynthetic activity on Earth.Thus phytoplankton are responsible for much of the oxygen present in the Earth's atmosphere – half of the total amount produced by all plant life. Their cumulative energy fixation in carbon compounds (primary production) is the basis for the vast majority of oceanic and also many freshwater food webs (chemosynthesis is a notable exception). As a side note, one of the more remarkable food chains in the ocean – remarkable because of the small number of links – is that of phytoplankton fed on by krill (a type of shrimp) fed on by baleen whales.

Phytoplankton are also crucially dependent on minerals. These are primarily macronutrients such as nitrate, phosphate or silicic acid, whose availability is governed by the balance between the so-called biological pump and upwelling of deep, nutrient-rich waters. However, across large regions of the World Ocean such as the Southern Ocean, phytoplankton are also limited by the lack of the micronutrient iron. This has led to some scientists advocating iron fertilization as a means to counteract the accumulation of human-produced carbon dioxide (CO2) in the atmosphere.Large-scale experiments have added iron (usually as salts such as iron sulphate) to the oceans to promote phytoplankton growth and draw atmospheric CO2 into the ocean. However, controversy about manipulating the ecosystem and the efficiency of iron fertilization has slowed such experiments.
While almost all phytoplankton species are obligate photoautotrophs, there are some that are mixotrophic and other, non-pigmented species that are actually heterotrophic (the latter are often viewed as zooplankton). Of these, the best known are dinoflagellate genera such as Noctiluca and Dinophysis, that obtain organic carbon by ingesting other organisms or detrital material.
The term phytoplankton encompasses all photoautotrophic microorganisms in aquatic food webs. Phytoplankton serve as the base of the aquatic food web, providing an essential ecological function for all aquatic life. However, unlike terrestrial communities, where most autotrophs are plants, phytoplankton are a diverse group, incorporating protistan eukaryotes and both eubacterial and archaebacterial prokaryotes. There are about 5,000 species of marine phytoplankton. There is uncertainty in how such diversity has evolved in an environment where competition for only a few resources would suggest limited potential for niche differentiation.
In terms of numbers, the most important groups of phytoplankton include the diatoms, cyanobacteria and dinoflagellates, although many other groups of algae are represented. One group, the coccolithophorids, is responsible (in part) for the release of significant amounts of dimethyl sulfide (DMS) into the atmosphere. DMS is converted to sulfate and these sulfate molecules act as cloud condensation nuclei, increasing general cloud cover. In oligotrophic oceanic regions such as the Sargasso Sea or the South Pacific Gyre, phytoplankton is dominated by the small sized cells, called picoplankton, mostly composed of cyanobacteria (Prochlorococcus, Synechococcus) and picoeucaryotes such as Micromonas.

Freshwater ecosystem

Freshwater ecosystems are among the earth aquatic ecosystems. They include lakes and ponds, rivers, streams and springs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, and vegetation

Tropical marine ecosystem

Tropical marine climate

Islands and coastal areas 10° to 20° north or south of the equator usually have a tropical marine climate. The climate of the tropical marine system is influenced by the sea. There are two main seasons the wet season and the dry season. The annual rainfall is 1000 to over 1500 mm. The temperature ranges from 27°C to 30°C. The trade winds blow all year round. The trade winds are moist as they have passed over warm seas.

Wet season

The wet season of the tropical marine climate occurs during the period when the conditions of the atmosphere are not stable. At this time, the regions (10° to 20° north or south of the equator) experience tropical disturbances. Around this time islands like Grenada are affected by the ITCZ (Intertropical Convergence Zone). The most rainfall comes between July to September.

Dry season

The dry season occurs when the conditions in the atmosphere are stable. During the dry season there is less rainfall than in the wet season. Around this time the tropical marine regions is influenced by anti cyclones. There is little difference between the wet and dry seasons.

Adaptations

The ecosystems of the tropical marine climate have to adapt to the dry season. Plants during the dry season must conserve water/moisture. However the extent of the adaptation depends much on the annual rainfall. Hygrophytic ecosystems occur when there is a short dry period with a few rain showers. The soil in this ecosystem holds adequate water for plant growth. Most of the tropical marine ecosystems are close to true rain forests.

Mesophytic ecosystem

The mesophytic ecosystem is also known as a semi-evergreen forest. It is found where there is a long dry season that has little rainfall. There is less vegetation than in a rainforest and the layer structure is simpler. There are only 2 tree stories, trees shed their leaves or have very small leaves. This provides the plants a way to conserve moisture. There are fewer epiphytes than a rain forest has as the canopy is dry. In the dry season the ground is covered by leaves that will not decay until the soil is moist. The trees often flower during the dry season and start to grow during the wet season. The soil is usually latasol.

Xerophytic ecosystem

The xerophytic ecosystem is also known as dry woodland. It is found in areas of rain shadow in the tropical marine climate. This ecosystem often develops soils that drain quickly. The dry woodland is very different than the rainforest. The biomass is a lot less than a rainforest as there is little rain. The tallest of trees are only 15 to 25 meters high in the dry woodland. Dry woodland trees either have small leaves or shed their leaves. The trees have very thick bark and the trunks are crooked.

Variations

Mangroves grow in coastal wet lands which are called hydrophytic ecosystems. The vegetation at the coast are usually adapted to sandy soil. The montane forests and elfin wood lands grow on the cool, moist, mountainous regions.

Oceanic trench

The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor.
Trenches define one of the most important natural boundaries on the Earth’s solid surface; that between two lithospheric plates. There are three types of lithospheric plate boundaries: divergent (where lithosphere and oceanic crust is created at mid-ocean ridges), convergent (where one lithospheric plate sinks beneath another and returns to the mantle), and transform (where two lithospheric plates slide past each other).
Trenches are a distinctive morphological feature of plate boundaries. Along convergent plate boundaries, plates move together at rates that vary from a few millimeters to over ten centimeters per year. A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab. Trenches are generally parallel to a volcanic island arc, and about 200 km from a volcanic arc. Oceanic trenches typically extend 3 to 4 km (1.9 to 2.5 mi) below the level of the surrounding oceanic floor. The greatest ocean depth to be sounded is in the Challenger Deep of the Mariana Trench, at a depth of 10,911 m (35,798 ft) below sea level. Oceanic lithosphere moves into trenches at a global rate of about a tenth of a square meter per second.

Water and biosphere

The volume of water escaping from within and beneath the forearc results in some of Earth’s most dynamic and complex interactions between aqueous fluids and rocks. Most of this water is trapped in pores and fractures in the upper lithosphere and sediments of the subducting plate. The average forearc is underrun by a solid volume of oceanic sediment that is 400 m thick. This sediment enters the trench with 50-60% porosity. These sediments are progressively squeezed as they are subducted, reducing void space and forcing fluids out along the decollement and up into the overlying forearc, which may or may not have an accretionary prism. Sediments accreted to the forearc are another source of fluids. Water is also bound in hydrous minerals, especially clays and opal. Increasing pressure and temperature experienced by subducted materials converts the hydrous minerals to denser phases that contain progressively less structurally-bound water. Water released by dehydration accompanying phase transitions is another source of fluids introduced to the base of the overriding plate. These fluids may travel through the accretionary prism diffusely, via interconnected pore spaces in sediments, or may follow discrete channels along faults. Sites of venting may take the form of mud volcanoes or seeps and are often associated with chemosynthetic communities. Fluids escaping from the shallowest parts of a subduction zone may also escape along the plate boundary but have rarely been observed draining along the trench axis. All of these fluids are dominated by water but also contain dissolved ions and organic molecules, especially methane. Methane is often sequestered in an ice-like form (methane clathrate, also called gas hydrate) in the forearc. These are a potential energy source and can rapidly break down. Destabilization of gas hydrates has contributed to global warming in the past and will likely do so in the future.
Chemosynthetic communities thrive where cold fluids seep out of the forearc. Cold seep communities have been discovered in inner trench slopes down to depths of 6000 m in the western Pacific, especially around Japan, in the Eastern Pacific along North, Central and South America coasts from the Aleutian to the Peru-Chile trenches, on the Barbados prism, in the Mediterranean, and in the Indian Ocean along the Makran and Sunda convergent margins. These communities receive much less attention than the chemosynthetic communities associated with hydrothermal vents. Chemosynthetic communities are located in a variety of geological settings: above over-pressured sediments in accretionary prisms where fluids are expelled through mud volcanoes or ridges (Barbados, Nankai and Cascadia); along active erosive margins with faults; and along escarpments caused by debris slides (Japan trench, Peruvian margin). Surface seeps may be linked to massive hydrate deposits and destabilization (e.g. Cascadia margin). High concentrations of methane and sulfide in the fluids escaping from the seafloor are the principal energy sources for chemosynthesis.

Zooxanthella

Zooxanthellae (plural, pronounced are flagellate protozoa that are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the scleractinian corals and the tropical sea anemone, Aiptasia.
Zooxanthella live in other protozoa (foraminiferans and radiolarians) and in some invertebrates. Most are autotrophs and provide the host with energy in the form of translocated reduced carbon compounds, such as glucose, glycerol, and amino acids, which are the products of photosynthesis .Zooxanthellae can provide up to 90% of a coral’s energy requirements.In return, the coral provides the zooxanthellae with protection, shelter, nutrients (mostly waste material containing nitrogen and phosphorus) and a constant supply of carbon dioxide required for photosynthesis. Available nutrients, incident light, and expulsion of excess cells limits their population.
Hermatypic (reef-building) corals largely depend on zooxanthellae, which limits that coral's growth to the photic zone. The symbiotic relationship enables corals' success as reef-building organisms in tropical waters. However, under high environmental stress, corals die after losing their zooxanthellae either by expulsion or digestion.

Oceanic climate

An oceanic climate (also called marine west coast climate, maritime climate, subtropical highland and British climate) is the climate typically found along the west coasts at the middle latitudes of all the world's continents, and in southeastern Australia. Climates near the ocean have moderately cool summers and comparatively cool winters, they are generally characterized by a narrower annual range of temperatures than are encountered in other places at a comparable latitude, and do not have the extremely dry summers of Mediterranean climates.
Similar climates, at least in thermal range, are also found in tropical highlands even at considerable distance from any coastline. Generally, they fall into Köppen climate classification Cfb or Cwb. The narrow range of temperatures results not from proximity to a coastline but instead to the slight thermal range of temperatures between seasons characteristic of tropical lowlands; altitudes are high enough that somes places have at least one month cooler than 18 °C and do not qualify for grouping in the true tropical climates. Unlike the norm in true oceanic climates, these moist highland tropical climates may have a marked winter drought, as in Mexico City. Agricultural potential in both oceanic climates and moist tropical highland climates are practically identical. These climates are most dominant in Europe, where it spreads much farther inland than in other continents.

Aquaculture

Aquaculture is the farming of freshwater and saltwater organisms such as finfish, molluscs, crustaceans and aquatic plants. Also known as aquafarming, aquaculture involves cultivating aquatic populations under controlled conditions, and can be contrasted with commercial fishing, which is the harvesting of wild fish.One half of the world commercial production of fish and shellfish that is directly consumed by humans comes from aquaculture.Mariculture refers to aquaculture practiced in marine environments. Particular kinds of aquaculture include algaculture (the production of kelp/seaweed and other algae), fish farming, shrimp farming, oyster farming, and the growing of cultured pearls. Particular methods include aquaponics, which integrates fish farming and plant farming.

Aquaculture began in China circa 2500 BC. When the waters subsided after river floods, some fishes, mainly carp, were trapped in lakes. Nascent aquaculturists fed their brood using nymphs and silkworm feces, and ate the fish for their protein. A fortunate genetic mutation of carp led to the emergence of goldfish during the Tang Dynasty.
Hawaiians practiced aquaculture by constructing fish ponds (see Hawaiian aquaculture). A remarkable example is a fish pond dating from at least 1,000 years ago, at Alekoko. Legend says that it was constructed by the mythical Menehune. The Japanese cultivated seaweed by providing bamboo poles and, later, nets and oyster shells to serve as anchoring surfaces for spores. The Romans bred fish in ponds.
In central Europe, early Christian monasteries adopted Roman aquacultural practices.

Aquaculture spread in Europe during the Middle Ages, since away from the seacoasts and the big rivers, fish were scarce/expensive. Improvements in transportation during the 19th century made fish easily available and inexpensive, even in inland areas, making aquaculture less popular.
In 1859 Stephen Ainsworth of West Bloomfield, New York, began experiments with brook trout. By 1864 Seth Green had established a commercial fish hatching operation at Caledonia Springs, near Rochester, NY. By 1866, with the involvement of Dr. W. W. Fletcher of Concord Mass, artificial fish hatching operations were under way in both Canada and the United States.When the Dildo Island fish hatchery opened in Newfoundland Canada in 1889, it was the largest and most advanced in the world.
California residents harvested wild kelp and attempted to manage supply starting circa 1900, later labeling it a wartime resource.

Tilapia, a commonly farmed fish due to its adaptability
About 430 (97%) of the aquatic species cultured as of 2007 were domesticated during the 20th century, of which an estimated 106 aquatic species came in the decade to 2007. Given the long-term importance of agriculture, it is interesting to note that to date only 0.08% of known land plant species and 0.0002% of known land animal species have been domesticated, compared with 0.17% of known marine plant species and 0.13% of known marine animal species. Domesticating an aquatic species typically involves about a decade of scientific research.Aquatic species involve fewer risks than that of land animals, which took a large toll in human lives through diseases such as smallpox and bird and swine flu, that like most infectious diseases, are transferred to humans from animals. No human pathogens of comparable virulence have yet emerged from marine species.
Stagnation in harvests from wild fisheries and overexploitation of popular marine species, combined with a growing demand for this high quality protein encourages aquaculturists to domesticate other marine species.

Environmental impact

As aquaculture has grown, so have concerns about its environmental impact. In fact, aquaculture can be more environmentally damaging than exploiting wild fisheries. Concerns include waste handling, side-effects of antibiotics, competition between farmed and wild animals, and using other fish to feed consumer-desired carnivorous fish. However, research and commercial feed improvements during the 1990s & 2000s have lessened many of these .About 20 percent of mangrove forests have vanished since 1980, partly due to aqua-farming.
Fish waste is organic and composed of nutrients necessary in all components of aquatic food webs. In-ocean aquaculture often produces much higher than normal concentrations of fish waste in the water. The waste collects on the ocean bottom, damaging or eliminating bottom-dwelling life. Waste can also decrease dissolved oxygen levels in the water column, putting further pressure on wild animals.
Cultivators often supply their animals with antibiotics to prevent disease. As with livestock, this can accelerate the evolution of bacterial resistance.
Fish can escape, where they can encounter wild fish and dilute wild genetic stocks through interbreeding.Escaped fish can become invasive and therefore can have a damaging environmental impact.
Farming carnivorous fish such as salmon typically increases the pressure on wild fish, because producing one kilo of farmed salmon requires up to six kilo of fish or other protein. Adequate diets for salmon and other carnivorous fish can be formulated from protein sources such as soy, although are concerns about changes in the balance between omega-6 and omega-3 fatty acids.
Other aquaculture "crops" such as seaweed and filter-feeding bivalve mollusks such as oysters, clams, mussels and scallops are relatively benign or even restorative environmentally. Filter-feeders filter pollutants as well as nutrients from the water, improving water quality.Seaweeds extract nutrients such as inorganic nitrogen and phosphorus directly from the water, and filter-feeding mollusks can extract nutrients as they feed on particulates phytoplankton and detritus.
Despite the environmental concerns, profitable aquaculture can funnel money into promoting sustainable practices.New methods lessen the risk of biological and chemical pollution through minimizing fish stress, fallowing netpens, and applying Integrated Pest Management. Vaccines are being used more and more to reduce antibiotic use for disease control.
Onshore recirculating aquaculture systems, facilities using polyculture techniques, and properly-sited facilities (e.g. offshore areas with strong currents) are examples of ways to manage the negative environmental effects.

Mariculture

Mariculture is a specialized branch of aquaculture involving the cultivation of marine organisms for food and other products in the open ocean, an enclosed section of the ocean, or in tanks, ponds or raceways which are filled with seawater. An example of the latter is the farming of marine fish, including finfish and shellfish e.g.prawns, or oysters and seaweed in saltwater ponds. Non-food products produced by mariculture include: fish meal, nutrient agar, jewelries (e.g. cultured pearls), and cosmetics.

Integrated Multi-trophic Aquaculture

Integrated Multi-Trophic Aquaculture (IMTA) is a practice in which the by-products (wastes) from one species are recycled to become inputs (fertilizers, food) for another. Fed aquaculture (e.g. fish, shrimp) is combined with inorganic extractive (e.g. seaweed) and organic extractive (e.g. shellfish) aquaculture to create balanced systems for environmental sustainability (biomitigation), economic stability (product diversification and risk reduction) and social acceptability (better management practices).
"Multi-Trophic" refers to the incorporation of species from different trophic or nutritional levels in the same system.This is one potential distinction from the age-old practice of aquatic polyculture, which could simply be the co-culture of different fish species from the same trophic level. In this case, these organisms may all share the same biological and chemical processes, with few synergistic benefits, which could potentially lead to significant shifts in the ecosystem. Some traditional polyculture systems may, in fact, incorporate a greater diversity of species, occupying several niches, as extensive cultures (low intensity, low management) within the same pond. The "Integrated" in IMTA refers to the more intensive cultivation of the different species in proximity of each other, connected by nutrient and energy transfer through water.
Ideally, the biological and chemical processes in an IMTA system should balance. This is achieved through the appropriate selection and proportions of different species providing different ecosystem functions. The co-cultured species are typically more than just biofilters; they are harvestable crops of commercial value.A working IMTA system can result in greater total production based on mutual benefits to the co-cultured species and improved ecosystem health, even if the production of individual species is lower than in a monoculture over a short term period.
Sometimes the term "Integrated Aquaculture" is used to describe the integration of monocultures through water transfer. For all intents and purposes however, the terms "IMTA" and "integrated aquaculture" differ only in their degree of descriptiveness.Aquaponics, fractionated aquaculture, IAAS (integrated agriculture-aquaculture systems), IPUAS (integrated peri-urban-aquaculture systems), and IFAS (integrated fisheries-aquaculture systems) are other variations of the IMTA concept.

Species cultivated

Fish

Fish farming

Fish farming is the most common form of aquaculture. It involves raising fish commercially in tanks or enclosures, usually for food. A facility that releases juvenile fish into the wild for recreational fishing or to supplement a species' natural numbers is generally referred to as a fish hatchery. Fish species raised by fish farms include salmon, catfish, tilapia, cod, carp, tuna and trout.

Shellfish

Abalone farm
Oyster farming

Farming of abalone began in the late 1950s and early 1960s in Japan and China.Since the mid-1990s, there have been many increasingly successful endeavours to commercially farm abalone for the purpose of consumption.Over-fishing and poaching have reduced wild populations to such an extent that farmed abalone now supplies most of the abalone meat consumed.

Shrimp farm

A shrimp farm is an aquaculture business for the cultivation of marine shrimp for human consumption. Commercial shrimp farming began in the 1970s, and production grew steeply thereafter. Global production reached more than 1.6 million tonnes in 2003, representing a value of nearly 9,000 million U.S. dollars. About 75% of farmed shrimp is produced in Asia, in particular in China and Thailand. The other 25% is produced mainly in Latin America, where Brazil is the largest producer. Thailand is the largest exporter.
Shrimp farming has changed from its traditional, small-scale form in Southeast Asia into a global industry. Technological advances have led to ever higher densities per unit area, and broodstock is shipped worldwide. Virtually all farmed shrimp are penaeids (i.e., shrimp of the family Penaeidae), and just two species of shrimp—the Penaeus vannamei (Pacific white shrimp) and the Penaeus monodon (giant tiger prawn) account for roughly 80% of all farmed shrimp. These industrial monocultures are very susceptible to disease, which has decimated shrimp populations across entire regions. Increasing ecological problems, repeated disease outbreaks, and pressure and criticism from both NGOs and consumer countries led to changes in the industry in the late 1990s and generally stronger regulation by governments. In 1999, governments, industry representatives, and environmental organizations initiated a program aimed at developing and promoting more sustainable farming practices.

Freshwater prawns

Freshwater prawn farming shares many characteristics with, and many of the same problems as, marine shrimp farming. Unique problems are introduced by the developmental life cycle of the main species (the giant river prawn, Macrobrachium rosenbergii).The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tons, of which China produced 180,000 tons, followed by India and Thailand with 35,000 tons each. Additionally, China produced about 370,000 tons of Chinese river crab .

Algaculture

Algaculture is a form of aquaculture involving the farming of species of algae.
The majority of algae that are intentionally cultivated fall into the category of microalgae (also referred to as phytoplankton, microphytes, or planktonic algae). Macroalgae, commonly known as seaweed, also have many commercial and industrial uses, but due to their size and the specific requirements of the environment in which they need to grow, they do not lend themselves as readily to cultivation.
Commercial and industrial algae cultivation has numerous uses, including production of food ingredients, food, fertilizer, bioplastics, dyes and colorants, chemical feedstock, pharmaceuticals, and algal fuel, and can also be used as a means of pollution control.

Monoculture

Most growers prefer monocultural production and go to considerable lengths to maintain the purity of their cultures. With mixed cultures, one species comes to dominate over time and if a non-dominant species is believed to have particular value, it is necessary to obtain pure cultures in order to cultivate this species. Individual species cultures are also needed for research purposes.
A common method of obtaining pure cultures is serial dilution. Cultivators dilute a wild sample or a lab sample containing the desired algae with filtered water and introduce small aliquots into a large number of small growing containers. Dilution follows a microscopic examination of the source culture that predicts that a few of the growing containers contain a single cell of the desired species. Following a suitable period on a light table, cultivators again use the microscope to identify containers to start larger cultures.
Alternatively, mixed algae cultures can work well for larval mollusks. First, the cultivator filters the sea water to remove algae which are too large for the larvae to eat. Next, the cultivator adds nutrients and possibly aerates the result. After one or two days in a greenhouse or outdoors, the resulting thin soup of mixed algae is ready for the larvae. An advantage of this method is low maintenance.

Algae fuel

Algae fuel, also called algal fuel, oilgae, algaeoleum or third-generation biofuel, is a biofuel from algae.
High oil prices, competing demands between foods and other biofuel sources and the world food crisis have ignited interest in algaculture (farming algae) for making vegetable oil, biodiesel, bioethanol, biogasoline, biomethanol, biobutanol and other biofuels. Among algal fuels' attractive characteristics: they do not affect fresh water resources,can be produced using ocean and wastewater, and are biodegradable and relatively harmless to the environment if spilled. Algae cost more per unit mass yet can yield over 30 times more energy per unit area than other, second-generation biofuel crops. One biofuels company has claimed that algae can produce more oil in an area the size of a two car garage than a football field of soybeans, because almost the entire algal organism can use sunlight to produce lipids, or oil. The United States Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require 15,000 square miles (40,000 km2). This is less than 1⁄7 the area of corn harvested in the United States in 2000.
During photosynthesis, algae and other photosynthetic organisms capture carbon dioxide and sunlight and convert it into oxygen and biomass. Up to 99% of the carbon dioxide in solution can be converted, which was shown by Weissman and Tillett (1992) in large-scale open-pond systems. The production of biofuels from algae does not reduce atmospheric carbon dioxide (CO2), because any CO2 taken out of the atmosphere by the algae is returned when the biofuels are burned. They do however eliminate the introduction of new CO2 by displacing fossil hydrocarbon fuels.
As of 2008, such fuels remain too expensive to replace other commercially available fuels, with the cost of various algae species typically between US$5–10 per kilogram.But several companies and government agencies are funding efforts to reduce capital and operating costs and make algae oil production commercially viable.

Physical extraction

In the first step of extraction, the oil must be separated from the rest of the plant. The simplest method is mechanical crushing. When algae is dried it retains its oil content, which then can be "pressed" out with an oil press. Many commercial manufacturers of vegetable oil use a combination of mechanical pressing and chemical solvents in extracting oil. Since different strains of algae vary widely in their physical attributes, various press configurations (screw, expeller, piston, etc) work better for specific algae types. Often, mechanical crushing is used in conjunction with chemical solvents, as described below.
Osmotic shock is a sudden reduction in osmotic pressure, this can cause cells in a solution to rupture. Osmotic shock is sometimes used to release cellular components, such as oil.
Ultrasonic extraction, a branch of sonochemistry, can greatly accelerate extraction processes. Using an ultrasonic reactor, ultrasonic waves are used to create cavitation bubbles in a solvent material. When these bubbles collapse near the cell walls, the resulting shock waves and liquid jets cause those cells walls to break and release their contents into a solvent.Ultrasonication can enhance basic enzymatic extraction. The combination "sonoenzymatic treatment" accelerates extraction and increases yields.

Chemical extraction

Chemical solvents are often used in the extraction of the oils. The downside to using solvents for oil extraction are the dangers involved in working with the chemicals. Care must be taken to avoid exposure to vapors and skin contact, either of which can cause serious health damage. Chemical solvents also present an explosion hazard.
A common choice of chemical solvent is hexane, which is widely used in the food industry and is relatively inexpensive. Benzene and ether can also separate oil. Benzene is classified as a carcinogen.
Another method of chemical solvent extraction is Soxhlet extraction. In this method, oils from the algae are extracted through repeated washing, or percolation, with an organic solvent such as hexane or petroleum ether, under reflux in a special glassware.The value of this technique is that the solvent is reused for each cycle.
Enzymatic extraction uses enzymes to degrade the cell walls with water acting as the solvent. This makes fractionation of the oil much easier. The costs of this extraction process are estimated to be much greater than hexane extraction.The enzymatic extraction can be supported by ultrasonication. The combination "sonoenzymatic treatment" causes faster extraction and higher oil yields.
Supercritical CO2 can also be used as a solvent. In this method, CO2 is liquefied under pressure and heated to the point that it becomes supercritical (having properties of both a liquid and a gas), allowing it to act as a solvent.
Other methods are still being developed, including ones to extract specific types of oils, such as those with a high production of long-chain highly unsaturated fatty acids.