Econstudentlog

Marine Biology (I)

This book was ‘okay’.

Some quotes and links related to the first half of the book below.

Quotes:

“The Global Ocean has come to be divided into five regional oceans – the Pacific, Atlantic, Indian, Arctic, and Southern Oceans […] These oceans are large, seawater-filled basins that share characteristic structural features […] The edge of each basin consists of a shallow, gently sloping extension of the adjacent continental land mass and is term the continental shelf or continental margin. Continental shelves typically extend off-shore to depths of a couple of hundred metres and vary from several kilometres to hundreds of kilometres in width. […] At the outer edge of the continental shelf, the seafloor drops off abruptly and steeply to form the continental slope, which extends down to depths of 2–3 kilometres. The continental slope then flattens out and gives way to a vast expanse of flat, soft, ocean bottom — the abyssal plain — which extends over depths of about 3–5 kilometres and accounts for about 76 per cent of the Global Ocean floor. The abyssal plains are transected by extensive mid-ocean ridges—underwater mountain chains […]. Mid-ocean ridges form a continuous chain of mountains that extend linearly for 65,000 kilometres across the floor of the Global Ocean basins […]. In some places along the edges of the abyssal plains the ocean bottom is cut by narrow, oceanic trenches or canyons which plunge to extraordinary depths — 3–4 kilometres below the surrounding seafloor — and are thousands of kilometres long but only tens of kilometres wide. […] Seamounts are another distinctive and dramatic feature of ocean basins. Seamounts are typically extinct volcanoes that rise 1,000 or more metres above the surrounding ocean but do not reach the surface of the ocean. […] Seamounts generally occur in chains or clusters in association with mid-ocean ridges […] The Global Ocean contains an estimated 100,000 or so seamounts that rise more than 1,000 metres above the surrounding deep-ocean floor. […] on a planetary scale, the surface of the Global Ocean is moving in a series of enormous, roughly circular, wind-driven current systems, or gyres […] These gyres transport enormous volumes of water and heat energy from one part of an ocean basin to another

“We now know that the oceans are literally teeming with life. Viruses […] are astoundingly abundant – there are around ten million viruses per millilitre of seawater. Bacteria and other microorganisms occur at concentrations of around 1 million per millilitre”

“The water in the oceans is in the form of seawater, a dilute brew of dissolved ions, or salts […] Chloride and sodium ions are the predominant salts in seawater, along with smaller amounts of other ions such as sulphate, magnesium, calcium, and potassium […] The total amount of dissolved salts in seawater is termed its salinity. Seawater typically has a salinity of roughly 35 – equivalent to about 35 grams of salts in one kilogram of seawater. […] Most marine organisms are exposed to seawater that, compared to the temperature extremes characteristic of terrestrial environments, ranges within a reasonably moderate range. Surface waters in tropical parts of ocean basins are consistently warm throughout the year, ranging from about 20–27°C […]. On the other hand, surface seawater in polar parts of ocean basins can get as cold as −1.9°C. Sea temperatures typically decrease with depth, but not in a uniform fashion. A distinct zone of rapid temperature transition is often present that separates warm seawater at the surface from cooler deeper seawater. This zone is called the thermocline layer […]. In tropical ocean waters the thermocline layer is a strong, well-defined and permanent feature. It may start at around 100 metres and be a hundred or so metres thick. Sea temperatures above the thermocline can be a tropical 25°C or more, but only 6–7°C just below the thermocline. From there the temperature drops very gradually with increasing depth. Thermoclines in temperate ocean regions are a more seasonal phenomenon, becoming well established in the summer as the sun heats up the surface waters, and then breaking down in the autumn and winter. Thermoclines are generally absent in the polar regions of the Global Ocean. […] As a rule of thumb, in the clearest ocean waters some light will penetrate to depths of 150-200 metres, with red light being absorbed within the first few metres and green and blue light penetrating the deepest. At certain times of the year in temperate coastal seas light may penetrate only a few tens of metres […] In the oceans, pressure increases by an additional atmosphere every 10 metres […] Thus, an organism living at a depth of 100 metres on the continental shelf experiences a pressure ten times greater than an organism living at sea level; a creature living at 5 kilometres depth on an abyssal plain experiences pressures some 500 times greater than at the surface”.

“With very few exceptions, dissolved oxygen is reasonably abundant throughout all parts of the Global Ocean. However, the amount of oxygen in seawater is much less than in air — seawater at 20°C contains about 5.4 millilitres of oxygen per litre of seawater, whereas air at this temperature contains about 210 millilitres of oxygen per litre. The colder the seawater, the more oxygen it contains […]. Oxygen is not distributed evenly with depth in the oceans. Oxygen levels are typically high in a thin surface layer 10–20 metres deep. Here oxygen from the atmosphere can freely diffuse into the seawater […] Oxygen concentration then decreases rapidly with depth and reaches very low levels, sometimes close to zero, at depths of around 200–1,000 metres. This region is referred to as the oxygen minimum zone […] This zone is created by the low rates of replenishment of oxygen diffusing down from the surface layer of the ocean, combined with the high rates of depletion of oxygen by decaying particulate organic matter that sinks from the surface and accumulates at these depths. Beneath the oxygen minimum zone, oxygen content increases again with depth such that the deep oceans contain quite high levels of oxygen, though not generally as high as in the surface layer. […] In contrast to oxygen, carbon dioxide (CO2) dissolves readily in seawater. Some of it is then converted into carbonic acid (H2CO3), bicarbonate ion (HCO3-), and carbonate ion (CO32-), with all four compounds existing in equilibrium with one another […] The pH of seawater is inversely proportional to the amount of carbon dioxide dissolved in it. […] the warmer the seawater, the less carbon dioxide it can absorb. […] Seawater is naturally slightly alkaline, with a pH ranging from about 7.5 to 8.5, and marine organisms have become well adapted to life within this stable pH range. […] In the oceans, carbon is never a limiting factor to marine plant photosynthesis and growth, as it is for terrestrial plants.”

“Since the beginning of the industrial revolution, the average pH of the Global Ocean has dropped by about 0.1 pH unit, making it 30 per cent more acidic than in pre-industrial times. […] As a result, more and more parts of the oceans are falling below a pH of 7.5 for longer periods of time. This trend, termed ocean acidification, is having profound impacts on marine organisms and the overall functioning of the marine ecosystem. For example, many types of marine organisms such as corals, clams, oysters, sea urchins, and starfish manufacture external shells or internal skeletons containing calcium carbonate. When the pH of seawater drops below about 7.5, calcium carbonate starts to dissolve, and thus the shells and skeletons of these organisms begin to erode and weaken, with obvious impacts on the health of the animal. Also, these organisms produce their calcium carbonate structures by combining calcium dissolved in seawater with carbonate ion. As the pH decreases, more of the carbonate ions in seawater become bound up with the increasing numbers of hydrogen ions, making fewer carbonate ions available to the organisms for shell-forming purposes. It thus becomes more difficult for these organisms to secrete their calcium carbonate structures and grow.”

“Roughly half of the planet’s primary production — the synthesis of organic compounds by chlorophyll-bearing organisms using energy from the sun—is produced within the Global Ocean. On land the primary producers are large, obvious, and comparatively long-lived — the trees, shrubs, and grasses characteristic of the terrestrial landscape. The situation is quite different in the oceans where, for the most part, the primary producers are minute, short-lived microorganisms suspended in the sunlit surface layer of the oceans. These energy-fixing microorganisms — the oceans’ invisible forest — are responsible for almost all of the primary production in the oceans. […] A large amount, perhaps 30-50 per cent, of marine primary production is produced by bacterioplankton comprising tiny marine photosynthetic bacteria ranging from about 0.5 to 2 μm in size. […] light availability and the strength of vertical mixing are important factors limiting primary production in the oceans. Nutrient availability is the other main factor limiting the growth of primary producers. One important nutrient is nitrogen […] nitrogen is a key component of amino acids, which are the building blocks of proteins. […] Photosynthetic marine organisms also need phosphorus, which is a requirement for many important biological functions, including the synthesis of nucleic acids, a key component of DNA. Phosphorus in the oceans comes naturally from the erosion of rocks and soils on land, and is transported into the oceans by rivers, much of it in the form of dissolved phosphate (PO43−), which can be readily absorbed by marine photosynthetic organisms. […] Inorganic nitrogen and phosphorus compounds are abundant in deep-ocean waters. […] In practice, inorganic nitrogen and phosphorus compounds are not used up at exactly the same rate. Thus one will be depleted before the other and becomes the limiting nutrient at the time, preventing further photosynthesis and growth of marine primary producers until it is replenished. Nitrogen is often considered to be the rate-limiting nutrient in most oceanic environments, particularly in the open ocean. However, in coastal waters phosphorus is often the rate-limiting nutrient.”

“The overall pattern of primary production in the Global Ocean depends greatly on latitude […] In polar oceans primary production is a boom-and-bust affair driven by light availability. Here the oceans are well mixed throughout the year so nutrients are rarely limiting. However, during the polar winter there is no light, and thus no primary production is taking place. […] Although limited to a short seasonal pulse, the total amount of primary production can be quite high, especially in the polar Southern Ocean […] In tropical open oceans, primary production occurs at a low level throughout the year. Here light is never limiting but the permanent tropical thermocline prevents the mixing of deep, nutrient-rich seawater with the surface waters. […] open-ocean tropical waters are often referred to as ‘marine deserts’, with productivity […] comparable to a terrestrial desert. In temperate open-ocean regions, primary productivity is linked closely to seasonal events. […] Although occurring in a number of pulses, primary productivity in temperate oceans [is] similar to [that of] a temperate forest or grassland. […] Some of the most productive marine environments occur in coastal ocean above the continental shelves. This is the result of a phenomenon known as coastal upwelling which brings deep, cold, nutrient-rich seawater to the ocean surface, creating ideal conditions for primary productivity […], comparable to a terrestrial rainforest or cultivated farmland. These hotspots of marine productivity are created by wind acting in concert with the planet’s rotation. […] Coastal upwelling can occur when prevailing winds move in a direction roughly parallel to the edge of a continent so as to create offshore Ekman transport. Coastal upwelling is particularly prevalent along the west coasts of continents. […] Since coastal upwelling is dependent on favourable winds, it tends to be a seasonal or intermittent phenomenon and the strength of upwelling will depend on the strength of the winds. […] Important coastal upwelling zones around the world include the coasts of California, Oregon, northwest Africa, and western India in the northern hemisphere; and the coasts of Chile, Peru, and southwest Africa in the southern hemisphere. These regions are amongst the most productive marine ecosystems on the planet.”

“Considering the Global Ocean as a whole, it is estimated that total marine primary production is about 50 billion tonnes of carbon per year. In comparison, the total production of land plants, which can also be estimated using satellite data, is estimated at around 52 billion tonnes per year. […] Primary production in the oceans is spread out over a much larger surface area and so the average productivity per unit of surface area is much smaller than on land. […] the energy of primary production in the oceans flows to higher trophic levels through several different pathways of various lengths […]. Some energy is lost along each step of the pathway — on average the efficiency of energy transfer from one trophic level to the next is about 10 per cent. Hence, shorter pathways are more efficient. Via these pathways, energy ultimately gets transferred to large marine consumers such as large fish, marine mammals, marine turtles, and seabirds.”

“…it has been estimated that in the 17th century, somewhere between fifty million and a hundred million green turtles inhabited the Caribbean Sea, but numbers are now down to about 300,000. Since their numbers are now so low, their impact on seagrass communities is currently small, but in the past, green turtles would have been extraordinarily abundant grazers of seagrasses. It appears that in the past, green turtles thinned out seagrass beds, thereby reducing direct competition among different species of seagrass and allowing several species of seagrass to coexist. Without green turtles in the system, seagrass beds are generally overgrown monocultures of one dominant species. […] Seagrasses are of considerable importance to human society. […] It is therefore of great concern that seagrass meadows are in serious decline globally. In 2003 it was estimated that 15 per cent of the planet’s existing seagrass beds had disappeared in the preceding ten years. Much of this is the result of increasing levels of coastal development and dredging of the seabed, activities which release excessive amounts of sediment into coastal waters which smother seagrasses. […] The number of marine dead zones in the Global Ocean has roughly doubled every decade since the 1960s”.

“Sea ice is habitable because, unlike solid freshwater ice, it is a very porous substance. As sea ice forms, tiny spaces between the ice crystals become filled with a highly saline brine solution resistant to freezing. Through this process a three-dimensional network of brine channels and spaces, ranging from microscopic to several centimetres in size, is created within the sea ice. These channels are physically connected to the seawater beneath the ice and become colonized by a great variety of marine organisms. A significant amount of the primary production in the Arctic Ocean, perhaps up to 50 per cent in those areas permanently covered by sea ice, takes place in the ice. […] Large numbers of zooplanktonic organisms […] swarm about on the under surface of the ice, grazing on the ice community at the ice-seawater interface, and sheltering in the brine channels. […] These under-ice organisms provide the link to higher trophic levels in the Arctic food web […] They are an important food source for fish such as Arctic cod and glacial cod that graze along the bottom of the ice. These fish are in turn fed on by squid, seals, and whales.”

“[T]he Antarctic marine system consists of a ring of ocean about 10° of latitude wide – roughly 1,000 km. […] The Arctic and Antarctic marine systems can be considered geographic opposites. In contrast to the largely landlocked Arctic Ocean, the Southern Ocean surrounds the Antarctic continental land mass and is in open contact with the Atlantic, Indian, and Pacific Oceans. Whereas the Arctic Ocean is strongly influenced by river inputs, the Antarctic continent has no rivers, and so hard-bottomed seabed is common in the Southern Ocean, and there is no low-saline surface layer, as in the Arctic Ocean. Also, in contrast to the Arctic Ocean with its shallow, broad continental shelves, the Antarctic continental shelf is very narrow and steep. […] Antarctic waters are extremely nutrient rich, fertilized by a permanent upwelling of seawater that has its origins at the other end of the planet. […] This continuous upwelling of cold, nutrient-rich seawater, in combination with the long Antarctic summer day length, creates ideal conditions for phytoplankton growth, which drives the productivity of the Antarctic marine system. As in the Arctic, a well-developed sea-ice community is present. Antarctic ice algae are even more abundant and productive than in the Arctic Ocean because the sea ice is thinner, and there is thus more available light for photosynthesis. […] Antarctica’s most important marine species [is] the Antarctic krill […] Krill are very adept at surviving many months under starvation conditions — in the laboratory they can endure more than 200 days without food. During the winter months they lower their metabolic rate, shrink in body size, and revert back to a juvenile state. When food once again becomes abundant in the spring, they grow rapidly […] As the sea ice breaks up they leave the ice and begin feeding directly on the huge blooms of free-living diatoms […]. With so much food available they grow and reproduce quickly, and start to swarm in large numbers, often at densities in excess of 10,000 individuals per cubic metre — dense enough to colour the seawater a reddish-brown. Krill swarms are patchy and vary greatly in size […] Because the Antarctic marine system covers a large area, krill numbers are enormous, estimated at about 600 billion animals on average, or 500 million tonnes of krill. This makes Antarctic krill one of the most abundant animal species on the planet […] Antarctic krill are the main food source for many of Antarctica’s large marine animals, and a key link in a very short and efficient food chain […]. Krill comprise the staple diet of icefish, squid, baleen whales, leopard seals, fur seals, crabeater seals, penguins, and seabirds, including albatross. Thus, a very simple and efficient three-step food chain is in operation — diatoms eaten by krill in turn eaten by a suite of large consumers — which supports the large numbers of large marine animals living in the Southern Ocean.”

Links:

Ocean gyre. North Atlantic Gyre. Thermohaline circulation. North Atlantic Deep Water. Antarctic bottom water.
Cyanobacteria. Diatom. Dinoflagellate. Coccolithophore.
Trophic level.
Nitrogen fixation.
High-nutrient, low-chlorophyll regions.
Light and dark bottle method of measuring primary productivity. Carbon-14 method for estimating primary productivity.
Ekman spiral.
Peruvian anchoveta.
El Niño. El Niño–Southern Oscillation.
Copepod.
Dissolved organic carbon. Particulate organic matter. Microbial loop.
Kelp forest. Macrocystis. Sea urchin. Urchin barren. Sea otter.
Seagrass.
Green sea turtle.
Manatee.
Demersal fish.
Eutrophication. Harmful algal bloom.
Comb jelly. Asterias amurensis.
Great Pacific garbage patch.
Eelpout. Sculpin.
Polynya.
Crabeater seal.
Adélie penguin.
Anchor ice mortality.

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March 13, 2018 - Posted by | Biology, Books, Botany, Chemistry, Ecology, Geology, Zoology

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