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Marine ecology notes

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Introduces Oceanography: oceanic plates, continental shelf, abyssal plain, trenches, hydrothermal vents, black smoke, temperature stratification, water masses and circulation, coriolis effect, el …

Introduces Oceanography: oceanic plates, continental shelf, abyssal plain, trenches, hydrothermal vents, black smoke, temperature stratification, water masses and circulation, coriolis effect, el nino, larvae and larval ecology.

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  • 1. Semester 1Aug – Dec 2012
  • 2. • Study of all the aspect of the physics, chemistry, geology and biology of the sea.• 5 major oceans: Arctic (smlst), Pacific (lgst), Atlantic, Indian and the Antarctic Oceans.• Oceans cover more than 80% of the Southern Hemisphere and only 61% of the Northern Hemisphere.• Oceans also have several seas including Caribbean, Bering, Mediterranean, Baltic,
  • 3. • At the end of the landmasses, the ocean is very shallow due to the extension of the continent – continental shelf• The continental shelf slopes from shore to depths of 100-200meters and can extend offshore for up to 400km.• At the far end of the shelf, there is an abrupt steepening of the bottom called the continental slope.• Descending lower to about 2-3km is the continental rise.
  • 4. • At 4-5km, the bottom becomes flat, extensive, sediment-covered now called the abyssal plain. This is what covers most of the oceans at depths between 3 & 5km.• Abyssal plains are broken in several places by various submarine ridges. These have been found in all oceans and is a contiguous chain.• Example: Mid-Atlantic ridge (separates the Atl ocean i/o east & west)
  • 5. • Occasionally, the ridges break the surface & form islands.• They also mark the boundaries of the various crustal plates of the Earth and are sites of volcanic activity.• In certain areas, the abyssal plains are cut by deep, narrow troughs called trenches that lie in an arc bordering the islands & continents in the Pacific ocean.• Trenches- depths from 7000 to more than 11000m.
  • 6. 1 – Geothermal fields producing electricity2 – mid-ocean ridges crossed by transform faults (transversal fractures)3 – subduction zones (subdecting plate bends downwards
  • 7. • Lge divisions in the Earth’s crust bounded by ridges and trenches – plates• Sizes of the plates vary; 7 plates cover the Earth.• Plates are ridged and float on the mantle covering continental and oceanic crust.• b/c of the slow, continuous mov’t of the plates over geologic time, the continents may take up different positions over time – continental drift.
  • 8. • Plates move b/c the oceanic ridges are centres of volcanic activity where new material is formed & added to the crust.• As volcanism takes place, the plates move in opposite directions causing seafloor spreading.• The opposite would happen in trench systems where the margin of 1 plate dives beneath the other – subduction. The subducting crust melts i/o the mantle once again.• Oceanic ridge sys & subduction zones of the trenches are sites of volcanic & seismic
  • 9. 1 – Cold seawater seeps down thru cracks i/o theocean floor2 – The water seeps further down & the T raises to350-400 degrees C & reacts w/ the rocks as it isheated.3 – Hot liquids are less dense & thus, more buoyantthan cold liquids. Hydrothermal fluids rise up thruthe ocean’s crust carrying dissolved metals &hydrogen sulfide w/ them.4 – The hydrothermal fluid pushes up thru thechimney & mixes w/ the cold seawater. HYDROTHERMAL VENT
  • 10. • The chemical rxns in #2 (prev slide) change the water in the following ways: • Removal of oxygen • Becomes acidic • Picks up dissolved metals including iron, copper & zinc • Picks up hydrogen sulfide• The metals carried in the hydrothermal fluids mix with sulphur to form metal sulfides (black minerals) & give the hydrothermal fluid the appearance of smoke.http://www.divediscover.whoi.edu/vents/vent-infomod.html#
  • 11.
  • 12. • Based on the surface ocean Ts & the overall distribution of organisms, 4 major biogeographical zones can be established: • Polar • Cold temperate • Warm temperate (subtropical) • Tropical (equatorial)• The zones are not absolute since their boundaries may vary with season• Surface waters in Tropical regions are warm (20-30°C) thruout the yr, while the surface water in temperate zones are warm only in the summer
  • 13. • The T begins to fall below the surface water & rapidly decreases as 50-300m is passed (thermocline – depth zone of the most rapid T decline)• T also has an effect on the density of sea water: • Warm sea water is less dense than cold sea water of the same salinity • Increase in salinity causes an increase also in density• The rapid change in T that produces the thermocline suggests that the seawater changes rapidly over the same depth range producing then a zone of rapid density change called the pycnocline
  • 14. • Upper water mass – surface water mass; all well- mixed water above the thermocline • In constant motion due to winds blowing across the surface of the water, earthquakes, volcanic explosions & underwater landslides • The winds produce 2 kinds of motions: waves & currents • Waves range in size from ripples only a few centimetres in height to storm waves 30m high • Wavelength is the horizontal distance btw the tops of crests of successive waves • Earthquakes, volcanic explosions & underwater landslides create tsunamis • The attraction of the moon and the sun create the waves
  • 15. • Wave height in the open ocean is dependent on: 1. Wind speed 2. The distance, or fetch, over which the wind blows 3. The duration that the wind blows• Currents are water movts that result in the horizontal transport of water• The major shallow ocean currents are produced by wind belts in which the winds are steady & persistent in direction• These winds are caused by differential heating of the atmospheric air masses, aided by the Coriolis Effect• Northeast trade winds blow from northeast to southwest btw the equator, while southeast trade winds move air from the southeast to the northwest• Westerlies blow from the southwest to the northeast in the Northern hemisphere & to the southeast in the Southern hemisphere, while the easterlies blow cold air towards the equator (diagram of wind belts)
  • 16. • A phenomenon having to do with the sea-air interaction on a global scale• Occur several times each decade & begin in the tropical Pacific• Warm water builds up in the western pacific & moves eastward across the Pacific bringing warm water to the coasts of South America which are normally cool due to upwelling• The influx of warm water is related to the weakening of the winds @ the equator
  • 17. • Now the higher Ts all across the Pacific in turn changes the atmospheric circulation so that the terrestrial areas that normally receive little rain are rainy & rainy areas undergo droughts• In the marine envt, the increased Ts change shallow-water marine communities & the distribution of spp• Is also destructive on coral reefs due to an increase in T
  • 18. • Deep water masses – below thermocline extending to the bottom• Are not dependent on the wind; when seawater increases in density, it sinks• To move water into the deep basin of the oceans, the density must be increased at the surface• This is accomplished in 2 ways: 1. Losing heat: • Warm water from the tropics or subtropics is high in salinity due to evaporation; this warm saline water is transported out of the Tropics by the Gulf Stream where it meets cold water in Greenland & Iceland’s Labrador Current that is moving south • Cooling at the surface increases the density of this highly saline water & so it sinks to form the North Atlantic deep water • Warm water moving south in the Atlantic loses heat to the atmosphere causing the water masses to sink
  • 19. 2. Becoming more saline • Very high density water mass produced in the Weddell Sea in Antarctica became more saline when winter freezing occur • The water sinks to become the bottom water of most ocean basins• Since these waters are cold & produced @ the surface, they contain large amounts of oxygen which is then transported to the depths. W/o this oxygen deep water would be anoxic• The ocean conveyer belt is due to the temperature & salinity differences in the ocean water that produce vertical & horizontal surface & subsurface ocean currents(See page 17 for diagram in Figure 1.15)
  • 20. • A lge # of marine organisms produce larvae in their lifecycles• Larvae are independent, morphologically different stages that develop from fertilized eggs that must undergo a profound change before assuming adult features• They are almost always smaller than the adult stages• These are important b/c they establish and maintain many marine communities & associations• In any given marine habitat, the distribution & abundance of benthic invertebrates are maintained by 4 factors: • Larval recruitment • Migration • Asexual reproduction • mortality
  • 21. • Many benthic communities are composed of spp that reproduce by producing various larval types that undergo a free-swimming, drifting or crawling stage in the water column or on the bottom before metamorphosing in benthic adultsLarval types & Strategies• There are 3 paths that a benthic invertebrate may take for development: • To produce very many small eggs which hatch quickly i/o larvae that are free swimming in the plankton. They depend on food sources in the water column for nutrition & are called planktotrophic larvae • To produce fewer eggs & give each more nrg in the form of yolk. This allows the larvae to become settled quickly & are called lecithotrophic larvae • To produce few eggs with a large amount of yolk. This involves long dev’t w/o additional nrg sources. The young passes thru the larval stages in the egg & hatch as juveniles. These are called nonpelagic larvae or juveniles
  • 22. • Adv of planktotrophic larvae: - a lge amt of young can be produced w/ the givennrg - wide dispersal is assured thru the long time spent inthe plankton• Disadv of planktotrophic larvae: - larvae depend on the plankton for nutrition, thusallowing the larvae to be exposed to predators• Adv of lecithotrophic larvae: - spends less time in the plankton, thus less chanceof being consumed - do not depend on the plankton for nutrition• Disadv of lecithotrophic larvae: - b/c of the amt of nrg that must be placed i/o eachegg, fewer eggs & larvae are produced - is a larger target for predators - short time in the plankton = less time to disperse
  • 23. • Adv of the nonpelagic larvae: - reduces the planktonic mortality to zero• Disadv of the nonpelagic larvae: - only a few eggs can be produced - there is no dispersal• In polar waters, nonpelagic devt is common although productivity & confined to a narrow summer peak• Lecithotrophic are also common in conditions similar to those in polar waters• Planktotrophic larvae are common in tropical waters bec planktons are high in abundance
  • 24. • Larvae have the ability to “test” the substrate that they land on• If it is not suitable then they find 1 that is suitable• They prefer substrates that already have adults living there• They are attracted to the pheromones released by the adults & so they find substrates that are in close proximity to the adults• Some larvae can even delay their metamorphosis if they do not find a suitable substrate, but at some point, they will metamorphose whether or not they find a suitable substrate to land on• They also respond to light, pressure & salinity….. Some larvae prefer certain pressure & light & so live in certain
  • 25. • Most marine communities are comprised of species having a free swimming larval stage with the exception of polar waters.• Organisms here depend on the settlement of larvae, while adults only live a short time – how do organisms survive?• Wilson [1952] concluded that larval settlement and metamorphosis is dependent on environmental stimuli such as light, gravity, and fluid movement.• Larvae are able to ‘test’ the substrate before settling down to metamorphose. This means certain substrate will always be suitable while others will not.
  • 26. • Larvae also respond to the presence or absence of adults of their own species. They are attracted by the adults’ pheromone [presence of adults suggests suitability of habitat].• Larvae of many invertebrates are able to delay their metamorphosis for a certain period until they find suitable substrates.• After certain time, the larvae will metamorphose whether it finds suitable substrate or not.• Larvae also respond to other physicochemical factors such as light, pressure, and salinity.• Many free floating organisms are positively phototactic in their early stages of their larval life, making the upper, faster moving waters more suitable for living.
  • 27. • Later, they become phototactic and migrate toward the bottom.• Some, however, are highly sensitive to light and pressure and inhabit only certain levels in the water column.• Most studies favour the hypothesis that larvae select their habitat, however, most of these studies have been done in the lab where there is still water.• Along with the still water limitation, there is also the different timing for reproduction making the time in the plankton different.
  • 28. • Physical and chemical differences -