The document provides an overview of oceanic features and processes, detailing the structure and movement of the Earth's oceans, including the continental shelf, abyssal plains, and tectonic plates. It also discusses the biogeographical zones based on temperature and the importance of larval stages in marine communities, explaining the various development paths of benthic invertebrates. Additionally, it highlights environmental factors influencing larval settlement and metamorphosis, which are crucial to maintaining marine biodiversity.

1. Semester 1
Aug – 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,

4. • 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.

6. • 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)

7. • 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.

9. 1 – Geothermal fields producing electricity
2 – mid-ocean ridges crossed by transform faults (transversal fractures)
3 – subduction zones (subdecting plate bends downwards

10. • 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.

11. • 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

13. 1 – Cold seawater seeps down thru cracks i/o the
ocean floor
2 – The water seeps further down & the T raises to
350-400 degrees C & reacts w/ the rocks as it is
heated.
3 – Hot liquids are less dense & thus, more buoyant
than cold liquids. Hydrothermal fluids rise up thru
the ocean’s crust carrying dissolved metals &
hydrogen sulfide w/ them.
4 – The hydrothermal fluid pushes up thru the
chimney & mixes w/ the cold seawater.
HYDROTHERMAL VENT

14. • 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#

15. •

16. • 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

17. • 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

19. • 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

20. • 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)

23. • 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

24. • 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

25. • 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

26. 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)

27. • 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

28. • 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
adults
Larval 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

29. • Adv of planktotrophic larvae:
- a lge amt of young can be produced w/ the given
nrg
- wide dispersal is assured thru the long time spent in
the plankton
• Disadv of planktotrophic larvae:
- larvae depend on the plankton for nutrition, thus
allowing the larvae to be exposed to predators
• Adv of lecithotrophic larvae:
- spends less time in the plankton, thus less chance
of 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 each
egg, fewer eggs & larvae are produced
- is a larger target for predators
- short time in the plankton = less time to disperse

30. • 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

31. • 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

32. • 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.

33. • 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.

34. • 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.

35. • Physical and chemical
differences -