This document summarizes key concepts from a lecture on life in water. It discusses the hydrologic cycle and how it exchanges water among different reservoirs. It then describes various aquatic systems in more detail, including the ocean and its structure, shallow waters like coral reefs and kelp forests, marine shores and the intertidal zone, estuaries and wetlands, rivers and streams, and lakes. For each system, it outlines characteristics like temperature, salinity, oxygen levels, and how organisms have adapted to conditions in different parts of the system. It also discusses human impacts like pollution, overharvesting, and invasive species.

1. Biology 205
Ecology and Adaptation
Lecture 4
Life in Water
Dr. Erik D. Davenport

2. Lecture outline
 Hydrologic cycle.
 Aquatic environmental factors: what, why and
how are they distributed in different aquatic
systems.
 The responses of living organisms to these
factors in different aquatic systems.

3. Water on Earth
-Water covers 71% of the
earth.
– The ocean contains over
97% of total water.
– The polar ice caps and
glaciers contain additional
2%.
– Only 1% of the water is
freshwater that is in
lakes, rivers, and actively
exchanged groundwater.

4. “Distribution of water is not static.”
– Heat
– Evaporation
– Clouds
– Precipitation
 Evaporation
 Consumed by
organisms
 Groundwater
 Surface water

5. “The Hydrologic cycle exchanges water
among reservoirs .”
 The hydrologic cycle
is powered by solar
radiation.
 “Reservoirs” are
places where water
is stored for some
period of time during
the hydrologic cycle.

6. “Turnover times vary among
reservoirs”
 Turnover time: is the
time that required for
entire volume of a
particular reservoir to
be renewed.
 volume/exchange
rate.
 air ~ 9 days.
 ocean ~ 3,100 years.

7. Largest
Ocean Basins:
 Pacific : ~180 million km2
 Atlantic: ~106 million km2
 Indian: ~75 million km2

8. Deepest Ocean – Marianas - 10,000 m
deep (west Pacific)
– Would engulf Mt.
Everest with 2 km to
spare.

9. Ocean Structure:
 Oceanic Zone:
– Epipelagic 0 - 200 m
– Mesopelagic 200 - 1,000 m
– Bathypelagic 1,000 - 4,000 m
– Abyssal 4,000 - 6,000 m
– Hadal 6,000 + m
 Benthic: Habitat on bottom.
 Pelagic: Habitat off the bottom.

10. “Oceans are never still.”
Wind-driven surface
currents across open
ocean create gyres
that move right in the
Northern Hemisphere
and left in the
Southern
Hemisphere.
Deepwater
currents cause
upwelling.

11. Light Penetration in the
Ocean – Approximately
80% of solar
energy striking the
ocean is absorbed
in first 10 m.
– Very little, if any
penetrates past
600 m.
– Leaves
approximately
3,400 m of deep
black water with
only light
produced by
bioluminescence.

12. Temperature
Satellite Sea Surface Temperature from NOAA

13. Temperature in the Ocean – Warm water will
decreases density,
thus warm water
floats on top of
cooler water.
– Ocean water
temperature is
more stable than
terrestrial
temperature.
– Thermocline: a
layer of water
where temperature
changes rapidly
with depth (usually
above 200m).
 Creates
thermal
stratification.

14. Salinity

15. Salinity in the Ocean  Salinity is the
amount of salt
dissolved in
water.
 Salinity unit: parts
per thousand (‰)
or ppt, so 34 ppt
means 34 g of
salt in 1 kilogram
of water.
 Precipitation
affects salinity.

16. Salinity in the Ocean
– In the open
ocean, salinity
varies from about
34 ppt to 36.5 ppt.
– Lowest salinity
occurs near
equator where
precipitation
exceeds
evaporation.
– Highest salinity
occurs in
subtropics where
evaporation
exceeds
precipitation.

17. Oxygen in the Ocean
– A liter of air
contains about
200 ml of oxygen
at sea level, while
a liter of seawater
contains a
maximum of 9 ml
of oxygen.
– Typically
concentration is
highest near
ocean surface,
and decreases
with depth.
Why?????
– Minimum usually
< 1,000m.

18. Biology in the ocean
Ecologists classify
ocean habitat and
their organisms on
the basis of light
levels, depth, and
bottom type.

19. •In the deep of the
ocean, there are
some
chemosynthetic
communities.
•Photosynthetic organisms
are limited to the lighted
epipelagic zone. (also
called euphotic zone)
•The most significant
photosynthetic organisms
are phytoplankton, which
are microscopic
organisms that drift with
the current.

20. Female deep-sea angler fish with her male
partner.

21. Human Influences on the Ocean
 For most of human history, vastness of
oceans has acted as a buffer against human
intrusion. But things have changed.
Over-harvesting Ocean Dumping

22. Shallow Marine
Waters
Among the most productive and
diverse of all ecological systems in
the biosphere are:
“Shallow waters along the continents and islands
support marine communities of very high diversity
and biomass”
•Kelp: seaweed
in the temperate
latitude.
•Coral: only
in tropical
area.

23. Coral Reef
Reefs and kelp beds
both grow in surface
waters with
sufficient light for
photosynthesis.
Both limited by
temperature.
Currents deliver oxygen
and nutrients, and remove
waste products.
Biological productivity
may depend on
flushing action
Kelp Forest

24. Marine Shore

25. Marine shore: Life between low and
high tides
 Marine shores are the
most dynamic
environments in the
biosphere.
 It can be divided into
sandy and rocky
shore.
 Wide variation in light
intensity.

26. Diurnal tides: Single low
and high tide each day.
“Most important water
movements affecting distribution
and abundance of intertidal
organisms are waves and tides.”
Semidiurnal tides: Two
periods of low and high tides
daily.

27. Marine Shores  Intertidal Zone can
be divided
vertically:
– Supratidal Fringe:
Covered by highest
tides.
– Upper Intertidal:
Covered only
during high tides.
– Lower Intertidal:
Uncovered during
lowest tides.
– Subtidal: Covered
by water even
during lowest tides.

28. Marine Shores
 Inhabitants of intertidal zone
are adapted to amphibious
existence.
– Differential tolerances to
periodicity of air exposure leads
to zonation of species.
 Due to increased accessibility,
intertidal zones are
experiencing increasing human
exploitation.

29. Estuaries, Salt
marshes and
mangrove forests
 Salt marshes and mangrove forests
are the transition between land and
sea, however, salt marshes are
distributed mainly along the sandy
shores from temperate to high
latitude, and mangrove forests are
in subtropical and tropical shores.
What is
estuarine? The
area where
rivers meet the
sea.
Salt marsh
Mangrove
Estuary

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Salt marsh and mangrove swamps
Figure 3.22
3-10 Source: Chapman 1977, Long and Mason 1983

31. Physical conditions
 Experience the significant variations in tidal
level.
 Exposed to highly light variations.
 Ocean tide and river flow drive the complex
water movements in the estuaries. And
further influence the nutrients delivery,
oxygen distributions, etc….
 Extremely vulnerable to human intrusion.

32.  Salinity may fluctuate widely, particularly
where the tidal and river flow are
substantial.

33. Rivers and Streams
 Riparian zone is a
transition area
between the aquatic
and upland
terrestrial
environments.

34. Rivers and streams can be divided along
three dimensions:
Length: Pools, runs, riffles, rapids
Width : Wetted / active channels
Vertical: Water surface, column

35. Major Rivers

36. Rivers and Streams
Stream Order
– First Order -
Headwater
– Second Order -
Joining of two first
order.
– Third Order -
Joining of two
second order.
Rivers and streams are vertically
divided into water surface, water
column, and bottom (benthic).
Hyporheic Zone: Transition
between surface water and
groundwater.
Phreatic Zone: Groundwater

37. Rivers and Streams - Physical
Conditions
 Light
– How much light shines on the surface.
– How far light penetrates the water column.
 Water Movements
– Erosion from land.
– Suspended bottom sediments.
 Temperature
– Closely tracks air temperature.

38. Rivers and Streams
 Chemical Conditions
– Salinity
 Reflects history of leaching in the basin.
– Oxygen
 Inversely correlated with temperature.
 Human Influence
– Long, intense history of human use.
 Transportation, Irrigation, Waste Disposal.

39. Lakes
 Most of the world’s freshwater resides in a few
large lakes.
– Great Lakes of North America contain 20% of freshwater
in the world.

40. Lake Structure

41. Lakes - Physical Conditions
 Light
– Lake color depends on light absorption and biological
activity.
 Temperature
– Lakes become thermally stratified as they warm.
 Water Movement
– Wind-driven mixing of the water column is ecologically
important.

42. Seasonal Temperature Changes

43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Oligotrophic and eutrophic lakes
Figure 3.39
3-22

44.  Oligotrophic lake: well-mixed lakes of low
biological productive, and have high oxygen
concentration.
 Eutrophic lakes: lakes with high biological
productivity, and also associated with low or
depleted oxygen concentration.

45. Lakes - Chemical Conditions
 Oxygen
– Oligotrophic: Low biological production, although
often well oxygenated.
– Eutrophic: High biological production, but may be
depleted of oxygen.

46. Lakes - Human Influences
 Human populations have had profound,
usually negative effect.
– Municipal and agricultural run-off ------ increase of
the nutrient concentration. Why excess nutrients
input is bad for lakes?
– Exotic species - Zebra Mussels

47. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Species introduced to the Great Lakes
Figure 3.40
3-23 Source: Mills et al. 1994

48. Review
 Hydrologic Cycle
 Deep Blue Sea
 Shallow Marine Waters
 Marine Shores
 Estuaries, Salt Marshes, and Mangrove
Forests
 Rivers and Streams
 Lakes