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Chapter 3

BIOL150 Chapter Notes - Chapter 3: Peruvian Anchoveta, Thermocline, Neritic Zone


Department
Biology
Course Code
BIOL150
Professor
Rebecca Rooney
Chapter
3

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chapter 3
-abiotic or physical aspects include temperature, precipitation, sunlight, and wind
-biotic (living) components are members of the same or different species
-In freshwater and salt water, 3 key physical factors affect distribution and abundance of organisms: nutrient availability,
water depth, and water movement
NUTRIENT AVAILABILITY:
- nitrogen and phosphorus are in short supply in many aquatic ecosystems
-moving water-> washes away nutrients
-still water-> nutrients fall to the bottom and collect in the form of debris
-nutrient levels important--> limit growth rates in the photosynthetic organisms that food for other species
-2 important events that affect nutrient availability in lakes and oceans: ocean upwelling and lake turnover; bring nutrients
from the bottom to the top where they can be used for the growth of photosynthetic species
Ocean upwelling:
-sometimes the ocean currents bring the nutrients up to the top
-nutrients are being lost in the form of dead organisms in the sunlit surface because of the rain which puts them into the
depths
-upwelling water is nutrient rich. In effect, it recycles nutrients that earlier had fallen to the bottom; the nutrients allow the
growth of photosynthetic cell which feeds small grazing animals and which in turn feeds a small fish called anchoveta
Lake turnover:
-each year, the lakes go under significant changes known as spring and fall turnover; these turnovers are a result of changes
in the air temperature during these two season
-Winter stratification: In winter, top layer of the lake covered with ice at 0 degrees, water just below that is slightly warmer
and very oxygen rich because it was exposed to the atmosphere as winter came in. Below that, the temperature of the
water is around 4-5 degrees and has poor oxygen because the organic material decomposing uses the oxygen.
- gradient (rise) in temperature like this is called thermocline
-Spring turnover: In spring, when ice starts to melt, surface temperature goes to 4 degrees, making the surface water
denser than the bottom, due to this the surface water sinks to the bottom, taking oxygen to the bottom and is replaced by
the water at the bottom. The water from the bottom contains nutrients that come up to the top which triggers the growth
of photosynthetic algae and bacteria called spring bloom
-Fall turnover: In fall, temperature cool, surface temperature goes to 4 degrees -----> rests same as spring turnover.
-without spring and fall turnovers, the nutrients would stay at the bottom
WATER FLOW:
-critical factor because it presents a physical challenge; can sweep away organism
-organism living in fast flowing streams have to deal with the physical force of water, which threatens to move them
downstream
-nutrient and light availability affects productivity and so does water movement
WATER DEPTH
-water absorbs and scatters light, therefore amount and type of wavelength available to organisms change as depth
increases
-light has major influence on productivity-total amount of carbon fixed by photosynthesis per unit area per year
-at water surface, all wavelengths of light equally available
-wavelength in the blue and red regions are required for photosynthesis
-in pure sea water, light penetration is very less; the total light available at 10m is 40 percent less than what available at teh
surface; no light reaches the depth greater than 40m
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