L10 - Estuaries and oceans

Question 1

What are estuaries?

Answer 1

TRANSIENT ZONES BETWEEN RIVERS AND THE SEA

Question 2

What are the characteristics of estuaries?

Answer 2

Intermediate levels of salinity (defining factor - separates them from other water bodies)

Includes harbours, inlets/sounds, lagoons, and bays (but not brackish seas – sorry Baltic!)

Complex and dynamic habitats – daily fluctuations in abiotic factors (water depth, temperature, salinity, etc.)

Characterized by high nutrients, low species diversity, but the highest biomass of all aquatic habitats

Question 3

What is meant by tidal range?

Answer 3

height difference between maximum (Spring tide) and minimum (Neap tide)

Question 4

How do fluctuations in tidal water, within estuaries, lead to a stressful environment?

Answer 4

Organisms need good osmoregulation to deal with salinity changes
Options for dealing with water level changes:
- Move with the water
- Bury in the sediment
- Close shells

Question 5

Why is freshwater less dense than seawater?

Answer 5

• warmer
• less saline (salty)

Question 6

Why does mixing occur in esturies?

Answer 6

BECAUSE DEPTH DECREASES TOWARDS THE RIVER

Question 7

What does mixing in estuaries create?

Answer 7

a salinity gradient

Question 8

What equation is used for particle sinking?

Answer 8

Stokes Equation

Question 9

What does a sediment gradient of clay to sand affect, why?

Answer 9

Water turbidity
- sand is bigger and heavier than clay so settles quicker

Question 10

What is estuary production dominated by, and why?

Answer 10

Periphyton
- Turbid water → light-limitation for phytoplankton
- Sediments exposed by low tide get plenty of sunlight

Question 11

What are periphyton?

Answer 11

Attached microbial communities
- Algae and heterotrophic microbes (bacteria, protozoa, and fungi) live in a jelly-like matrix
- Major algae = pennate diatoms
- Matrix prevents dehydration and stores nutrients
- Community can function in and out of water

Question 12

Why are rivers dominated by periphyton, compared to estuaries?

Answer 12

Rivers: flowing water flushes phytoplankton faster than they can reproduce, so producer community needs to be attached

Estuaries: high turbidity means phytoplankton are light-limited, but periphyton on sediment is exposed to sun

Question 13

What is the most productive aquatic habitat?

Answer 13

Estuaries
- Nutrient rich - estuaries have excess N and P from both river and sea
- Instead, productivity is limited more by light
- Macroinvertebrates compete for space in the sediments

Question 14

How much of the earth’s surface covered by oceans?

Answer 14

~70%

Question 15

Where does most marine life ive in the oceans?

Answer 15

IN THE TOP 200M
- Epipelagic: Most life – phytoplankton based

• Mesopelagic: The “twilight zone” – high vertical migration to look for food (600m)
• Bathypelagic: Eternal darkness – sharp reduction in biomass
• Abyssopelagic: Colourless inhabitants, no eyes

Question 16

What are the major differences in the food web of oceans and lakes?

Answer 16

• Marine zooplankton are more diverse, can be larger
• Krill are the keystone species
• Other important groups: Copepods, rotifers, gelatinous (e.g., jellyfish), and barnacle/fish larvae

Question 17

Why are ocean currents important for marine ecosystems?

Answer 17

Driven by wind & the Coriolis effect (from earth’s rotation), which forces water:
- Clockwise in the northern hemisphere
- Anti-clockwise in the southern hemisphere