Lecture 9

Question 1

Define estuaries

Answer 1

Semi I closed coastal bodies of water with free connection to the open ocean, within which the sea water is measurable dilute with freshwater derived from land drainage

Question 2

What are the four different today ranges?(and numbers)

Answer 2

Micro tidal-<2m variation
Mesotidal- 2-4 m variation
Macrotidal- 4-6 m height difference
Hyper tidal- >6m differences

Question 3

When does sea water enter an estuary?

Answer 3

Twice daily

Question 4

What happens with twice daily sea water inputs?

Answer 4

Changes in: salinity, temperature,oxygen content

Question 5

What are rather adaptations of invertebrates in response to the stressful changes in sea water quality?

Answer 5

Migrate, close shells, bury themselves in sediment to limit impacts

Question 6

How does changes in estuary salinity impact fish?

Answer 6

It impacts their OSMOREGULATION(the maintenance of the organisms water and salt balance across membranes within the body)

Question 7

What is the density of seawater at 3.94 degrees Celsius compared to freshwater?why?

Answer 7

It’s 0.26 g/ml heavier

Due to the salt content

Question 8

What are estuary zones based on?

Answer 8

The salinity of the water

Question 9

What are the estuary zones?

Answer 9

-eurohaline (>30 ppm)
Polyhalie (30 to 18 ppm)
-mesohaline (18-5 ppm)
-oligohaline (5-0.5 ppm)
- limnetic (<0.5 ppm)

Question 10

What are the sediment characteristics of an estuary?

Answer 10

As you move up an estuary, there’s a reduction in sand particles and an increase in clay particles

Question 11

How is the nutrient availability of ALL estuaries classed?

Answer 11

Hypereutrophic

Question 12

What limits primary production is estuaries? Why?

Answer 12

Light availability. This because the increased turbidity causes a decrease in the light penetration, reducing the size of the euphotic zone.

Question 13

Which is the most productive type of algae in estuaries? Why

Answer 13

Diatoms.
They are preserved in periphyton, so when the sea retreats and they aer not limited by light, they can fully photosynthesises

Question 14

What type of feeding organisms are estuaries dominated by?

Answer 14

Collectors

Question 15

Why is there high levels of competition for space on the substrate floor in estuaries?

Answer 15

The hyper eutrophic conditions mean that food isn’t limiting

Question 16

What are the food types fro benthic invertebrates?

Answer 16

Aerobic:
-filter feeders
-selective deposit feeders 
Anaerobic:
-bacteria and silicates at high density
Both: 
No selective deposit feeders

Question 17

how does salinity, temperature and oxygen availability change along estuaries with gradients

Answer 17

• salinity decreases in psu with distance along the estuary
• temperature increases with distance along the estuary
• oxygen availability decreases with distance along the estuary

Question 18

what are different estuary zones based off?

Answer 18

-water salinity

Question 19

what are the different estuary zones and their salinity in psu

Answer 19

>30 is eurohaline
18-30 is polyhaline
5-18 is mesohaline
0.5-5 is oligohaline
<0.5 is limnetic (freshwater)

Question 20

explain the light climate and periphyton in algae communities

Answer 20

• algae are light limited due to increased turbidity. this reduces the size of the euphotic zone
• light can reach the algae when diatoms in periphyton are exposed when the tide goes out, making them the most productive algae types in this environment

Question 21

what is the impact of poorly productive algae in these environments

Answer 21

-a small zooplankton biomass

Question 22

summarise the nutrient, light and oxygen availability in estuaries

Answer 22

• not limited by C,N,P
• anoxic sediments release nutrients, making the nutrient problem worse
• primary production is limited by light

Question 23

why are estuaries so productive?

Answer 23

-biofilms are 100% exposed to sunlight when the tide goes out, giving maximum light for photosynthesis. At the same time ,the dominating form of algae within biofilm are diatoms, which are incredibly efficient.

Question 24

what resource has the most competition in estuaries between benthic invertebrates?

Answer 24

-nutrients are non limiting, meaning that populations can be large and fight for SPACE

Question 25

give information on an example estuary filter feeder (feeding habits, amount per m^2 etc)

Answer 25

• Muscles (Bivalves)
• have inlet and outlet siphons that they use to feed on suspended prey
• non selective feeders, so can easily accumulate dangerous toxins
• 1500 m^2

Question 26

give information on an example estuary selective deposit feeders (feeding habits, amount per m^2 etc)

Answer 26

• Hydrobia mud snails, 300000 m^2
• feed on biofilm by producing a mucas net which lays across it. The snails then consume the biofilm and the net
• these snails only exist in regions of eutrophic conditions, so are subsequently indicators of regions with high nutrient availability

Question 27

what do hydrobia snails do to avoid space competition?

Answer 27

-character displacement to establish niches and avoid intense competition

Question 28

give information on an example non selective deposit feeders (feeding habits, amount per m^2 etc)

Answer 28

• Arenicola Marina (lugworms), density 150m^2
• consumes sediment and sand to acquire food.
• will also reingest their own faeces, once cultivated by microbes

Question 29

what is the dominate deposit feeder is estuaries?

Answer 29

polychaete worms

Question 30

What is Macoma balthica

Answer 30

• a filter feeder and non selective deposit feeder -3500 per M^2
• reside underneath sediment surface
• have inlet (long) and outlet (short)siphons

Question 31

describe the feeding habits of Macoma balthica

Answer 31

• protrudes inlet sihpons into overflowing water, and “sucks up” the water and any food it contains
• when the tide goes out, they feed by deposit feeding by “hoovering” the sediment in a circle (with siphon)

Question 32

what is the significance of Macoma balthica deposit feeding shape?

Answer 32

• they hoover with siphons in absolute circles, and every organism requires enough space. They space perfectly to avoid crossing
• this is an example of interspecfic competition

Question 33

what is the feeding breakdown of Macoma balthica

Answer 33

-10-4-% filter feeder

60-90% deposit feeder (preferential)

Question 34

what are polychaete worms examples of? explain their feeding habits

Answer 34

• some are filter feeders and deposit feeders

- they use palps which expand into the water column for filter feeding, or hoover the surface for deposit feeding

Question 35

what is the main competition between polychete worms?why?

Answer 35

• space

- palps collide when theyre too close

Question 36

what is the dominant predator in estuaries(give information on habitat, density, feeding etc)

Answer 36

• Ragworm, 1000000m^2 density

- live in J burrows and predate invertebrates (will feed with mucus like snails when food levels too low)

Question 37

how do ragworms deal with competition?

Answer 37

-bit off tails of competitors (same species), so while they spend resources regrowing their tails they cant feed and this reduces the food competition

Question 38

describe feeder distribution along estuaries

Answer 38

• at the mouth, theres more filter feeders

- as you progress up and clay content increases, the deposit feeders increase

Question 39

what are oligohaline, true esturine and eurohaline organisms?

Answer 39

• oligohaline organisms live in 0.5-5 psu salinity
• true estuarine organisms line in 5-18 psu
• eurohaline organisms live in 18-30 psu

Question 40

what is the biggest current threat to estuaries? why?

Answer 40

• rising sea water levels

- could cause tides to increase above a level that causes flooding