Lecture 9 Flashcards
Define estuaries
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
What are the four different today ranges?(and numbers)
Micro tidal-<2m variation
Mesotidal- 2-4 m variation
Macrotidal- 4-6 m height difference
Hyper tidal- >6m differences
When does sea water enter an estuary?
Twice daily
What happens with twice daily sea water inputs?
Changes in: salinity, temperature,oxygen content
What are rather adaptations of invertebrates in response to the stressful changes in sea water quality?
Migrate, close shells, bury themselves in sediment to limit impacts
How does changes in estuary salinity impact fish?
It impacts their OSMOREGULATION(the maintenance of the organisms water and salt balance across membranes within the body)
What is the density of seawater at 3.94 degrees Celsius compared to freshwater?why?
It’s 0.26 g/ml heavier
Due to the salt content
What are estuary zones based on?
The salinity of the water
What are the estuary zones?
-eurohaline (>30 ppm) Polyhalie (30 to 18 ppm) -mesohaline (18-5 ppm) -oligohaline (5-0.5 ppm) - limnetic (<0.5 ppm)
What are the sediment characteristics of an estuary?
As you move up an estuary, there’s a reduction in sand particles and an increase in clay particles
How is the nutrient availability of ALL estuaries classed?
Hypereutrophic
What limits primary production is estuaries? Why?
Light availability. This because the increased turbidity causes a decrease in the light penetration, reducing the size of the euphotic zone.
Which is the most productive type of algae in estuaries? Why
Diatoms.
They are preserved in periphyton, so when the sea retreats and they aer not limited by light, they can fully photosynthesises
What type of feeding organisms are estuaries dominated by?
Collectors
Why is there high levels of competition for space on the substrate floor in estuaries?
The hyper eutrophic conditions mean that food isn’t limiting
What are the food types fro benthic invertebrates?
Aerobic: -filter feeders -selective deposit feeders Anaerobic: -bacteria and silicates at high density Both: No selective deposit feeders
how does salinity, temperature and oxygen availability change along estuaries with gradients
- salinity decreases in psu with distance along the estuary
- temperature increases with distance along the estuary
- oxygen availability decreases with distance along the estuary
what are different estuary zones based off?
-water salinity
what are the different estuary zones and their salinity in psu
>30 is eurohaline 18-30 is polyhaline 5-18 is mesohaline 0.5-5 is oligohaline <0.5 is limnetic (freshwater)
explain the light climate and periphyton in algae communities
- 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
what is the impact of poorly productive algae in these environments
-a small zooplankton biomass
summarise the nutrient, light and oxygen availability in estuaries
- not limited by C,N,P
- anoxic sediments release nutrients, making the nutrient problem worse
- primary production is limited by light
why are estuaries so productive?
-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.
what resource has the most competition in estuaries between benthic invertebrates?
-nutrients are non limiting, meaning that populations can be large and fight for SPACE
give information on an example estuary filter feeder (feeding habits, amount per m^2 etc)
- 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
give information on an example estuary selective deposit feeders (feeding habits, amount per m^2 etc)
- 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
what do hydrobia snails do to avoid space competition?
-character displacement to establish niches and avoid intense competition
give information on an example non selective deposit feeders (feeding habits, amount per m^2 etc)
- Arenicola Marina (lugworms), density 150m^2
- consumes sediment and sand to acquire food.
- will also reingest their own faeces, once cultivated by microbes
what is the dominate deposit feeder is estuaries?
polychaete worms
What is Macoma balthica
- a filter feeder and non selective deposit feeder -3500 per M^2
- reside underneath sediment surface
- have inlet (long) and outlet (short)siphons
describe the feeding habits of Macoma balthica
- 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)
what is the significance of Macoma balthica deposit feeding shape?
- 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
what is the feeding breakdown of Macoma balthica
-10-4-% filter feeder
60-90% deposit feeder (preferential)
what are polychaete worms examples of? explain their feeding habits
- 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
what is the main competition between polychete worms?why?
- space
- palps collide when theyre too close
what is the dominant predator in estuaries(give information on habitat, density, feeding etc)
- Ragworm, 1000000m^2 density
- live in J burrows and predate invertebrates (will feed with mucus like snails when food levels too low)
how do ragworms deal with competition?
-bit off tails of competitors (same species), so while they spend resources regrowing their tails they cant feed and this reduces the food competition
describe feeder distribution along estuaries
- at the mouth, theres more filter feeders
- as you progress up and clay content increases, the deposit feeders increase
what are oligohaline, true esturine and eurohaline organisms?
- oligohaline organisms live in 0.5-5 psu salinity
- true estuarine organisms line in 5-18 psu
- eurohaline organisms live in 18-30 psu
what is the biggest current threat to estuaries? why?
- rising sea water levels
- could cause tides to increase above a level that causes flooding
