Sandy/Muddy Shores & Estuaries Flashcards
What did Fenberg (lecturer) study when looking into global patterns of the sedimentary environment?
How the distribution of rock affected rocky shore species
How did Fenberg (lecturer) study the effect of rock distribution on rocky shore species?
- Used Google Earth
- Measured the length of each beach or soft-sediment stretch of coastline across the most eastern Pacific coast, from Chile up to N. Washington State, USA (>90° Latitude, spanning 23,000km of coastline)
What did Fenberg (lecturer) find in his study of the effect of rock distribution on rocky shore species?
- In the southern and northern latitudes it is very rocky
- In mid-latitudes areas around the equator is was sandy and muddy
- Lot more beaches in the tropics
What are the gaps found in relation to the rock distribution along coastlines and how big are the?
- Northern Peruvian Gap (171km)
- Columbian Gap (289km) (mostly mangroves)
- Central American Gap (671km)
- Northern Gulf of California Gaps (317km combined)
- Nayarit/Sinaloan Gap (207km)
- 2 Sinaloan Gaps (701km combined)
Is the coastal rock distribution that Fenberg (lecturer) found in his study a global pattern?
- Has been done globally using satellites
- Similar findings:
> On average there is a lot less rock in the tropics
> Sandy beaches are NOT evenly distributed across the globe
> Has been known since the 1960s but never made it out of marine geology literature
What possible explanations are there for global coastal rock distribution patterns?
- Tropics: possibly impacted by rainfall, big rivers create large estuaries and beaches, lot more erosion/river influx
- Polar regions: glaciation & isostatic rebound = more rocky
- Seems to be related to coastal climate, freshwater inflow and glaciation history
- Abiotic factors influence biotic factors - beaches create abiotic barriers which inhibits gene flow
What are rocky shores usually inhabited by?
Sessile and mobile epifauna
What are soft shores usually inhabited by?
Mobile epifauna and infauna - usually burrow down
What is porosity of a shoreline?
The volume of pore space between each sediment particle
How does particle size of sediment effect porosity of a shoreline?
- Small particles fill up more space and reduce porosity
- Large particles = more empty spaces and increased porosity
What is permeability of a shoreline?
The rate of percolation of water through the sediment
On the shoreline how does porosity effect permeability?
- Low porosity = low permeability
- High porosity = high permeability
What is water content of a shoreline related to?
- Particle size
- Beach profile
- Water table height
What are trait of dilatant sands?
- When pressure is applied, the sand becomes dry and hard packed as water is driven out
- Harder to burrow into = less biodiversity
What are the traits of thixotropic sands (quick-sands)?
- Sands with high clay content become wetter and more easily penetrated when agitated
- Sand it easier to burrow in to = more biodiversity
What are the traits of muds?
- Do not drain and are saturated with water - very soft
- Easiest to burrow in to = more biodiversity
Oxygen & sediment chemistry: What does aerobic bacteria in sediment do?
Decompose organic material at the surface where oxygen is abundant
Oxygen & sediment chemistry: What does oxygen consumption at the surface do?
Deprives deeper layers of oxygen, so sediments below the surface are anaerobic
Oxygen & sediment chemistry: Why does the depth of the oxygenated layer vary?
It varies according to grain size of the shore - which determines its permeability
Oxygen & sediment chemistry: What happens as oxygen concentrations diminish with depth?
Anaerobic bacteria start to dominate
Oxygen & sediment chemistry: What is the redox continuity layer?
The transition layer between oxygen rich and oxygen poor sediment layers
Oxygen & sediment chemistry: How does beach profile effect oxygen concentrations?
- Exposed beach = larger particles - aerobic yellow sand
- Semi-sheltered beach = smaller particles - aerobic yellow sand & anaerobic black sand
- Sheltered beach - much smaller particles - aerobic black sand / small top layer of aerobic brown sand
Oxygen & sediment chemistry: What do burrowing animals do?
Generate a respiratory current within their burrows to receive oxygen
Oxygen & sediment chemistry: What do some animals do to be able to respire and feed whilst sheltered from predation deeper in the sediment?
- Extend a long siphon into the oxygenated waters
- E.g. some bivalves / Geoduck (Panopea generosa) – largest burrowing clam in the world! Can live >140 years old
Biodiversity: What plants can be found on Spartina mudflats?
- Generally no macroalgae
- Sometimes see blooms of Enteromorpha & Ulva (sea-lettuce)
- Brown seaweeds (e.g. Fucus) present if attached to pebbles
Biodiversity: What do single cell diatoms do in coastal environments?
Create biofilms that animals graze upon
Biodiversity: What is found in large abundances in soft sediment habitats?
Deposit feeders:
- Corophium volutator
- Amphipods
- Arenicola (Lugworm)
Biodiversity: What are examples of predators in coastal environments?
- Shore crab
- Cerianthus
- Sagaritia
- Nereis (Ragworm)
Biodiversity: What are examples of detritivores in coastal environments?
- Heart urchin
Biodiversity: What are examples of omnivores in coastal environments?
- Cerianthus (anemone)
- Nereis (Ragworm)
Biodiversity: In coastal environments, what are grazers dominated by?
Hydrobia - snails
Biodiversity: What are examples of filter feeders in coastal environments?
- Lanice
- Cerastoderma - Cockle (most common)
- Mya - soft-shelled clam
Biodiversity: What is special about Macoma balthica clams?
- They are both deposit feeders and filter feeders
- High flow (more food = filter feed)
- Low flow (less food = deposit feed)
- Not too many species can switch feeding modes dependent on whether its high or low flow
Biodiversity: What are the macrofauna feeding modes?
- Deposit feeders
- Suspension/filter feeders
Biodiversity: What determines meiofauna?
Pass through 0.5 or 1mm sieve but retained on 45um mesh
Biodiversity: What are examples of meiofauna that can be found in the sediment?
- Nematode
- Polychaete (temporary)
- Ostrocod
- Ciliate
- Gatrotrich
- Harpacticoid
Biodiversity: How many individual meiofauna can be found per m^2?
Estimated to be >1 million
Biodiversity: What percentage of all individuals on earth do meiofauna make up?
~80%
Biodiversity: What is the issue with the role of meiofauna in benthic ecology?
- Very few people study it
- There are few marine ecologists or taxonomists that study meiofauna
- We know very little about their spatial distribution, seasonal abundance, diversity, between and within habitats
Biodiversity: What is the differences in abundance of meiofauna and macrofauna?
Typical sandy beach in Europe:
- More meiofauna than macrofauna
- Macrofauna has larger biomass but there’s greater numbers of meiofauna
Distribution: What is the relationship between meiofauna and sediment particle size?
- Species richness, abundance and total biomass increase with increasing sediment stability (decrease wave exposure)
- Hard for animals to burrow into exposed zones - less biodiversity
- Highest biodiversity in muddy/sheltered habitats - easier to burrow
Distribution: What is the relationship between macrofauna and tidal height?
- Number of individuals overlap - not a distinctive gradient
- Lack of vertical zonation in muddy/sandy shore habitats
- Sediments buffer physical stresses and organisms are mobile
- Organisms can burrow deeper in intertidal regions
- Distribution related to particle size, emersion period, depth and water table
- On sandy shore, zonation schemes have been related to hydrodynamics (water table and wave action)
Distribution: What is the relationship between macrofauna and sediment depth?
- Slight zonation pattern
- Lot of overlap to how far animals can burrow
- Not that many studies into depth zonation patterns as it’s hard to do
