EVSC20004 Lecture Notes - Lecture 3: Intertidal Zone, Bioturbation, Stenohaline
18 May 2018
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LECTURE 3: ESTUARIES – BIOLOGICAL CHARACTERISTICS
Factors Affecting Biota
• Relatively sheltered, low energy environments, high productivity
• Complex food webs
• Influenced by factors, and regular/rapid changes in factors
Salinity
• Salinity Level
o Tolerance: species have varying levels of tolerance to salinity
▪ Stenohaline - high salinity
▪ Euryhaline - most salinity, from high to low (most abundant)
▪ Brackish-water - little salinity
▪ Freshwater - very little salinity, river end of estuary
• Fluctuations
o Osmotic balance: (movement of water and salt ions across a balance)
▪ Osmoregulation: regulates internal ion concentration
• Some fish: by restricting movement of ions, or actively moving
water (Salmon)
▪ Osmoconformer: internal ion concentrations change with ambient
salinity
• Softer bodied organism - worms etc
• Mangroves: halophytes (plants which like saline conditions), adapted to conditions in
mid-high intertidal zone, need to be frequently inundated
o Reduce salt intake - root surface
o Reduce water loss - leaves, reduced stomata for evaporation
o Increase salt loss - leaves shed
o Salt glands - expel salt
• Fish:
o Marine: body fluids less concentrated than seawater - water loss by osmosis -
due to gradient
▪ Response: drinks seawater, secretes small volumes of waste, urine
concentration salty as possible
o Freshwater: body fluids more concentrated than seawater - water gain by
osmosis
▪ Response: does not drink, secretes large volumes of waste
• Behavioural Strategies:
o Mobile species: change longitudinal position within estuary, change position
within water column
o Sessile or sedentary species: hide in burrows, close shell
Temperature
• Fluctuations vary with: depth and surface area
• Variability exacerbated by tides
Sediment
• Most fluvial in origin, mostly rich in organic material, is transported, small, fine
particles
• Spaces within sediments (interstitial spaces) important: contain water, organic matter
and gases, also provide habitat
• Bioturbation: biota very important in turnover of sediments
o May ingest/excrete sediments & associated organic matter
o May actively irrigate burrows
o Increase water-sediment interface
o In Melbourne, process nitrogen loads from effluent we dispose of in Port
Phillip Bay
Document Summary
Factors affecting biota: relatively sheltered, low energy environments, high productivity, complex food webs. Influenced by factors, and regular/rapid changes in factors. Temperature: fluctuations vary with: depth and surface area, variability exacerbated by tides. In melbourne, process nitrogen loads from effluent we dispose of in port. Connectivity: suspended sediments: reduce penetration of light needed for photosynthesis, may clog feeding mechanisms of filter feeders, high primary productivity!, nutrients carried in by tide & river, nutrients released by nitrogen-fixing bacteria, nutrients used bacteria, algae & plants. Longitudinal connectivity upstream/downstream estuary -(mangrove seeds float on surface, then sink after 3 days, adrift for 5 months before taking root (dispersal mechanism)) Larvae in estuaries: blue crab migrates to mouth of estuaries, larvae stay in open ocean, then migrate back into the estuary - regular migration, selectively use the tides. Fish: anadromous (upstream to freshwater to spawn) - salmon (regular migration), catadromous (downstream to saltwater to spawn) - eels.
