What is an estuary?
– tidal-influenced lower part of river and its valley – sink for both fluvial & marine sediments -estuaries are relatively sheltered, low energy environments
What is a delta?
- composed of river- derived sediments
What are the key physical factors affecting the biota in estuaries? (3)
1. Salinity (levels, fluctuations) 2. Temperature (fluctuations) 3. Sediments (suspended, benthic)
Does salinity differ a lot in estuaries?
-yes, over small temporal and spatial scales -organisms need to be adaptive to survive
What are stenohaline marine species?
-tolerate narrow range of salinities
What are euryhaline marine species?
-tolerate side range of salinities -most common in estuaries
What are brackish water species?
-tolerate saline waters but lower salinity than full sea water (35ppt)
What are freshwater species?
-low salinity tolerance
What is the distribution of types of salinity tolerance species in estuaries?
What is an osmoregulator?
-regulates internal ion concentrations
What is an osmoconformer?
-internal ion concentrations change with ambient salinity
Can a species be both an osmoconformer and an osmoregulator?
-yes -eg. crab: bit of each, at low salinities= conforming,
-in inbetween salinities= regulating,
-when salinity high= conforming
-strategy varies with the outside conditions
What is an example of a perfect osmoconformer?
-polychaete worm= almost the perfect osmoconformer, energetically easier option provided your internal structures can cope with it
What are two examples of perfect osmoregulators?
-salmon and eel= almost perfect osmoregulators= hard work in a physiological sense
What are characteristics of mangroves?
-trees and shrubs -halophytes= salt loving -adapted to conditions in mid-high intertidal -usual tropical but have them in Victoria
What are the 4 ways in which mangroves cope with salt?
1. Reduce salt intake= have selectively permeable surface of roots 2. Reduce water loos=via leaves, fewer stomata, don't let water evaporate as much 3. Isolate salt=for the salt that gets in, isolated in cell vacuoles, pump it into older leaves so when they are shed the salt is dispensed with 4. Increase salt loss= via leaves, have salt glands that exude salt to the outside, encrusted salt on the surface then falls off
How do marine fish cope with salt water?
-body fluids are less concentrated than seawater
-thus water loss via osmosis
-marine fish are always battling losing water
-to prevent it they drink water
-then get more salt in than they want
-so they excrete lot of urine, to try to get rid of the salt
What are the behavioural strategies of species living in salty water?
-mobile species:change longitudinal position within estuary, change position within water column -sessile or sedentary species: hide in burrows or close shells -deep in the sediment the salinity does not change very much -on the top it does change -burrowing is very helpful when tide changes so you escape change in salinity -bivalves= close the shell and keep water out so you control internal environment -some mussels can stay closed for a couple of months= salinity control
What are the temperature conditions in estuaries?
-can vary greatly -shallow depths= varies very quickly -large surface area -variability is exacerbated by tides
How does Northern Pacific seastar deal with temperature and salinity?
-can withstand: 19-41 ppt salinity (28.5-34.5 ppt for reproduction) -temperature: 0-25C (5-23C for reproduction) -but larvae survive in 35ppt only if temp is low -few larvae survive 34 ppt at 20C -strongly adaptive, strongly euryhaline end eurythermal, but larvae not as tolerant, can survive in full sea water only if the water is colder
What are the sediments in estuaries like?
-much fluvial in origin -mostly rich in organic material -transport of nutrients
Does sand have different grain sizes?
-yes -wentworth classification -really fine= mud -then fine sand, medium sand etc. eventually boulder -the type of sand can indicate what species will be present as many have different preferences
What is space between grains important for?
-circulation of water, dissolved nutrients and gases
-sorted= how uniform the grain size is
-well sorted (coarse)= water drains quickly
-well sorted (fine)= water drains slowly
-poorly sorted(uneven grain size)= water blocked
What is bioturbation?
-biota disturbs the sediment and allows oxygen in etc. -biota is very important for turnover of sediments -may ingest/excrete sediments and associated organic matter -may actively irrigate burrows -increase water-sediment interface
What are ghost shrimps important for?
-ghost shrimp- have burrows -up to 58cm high -help with sediment turnover, the edges of the burrow are chemically are different than therest of the sediment as it is open to air and water= so will help oxygenate the sediment and help with nutrient exchange -makes a difference to organisms living in those sediments
What are anoxic sediments?
-low in oxygen in sediments -reduced circulation + decay of organic matter -black in colour -rotten egg smell -little biota
What do suspended sediments do?
• Reduce penetration of light needed for photosynthesis • May clog feeding mechanisms of filter feeders -murky water= suspended sediment if too much sediment then too bad for filter feeders -bigger grains settle quickly -fine sediment hangs around for a long time before settling
What is the productivity and nutrient level in estuaries?
• High primary productivity –nutrients carried in by tide & river –nutrients released by nitrogen-fixing bacteria & decomposition of detritus –nutrients then used by bacteria, algae & plants
What is the estuarine food web?
-detritus is at the centre of the food web
-open water, mangroves and further inland salt marsh= common in victoria
Why is connectivity between estuaries important and what are its two types?
1. Lateralconnectivity – between estuaries 2. Longitudinalconnectivity – upstream/downstream within estuary -how one habitat can be a source or a sink for another habitat -connectivity is important (larvae movement)
How does white mangrove disperse?
• Avicennia marina – seed germinates on tree – drops off, floats about 3 days, then sinks – adrift up to 5 months -while floating a root system starts developing, tides can carry them -they move around the bottom for up to few months, then grow enough to get a grip -can attach to the sediment and get leaves etc.
What is the life cycle of a blue crab?
-important commercial species
-eggs on the underside of the female, females move towards the mouth of the estuary
-migration, then release the larvae
-the larvae go trough the mouth into the ocean for a bit
-when well developed, they position themselves so they get carried bacjk into the estuary(behavioural adaptation to get back into the estuary)
-tide carries them back
-evetually mass of adult crabs in the same spot where the females walked from
What are anadromous fish?
-• anadromous – from sea upstream to spawn in freshwater • e.g. salmon -much of adult life in the North Pacific, then start going up the rivers when ready to spawn, then die -larvae move down and swim in the pacific -then again...
What are catadromous fish?
• catadromous – from freshwater downstream to sea to spawn • e.g. most eels
What are shorebirds?
-• 36 international migrant species to Aust • about 2 million individuals annually • mostly using East Asian Australasian Flyway -godwit= 11000 km direct -estuaries= birds stop there and feed and rest before going on on their journey again -• many come to estuarine wetlands – feed on benthic invertebrates