Lecture 23- Life in estuaries

Question 1

What is an estuary?

Answer 1

– tidal-influenced lower part of river and its valley – sink for both fluvial & marine sediments -estuaries are relatively sheltered, low energy environments

Question 2

What is a delta?

Answer 2

• composed of river- derived sediments

Question 3

What are the key physical factors affecting the biota in estuaries? (3)

Answer 3

1. Salinity (levels, fluctuations) 2. Temperature (fluctuations) 3. Sediments (suspended, benthic)

Question 4

Does salinity differ a lot in estuaries?

Answer 4

-yes, over small temporal and spatial scales -organisms need to be adaptive to survive

Question 5

What are stenohaline marine species?

Answer 5

-tolerate narrow range of salinities

Question 6

What are euryhaline marine species?

Answer 6

-tolerate side range of salinities -most common in estuaries

Question 7

What are brackish water species?

Answer 7

-tolerate saline waters but lower salinity than full sea water (35ppt)

Question 8

What are freshwater species?

Answer 8

-low salinity tolerance

Question 9

What is the distribution of types of salinity tolerance species in estuaries?

Answer 9

-

Question 10

What is an osmoregulator?

Answer 10

-regulates internal ion concentrations

Question 11

What is an osmoconformer?

Answer 11

-internal ion concentrations change with ambient salinity

Question 12

Can a species be both an osmoconformer and an osmoregulator?

Answer 12

• yes -eg. crab: bit of each, at low salinities= conforming,
• in inbetween salinities= regulating,
• when salinity high= conforming
• strategy varies with the outside conditions

Question 13

What is an example of a perfect osmoconformer?

Answer 13

-polychaete worm= almost the perfect osmoconformer, energetically easier option provided your internal structures can cope with it

Question 14

What are two examples of perfect osmoregulators?

Answer 14

-salmon and eel= almost perfect osmoregulators= hard work in a physiological sense

Question 15

What are characteristics of mangroves?

Answer 15

-trees and shrubs -halophytes= salt loving -adapted to conditions in mid-high intertidal -usual tropical but have them in Victoria

Question 16

What are the 4 ways in which mangroves cope with salt?

Answer 16

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

Question 17

How do marine fish cope with salt water?

Answer 17

• 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

Question 18

What are the behavioural strategies of species living in salty water?

Answer 18

-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

Question 19

What are the temperature conditions in estuaries?

Answer 19

-can vary greatly -shallow depths= varies very quickly -large surface area -variability is exacerbated by tides

Question 20

How does Northern Pacific seastar deal with temperature and salinity?

Answer 20

-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

Question 21

What are the sediments in estuaries like?

Answer 21

-much fluvial in origin -mostly rich in organic material -transport of nutrients

Question 22

Does sand have different grain sizes?

Answer 22

-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

Question 23

What is space between grains important for?

Answer 23

• for organisms
• 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

Question 24

What is bioturbation?

Answer 24

-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

Question 25

What are ghost shrimps important for?

Answer 25

-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

Question 26

What are anoxic sediments?

Answer 26

-low in oxygen in sediments -reduced circulation + decay of organic matter -black in colour -rotten egg smell -little biota

Question 27

What do suspended sediments do?

Answer 27

• 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

Question 28

What is the productivity and nutrient level in estuaries?

Answer 28

• 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

Question 29

What is the estuarine food web?

Answer 29

• detritus is at the centre of the food web
• open water, mangroves and further inland salt marsh= common in victoria

Question 30

Why is connectivity between estuaries important and what are its two types?

Answer 30

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)

Question 31

How does white mangrove disperse?

Answer 31

• 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.

Question 32

What is the life cycle of a blue crab?

Answer 32

• 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

Question 33

What are anadromous fish?

Answer 33

-• 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…

Question 34

What are catadromous fish?

Answer 34

• catadromous – from freshwater downstream to sea to spawn • e.g. most eels

Question 35

What are shorebirds?

Answer 35

-• 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