ECOL 203 : Lecture 17
Aquatic Ecosystems
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Marine vs Inland waters
Adaptations and Life in Water
Ecological Processes in Aquatic Ecosystems
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Disturbance
Dispersal
• Functional groups and food webs
• Interconnected systems
Water Resources
Aquatic systems: The salty divide
• Marine vs Inland waters
• Transitional ecosystems – estuaries & saltmarshes
• More ecological overlap
– Turbulent rivers and rocky shores
– Large lakes and the open ocean
– Physiological similarities between inland salt lakes and
coastal lagoons
Key defining characteristics
Marine and Freshwater Systems
Spatial
Extent-depth
The area of inundation and the depth
of the water.
Volume
Extent and depth influence the
amount of water at any given time.
Temporal
Timing
When water is present.
Frequency
How often filling and drying occur.
Duration
Period of inundation.
Variability
The above features change at a range
of time scales.
Key defining characteristics
Marine and Freshwater Systems
Benthic Zone/ photic
Benthic Zone / aphotic
Physical properties of water
• Physical
– Turbulence/wave action/flow
– Light and Temperature
• Chemical
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Salinity (mg/L)/Conductivity (µS/cm)
Acidity/alkalinity (pH)
Dissolved organic matter
Pollution and contaminants
A dash of salt ………
Seawater vs Fresh water
• Marine systems: Approximately 85% of the dissolved
materials in seawater are sodium and chlorine.
• Freshwater systems: dominated by Sodium, Calcium,
Potassium and/or Magnesium salts.
• Seawater has an average salinity of 35 g/L
Image coutesy of http://www.mangrovewatch.org.au
Majewsky - Sea_salt-e_hg.svg. Licensed under CC BY-SA 2.5
via Wikimedia Commons – uploaded Feb 19, 2015
Estuarine Ecosystems
River
Freshwater
Pycnocline – density
difference due to
salinity
Sea
‘Salt wedge’
Upwelling
nutrients
Tidal surges
import sea water
• Ecotone – transition zone between ecosystems
• Position will vary with flow conditions over time
Salinity in inland waters
• This salt primarily comes from weathering, historic
deposits of marine sediments
• Can exceed that of seawater (35 g/L)
• Over 360 g/L recorded (maximum solubility of
sodium chloride)
Primary salinization (natural process)
• Naturally saline standing and running waters are
common across Australia
Secondary salinization (Anthropogenic)
– land clearing and irrigation
– mining and other industries, effluent from
sewage treatment plants
Osmoconformersinternal = osmotic
conc of the external
environment.
Osmoregulatorsinternal osmotic
concentration
regulation
maintain levels that
may be different from
the external
environment
Matters of light and depth..
• Red (long wavelengths)
are absorbed first –
vertical distribution of
plants
• Absorbed light photon
releases energy as heat
• Temperature profiles
with depth differ from
those of light because of
stratification
Boulton et al. (2014) Australian Freshwater Ecology.Fig 2.4.
No flow: Thermal stratification and oxygen
Vertical temperature profile with depth
under conditions of direct stratification in a
standing water.
From Boulton et al, 2015. Ch2.
Holding on …
Physical disturbance
• Tidal cycles cause abiotic factors to vary over short vertical
range of the intertidal zone
• Distinct zones or bands of species
www.poulsbomsc.org/coastaljourney/intertidal.htm
Living in the fast lane
Morphological Adaptation:
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Flattened form
Stream-lined and fusiform
Permanent attachment
Tiny size
Sucker-like modifications
Images: Boulton et al. (2014) Australian Freshwater Ecology. Ch 7.
Living
in the
thefast
fastlane
lane
Living in
Behavioural
• Seeking refuge below or
behind particles
• Postural changes and facing
upstream
• Powerful bursts of swimming
Yabbie in hole: Doyle. http://www.flickr.com/photos
Blackfly larvae: Waterbug Book, Courtesy of J.Gooderham
Dispersal in aquatic systems
• Benthic species: primary
dispersal phase (spore, egg, or
larva).
• Mobile species: juveniles and
adults may disperse.
• Consequences for processes of
colonization, gene flow.
Active or Passive Dispersal
(freshwater),
• Active: flight in adult freshwater
insects
• Passive dispersal: transport by
animal vectors, wind,
desiccation-resistant stage in
the life cycle.
Migrations
WHY MIGRATE: Dispersal Habitat Food
• Trigger to migrate
– Increased flow,
– Changed temperature and salinity,
– Day/night length.
• Reproductive migrations:
– Diadromous (migrate to salt water for breeding)
• Catadromous (downward running): fishes hatch or are born in marine habitats, but
migrate to freshwater areas where they spend the majority of their lives growing
and maturing. As adults they return to the sea to spawn (e.g., Long-finned eel).
• Anandromous (upward running) hatching and a juvenile period occur in freshwater.
This is followed by migration to and maturation in the ocean (e.g., salmon).
– Potamodromous (migrate within freshwaters, e.g., Murray Cod)
Long-distance marine migrations
Connecting foraging and reproductive
sites
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Fish - Atlantic bluefin tuna
Sea turtles
Northern elephant seal
Cetaceans
Blue fin tuna migration
Balazs & Ellis. http://www.turtles.org/ffs/migrate/ffsmigrt.htm
Interconnected Ecosystems
Ecological Groupings of Aquatic
Organisms
Functional Groups
producers, grazers, consumers, detritivores
• Eg. Pelagic foodwebs
– Phytoplankton (algae)
grazers
predators
BUT
– Bacteria/ cyanobacteria/ microprotozoans/algae all in the production
network
– Phytophagous protists (grazers and predators)
Food webs
• Consumers are
heterotrophs
• Grazer-based
foodwebs
• Detrital based
foodwebs
Boulton et al. (2014) Australian Freshwater Ecology. Ch 4.
Interconnected Ecosystems
Autochthonous
• Organic matter derived from
photosynthetic production within the
water column
– Attached algae/cyanobacteria
– Planktonic algae
– Macrophytes
Allochthonous
• Organic matter derived from
photosynthetic production of
terrestrial origin
– Mangroves
– Riparian vegetation
– Catchment vegetation
Connectivity in Rivers
• LONGITUDINAL: This is the
way that water moves
downstream.
– nutrients, sediments,
– animals
• LATERAL: links with the
riparian vegetation, river
banks and the floodplain.
• VERTICAL: This is how the
river links with the
groundwater system
Boulton et al. (2014) Australian Freshwater Ecology.
Fig1.7
Groundwater Connectivity
Water occurring below ground in saturated and unsaturated
sediments, rock fissures, or solute cavities
Fractured rock
(confined) aquifer
Cave / karst
Alluvial (unconfined) aquifer
Impermeable layer
Groundwater Ecosystems
• Aquifers not inert bodies of water, but contain
active biological communities.
• No primary production - detritus-based food webs
• bacteria – base of food web,
Stygofauna
(groundwater
animals)
denitrification, bioremediation, process
OM
• invertebrates – mediate bacterial
activity, dominated by crustacea
• fish – 2 species in Australia
Adaptations to Groundwater Life
• Life cycles – low fecundity, long-lived
• Low species richness/ abundance (compared to
surface)
• Many short-range endemics (restricted to single
aquifers)
• Therefore, at risk from disturbance
Interconnected Ecosystems
Summary
Zones have common features & processes across marine & freshwater systems
Living in water
– Salt : adaptations, estuaries a special ecotone
– Light
– Stratification – thermal, oxygen
Ecological Processes in aquatic communities
– Disturbance
• tidal, flowing water – morphological and behavioural adaptations
– Dispersal – active and passive methods & migration
Functional groups and food webs
– Producers, grazers, consumers - key function of detrital based food webs in aquatic
systems
Interconnected systems:
– Groundwater
– Allochthonous and Autochthonous organic matter sources