Adelaide
Coastal Waters Study 
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EP 1—Assessment of the effects
of inputs to Adelaide's coastal waters
on seagrass ecosystems and key biota
Issue: Seagrasses are
being put under increased stress. How
are they reacting?
Response: Ecological
Processes Study
The Ecological Processes Study seeks to
find out the things we don’t know
about seagrasses and their way of living
(their ecology) in the Adelaide coastal
environment. Seagrass beds form habitats
for a range of species. They have been
selected for intensive investigation in
recognition of their role as overall indicators
of marine conditions. Changes in seagrass
beds can be useful triggers for management
actions. Seagrass remains the major marine
habitat type and is common along the coast
and in the Port Adelaide River and Barker
Inlet.
 Seagrass
is the name given to any member of a group
of flowering plants that grow underwater
- some of them up to the low to mid water
mark and some in deeper waters. (Despite
its name, seagrass is not a kind of grass,
although it resembles it in general appearance).
Since the 1970s, the South Australian Coast
Protection Board (CPB), and more recently
the South Australian Environment Protection
Authority (EPA), have been concerned about
the losses of seagrasses and the possible
effects of the loss, both on biological
processes and on physical processes such
as sand movement. Some areas that used
to be dominated by seagrasses are now dominated
by algae, particularly Giffordia, a kind
of brown seaweed, and Ulva, also known
as ‘sea lettuce’. The reduction
of seagrass and its partial replacement
with seaweed is a clear indicator of decline
in water quality and the effects of nutrient
enrichment.
Some basic questions remain to
be answered before effective management
strategies can be devised:
- What inputs are affecting the important
combinations of species that include
seagrasses and other plants, fish and
other animals, in the Adelaide coastal
waters?
- Why do seagrasses struggle to recolonise
once they have suffered an initial loss?
- How does the nutrient cycle (of nitrogen,
phosphorus, carbon, for instance) operate
in seagrass ecosystems?
- Does the cycle vary from place to place
or situation to situation?
- What are the existing and tolerable
concentrations of metals and organic
chemicals in the life cycles of these
biota?
The teams will be looking for correlations
between the conditions in various parts
of the Gulf and changes in the seagrass
ecosystems. Observations and experiments
by divers will complement observations
and experiments done in large seawater
tanks (called ‘mesocosms’)
containing replicas of the coastal waters
environment. Factors to be investigated
include turbidity, nutrients, toxic substances,
low salinity and sedimentation. Stormwater,
sewage and industrial discharges are common
sources of these factors.
Just because a toxic substance can be
detected by chemical analysis of seawater,
it does not necessarily mean it will affect
sea creatures. The substance may not be ‘bioavailable’ (that
is, it may not be able to be absorbed by
plants and/or animals). Conversely, even
very small, possibly unmeasurable, concentrations
of some substances can stop a species breeding
effectively, or damage some other part
of its life cycle, for example, reproduction.
Therefore, ecotoxicological testing will
complement the chemical analyses of water
contaminants. The research team will measure
the bioavailability of contaminants to
selected organisms by examining their effects
on the organisms at a range of concentrations — that
is, via ‘bioassays’. Bioassays
will provide data on the effects of mixtures
of pollutants and environmental variables
such as turbidity, salinity and dissolved
oxygen. There will be bioassays on several
sensitive species because their responses
to the mixtures may differ.
Rather than just watch more of the seagrass
ecosystems disappear, the team will also
find ‘biomarkers’ in various
marine plants or animals, as early warning
indicators of toxic effects. Monitoring
of biomarkers (particular biochemical indicators)
which change as a result of exposure to
a substance should also show up the effects
of management actions that reduce the loads
of nutrients, toxicants or freshwater discharged
into the sea.
The knowledge generated from this task
will be valuable for the management of
the Adelaide marine environment. At present,
too little is known about the complex coupled
processes (physical, chemical and biological)
that operate there. Although other coastal
seagrass systems have already been studied
(for example, off Brisbane, Melbourne and
Perth), the Adelaide coastal waters and
seafloor are different and the ecosystem
is thought to function differently as a
result. Previous studies have indicated
that seafloor sediment is both a source
of and a sink for toxic substances. In
the Adelaide Coastal Waters Study, divers
will survey the seafloor and measure the
way seafloor communities (plants and animals)
vary from place to place and through time.
Then the teams will try and correlate the
variations with concentrations of nutrients,
heavy metals and organic compounds measured
in the sediments of the seafloor. The third
prong of this ‘triad’ approach
will use amphipods (small prawn-like crustaceans)
to show up toxicity in the same sediments.
The triad approach is a recognised method
for making an integrated assessment of
sediment quality in the marine environment.
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