Download ThE WatEr OF LIFE - Marine WATERs

WF Feature
THE
WATER
OF LIFE
Cathy Anderson discovers some astonishing facts about
a substance many of us take for granted: sea water.
Antarctic sea ice. Photo: Larisa Vanstien
50 Western Fisheries MARCH 2009
T
his complex organic soup is credited
with being the cradle of life on earth.
We all re-enact our evolution as we grow
in our mother’s salty amniotic fluid, but if
we drink it, it will kill us.
It covers more than 70 per cent of our
planet and we know less about the
organisms in it and the land beneath it than
we know about rocks from the moon.
We treat it as infinite resource – extracting
valuable minerals from it, hunting the
creatures that live in it, and dumping toxic
chemicals and ever-increasing amounts of
waste in its concealing depths.
We hope that since it makes up 95 per cent
of the total water on the planet, it is simply
too vast to really change it.
Because if we change sea water, life on
Earth (“as we know it, Jim”) might end.
What is seawater?
In 1884, William Dittmar set out in
the British corvette HMS Challenger
on an expedition to study the biology
of the sea, examine the chemical and
physical properties of the water, sample
deposits on the ocean floor and measure
water temperatures.
After four years and almost 70,000
nautical miles, Dittmar returned with
77 samples of sea water. The expedition
remains the longest continuous scientific
investigation of the ocean basins and the
samples are still the only worldwide set
of samples on which complete analyses of
chemical composition are available.
Since then, improved analysis techniques
have shown slight variations, but his work
still provides a valuable foundation.
Sea water is about 97 per cent pure water,
which is a very effective solvent. Over the
earth’s lifetime, the action of weathering
on rock and water runoff has dissolved
salts into the sea to the current salinity
level of about 35 ppt (parts per thousand,
though just the number is usually used).
It is thought equilibrium was reached
about 600 million years ago when the
sea could no longer dissolve any more
material in solution, and the composition
of sea water has barely changed since then.
Of the salts in sea water, chlorine makes
up about 55 per cent, sodium 30.5 per
cent, sulphur 7.7 per cent, and magnesium,
calcium and potassium make up most of
the remainder.
This relative abundance of elements
remains constant wherever you are in the
world’s oceans, but the water content (and
therefore salinity) can vary locally because
of rainfall, runoff and evaporation.
It’s an urban myth that sea water contains
every element in the periodic table, but it
does contain 80 elements in minute traces;
and although drinking sea water is fatal,
a mouthful now and then will probably
provide you with a micro-dose of every
mineral you need and the health benefits
of sea bathing have been vigorously
promoted for centuries.
There are gold and silver, mercury and
lead, krypton and uranium, arsenic and
iodine, right down to the minutest levels
of radon at an average of 6x10-16 parts
per million.
Sea water teems with fish eggs, an important food source for many marine creatures. Photo: Jan Richards
Wind action at the surface of the sea
also means sea water contains traces of
dissolved gases, but again an equilibrium
is reached and the capacity of the
ocean’s surface to continue to absorb
carbon dioxide is much discussed by
climate scientists. The amount of gases
Western Fisheries MARCH 2009 51
absorbed will depend on the salinity and
temperature of the water; as they increase,
the less gas can be dissolved so a warming
of the sea will mean more carbon dioxide
remains in the atmosphere.
There are pockets of high salinity such as
the Red Sea (40) and the Sargasso Sea, far
west of the Canary Islands in the North
Atlantic, where a high sea temperature
causes evaporation and it is too far from
land to get any freshwater runoff.
Average salinity is found at the equator,
where the high rainfall is offset by high
temperatures and evaporation.
Low salinity areas occur in polar seas
where the sea water is diluted by melting
ice and rainfall, such as the Baltic Sea
which can range from 5-15.
By comparison, human fluids like tears,
blood and amniotic fluid have a salinity of
about 9.
Most sea creatures have developed
efficient systems to excrete excess
salt or contain membrane barriers that
prevent salt crossing from sea water
into their bodies. That’s why the flesh of
sea creatures such as lobsters and squid
doesn’t taste salty; the briny liquid found
in oysters is trapped there when the oyster
is harvested, but it is full of excreted salts
that would have been flushed.
The reason we can’t drink sea water is
that our kidneys are unable to excrete
all the salt without diluting it with more
fresh water from body tissues, so we die
of dehydration. However, some terrestrial
creatures, such as seagulls and desert
rats, have evolved filter systems to expel
salt and are able to drink salt water if
they have to. In desperate circumstances,
mixing fresh water and sea water has
worked and Thor Heyerdahl reported a
ratio of 40 per cent sea to 60 per cent fresh
was drunk during his Kon Tiki expedition.
Borrowing the ocean
When the new Department of Fisheries
marine research facilities were planned
and built at Hillarys several years ago,
the system that needed most careful
consideration was probably the one the
public, and a lot of the staff, never see.
Every day, about 1.5 million litres of
sea water must be drawn from the
ocean, pumped, filtered, stored and
fed into the many aquariums and
aquaculture tanks that are part of the
Western Australian Fisheries and Marine
Research Laboratories.
A range of marine creatures with varying
environmental needs must be catered for,
and the water and anything filtered out
of it returned to the ocean without any
environmental consequences.
The man in charge of this vital
process is Ivan Lightbody, who
understands and maintains a system
partly mechanical, partly electronic and
partly environmental.
Ivan’s first system was the one at the
old marine laboratories at Waterman’s
Bay, which he rebuilt and improved
over the years. The new system, though
not entirely state-of-the-art (budget
considerations), is designed to deliver the
best quality sea water possible.
Sea water is drawn from intake lines on
the sea bed north of the Hillarys complex
to a pumping station, which delivers it to
the laboratories.
“We run a 24/7 continuous operation and
all the conditions have to be right,” Ivan
says. “For example, if the tide is low it
puts extra stress on the pumps because
there’s less water pressure and you need
a higher suction rate, so I have to find the
right balance and adjust everything.”
The water will travel through almost
a kilometre of piping and several
filtration systems before reaching the
aquariums, which also have their own
aeration and filtration.
52 Western Fisheries MARCH 2009
The first filters are 12 millimetre stainless
steel mesh on the intake lines to filter out
the ever-present seaweed and sea wrack
that would block up the lines.
As the water enters the pumping station,
it passes through baskets of 4 millimetre
steel mesh (that Ivan hoses out at least
weekly with fresh water), which catch a lot
of particulates and detritus.
“The water goes into a hydrocyclone,
which is a centrifugal separator, and
that separates out the sand and a high
percentage of solid matter,” Ivan explains.
“The sand and anything else extracted is
then returned to the sea via a drain.”
Then the water is pumped at around 52-53
cubic metres per hour down the line to the
research facility where it encounters a set of
disc filters.
“These filters separate out whatever is
left in the water down to 120 microns
by collecting everything in a series of
discs, about 150 in each of six chambers,”
Ivan says.
“The discs have little grooves in them that
pick up all the weed. As it builds up, it
slows the flow down so the pump starts
to work hard. When the water reaches a
certain pressure, a backwash pump turns
on and washes the filters.”
This water then waits in a huge reservoir
tank. A little marine ecosystem lives here
because sea water is packed with life of
every size and, in spite of all the filtering
so far, microscopic larvae and eggs still
sail through.
“When we last cleaned out the reservoir
tank, I found big leader prawns, pearl shell
spat, filter feeder sponges, orange and
red sea stars, and a whole host of stuff
growing, but I leave it because it does no
harm,” Ivan says.
A gravity-feed header tank holding 65,000
litres which supplies the aquariums calls on
water from the reservoir, and water moving
into the header tank goes through the final,
and most expensive, set of filters.
“Now hopefully we get the filtering down
to about 35-45 microns; there are three
special sand filters, using silica sand from a
beach in Scotland.
“It has very, very sharp edges – like little
diamonds – and at a cost of around $600
for a 20 kilogram bag, it costs around
$15,000 to change all three filters.”
Ivan therefore maintains these very carefully.
Salinity and temperature are measured
just before the water is finally filtered and
these simple daily records reveal a lot
about our coastline.
“The salinity here at Hillarys is 36-38
and that is saltier than at Waterman just
down the coast because there are a lot
of underground water springs further
inland, so fresh water runs out through the
limestone into the sea around Waterman,”
Ivan says.
“The water temperature is slightly different
here too, because we seem to be in an
open area, whereas the Waterman intakes
were within a protected reef.
“The water at Waterman was always
warmest at midnight to 2am in summer, but
here it’s cold.”
Beside the header tank is the heated sea
water tank, where water for the tropical
fish aquariums reaches 50ºC. By the time
it reaches the tanks and is diluted, it is at
about 30-32ºC.
“The salinity takes care of itself; we don’t
want to artificially change that, but we have
a 100 per cent dissolved oxygen rating,
which is the best you can get.
“By the time it’s gone through all the
processes, that sea water is 100 per cent
saturated with dissolved oxygen.
Sea water is usually slightly alkaline, with
a pH (measure of acidity) ranging between
7.5 and 8.4, and its ionisation is quite
different from that of fresh water. This is
the tricky bit for people trying to make
artificial sea water for marine aquariums.
There is current concern about increasing
acidification of the world’s oceans because
any changes to pH will affect the ability of
organisms to form and maintain shells and
carapaces. The consequences for corals
that build reefs and tiny zooplankton,
which underpin the marine food chain,
could be disastrous as more acid waters
can dissolve many of these hard structures,
which are mostly calcium.
“We also have two blowers that deliver
extra air to the tanks if the people running
the tanks want them – maybe high stocking
density and feeding regimes might lower
oxygen levels.”
The final control of the sea water flow will
be at aquarium level and that will depend
on the species inside, feeding regimes
(more fresh water and oxygen is used
during feeding activity), how many animals
are in the tank and so on.
Tanks at the laboratories often hold
abalone, snapper, barramundi, rock
lobster, yellowtail kingfish and assorted
species in display aquariums, including
reef animals that are used to a high water
flow in tidal zones.
If anything goes wrong, Ivan has up to an
hour, depending on tank demand (about
95 per cent is used by the aquaculture
aquariums), to fix it.
What does it do?
of these planetary motions and daily and
seasonal temperature changes.
The water in earth’s seas is in constant
motion, affected by the swing of the
planet’s orbits and the gravity of the
moon (creating tides and waves),
volcanic and seismic activity (tsunamis
and undersea thermal vents), and winds
generated by atmospheric conditions
(storms and sea spouts).
Water expands and rises as it heats, and
contracts and sinks as it cools, so the seas
are full of currents made up of dense,
cold, high salinity water close to the ocean
floor with warmer, less saline water nearer
the surface, mixing under the influence
Always on call, he spent Christmas
Day in 2007 with two helpers nursing
the system after its computer monitoring
system crashed.
“My experience tells me the best seasonal
and daily settings, and I have instruments
on all the tanks to tell me what’s going on,
but a lot of things can happen, so it always
has to be checked and run manually.”
Maintenance has to be carefully planned
ahead for times when projects finish and
tanks may be emptied, and the expense
of imported parts has also made Ivan an
expert at devising cheaper alternatives
where possible.
It’s a million dollar system, but the clever
filtration technology (much of it developed
by Israeli desert agriculturalists) is
combined with simple, reliable pumping
systems that can be adapted when
necessary.
This planetary coating of swirling sea
water drives earth’s weather systems,
distributing heat and moisture in a
continual cycle of evaporation and
precipitation –and one of the scariest
doomsday scenarios involves the cessation
of the massive current system which
carries warm water across the Atlantic and
stops northern Europe from freezing solid.
We owe our mild climate in Western
Australia to the unusual Leeuwin Current,
which brings warm water from the tropics
down the coast in winter, contrary to all
There are two sea intake lines, one 100
metres further offshore, so if a lot of
weed comes in, better water can be
sourced, The unused line is kept filled
with fresh water to reduce bio-fouling
but, sea water being full of life, some
large-scale cleaning of tanks and lines
is inevitable.
“We have a good system for cleaning
here – we can get access to all out pipes
through inspection plates and we pump
medical oxygen into the water to the
aquariums while the pumps are offline
when we clean the reservoir and pipes.
“The most satisfying part is that the water
we return to the ocean is cleaner that
when we brought it in,” Ivan says.
“All the weed that we take out is returned
and nothing is removed – even the
creatures that go through the filtration
system eventually get back to the sea.”
Ivan Lightbody checks the system of disk filters –
a clear hood allows him to monitor water flow and
see when the stacks of fine filters need flushing.
Photo: Cathy Anderson
Western Fisheries MARCH 2009 53
the other west coast current patterns in the
southern hemisphere.
beach knows this – and can strip or
smother reef systems.
It constantly erodes the edges of land
masses but it also deposits sand as beaches
– anyone who has watched the changes
throughout the year at their favourite
Sea water behaves differently to fresh
water. The salts make it denser, so it is
easier to float in and it is much more
conductive, so you are less likely to be
electrocuted in salt water (as the water is
more conductive than the human body) –
but don’t test this at home.
200m
Sunlight Zone
Twilight Zone
1,000m
Midnight Zone
4,000m
Abyssal Zone
When sea water freezes (a freezing point
lower than fresh water at around –1.9ºC,
and even lower if saltier), the salts are
rejected by the freezing process, which
forms ice crystals, so sea ice is virtually
fresh water. Because fresh water is
less dense, sea ice floats.
Scientists measure the properties of sea
water, mainly temperature and pressure.
These in turn allow calculations of
salinity, viscosity, conductivity and
saturated vapour pressure. Scientists
may also measure sedimentation (how
much material is suspended in it) and
chlorophyll, which allows calculation of
the biomass of phytoplankton.
Two types of silica can be detected
– lithogenic silica from the land and
biogenic silica from the shells of
marine creatures.
It’s alive!
Sea water is far more than a recipe of
elements; it is teeming with natural organic
compounds, plants and animals. Add to
that by-products of decomposition, human
pollution, land runoff and even material
from comets and volcanoes, and you have a
dynamic and complex fluid. It is an eternal
chemical reaction as substances combine,
dissolve and precipitate.
Marine organisms affect the composition
of sea water by concentrating or secreting
chemicals in minute amounts (almost
undetectable, but sea creatures are
incredibly sensitive to water changes).
Lobsters concentrate copper and cobalt,
snails secrete lead, sea cucumbers extract
vanadium, and certain sponges and
seaweeds remove iodine from the sea.
Animals and plankton extract calcium
and silica to form shells, bones and
reefs. However, no biological processes
remove sodium.
In turn, the water leaves its imprint on
the creatures that build their bones and
shells from the elements in it, and modern
technology has given scientists the means
to track the movements of such creatures.
Even though sea water mixes well in the
open ocean, there are local differences
6,000m
Hadal Zone
Above: The Ocean is divided into five zones
according to how far down sunlight penetrates.
Antarctica contains approximately 90 per cent
of all the ice in the world and 75 per cent of the
world’s fresh water. Photo: Larisa Vanstien
54 Western Fisheries MARCH 2009
All these tiny creatures form their structures from elements in sea water and are drastically affected if the water changes pH or composition. Clockwise
from top left: Single cells can be seen forming around the edge of the bivalve shell larva; the crustacean larva creates its external shell, the cuttlefish forms
its internal quill and the algae forms its plant structures from seawater. Photos: Jan Richards
closer to land, and by analysing the
isotopes of elements like oxygen and
strontium in fish bones and mollusc shells,
researchers can tell where the animal was
born, lived and travelled (see Western
Fisheries, December 2008, ‘What are
fishes made of?’).
Fish and shellfish also lay down growth
rings when they build calcium into their
otoliths (earbones) and shells, and this
is also a valuable tool for scientists to
determine the age and growth rates of
various species.
The food supply varies greatly in the
sea – warm clear tropical waters usually
have much less plankton and microscopic
organisms, which form the basis of the
oceanic food web, than colder waters.
As nutrients go, Western Australia has
relatively poor waters and fisheries
managers need to take this into account –
populations of fish will always be limited
by the capacity of the sea to feed them.
However, recent estimates are that there
are up to 20,000 naturally occurring
species of bacteria in a litre of sea water,
and the sea could host between five and
ten million species of bacteria.
Life has been found in every one of the
sea’s five zones. At the surface is the
epipelagic (or sunlit) zone, where sunlight
allows marine plants to photosynthesise.
The mesopelagic (twilight) zone allows
some light to penetrate, but not enough
for photosynthesis. The bathypelagic
(midnight) zone is the deep layer where
no light penetrates; the abyssal zone
is the pitch-black bottom layer of the
ocean where water is almost freezing and
pressure is immense; and finally the hadal
zone describes water found in the deepest
ocean trenches (like the Mariana Trench at
11,033 metres deep).
It is thought that over 90 per cent of ocean
species dwell on the ocean bed, anchored
to rocks, but the bed environment changes
dramatically with depth. Scientists were
amazed to discover colonies of shrimp
thriving around near-boiling eruptions of
poisonous gases and sulphurous water on
the ocean floor, able to live on the bacteria
adapted to conditions similar to those
endured by the earliest life on earth.
The origin and the future
Fossils of the oldest organism on earth
were discovered in Western Australia.
It is a bacteria-like organism about 0.1
millimetres in size and dated at 3.5 billion
years. It was found in chert, composed of
fine sand formed on a seabed at a time of
violent volcanic activity when the water
was extremely hot, but a functional cell
capable of transporting and processing
material would have found useful
chemicals in the water. Sea creatures
continued to evolve systems to cope with
gradually changing water composition, but
over vast time scales, and their abilities
to adapt will be greatly tested if the sea
changes quickly.
In spite of mass extinctions of sea life,
particularly in the Devonian period (417354 million years ago, also known as the
Age of Fishes), most species on Earth still
live in the sea.
Next time you dive in for a cooling dip on
a summer’s day, reflect on the remarkable
substance you are swimming in and how
it is both the origin and the future of life
on Earth. g
Water is essential to carbon-based life and
there is consensus that it began in Earth’s
early chemical-rich seas, though how and
when is unknown.
Western Fisheries MARCH 2009 55