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 Macro
algae are much more diverse than vascular or terrestrial plants in
their ability to uptake and process nutrients. They generally
require a larger range of nutrients in an inorganic form than
vascular plants do, but are able to derive a few essential
nutrients from organic compounds such as some aquarium
substrates. Few studies have been done on individual species of
macro algae to determine which major and minor nutrients are
essential to the plants survival and growth. This is due
largely to the fact that natural seawater is used in most research
and aquaculture production, which typically contains such high
concentrations of the major and minor nutrients needed for plants
to grow that specific data is never collected. However, it is
commonly accepted that macro algae and sea grasses need the same
essential elements as higher plants do. Unlike vascular plants,
marine macro algae must be supplied nutrients through the water
column and not through the substrate. This is achieved by
providing all needed elements through the aquarium water.
The
macro nutrients, or primary nutrients, that marine plants need to
achieve photosynthesis are: nitrogen, phosphate, potassium,
sulphur, calcium, magnesium and carbon. Some marine algae that is heavily
calcified, such as Halimeda Optunia, need large amounts of calcium
to grow. These plants in turn produce calcium based sand as a
byproduct, which accounts for the majority of all Caribbean sand.
Nitrogen Nitrogen
is one of the major nutrients required by all plants and algae,
both aquatic and terrestrial. It is used by the plants or algae in
the production of stored proteins. Marine plants take up nitrogen
in several forms, some more effectively than others. In the
aquarium they include ammonia, ammonium, nitrite and nitrate. Nitrate is preferred among all marine plants and is a readily
available nutrient in most aquariums. In most marine planted tanks
and refugiums there is usually sufficient amounts of nitrates
available in the water column due to the nitrogen cycle and fish
waste to sustain small populations of plants without adding any
additional nutrients. However, in heavily planted or sea grass
dominated systems it will become necessary to keep nitrates
elevated just enough to encourage growth. It is commonly
suggested that a range of 5-10 ppm of nitrates is acceptable in
marine plant dominated systems, perhaps more in more densely
populated systems.
Nitrate can be added as a supplement such as KNO3 (potassium
nitrate) or CaNO3 (calcium nitrate) in dry form or premixed as a
liquid. Another alternative is to use treated tap water without
removing the nutrients. Great care must be taken with any periodic
dosing as it can be harmful to both the plants as well as fish and
invertebrates in the aquarium. Phosphorus Phosphorus
is another important nutrient that marine plants need to grow.
Marine plants readily absorb phosphorus in the form of phosphate
(PO4). Phosphorus can be a limiting nutrient in the growth of
marine plants but it is usually sufficiently present in the aquarium due to
the addition of fish
food, through detritus buildup and fish waste. In comparison with
nitrogen, marine plants absorb far less phosphorus so care should
be taken to limit the amount of phosphate in the aquarium
Phosphate levels should
be maintained below 0.07 ppm to rule out as a limiting nutrient. Dosing can be
detrimental, causing algae blooms. Potassium Potassium
is absorbed by marine plants as an ion from aquarium water and is
generally available in sufficient amounts in most salt mixes and
tap water. Potassium is a key component that is used for
photosynthesis in marine plants. Dosing is generally not needed or
required. Sulphur Sulphur
is used by marine algae and plants in the production of amino
acids, proteins and chlorophyll. It is generally present in
sufficient amounts in both salt mixes and tap water. Sulphur can
be toxic in large quantities so it should never be added as a
fertilizer to the aquarium. Calcium Calcium
is a very necessary element for all marine plants, as it is used in
the formation of cell wall structure. As mentioned earlier, some
macro algae such as coralline and calcareous algae readily absorb
large amounts of calcium and are composed of almost pure calcium
carbonate. Calcium, alkalinity and ph
are all directly connected to each other, as the availability of
carbonate mostly depends upon pH and alkalinity levels. So it is
important to keep all three at acceptable levels so that calcium
carbonate is freely available to the plants. Ideal dosing ranges
are 7-10 DKH alkalinity, 8.4-8.5 ph and calcium levels between
380-450 ppm. Most commercially available products offer a
simplified solution to maintaining the balance between alkalinity,
ph and calcium levels. Calcium reactors can keep calcium levels
high on a constant basis so are a welcome addition to any aquarium
containing marine plants and invertebrates. Not only will keeping the ph and calcium
levels high in a planted tank produce healthy plants, but the
amount of micro algae will decrease as well. Magnesium Magnesium
is another element that aids in the formation of cell wall
structure within marine plants and especially coralline algae. It
is often directly proportionate to the calcium levels found in
both salt mixes and tap water. Because magnesium is an ingredient in most
commercial salt mixes it is not normally necessary to dose this
nutrient. However, magnesium will be depleted quickly with the
formation of calcium carbonate in both plants and encrusting algae
and needs to be monitored periodically. A target range of
1250-1350 ppm is sufficient for most marine aquariums containing calcareous
and coralline algae. Carbon Carbon
is used by all living organisms in varying amounts and is
particularly important in the growth and structure of vascular
plants. Plants obtain carbon from carbon dioxide, which is turned
into oxygen through the process of photosynthesis. Most species of
sea grasses can absorb large amounts of carbon from the both their
roots and leaves, while macro algae are thought to need varying
amounts depending on the species. It is generally accepted that
the aeration/circulation provided by the filtration system creates
enough free carbon to satisfy the needs of marine plants. The
process of introducing carbon into the aquarium water through
carbon dioxide fertilization does little to help in the growth of
marine macro algae, but it would benefit a sea grass dominated
system. However, the danger of a drastic fall in ph due to over
saturation of carbon dioxide could be harmful and unproductive at
best so it is seldom done in the marine aquarium hobby.
The
minor nutrients marine plants need to grow are: iron,
manganese, copper, zinc & molybdenum, boron, iodine, bromine. These nutrients are
normally needed in very small amounts so are often referred to as
"trace elements" . Most commercially available salt
mixes contain all of the minor nutrients needed for marine plant
growth, so they are generally replenished by regular water
changes. Iron Iron
is an important micro nutrient absorbed by marine plants and is used
in respiration and photosynthesis. The most readily absorbed form
of iron is iron chelate. It is available in both dry and liquid
forms and can be added safely to most aquariums without damage to
its inhabitants. It is unknown how much available iron is used by
marine plants but studies have shown that plants benefit from
improved growth and color in systems that keep it at acceptable
levels. There is some debate as to the quantity that should be
dosed but most hobbyists add enough iron to rule it out as a
limiting nutrient. Manganese Manganese
is absorbed as an ion by marine plants and is used in
photosynthesis. It is not normally a limiting nutrient in most
marine aquariums as it is present in both salt mixes and tap
water. Copper Copper
is absorbed in very low concentrations as an ion and is used in
respiration by marine plants. Marine invertebrates are very
sensitive to copper so it should never be added to the aquarium
water as it is present in significant amounts in both salt mixes and
tap water. Zinc Zinc
is used by marine plants in the formation of chlorophyll and is
present in both substrates and tap water. At high levels it is
very toxic and should never be added to the aquarium water. Molybdenum It
is
unclear what role this element plays in the growth of marine
plants. In terrestrial plants it is used by the plant to break
down nitrates into ammonium to be used as a source of nitrogen.
Trace amounts are present in salt mixes and tap water.
Boron
Vascular
plants require small levels of this nutrient for cellular membrane
function, root growth and flower production. Boron has been shown
to be essential for some marine algae, but not for most macro
algae. Most salt mixes and tap water contain significant amounts necessary
for the algae and plants that utilize them. Iodine It
is believed that some varieties of red and brown macro algae require iodine and bromine as essential nutrients for growth. It
has an obscure place in the marine aquarium hobby but is
available as a supplement for species that require it. Vitamin
B12 Several
species of macro algae utilize Vitamin B as an essential element
of growth. It is also thought to be necessary in the growth of
several sea grass species including turtle grass. Not much is know
on the quantities needed as most prepared salt mixes have
sufficient amounts present.
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