the Marine Biosystem
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Transcript of the Marine Biosystem
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7/27/2019 the Marine Biosystem
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THE MARINE BIOSYSTEM
The successful maintenance of a marine biosystemrequires an understanding of certain basic scientific
principles. The more deeply one considers the problems
of designing and running a life-support system for themore delicate creatures of the coral reef, such as living
corals, certain plants, and the Moorish Idol (Zanclus
cornutus), the deeper becomes ones involvement in
fundamental physics, chemistry and biology.
PHYSICAL FACTORS
SalinityThe density of sea water is greater than that ofpure water that is, the weight of a given volume of
sea water is greater than that of the same volume of pure
waterbecause it contains dissolved salts. The higher
the salt concentration of the water the greater is itsdensity; measurement of water density thus provides an
indication of salinity. The density of a substance is
usually expressed as its specific gravity the ratio ofthe weight of a fixed volume of the substance to the
weight of the same volume of pure water. The specific
gravity can be measured simply and directly with ahydrometer. For sea water typical values of specific
gravity are in the region of 1.020.
Salinity is important because it influences the
exchange of salts and water which takes place between
marine animals and their surroundings. Most marinefishes have body fluids which are less concentrated than
the sea water in which they live. The intake of salt waterthrough the mouth and the loss of fluid through the skinand kidney creates a tendency for the fishs body fluid
to become as concentrated as the sea water.
It is obvious that the intake of sea water will raisethe fishs salt content. The loss of fluid through the skin
and kidney results in a net loss of water because these
organs are selective barriers to the movement of salt and
water: molecules of water move across them withrelatively greater ease than do the molecules of salts and
other substances in the body fluids. At the skin,
therefore, water moves out of the fish leaving saltsbehind in preference to an inward movement of salts
from the sea. This movement of water from a region of
low solute concentration into a region of high soluteconcentration across a barrier which selectively restricts
movement of solute is called osmosis. One can
alternatively think of the fishes body fluid as having ahigher concentration of water than the surrounding sea.
At the kidney the restriction to salt movement is
relatively less severe; the urine is nevertheless a weaker
solution than the blood from which it is formed andrepresents a further net loss of water. In order to balan
the tendency towards increased salt concentrat
marine fishes have salt-secreting cells located in gills. In effect fishes take in salt water and remove
excess salt from their body fluids.
The energy expended by the fish in maintaining
concentration of its body fluids at an appropriate levedirectly related to the difference in concentrat
between the fish and its environment, the higher the s
concentration of sea water, the heavier the load on
salt-secreting cells. There is a limit to the ability of fish to hold its internal environment constant and i
most important not to allow the specific gravity of
water to rise significantly above the preferred levMost coral fishes should be kept in water of speci
gravity 1.020. For fishes from the Red Sea the speci
gravity should be 1.022. In either case the limits
acceptability are 0.002.Any genuine deviation from acceptability
probably due to failure to make good evaporation los
or to topping up the water incorrectly. As waevaporates from the tank leaving the salts behind,
salinity, and hence the density, of the aquarium wa
rises. The loss should therefore be made good with p
water to bring the specific gravity back down to acceptable level. Topping up with salt water will
work. Readings outside the preferred range may res
from incorrect use of the hydrometer or from the usea faulty hydro- meter. Both the hydrometer and the
water must be clean; the hydrometer must be calibra
at the water temperature of the aquarium; hydrometer must be a good instrument accurate
within 0.001.
Temperature The fishes and the invertebrinhabitants of a marine aquarium have little ability
regulate their own body temperature as mammals a
birds do. They are poikilothermic and their botemperature tends to follow that of their environme
The rates of all metabolic processes are hig
dependent upon temperature and the creatures inparticular marine environment are adapted to life wit
a narrow temperature range. The sea is a therma
stable environment, much less subject to temperatvariation than fresh water. Typical water temperatu
range from 75-78F (24-26C) for tropical mar
species.
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Lighting Correct lighting of the marine aquarium isessential to healthy plant growth. The presence of
photosynthesizing algae is an important feature in the
chemical cycle of the system. Algae use up carbon
dioxide dissolved in the water and convert it intooxygen. They also take up nitrates from the water to
build their own cellular protein, which may in turn be
eaten by the animals in the aquarium.
CHEMICAL FACTORS
Oxygen All animals and many of the beneficialmicrobes in a marine biosystem require oxygen as a
condition of life. It is essential to keep the oxygenconcentration high by thorough aeration of the water in
order to encourage the growth and well being of the
organisms present. Flourishing plant growth and
suitable lighting also help to oxygenate the tank.Organic pollutants often exert their chief effect by
driving vital oxygen out of solution.
pH The acidity of the marine environment, like thetemperature and oxygen concentration, is a determinant
of the metabolism of micro-organisms. Too great anacidity encourages the activity of harmful anaerobic
bacteria and this will ultimately affect all the inhabitants
of the aquarium. In physical terms the acidity is afunction of the concentration of hydrogen ions. This
concentration is most conveniently expressed on the
logarithmic pH scale. The pH of 7.0 obtained for
distilled water is taken as neutral; a lower value is acidic
while a higher one is alkaline. Natural sea water variesfrompH 7.8 topH 8.4 depending upon locality, time of
day, season of year and depth. The aquarium should bekept at this slightly alkaline pH. Methods of measuringpH with indicator dyes are dealt with in the fresh water
section.
Toxicity Apart from the introduction of uncured ordirty gravel, rocks, corals or shells, all organic materialentering the aquarium does so as food or as living
creatures which eventually die. Organic matter is
decomposed by bacteria into chemically simplercompounds, some of which are extremely toxic.Nitrogenous waste (food and excreta) is rapidly attacked
by certain bacteria known as gelatine liquefiers and
converted into ammonium compounds. These arepoisonous to marine life even in small quantities.
Nitrosomonas bacteria are responsible for oxidizing
ammonium compounds to nitrites still toxic toanimal life. In the next stage of the sequence
Nitrobacter bacteria effect the further oxidation ofnitrites to nitrates. Nitrates are relatively harmless and
can be taken up by green plants, incorporated into
proteins and eventually recycled when the plant is eaor dies.
The detoxification of nitrogenous waste is
aerobic processall three groups of bacteria involv
require oxygen. The reactions which they bring abcan be reversed by bacteria which flourish in anaerob
acid conditions. Promotion of the activity of benefic
micro-organisms is essential to good wamanagement.
In a clinical system aerobic bacteria will focolonies on the strands of filter wool and on
granulated charcoalmuch of the protein waste wilany case be dealt with by the protein skimmer and nev
become subject to decomposition. In a natural syst
the bacteria colonize the available surfaces of aquariumwalls, rocks and other objects.
STABILITY AND MATURATIONIt will be evident upon consideration of what has be
said already, that the integrity of a well-kept mar
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aquarium depends not simply on a number of separatefactors acting independently but on an interaction of
conditions affecting and affected by the activities of
living organisms. Because temperature alters metabolic
rates of activity it may also alter the levels of biologicaldecay products and ultimately the pH and oxygen
concentration. There is in any case a direct relation
between oxygen tension and temperature since oxygenis less soluble in warmer water. Similarly lighting may
have far reaching effects through its influence growth.The delicate balance existing in a stable system is
not arrived at suddenly. The accompanying graph showsthe kind of changes which occur in a newly established,
maturing aquarium. The time to maturity will obviously
vary considerably: it may even be as rapid as 26 days ifthe starting conditions (stocking, feeding, filtration rate,
temperature, etc.) coincide particularly well. Normamaturation will be a matter of several weeks and t
entails some risk to the animals present in view of
high levels of ammonium and nitrite compoun
obtaining in the earlier stages. Biological maturation cbe speeded by maintaining fierce aeration and ra
filtration turnover, by keeping stocking and, the amo
of food down to a minimum, by keeping the temperatas high as the animals are accustomed to, and
stocking with hardy species.It is above all important never to disturb
conditions in the aquarium suddenly. The effects sharp change on such a complex balanced system
unpredictable and most likely to be harmful. Even
conditions are clearly abnormal the situation must rectified carefully and slowly.