Introduction to the marine environment
The Marine Environment
Research in any area of marine biology is concerned, not only with the biological study of the
marine organisms but also with the organisms’ ocean environment and their dependence on
biotic and abiotic environmental factors. Thus, understanding organisms included in this course
means understanding ecological factors that deal with descriptions and analyses of biological
processes in the ocean. Since a principle goal in Marine Botany is to describe and understand the
relationships between the organisms and their physical environment, it is not enough to
concentrate solely on a survey of the of the flora of the seas. It is also vitally important to
quantitatively describe the specifics of the marine environments these organisms encounter
which may change structure, shape, cellular defenses and pigment distribution.
Any number of environmental parameters may be evaluated in the laboratory and the field, often
with extremely high precision. The choice of parameters and the precision with which they are
measured, depends upon the objectives of a study. Four parameters are regularly measured,
temperature, salinity, density and dissolved oxygen.
Temperature
The activity, distribution and survival or marine autotrophs are controlled by the oceanic
temperature range (generally between -2°C and 30°C). Consequently, the metabolism of these
organisms will vary dependent in part on external temperatures. This indicates first of all that
different temperatures and temperature zonations are present between high (Arctic and Antarctic)
and low latitudes (equator). In addition, vertical distribution of temperature, salinity and density
contribute to all marine zonation. An obvious feature in most oceans is the thermocline, a zone
located beneath the surface in which a rapid decrease in temperature occurs relative to an
increase in depth. The decrease in temperature is usually accompanied by an increase in salinity
(halocline) and density (pycnocline). The large density difference on either side of the
thermocline (or pycnocline) effectively separates the oceans into two layers. This “barrier”
impedes the exchange of gasses, nutrients and organisms between the two layers.
Figure 1: Separate graphs of the pycno-, thermo- and halocline (A-C) and all three in one graph to understand their
relationships.
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Figure 1 shows the different clines in one location. What would that location likely be? A high or
low latitude? How can you tell?
What would the clines or barriers be like at the opposite latitude to that in figure 1? Why?
Salinity
Marine organisms live in an environment that includes a vast array of dissolved salts. The
concentration of the salts is expressed salinity. The formal definition of salinity is complex and
somewhat intimidating:
“…the weight of solid materials in grams (in vacuo) contained in one kilo of water when all carbonate has been
oxidized, all the bromide and iodide have been replaced by chloride, all organic matter has been oxidized, and the
residue has been dried at 480°C to constant weight.”
Fortunately, the practicing marine biologist may set aside that cumbersome definition and work
with more easily understood conventions that relate the salinity to the chemistry of seawater.
Salinity refers to the amount of dissolved solids in seawater and is stated in units of parts per
thousand (NOT percentage, which would be parts be which of the following? Parts per ten, parts
per one hundred, parts per ten thousand), abbreviated as ppt or °/°°. While the latter notation
might seem foreign to you recall what equals parts per hundred (which is what?).
The concept of salinity results from scientists’ attitude to identify a simple analytical procedure
that reliably represents the chemical constitution of any given sample of seawater. The ratios of
the major dissolved ions (Na+, Mg++, Ca++, K+, Cl-, SO4--, HCO3-) in seawater are constant. It is
therefore possible to calculate the concentrations of all of these ions from the known
concentration of any one ion.
Of the major ions, the concentration of Cl- is the easiest to analyze with reasonable accuracy.
The chloride ion concentration is also known as chlorinity, and has the following relationship
with salinity:
Salinity = 1.80655 chlorinity
Open ocean salinity is approximately 35°/°°, which means that there are how many grams of
dissolved solids in each 1000 grams of water? Near shore, however, seawater is diluted by
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freshwater from river discharge and rain water run-off. In the mouth of the Chesapeake Bay, for
example, the regular salinity is 30°/°°. In the upper end of the estuary, the salinity is less than
1°/°°. Marine organisms must maintain a reasonably constant internal ion and water balance.
Animals are therefore generally conformers (= their ionic composition is similar to the external
oceanic ion composition) or regulators (= absorbing ions and preventing others from entering).
How do you imagine autotrophs will adjust to salinity changes?
While ocean water is ~35 parts per thousand (ppt or °/°°) but varies between 33 to 37 ppt. Water
between 0.5 ppt and 17 ppt is considered to be brackish; >17 ppt is considered seawater.
Density
Density is a measurement of the specific gravity of water and is usually expressed as grams per
milliliter (g/ml). However, by convention, oceanographers usually omit these units when
discussing density measurements. For example, density of pure water is 1; that of open ocean
water (35°/°°) is 1.025. Oceanographers have further modified their use of density values by
converting them to sigma-t values:
Sigma-t = (density -1)*1000
How des that transformation modify the numerals, i.e. 1.025 (35°/°°), 1.024 (33°/°°)? Why would
change the way the numerals may be interpreted?
Dissolved Oxygen
Oxygen dissolved in water is as essential to aquatic organisms as gaseous atmospheric oxygen is
to terrestrial forms. While the atmosphere is an important source of dissolved oxygen (DO),
phytoplankton, macroscopic algae and higher marine plants contribute to the increase of DO in
water.
Oxygen is generally not a limiting factor in the ocean. Seawater normally contains between 5 and
14 parts per million (ppm, =mg/L) DO. The survival of many organisms is threatened on
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occasions when the concentration decreases below that acceptable range (hypoxia = low oxygen,
anoxia = no oxygen). Oxygen content can be depleted in a variety of ways including through
elevated temperatures (increased temperature = increased metabolism of organisms =
consumption of more oxygen). In addition, elevated temperatures also decrease the solubility of
oxygen in water and therefore reducing its availability to aquatic organisms.
Exercise 1: Calculating salinity from density of seawater
Salinity and temperature affect the density of seawater in a highly predictable fashion. Therefore
salinity can be calculated from density of seawater at a known temperature. Hydrometer
(calibrated glass floats) are used to measure the density. The higher the hydrometer floats, the
denser the water
-
place a seawater sample into a 500 ml graduated cylinder
measure the temperature of the sample and record (would you record the temperature in
Celsius or Fahrenheit? Why?) it in column B
place a sample of the water into the plastic instant ocean hydrometer and record the
reading in column C
correct the observed density value at 15°C by referring to Figure X with the measured
values. Record the corrected density in column D
Determine the salinity of your sample by referring to Table 1 with the corrected density
data and record this value in column E.
Table 1: Density-salinity conversion table for 15°C
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Figure X: Temperature correction table for density measurements.
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Density worksheet: Determining salinity from density
A
B
C
Sample #
Temperature (°C)
Hydrometer
reading
D
E
Density
Salinity (o/oo)
corrected to 15°C
Exercise 2: Determining the refractive index of seawater
Refractometry is an accurate, simple and rapid method for measuring salinity. It is based on the
principle of light refraction or bending of light waves, as light passes from an optically thinner
medium (such as air) to an optically thicker medium (seawater). The degree of refraction
(recorded as refractive index) depends on the wavelength of light and increases with increasing
salinity.
Some refractometers will record a refractive index (between 1.3325 and 1.3425) of the water
may be measured with an optical device called a refractometer. However, the models we use in
lab provide a read-out of the specific gravity (between 1.000 and 1.070) and salinity and provide
automatic temperature compensation between 10 and 30°C.
1. Calibrate your refractometer
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-
place a drop of distilled water (using a plastic transfer pipet) onto the face of the prism
(figure X) and close the cover plate
- aim the prism end of the instrument at a bright light
- rotate the eyepiece diaphragm looking through eyepiece until the image is focused and
the scale becomes visible
- read the scale where the sharp boundary line (between the blue and white or light and
dark field, Figure X) crosses the scale value. For distilled water this value should be
1.000 on the specific gravity scale (left). What should the salinity be (right)?
= if this is not the case call Dr. Boettger to show you how to adjust the calibration on the
refractometer
- open the cover plate and dry the prism
Figure X: The refractometer. You see a drop of a liquid being placed onto the refractometers prism using a plastic
transfer pipet. The thumb of the is holding the cover in place
Figure X: The boundary layer and scales of the refractometer. The left scale displays the specific gravity, the right
the actual salinity. The boundary line between the blue and light area is the area where you will determine salinity.
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2. Determine the salinities of your samples (used in the previous exercise)
- place a drop of sample 1 (using a plastic transfer pipet) onto the face of the prism (figure
X) and close the cover plate
- aim the prism end of the instrument at a bright light
- rotate the eyepiece diaphragm looking through eyepiece until the image is focused and
the scale becomes visible
- read the scale where the sharp boundary line (between the blue and white or light and
dark field) crosses the scale value. Record the salinity and specific gravity (below)
- open the cover plate, dry the prism and repeat with samples 2 and 3
Sample #
Temperature (°C)
Specific Gravity
Salinity (o/oo)
Are the salinities different from the salinities of the same samples calculated using the
hydrometer? Explain!
3. Determine the salinities of unknown samples A-C (used in the previous exercise)
- place a drop of sample A (using a plastic transfer pipet) onto the face of the prism (figure
X) and close the cover plate
- aim the prism end of the instrument at a bright light
- rotate the eyepiece diaphragm looking through eyepiece until the image is focused and
the scale becomes visible
- read the scale where the sharp boundary line (between the blue and white or light and
dark field) crosses the scale value. Record the salinity and specific gravity (below)
- open the cover plate, dry the prism and repeat with samples B and C
- record the water type that the salinities you measured represent (i.e. freshwater, seawater,
brackish or open ocean water)
Sample #
Temperature (°C)
Specific Gravity
Salinity (o/oo)
Water type
What environment do these unknown water samples come from? Based upon the temperature,
salinity and therefore general location describe what you would expect the thermocline for the
samples to look like and what latitude (low or high) you would expect these samples to have
been taken from? Explain!
Exercise 3: Measuring Dissolved Oxygen
The Winkler test is used to determine the concentration of dissolved oxygen in water samples.
Dissolved oxygen (D.O.) is widely used in water quality studies and routine operation of water
reclamation facilities. An excess of manganese(II) salt, iodide (I−) and hydroxide (OH−) ions is
added to a water sample causing a white precipitate of Mn(OH)2 to form. This precipitate is then
oxidized by the dissolved oxygen in the water sample into a brown manganese precipitate.
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In the next step, a strong acid (either hydrochloric acid or sulfuric acid) is added to acidify the
solution. The brown precipitate then converts the iodide ion (I−) to iodine. The amount of
dissolved oxygen is directly proportional to the titration of iodine with a thiosulfate solution.
Today, the method is effectively used as its colorimetric modification, where the trivalent
manganese produced on acidifying the brown suspension is directly reacted with EDTA to give a
pink color. As manganese is the only common metal giving a color reaction with EDTA, it has
the added effect of masking other metals as colorless complexes.
There are 4 kits available in the lab with 3 different environmental samples. Please use the kit
instructions carefully to determine the amount of dissolved oxygen in each sample. What are the
implications of the amount of oxygen in an environment. What contributes to increase oxygen in
a water sample? What detracts from oxygen in an environmental sample?
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General Algal Morphology
Todays lab allowed you to understand how changes in salinity which organisms in this course
have to deal with may change the specific gravity of the environment. The organisms covered in
this course will need to not just navigate these changes in specific gravity (dependent on
temperature and oxygen content) but also adjust their shape and lifestyle in accordance. You will
therefore need to consider the organismal group you have been provided, determine their overall
lifestyle and build a model out of the materials you are provided with at the end of the lab.
The class will work in teams of two and each team will receive a kit in order to construct their
models as well as a picture and brief description of the organism your models should represent.
The paper in your kit will need to be used as the “thallus” or main body of your organism.
Your kit will contain the following:
- Two pieces of colored paper, the entire piece will need to be used in order to prepare a model
shape that is representative of the organismal group that it represents. Each paper should
represent one model and you explain the shape you will mold it into. Since all pieces of paper are
the same size, you will be allowed to mold them into the shape you determine but you CAN
NOT completely remove any part of the original paper (though you may cut out shapes and fold
and glue them together, using the glue stick provided). One model will be placed into freshwater,
the other into ocean water on September 16, 2015.
- In addition, there will be five other materials that you can use to build your model. The use of
each material and what structural detail of the organism it represents need to be explained. The
materials you have access to use in your model include the following:
a) pompons made out of polyester material
b) pipe cleaners that may be used to their full length or may be cut down to any length suitable to
your organism
c) bubblewrap which you may use as a whole or extract individual bubbles from
d) wooden craft sticks, which may be used in their full size or cut into smaller pieces
- All materials should be attached to the overall paper model using the glue stick provided. You
can use three of the materials maximum and will need to explain their structural resemblance of
the real thallus as well as their overall significance. You should draw any additional detail onto
your completed model as you deem appropriate but all structural detail also needs to be
explained.
- Each team should be prepared to “place” their models during the lab of September 16, 2015 in
freshwater and ocean water and explain the significance of their structural additions. Upon
completion of the lab, every student will need to complete a graded assignment that will allow
them to explain their overall model, additions an the reasons for these additions, based upon the
organismal lifestyle. These assignments will need to be completed by each student individually,
though models will be built in student pairs. The assignments are due electronically before 9am
on Wednesday September 23, 2015. Any assignments received after 9am will result in a compete
loss of points that can be attributed to the assignment.
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