BIO 13- Marine Biology
Raskoff
Lab 1- Measurement, Density and Buoyancy
This course looks at the marine realm through the eyes of ecology. Ecology is the
scientific study of the interactions between organisms and their environment. This
endeavor is empirical in nature, being dependent on evidence that is observable by the
senses. This evidence can include purely descriptive data, but more often it tries to make
sense of the world through the collection of numerical data. Being able to say a chiton
was 4.2 cm long is much more informative than saying it is “small”, or stating that the
water is 3º C and has a salinity of 33 is much more useful than stating that the water is
“cold and salty.”
There are two main components studied in ecology, the biotic, or living world, and the
abiotic, or non-living world. These components are quite different and likewise so are
the methods and tools which allow us to collect empirical, numerical data on these two
areas. Within the biotic realm we often concern ourselves with measures of an
organism’s abundance, density, and spacing. We will learn about these techniques and
tools in later labs. In addition we often try to quantify predation, competition, and other
biotic factors (which are not easily done!). Abiotic factors can include both physical and
chemical factors, such as location, temperature, light, pH, wave force, wind, etc. The
huge array of abiotic factors often are measured by a large variety of different tools,
many of which can measure the same thing in different ways, with different units. A
trend in recent years with the miniaturization of sensors, probes, and computer
technology is the creation of multipurpose tools which can measure many different
abiotic factors, sometimes all at once. Using some nifty tools, we will get some hands on
experience measuring some abiotic factors and practice graphing the results!
pH determination
1. You will spend time examining pH, a measure of the acidity of a solution in terms
of activity of hydrogen ions (H+).
2. Record the pH values of the three solutions A, B, and C using the pH paper and
the digital pH meter. Do the values agree?
Solution
Distilled Water
pH Paper
pH Meter
Solution “A”
Solution “B”
Solution “C”
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Salinity
 Salinity, the amount of dissolved solids in a solution can be measured in several
ways, including: electrical conductance; measuring changes in density of the
liquid with a hygrometer; and the difference in refracted light with a
refractometer. It is usually measured in “parts per thousand (‰).”
There are several different methods of the testing the amount of dissolved solids, or
salinity, in solutions. You can determine salinity using the difference in the refraction of
light through a sample. You can also measure the density of the solution with a floating
hydrometer. Electrical conductance is also commonly used, the higher the salinity in the
water, the more easily current can flow.
1. Using the hand-held refractometer, determine the salinity of the three solutions.
Place a drop of the solution on the glass plate and put the cover down on the drop.
While holding it up to the light, look in the scope and you should see a shadow
line which is where you read the sample. Make sure you read the number from
the right side of the meter (‰).
2. Using the glass, floating hydrometer, determine the density of the samples by
letting it float until still and then read the measurement off of the scale inside the
glass. You’ll need to convert the number you read into ‰ with the conversion
tables. Note: you need to know the temperature of the liquid!
3. Using the digital conductivity meter, measure the salinity of the three samples
again. Follow the printed directions carefully. How do the three values compare?
Solution
Distilled Water
Refractometer
Hydrometer
Conductivity Meter
Tap Water
Sea Water
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Temperature
Several different temperature measuring devices have been put into two beakers of liquid.
1. Record the temperature on each device for each liquid. Which device is most
accurate? How do you know?
Solution
Beaker 1
Pasco
Digital
Lab
Beaker 2
Density
Once of the most fundamental abiotic properties of water is it’s density. The density of
water is mainly determined by two things: salinity and temperature. The formula for
density is:
Where:
ρ is the object's density (measured in kilograms per cubic meter)
m is the object's total mass (measured in kilograms)
V is the object's total volume (measured in cubic meters)
So, for a given volume of water (like the amount in a tub on your desk), the only thing
that determines density is the mass (m), and the two things that do that are temperature
and salinity. Lowering temperature actually squeezes more water molecules into that
given volume (they are closer together), thereby increasing the mass. Salinity adds
dissolved salt into the volume of water, also raising the mass, and therefore the density.
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In this lab we will investigate the density of water layers and how they interact (or don’t)
by building miniature oceans. Using any combination of salinity (fresh water to saturated
with salt), temperature (very cold to very hot), and some food coloring, you will mix-up
and dye water ‘layers’ that will interact then you put them into a small plastic tub. If you
are careful about not mixing the water layer (don’t poor them roughly into the tub, etc),
you can expect your water layers to sit on top of each other, depending on density. See if
you can make a three layered ocean in your tub and experiment with making waves on
the surface by blowing with a straw. Additional instruction and tips will be provided
during the lab.
Here is a good website to calculate Density with Salinity and Temperature too!
http://www.csgnetwork.com/h2odenscalc.html
Buoyancy
Plankton are organisms that drift; they cannot swim against a current any stronger than 1
knot (1 nautical mile/hour). Usually, plankton are very small, microscopic organisms but
some larger animals, like certain jellyfish, are also considered plankton. Plankton are
divided into two groups, plants (phytoplankton) or they can be animals (called
zooplankton). Phytoplankton make their own food through photosynthesis (using sunlight
to combine carbon dioxide and water into sugar), but zooplankton must ingest or eat food
from the ocean. Plankton are usually heavier than water. This is important because if a
planktonic organism just floated on the surface of the water, it might not be able to get to
food sources below it or it might get too warm or too much light from the sun (even
phytoplankton can be "bleached" by the sun!). So plankton will tend to sink in the water
column. But phytoplankton do need to stay where sunlight penetrates. Zooplankton feed
on phytoplankton so the zooplankton want to stay where the phytoplankton are in the
water column. One important note is that zooplankton are usually able to swim upward in
the water column very slowly to maintain their position. But if they sink too quickly or
are too heavy, they will go straight to the bottom of the ocean and not be able to get back
up! Therefore, planktonic organisms will have adaptations that prevent them from sinking
too quickly. These adaptations include the following:
1) small size (small things sink slower than large things)
2) long spines or projections that increase drag
3) long, thin or flattened shape - also increases drag
4) contain small amounts of oil (which is lighter than water)
Start to think about how you would build a plankton (smaller than around 5 inches
across). What would you try to do to minimize sinking? Build your plankton in teams of
two and we’ll see who does the best in a head-to-head competition! The rules are simple:
1) you need to start 1cm below the water. 2) If it floats up it is disqualified. 3) The
plankton that takes the longest time to hit the bottom of the tank wins.
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Write-up
All organisms in the aquatic environment must deal with the challenges of having their
living tissues be denser than their surroundings. Proteins, organelles, muscle tissue, and
most other things inside of cells are denser than the surrounding fluid (sea water).

For this lab write-up, investigate the strategies used by three different organisms
and explain their adaptations and/or behaviors used in dealing with these
challenges. The three organisms will cover a wide size range, as the strategies
involved tend to vary with this parameter. Use any combination of the book,
magazines, the web, or other sources.
The organisms should fall in each of the three size classes:
1. Less than 1 cm in length
2. Between 1cm and 10 cm
3. Greater than 10cm
Please write up one paragraph on each of the organisms that:
a. Define that species particular challenges
b. Explains the morphological, physiological or behavioral strategy used to deal
with the situation.
c. List the sources you used.
Please turn this in typed next week at the beginning of the lab.
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