Marine Biology
Study Questions for Lecture 12 (Estuaries)
1.
What is an estuary?
2.
Describe some key roles that estuaries play both biologically and physically.
3.
List the four key types of estuaries and briefly describe how each is formed.
4.
Which type of estuary is most common in Oregon? Which type of estuary is the San Francisco
Bay? Which type of estuary can become “blind”, and what does that mean?
5.
What is the difference between a “slough” and a “bay” region of an estuary?
6.
Sketch a positive salt-wedge estuary (what the text calls an “idealized” estuary) and indicate
isosalinity lines. Then answer the following questions. (Your diagram should make the answers to
these questions obvious.)
a.
Looking at the estuary from river to sea at a given depth (i.e. the “horizontal” component
of the salinity gradient) which part along this longitudinal gradient has the highest salinity?
The lowest salinity? What causes this horizontal stratification?
b.
Looking at the estuary in a cross-section, mid-estuary, from top to bottom, (i.e. the vertical
gradient of the estuary) which depth has the lowest salinity? The highest salinity? What
causes this vertical stratification?
c.
Compare the salinity gradients during high tide compared to low tide, looking at both the
horizontal and vertical components of the gradient. Explain why this change occurs as the
tides change.
7.
Answer question 6, parts a and b, for a negative (“evaporite”) estuary. HINT: See PowerPoint to
check your diagram.
8.
Explain the potential impact of the Coriolis Effect on salinity within an estuary.
9.
How will seasonality affect the salinity of the estuary? Refer to the figure you drew for #6 and
explain how and why it will change with the seasons.
10.
What type of substrate is generally found in estuaries and what causes this to be the predominant
substrate type? What exceptions are there to this generalization?
11.
How do salinity and temperature within the substrate compare to salinity and temperature in the
water column itself? Explain why these differences occur.
12.
Why is temperature within an estuary more variable than the temperature within the adjacent
coastal waters?
13.
Why do tidal currents tend to be more intense within an estuary, especially a river-dominated one,
than in the coastal area outside the estuary?
14.
What is flushing time of an estuary and how is it related to productivity within the estuary?
15.
What is turbidity, and what causes it to be relatively high within the estuary?
16.
What is oxygen concentration like within the water column of the estuary? How does the oxygen
concentration of the sediment compare to that of the water column. Explain the difference.
17.
What physical factor primarily determines the distribution of organisms within the estuary?
18.
List and define the four different categories of estuarine organisms that are based on salinity, and
describe where each would be found within the estuary. Also, be sure you understand how to
interpret figure 12.5.
19.
What is the difference between an osmoconformer and an osmoregulator? Provide at least one
example of each. Do all estuarine organisms fit completely within one or the other category?
Explain. Also, be sure you understand how to interpret Fig. 12.6, and know the shape of a line
that an osmoconformer vs. an osmoregulator would make.
20.
Describe some adaptations for living within or on a muddy substrate.
21.
Define infauna, epifauna and meiofauna.
22.
Describe several adaptations for living within a low-oxygen substrate.
23.
What are the major “primary” sources of energy/materials within the estuary upon which the
consumers feed? Which of these sources is dominant in the estuarine food web (particularly in the
mud bottom portion as opposed to the salt marsh portion)? Is all of this energy fixed within the
estuary itself? Explain.
24.
Describe the key difference between deposit feeders and suspension feeders. Into which of these
categories does “filter-feeding” fall? What might be a drawback of true filter-feeding within an
estuary? Do both deposit feeders and suspension feeders eat detritus? Do both deposit and
suspension feeders eat live phytoplankton?
25.
What are the key types of predators within the estuary?
26.
What is niche-partitioning? Explain as it relates to wading birds feeding within an estuary.
27.
Since Callianassa californiensis is one of the most abundant and conspicuous estuarine animals
we will find, you should know a few things about it.
a.
In which category of species, with respect to salinity, does Callianassa californiensis
belong?
b.
Where, specifically, would you find Callianassa californiensis within the estuary?
c.
By which mechanisms (there are several) does C. californiensis cope with the low-oxygen
conditions of the estuary?
d.
How, and what, does C. californiensis eat?
28.
Where would you find a salt marsh? Why are salt marshes more prevalent on the East coast of
North American than on the West Coast?
29.
Where are you likely to find mangroves rather than salt marshes?
30.
Describe three ways that salt marsh/mangrove plants deal with the high salt contents of their
habitats.