Problem Set # 5 Answer Key Puget Sound Benthos
OCEAN 430 Fall 2008 Due: In class, 10 November 2008
Please answer the following questions on a separate sheet of paper. You should read the
assigned reading (Nichols 2003) and try to complete as much of Question 1 as you can before
class on Thursday to assist you in answering Question 3, and to enable a lively discussion of the
paper.
1. (20 points) Answer the following questions about the assigned Nichols (2003) paper.
a) (1 point) Rewrite the title of the paper in less-technical terms.
•Changes in deep sea animal communities over multiple decades in the Puget
Sound.
b) (2 points) State the scientific goal(s) of the Nichols (2003) study, and briefly
summarize the rationale for the work.
•Used long term sampling of the benthos at a single deep site to investigate
stability in the community composition and abundance. This type of study had not
(and still has not) been conducted frequently, so we have very little baseline
information about how benthic communities change over time in the absence of
disturbance, which makes it difficult to determine causality when disturbances like
climate change and eutrophication do occur.
c) (1 point) What characters/features/variables have historically been used to describe
benthic communities?
•water depth, salinity, and sediment particle size.
d) (2 points) Describe the sampling site FHN2, and briefly explain why the site was
chosen for this study. How often was the site usually sampled? How many
replicates were usually taken?
•Sampling site FHN2 is offshore of Seattle, located at a water depth of 230m on a
large mud flat at the southern end of the Main Basin. The sediment is characterized
by fine soft mud and the seawater generally flows south. FHN2 was chosen because
of these physical features and proximity to Seattle. The site was sampled biannually,
in spring and fall, and three replicates were usually taken.
e) (1 points) Sketch the benthic invertebrate sampling device used in this study. If the
area sampled were square, what would the lengths of the sides be?
•Sqrt(0.1) = 0.32m = 32 cm ~ 1 foot
f) (2 points) A statistical test called the Pearson correlation coefficient was employed to
evaluate whether variations of benthic invertebrate abundance changed over time, or
were correlated to other measured factors. What significance level was used by
Nichols (2003) to determine statistical significance? Besides time, what other types
of data were examined for potential correlations with changes in benthic community
composition and abundance?
•Significance levels (alpha) of 0.05 (5%) and 0.01 (1%) were used. Wet weight,
abundance, secchi depth, temperature, Biological Oxygen Demand, English sole
catch.
g) (2 points) A statistical test called a Student's t-test was employed to test the
significance of variations of benthic invertebrate biomass. Calculate the probability
associated with the t-test testing a difference in Molpadia biomass between samples in
the table below. (No need to show the math, but note which program and function
you used to calculate the value.) Is the difference significant at p < 0.05?
