Many marine phanerogam species are highly sensitive to changes in environmental conditions. In the article Posidonia oceanica:

Many marine phanerogam species are highly sensitive to changes in environmental con­ditions. In the article €œPosidonia oceanica: A Biological Indicator of Past and Present Mercury Contamination in the Mediterranean Sea€™€™ [Marine Environmental Research, March 1998 45: 101€“111], the ­researchers report the mercury concentrations over a period of about 20 years at several locations in the Mediterranean Sea. Samples of Posidonia oceanica were collected by scuba diving at a depth of 10 meters. For each site, 45 orthotropic shoots were sampled and the mercury concentration was determined. The average mercury concentration is recorded in the following table for each of the sampled years.

a. Generate a time-series plot of the mercury concentrations and place lines for both sites on the same graph. Comment on any trends in the lines across the years of data. Are the trends similar for both sites?
b. Select the most appropriate measure of center for the mercury concentrations. Compare the centers for the two sites.
c. Compare the variabilities of the mercury concentrations at the two sites. Use the CV in your comparison, and explain why it is more appropriate than using the standard deviations.
d. When comparing the centers and variabilities of the two sites, should the years 1969€“1972 be used for site 2?

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Mercury Concentration (ng/g dry weight) Site 1 Calvi Site 2 Marseilles-Coriou Year 1992 1991 1990 1989 1988 1987 1986 1985 1984 1983 1982 1981 1980 1979 1978 1977 1976 1975 1974 1973 1972 1971 1970 1969 70.2 160.5 102.8 100.3 103.1 129.0 156.2 14.8 12.9 180 8.7 18.3 10.3 19.3 12.7 15.2 24.6 21.5 182 25.8 11.0 16.5 28.1 50.5 60.1 96.7 100.4 170.6 139.6 147.8 197.7 262.1 123.3 363.9 329.4 542.6 369.9 705.1 462.0 556.1 461.4 628.8 489.2