Molluscan death assemblages in marine sediment of the western Canadian Arctic: how
useful is this existing baseline record for resolving current and future ecological change?
Preliminary author list: Mairi Best, Tom Okey, Karin Bibeau, Kathy Conlan, Alec Aitken
1. Introduction (Tom to start)
a. Rapid and broad physical and ecological change in the arctic
i. Examples of pressures: climate change, oil exploration, fishing, invasive
species, freshwater, scouring
ii. Examples of responses: changes in ice, charismatic species, coastal effects
b. The arctic is difficult to work in, and so most of the biology is poorly known
c. Ecological change is tracked using convenient and available ecological indicators:
i. Remotely sensed data
ii. Charismatic species
iii. Human interfaces
d. Paucity of sea-floor data and no sea-floor indicators--same for water-column
e. Sedimentary records are increasingly used for baselines (Kidwell 2007) and death
assemblages in pristine settings can provide good baselines.
f. The discordance between living and death assemblages can provide a good
indicator of the degree, rate, and character ecological change.
g. But sediment mixing blurs the ecological record, and the shell record can be
transported or degraded over time due to crushing, bioturbation, and other forces
related to natural disturbance regimes, so the baseline character of skeletal death
assemblages differs among settings.
h. Questions addressed by this paper:
i. How useful are the death assemblages of the western Arctic and measures
of live-dead discordance there in indicating rapid change, relative to other
settings around the world and relative to the Eastern Arctic
ii. What baseline does the Western Arctic death assemblage represent, i.e.
what period of time? Diversity, abundance? (Kidwell 2001, 2002, 2008)
iii. What are the potential explanations for the observed differences in livedead discordance between the western Arctic and the eastern Arctic?
iv. How useful will this indicator be for understanding arctic environmental
change? How would we design a methodology or program to detect and
track change?
v. Identify possible areas of impact because of discordance (Kidwell 2007)
2. Methods (All authors)
a. Sampling
b. Identification and enumeration
c. Analytical methods from Kidwell 2008 and other papers
i. Richness
ii. Evenness
iii. J-C Index
iv. Spearman Rho
d. Comparison with the global dataset
e. Methods from Karin’s thesis
i. Plotting rank-order comparisons, etc.
f. Comparison to the Eastern Arctic
g. Possible use of transformations and other methods from the more recent
Tomasovich and Kidwell papers
3. Discussion
a. How useful are the death assemblages of the western Arctic and measures of livedead discordance there in indicating rapid change, relative to other settings around
the world and relative to the Eastern Arctic
i. When things are well and good and not rapidly changing – the death
assemblages does represent the living, on ecologically-relevant time
scales. Framing the time scales we need to know to track ecological
change. The death assemblage can provide information on this scale
ii. When the death assemblages does not match the live, it’s a flag for recent
change, or it indicates a severe natural disturbance regime
iii. It looks like we can trust the Western Arctic death assemblage as a useful
baseline despite some apparently extreme environmental conditions -- The
data are coming out in a way that is in apparent concordance with the
other settings around the world
b. What baseline does the Western Arctic death assemblage represent, i.e. what
period of time? Diversity, abundance? (Kidwell 2001, 2002, 2008)
c. What are the potential explanations for the observed differences in live-dead
discordance between the western Arctic and the eastern Arctic?
i. Perhaps high sedimentation compensates for any disturbance
d. How useful will this indicator be for understanding arctic environmental change?
i. Good for detecting change
ii. Not good for attribution
e. How would we design a methodology or program to detect and track change?
i. Time and resource effective
ii. Identify possible areas of impact because of discordance (Kidwell 2007) –
this is an early warning system.
iii. Attribution of the causes of change?
f. Ongoing proposed methodology would continue to strengthen calibration and
overall test over time (something for DFO).
4. Conclusions