Santander, February 19th-22nd 2008 - Aranzadi

Analysis of malacofauna remains from archaeological sites on Adak Island (Aleutian Islands, USA)
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mussel decreases from layer 4 to layer 2 as well as
other epifaunal species – chitons, gastropods and
barnacles. On the contrary, Nuttall’s cockle remains
increase from layer 4 to layer 2 as well as other bivalves
inhabiting sandy substrates and sea urchins.
This situation illustrates the change of substrates
at Clam lagoon’s intertidal zone. Probably, the
intertidal zone was rocky around the end of the 6 th
millennium cal BC. During the existence of the
ancient settlement, the rocky portion decreased
and the sandy substrate began to dominate. As a
consequence the invertebrates’ taxonomic structure
changed.
It could be possible that this change was the
result of sea level transformations. At the same
time, the decrease of predator pressure (i.e. sea
otter) over sea urchin and clam populations led to
increasing their populations.
uncommon for this region, were found in the
same layers. On the contrary, arctic-boreal and
high-boreal species increased in layers III and II.
Probably, this increment was a consequence of a
change in temperature.
Analysis of mollusc taxonomic composition
suggests the following temperature periods in the
development of this shell midden. The period
from the 8 th to the middle of the 11 th centuries was
cold. A warmer period from the middle of the 11 th
to the middle of the 12 th centuries was identified
by the presence of low-boreal gastropod Nucella
heyseana into higher latitudes and a decrease of
psychrophilic species. The increase in arcticboreal
and high-boreal species from the middle
of the 12 th to the middle of the 16 th centuries was
the evidence of colder temperatures. This period
corresponds with the so-called “Little Ice Age”
(Cook et al. 2004, Savinetsky et al. 2004).
There were identified 7000 mollusc remains at
ADK-009. The bivalve remains dominate the sample.
Epifaunal molluscs dominate all layers of this
shell midden. They represent more than 90% of the
sample. This proportion did not change significantly
from layer to layer. They are evidence of a
rocky substrate at Sweeper Cove’s intertidal zone
from the 8 th century cal AD to nowadays
(Antipushina 2006b).
Three zoogeographical groups of species -
arctic-boreal, high-boreal and low-boreal, were
identified. However, the proportions of these different
zoogeographical groups were not constant
in all the layers (Fig. 3). For example, in layers IV
and I, there is a decrease of arctic-boreal and
high-boreal species. Moreover, remains of lowboreal
gastropods such as Nucella heyseana,
Figure 3. Zoogeographical spectra of molluscs from shell midden ADK-009.
4. CONCLUSIONS
The ancient Aleutians gathered molluscs, especially
a foolish mussel (Mytilus trossulus), a Nuttall’s
cockle (Clinocardium nuttallii), a limpet (Lottia pelta),
a periwinkle (Littorina sitkana), and a chiton
(Katharina tunicata). Analyses of mollusc taxonomic
compositions were used for palaeoenvironmental
reconstruction of ADK-009 and ADK-171.
A decrease in epifaunal species and an increase
in infaunal species illustrate a change of substrate
at Clam lagoon’s intertidal zone. The intertidal
zone was rockier 6500 years ago. During the existence
of the ancient settlement, the rocky environment
decreased, and the invertebrate species
changed. At the same time, the decrease of predator
pressure (i.e. sea otter) over sea urchin and clam
populations led to an increase in their populations.
The substrate type at Sweeper Cove’s intertidal
zone has not changed significantly from the 8th
century cal AD to our time. We made such conclusion
because of epifaunal molluscs’ remains dominated
in all layers of ADK-009.
Analysis of the mollusc taxonomic composition
allows us to distinguish different temperature
periods at ADK-009. The period from the 8 th to the
middle of the 11 th centuries was colder. Two warmer
periods were identified, one from the middle of
the 11 th to the middle of the 12 th centuries and the
other from the middle of the 16th to the 19th centuries.
The colder period from the middle of the 12 th
to the middle of the 16th centuries corresponds to
the “Little Ice Age”.
MUNIBE Suplemento - Gehigarria 31, 2010
S.C. Aranzadi. Z.E. Donostia/San Sebastián