World Congress of Malacology Antwerp ... - Unitas Malacologica

However, a growth trend related to the water quality has been observed. In rivers with good nutrient
supply and with neutral and stable pH the shells grow larger than expected while in rivers with low
buffer capacity (for example rivers that have granite bedrocks) grow smaller. There are good
indications that pH of the water together with the food availability and the amount of dissolved
oxygen in the water are the strongest factors that affect the shell length in relation to the age of the
mussel. Even though, the sclerochronologies based on variations in annual growth of mussel shells
exhibit a high degree of running similarity with local variations in summer temperature (especially in
localities with pristine conditions). Yet, changes in water quality, as example due to liming, affect the
annual growth rate of the shells. The immediate effect of liming is seen as strong growth disturbance
line in all collected shells. We demonstrate that M. margaritifera mussels, especially the juvenile
stages, are very sensitive to sudden changes of their environment. This project was financed by the
World Wildlife Fund (WWF) and County Board of Västernorrland.
Analysis of shell growth, structure and chemical composition of ocean quahog (Arctica
islandica)
Dunca, Elena 1 ; Mutvei, Harry 1 ; Göransson, Peter 2 ; Mörth, Carl-Magnus 3 ;
Whitehouse, Martin J 1 ; Elfman, Mikael 4
1. Swedish Museum of Natural History, Box 50007, 10405 Stockholm, Sweden,
Email: elena.dunca@nrm.se; harry.mutvei@nrm.se; martin.whitehouse@nrm.se
2. Miljökontoret, S-251 89 Helsingborg, Sweden,
Email: peter.goransson@helsingborg.se
3 Stockholm University, Dept of Geology and Geochemistry, Stockholm, Sweden,
Email: magnus.morth@geo.su.se
4 University of Lund, Dept of Nuclear Physics, Box 118, S-22100 Lund, Sweden,
Email: Mikael.Elfman@nuclear.lu.se
Recent studies of ocean quahog (Arctica islandica) demonstrate that the shell growth and structure,
as well as its chemical composition reflect changes in the environment. Sclerochronologies (growth
increment chronologies) together with isotope analyses allow reconstruction of palaeotemperatures.
Consequently, the bivalve shells are considered as reliable proxies for climate reconstructions and
there is an increasing trend to use bivalves as environmental bio-monitors. However, shells from
shallow water environments along the costal regions are more exposed to salinity fluctuations and to
pollutants from human activities than shells from deeper regions. This affects the reliability of
temperature reconstructions yet the chemistry of these shells reveals the history of water pollution.
In our work we compare the shell structure of ocean quahog collected recently from Kiel Bay, along
the Swedish West Coast to Iceland, Spitsbergen and the White Sea with sub-fossil shells from
museum collections dated from the Tertiary to Holocene.
Shells from Kiel Bay, Öresund and Kattegat, as well as shells from the White Sea, are considerable
thinner and smaller, with many growth disturbance lines, compared to shells from Skagerrak and the
North Sea. Shells from Iceland, Spitsbergen and from the Tertiary are particularly large sized, and
considerably thicker. They have also a highly organized crossed lamellar microstructure with a very
thin outermost granular homogenous sub-layer. In contrast, shells from the Swedish West Coast and
the White Sea have a very poorly organized microstructure, mostly homogenous, and only the outer
aragonitic layer shows sporadically crossed acicular microstructure. These observations indicate that
the microstructure, size and thickness of Arctica shells are induced by stress factors, such as salinity
changes and water pollution.
Analyses carried out with SIMS, ICP-OES, nuclear microprobe and neutron activation analysis show
that higher contents of S, N, Cu, Zn, As, Cd and P in shell portions formed during the last century are
related to human activities such as mining and industrial development.
In order to use shells as archives for climate change models it is necessary to evaluate the full range
of environmental data recorded in the shells by employing different analytical techniques including
chemical analyses that combine high multi-elemental capacity with high sensitivity and high spatial
resolution, as well as growth rate and structural analyses.
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