1. Unlocking the archive: Growth records from bivalve shells C. A. Richardson, C. A. Richardson, School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Angelsey, LL59 5AB School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Angelsey, LL59 5AB

2. The age of bivalves e.g. cockles Cerastoderma edule has traditionally been estimated from the clear concentric annual rings present on the outer surface of the shell

3. Shells contain within their structure a record of their past growth in the sea. One way of viewing this information is to embed the shell in resin, section it and prepare a peel of the polished and etched surface

4. The European cockle Cerastoderma edule is a common inhabitant of sandy sheltered shores throughout Europe. During low tide the cockle is uncovered and lays down a fine dark band in the shell (arrow) Common cockle with foot extended Tidal growth bands in the shell of the cockle. Each band (arrow) represents a low tide Richardson, C.A. 2001. Molluscs as archives of environmental change. Oceanography and Marine biology: an Annual Review, 39, 103-164

5. Diagrammatic section through a horse mussel, Modiolus modiolus shell to show the preferred line of section, shell layers and location of the annual growth lines

6. Acetate peels of sections of the shell of Modiolus modiolus reveal the presence of annually deposited growth lines Each pair of alternating dark and light lines represents respectively, a summer and winter period of shell growth. The age of each mussel can be determined from the number of winter (light) lines Anwar, N.A., Richardson, C.A. & Seed, R. 1990. Age determination, growth rate and population structure of the horse mussel Modiolus modiolus. Journal of the Marine Biological Association of the United Kingdom, 70, 441-457. Research in collaboration with Professor R. Seed

7. Fishing trawlers which tow beam trawls across the seabed can damage the delicate growing margin of some species of shells. A record of the damage caused by fishing gears is recorded in the shell structure as breaks in shell growth and sand grains are often incorporated in a cleft between the old and newly mineralised shell Recovery of a beam trawl Trawler Section of a razor clam shell with embedded sand grains Glycymeris glycymeris Ramsay et al 2000. Can shell scars on dog cockle (Glycymeris glycymeris L.) be used as a record of historic fishing disturbance. Journal of Sea Research, 43, 167-176) Henderson, R.F & Richardson, C.A. 1998. The indirect and direct effects of suction dredging on a razor clam (Ensis arcuatus) population. ICES Journal of Marine Science, 55, 970-977.

8. Growth line studies using the Tree of the sea Arctica islandica. Research currently funded by the EU (Holsmeer), NERC and DTI Research collaborators: Dr James Scourse and Dr Nicole Fraser (School of Ocean Sciences), Dr Graham Forsythe (Exeter University), Dr Simon Chenery (British Geological Survey (BGS), Professors Keith Briffa and Phil Jones (Climate Research Unit, University of East Anglia)

9. Arctica islandica Is a large clam that has an extraordinary longevity and can attain an age of 263 years

10. Dendrochronology (tree-ring dating): Trees in temperate zones grow one ring per year. A year-by-year record or ring pattern is formed that reflects the climatic conditions in which the tree grew. These patterns can be compared with other trees growing in the same geographical zone and under similar climatic conditions. The sum of these tree-ring patterns forms a chronology against which old wood can be cross-dated and the chronology extended back in time.

11. Inside view of an Arctica valve The preferred line of section incorporates the maximum growth axis of the shell.

12. Incremental Growth in Arctica

13. Arctica Hinge Area Band-width measurement

14. Arctica shell 010037 (left) Growth lines near umbo

16. Untreated Annual Growth Data

18. Correlation of growth line patterns between two shells, number 99 (010099) and number 88 (010088)

19. Single and articulated shell valves of Arctica islandica are abundant on the seabed. Radiocarbon dating of samples of shells indicates that they range in age from 7000 yrs BC to the present. Fifty shells have been radiocarbon dated providing a range of dates covering the past 1000 years.

21. The analysis and measurement of the growth lines in the shell of Arctica islandica have a number of applications The patterns of narrow and wide annually deposited growth increments in one shell can be cross-matched with the patterns from different shells from a similar time period. This chronology can then be matched with chronologies from shells of different time periods. Thus a chronology of shell growth spanning many centuries could be constructed. This will eventually enable the environment of shell growth and changes in the marine climate over hundreds and eventually thousands of years to be investigated The patterns of narrow and wide annually deposited growth increments in one shell can be cross-matched with the patterns from different shells from a similar time period. This chronology can then be matched with chronologies from shells of different time periods. Thus a chronology of shell growth spanning many centuries could be constructed. This will eventually enable the environment of shell growth and changes in the marine climate over hundreds and eventually thousands of years to be investigated Using chemical proxies (e.g. element ratios and stable oxygen isotopes) in the shell it will be possible to determine the seawater temperature at the time of shell deposition Using chemical proxies (e.g. element ratios and stable oxygen isotopes) in the shell it will be possible to determine the seawater temperature at the time of shell deposition Techniques are now available which allow the chemical analysis of the growth increments. One application is the determination of metal concentrations within the growth increments which will aid in investigating anthropogenic changes in the marine environment. Techniques are now available which allow the chemical analysis of the growth increments. One application is the determination of metal concentrations within the growth increments which will aid in investigating anthropogenic changes in the marine environment.

22. Section through the shell of the horse mussel Modiolus modiolus to show A) the annual growth lines (white arrows) and B & C) laser ablation marks Richardson, C.A., Chenery, S.R.N. & Cook, J.M. 2001. Assessing the history of trace metal (Cu, Zn & Pb) contamination in the North Sea through laser ablation ICP-MS of horse mussel, Modiolus modiolus shells. Marine Ecology Progress Series, 121, 157-167.

23. Concentrations of zinc in annual growth increments in shells of the horse mussel Modiolus modiolus collected from a dumping ground in the North Sea Horse mussel The longevity of Horse Mussels can be >40-50 years

24. Suggested applications of growth line analysis for studying environmental change in Strangford Lough. The following could be undertaken: The age of horse mussels and clams could be determined using the annual growth lines and growth rates ascertained The age of horse mussels and clams could be determined using the annual growth lines and growth rates ascertained The frequency of disturbance marks could be determined in the shell and related to historical changes in fishing activity in the Lough The frequency of disturbance marks could be determined in the shell and related to historical changes in fishing activity in the Lough Radiocarbon dating of dead shell valves would enable the history of the mussel beds in the Lough to be established (e.g. <50 years or 100-500 years) Radiocarbon dating of dead shell valves would enable the history of the mussel beds in the Lough to be established (e.g. <50 years or 100-500 years) LA-ICP-MS analysis could be used to investigate environmental impacts via studies of the changes in natural or anthropogenic chemical signatures in the shell LA-ICP-MS analysis could be used to investigate environmental impacts via studies of the changes in natural or anthropogenic chemical signatures in the shell