Unlocking the archive: Unlocking the archive: Growth records from Growth records from

bivalve shellsbivalve shells

• C. A. Richardson, C. A. Richardson,

• School of Ocean Sciences, University of Wales School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Angelsey, LL59 5ABBangor, Menai Bridge, Angelsey, LL59 5AB

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

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

The European cockle The European cockle Cerastoderma Cerastoderma edule is a common edule is a common inhabitant of sandy sheltered shores throughout Europe. inhabitant of sandy sheltered shores throughout Europe. During low tide the cockle is uncovered and lays down a fine During low tide the cockle is uncovered and lays down a fine dark band in the shell (arrow)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

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

Acetate peels of sections of the Acetate peels of sections of the shell of shell of Modiolus modiolusModiolus modiolus reveal reveal the presence of annually the presence of annually deposited growth linesdeposited 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

Fishing trawlers which tow beam trawls across the seabed can Fishing trawlers which tow beam trawls across the seabed can damage the delicate growing margin of some species of damage the delicate growing margin of some species of shells. A record of the damage caused by fishing gears is shells. A record of the damage caused by fishing gears is recorded in the shell structure as breaks in shell growth and recorded in the shell structure as breaks in shell growth and sand grains are often incorporated in a cleft between the old sand grains are often incorporated in a cleft between the old and newly mineralised shelland 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.

Growth line studies using the “Tree Growth line studies using the “Tree of the sea” of the sea” Arctica islandicaArctica islandica..

Research currently funded by the EU Research currently funded by the EU (Holsmeer), NERC and DTI(Holsmeer), NERC and DTI

Research collaborators: Dr James Scourse Research collaborators: Dr James Scourse and Dr Nicole Fraser (School of Ocean and Dr Nicole Fraser (School of Ocean Sciences), Dr Graham Forsythe (Exeter Sciences), Dr Graham Forsythe (Exeter University), Dr Simon Chenery (British University), Dr Simon Chenery (British Geological Survey (BGS), Professors Keith Geological Survey (BGS), Professors Keith Briffa and Phil Jones (Climate Research Unit, Briffa and Phil Jones (Climate Research Unit, University of East Anglia)University of East Anglia)

Arctica islandicaArctica islandica

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

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.

Inside view of an Inside view of an ArcticaArctica valve valve

The preferred line of section incorporates the maximum growth axis of the shell.

Incremental Growth in Incremental Growth in ArcticaArctica

Arctica Arctica Hinge Hinge AreaArea

Band-width measurement

ArcticaArctica shell 010037 (left) shell 010037 (left)

Growth lines near umbo

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Untreated Annual Growth DataUntreated Annual Growth Data

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

Single and articulated shell Single and articulated shell valves of valves of Arctica islandicaArctica islandica are are abundant on the seabed. abundant on the seabed. Radiocarbon dating of samples of Radiocarbon dating of samples of shells indicates that they range in shells indicates that they range in age from 7000 yrs BC to the age from 7000 yrs BC to the present.present.

Fifty shells have been Fifty shells have been radiocarbon dated providing a radiocarbon dated providing a range of dates covering the past range of dates covering the past 1000 years.1000 years.

The analysis and measurement of the growth lines The analysis and measurement of the growth lines in the shell of in the shell of Arctica islandicaArctica islandica have a number of have a number of applicationsapplications• The patterns of narrow and wide annually deposited growth The patterns of narrow and wide annually deposited growth

increments in one shell can be cross-matched with the increments in one shell can be cross-matched with the patterns from different shells from a similar time period. This patterns from different shells from a similar time period. This chronology can then be matched with chronologies from chronology can then be matched with chronologies from shells of different time periods. Thus a chronology of shell shells of different time periods. Thus a chronology of shell growth spanning many centuries could be constructed. This growth spanning many centuries could be constructed. This will eventually enable the environment of shell growth and will eventually enable the environment of shell growth and changes in the marine climate over hundreds and eventually changes in the marine climate over hundreds and eventually thousands of years to be investigatedthousands of years to be investigated

• Using chemical proxies (e.g. element ratios and stable Using chemical proxies (e.g. element ratios and stable oxygen isotopes) in the shell it will be possible to determine oxygen isotopes) in the shell it will be possible to determine the seawater temperature at the time of shell depositionthe seawater temperature at the time of shell deposition

• Techniques are now available which allow the chemical Techniques are now available which allow the chemical analysis of the growth increments. One application is the analysis of the growth increments. One application is the determination of metal concentrations within the growth determination of metal concentrations within the growth increments which will aid in investigating anthropogenic increments which will aid in investigating anthropogenic changes in the marine environment.changes in the marine environment.

Section through the shell of the horse Section through the shell of the horse mussel mussel Modiolus modiolusModiolus modiolus to show A) the to show A) the annual growth lines (white arrows) and B & annual growth lines (white arrows) and B & C) laser ablation marksC) 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.

Concentrations of zinc in annual growth Concentrations of zinc in annual growth increments in shells of the horse mussel increments in shells of the horse mussel Modiolus modiolusModiolus modiolus collected from a dumping collected from a dumping ground in the North Seaground in the North Sea

Horse mussel

The longevity of Horse Mussels can be >40-50 years

Suggested applications of growth line Suggested applications of growth line analysis for studying environmental change analysis for studying environmental change in Strangford Lough. The following could be in Strangford Lough. The following could be undertaken:undertaken:• The age of horse mussels and clams could be The age of horse mussels and clams could be

determined using the annual growth lines and determined using the annual growth lines and growth rates ascertainedgrowth rates ascertained

• The frequency of disturbance marks could be The frequency of disturbance marks could be determined in the shell and related to historical determined in the shell and related to historical changes in fishing activity in the Loughchanges in fishing activity in the Lough

• Radiocarbon dating of dead shell valves would Radiocarbon dating of dead shell valves would enable the history of the mussel beds in the Lough enable the history of the mussel beds in the Lough to be established (e.g. <50 years or 100-500 years)to be established (e.g. <50 years or 100-500 years)

• LA-ICP-MS analysis could be used to investigate LA-ICP-MS analysis could be used to investigate environmental impacts via studies of the changes environmental impacts via studies of the changes in natural or anthropogenic chemical signatures in in natural or anthropogenic chemical signatures in the shellthe shell