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Geo-Mar Lett (2008) 28:309–325 321

year shows that minimum annual offsets range from 0.0°C mean shell growth, while at San Vito lo Capo the least
to 0.7°C, while maximum annual offsets range between amount of growth was in summer. The ‘summer cohort’ at
3.1°C and 8.7°C. San Vito lo Capo showed that smaller/younger shells grow
Table 11 summarizes annual maximum and minimum more than larger/older ones. At both localities and in each
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SSTs as calculated from δ O SHELL edge values, as measured season there are wide differences between individuals, which
directly at the localities, and as obtained from mean monthly are partly attributable to varying growth rates, with smaller
and mean daily records from inshore recording stations. (younger) shells exhibiting the highest rates. Similar obser-
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Combining the offsets between δ O SHELL SSTs and vations were made by Regis (1972) on a population of O.
measured SSTs from all these data gives a mean offset of turbinatus at Bandol, southern France. Regis (1972) also
1.0°C (range: 0.1–2.6°C) for annual minimum temperatures showed that although shell growth occurred throughout the
and a mean offset of 3.1°C (range: 0.5–5.0°C) for annual year, it was greater in the summer and less in winter/spring.
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maximum temperatures. Table 11 also shows that δ O SHELL This difference with NW Sicily suggests there may be
values fail to record temperatures higher than 25°C. latitudinal trends in patterns of annual shell growth across
the geographical range of the species.

Discussion Effect of notching on shell growth

Shell growth All shells were notched on the aperture at the commence-
ment of the mark-recapture experiment and this could have
Growth occurs in most shells in all seasons of the year at affected subsequent growth. In a pilot survey, Mannino and
San Vito lo Capo and Mazzaforno, although around 75% of Thomas (unpublished data) noted that the notches on shells
linear shell growth occurs in the autumn and winter. At at Cala Grande and Monte Cofano were repaired within
Mazzaforno, spring was the season with the least amount of 1 month, with no distortion of growth. In the cases reported

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Table 11 Comparisons of minimum and maximum temperatures over sequence of δ O SHELL values in a single shell from Cala Grande; (3)
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the time periods indicated from (1) δ O SHELL edge values in monthly monthly sea surface temperatures recorded at the time of collection of
collected shells, including separately for ‘best fit’ and ‘worst fit’,and the shells; (4) mean monthly SSTs from inshore measuring stations and
larger and smaller shells from Mazzaforno; (2) an approximately annual (5) mean daily SSTs from those recording stations
Locality Measurement Period Minimum temperature (°C) Maximum temperature (°C)
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1. Cala Grande (Favignana) δ O SHELL edges 11.2002–10.2003 12.4 23.7
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1. Cala Grande (Favignana) δ O SHELL edges 11.2003–10.2004 14.1 23.3
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2. Cala Grande (Favignana) Marked δ O SHELL 09.2003–10.2004 13.9 24.6
3. Cala Grande (Favignana) SST at collection 11.2002–10.2003 15.0 25.9
3. Cala Grande (Favignana) SST at collection 11.2003–10.2004 14.5 25.6
4. Mazara del Vallo Mean monthly SST 11.2002–10.2003 14.4 25.3
4. Mazara del Vallo Mean monthly SST 11.2003–10.2004 14.4 23.8
5. Mazara del Vallo Mean daily SST 11.2002–10.2003 14.0 28.2
5. Mazara del Vallo Mean daily SST 11.2003–10.2004 13.2 26.1
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1. Monte Cofano δ O SHELL edges 11.2002–10.2003 13.9 24.7
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1. Monte Cofano δ O SHELL edges 11.2003–10.2004 13.5 22.9
3. Monte Cofano SST at collection 11.2002–10.2003 14.6 28.2
3. Monte Cofano SST at collection 11.2003–10.2004 14.4 27.7
4. Palermo Mean monthly SST 11.2002–10.2003 14.1 28.4
4. Palermo Mean monthly SST 11.2003–10.2004 14.2 27.2
5. Palermo Mean daily SST 11.2002–10.2003 13.5 29.5
5. Palermo Mean daily SST 11.2003–10.2004 13.6 27.9
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1. Mazzaforno (all shells) δ O SHELL edges 08.2004–07.2005 12.0 25.0
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1. Mazzaforno (best fit) δ O SHELL edges 08.2004–07.2005 12.0 25.0
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1. Mazzaforno (worst fit) δ O SHELL edges 08.2004–07.2005 12.1 24.2
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1. Mazzaforno (larger) δ O SHELL edges 08.2004–07.2005 12.0 25.0
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1. Mazzaforno (smaller) δ O SHELL edges 08.2004–07.2005 13.7 24.6
3. Mazzaforno SST at collection 08.2004–07.2005 12.8 28.1
4. Palermo Mean monthly SST 08.2004–07.2005 13.7 27.2
5. Palermo Mean daily SST 08.2004–07.2005 13.1 27.9