Page 7 - Shell_growth_2008

Geo-Mar Lett (2008) 28:309–325 315

Table 3 Shell growth statistics from the mark-recapture experiment at Mazzaforno (started in October 2005 when 100 shells were marked)
Growth intervals Oct-05 to Jan-06 Jan-06 to Apr-06 Apr-06 to Jul-06 Jul-06 to Oct-06 Oct-05 to Oct-06
Marked shells recovered (specimens 59 (100) 54 (40) 25 (22) 3 (3) 3
found on previous visit)

Mean linear growth (mm) 8.6 6.3 1.2 3.2 19.1
Standard error of mean 0.50 0.28 0.30 1.28 0.88
Minimum linear growth (mm) 1.0 2.2 0.0 0.7 17.7
Maximum linear growth (mm) 18.5 10.6 4.7 4.8 20.7
Seasonal % 44.5 32.8 6.0 16.7 100.0
Mean diameter growth (mm) 1.4 1.0 0.2 0.5 3.4
Standard error of mean 0.09 0.06 0.05 0.12 0.57
Minimum diameter growth (mm) 0.1 0.2 0.0 0.3 2.6
Maximum diameter growth (mm) 2.8 1.7 0.8 0.7 4.5
Seasonal % 43.7 33.3 6.8 16.2 100.0
Mean height growth (mm) 1.7 1.2 0.4 0.8 4.1
Standard error of mean 0.10 0.08 0.08 0.09 0.50
Minimum height growth (mm) 0.1 0.3 0.0 0.6 3.3
Maximum height growth (mm) 3.8 2.6 1.3 0.9 5.0
Seasonal % 42.1 30.1 9.0 18.9 100.0
The data are the growth increments laid down in the interval between visits and show growth for the autumn/fall, winter, spring and summer
seasons, and for the whole year of the experiment

Monthly shell edge values: Cala Grande offsets from locality SSTs in seven of 24 months and from
mean monthly SSTs at Mazara del Vallo in eight of
Temperatures derived from the monthly shell edge values 24 months. In both comparisons, there is a better degree
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(δ O SHELL ) follow both the SSTs measured at the locality of concordance in the final 12 months of the study than in
2
(Fig. 5; r =0.906) and the mean monthly SSTs recorded by the first 12 months.
2
the Mazara del Vallo station (r =0.843). However, the
offsets between monthly pairs in these sets of values are not Monthly shell edge values: Monte Cofano
constant. In some months the differences are significant,
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exceeding the 95% confidence interval of the isotope The δ O SHELL SSTs calculated from the monthly shell
determinations (equivalent to ±0.8°C), while in other edge samples follow the monthly SSTs measured at the
2
months there are no significant differences (Table 6). locality (Fig. 6; r =0.824) and the mean monthly SSTs at
2
18
In general, calculated SSTs from δ O SHELL are lower Palermo (r =0.745), although the differences between
than SSTs recorded at the time of collection. The largest paired monthly values are variable (Table 7). In December
offsets between measured and shell isotope SSTs are mainly 2003 and March 2004, the temperatures derived from the
in the spring and summer months, although this is variable shell edges significantly exceed (p>0.05) those of the local
(for example, May and June 2003 and July 2004 sets of seawater. For December 2003, this may be because the SST
values are not significantly different from directly recorded on the day of sampling was lower than the monthly average
temperatures). Shell isotope SSTs show non-significant (the difference with Palermo mean SST in that month is not

Table 4 Analyses of shell growth patterns at Mazzaforno (original shell size shell diameter at the time of marking)
Correlation tested r r 2 p

Linear growth by Jan. 2006 (autumn growth)/original shell size −0.235 0.055 0.07
Linear growth by Apr. 2006 (winter growth)/original shell size −0.399 0.159 0.01
Linear growth by Jul. 2006 (spring growth)/original shell size −0.165 0.027 0.46
Linear growth by Oct. 2006 (summer growth)/original shell size −0.892 0.795 0.30
Linear growth by Apr. 2006 (winter growth)/shell size in Jan. 2006 −0.263 0.069 0.10
Linear growth by Jul. 2006 (spring growth)/shell size in Apr. 2006 −0.047 0.002 0.83
Linear growth by Oct. 2006 (summer growth)/shell size in Jul. 2006 −0.419 0.175 0.72
Annual linear growth/original shell size −0.892 0.795 0.30