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garganese
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Città: cagnano varano
2 Messaggi
Flora e Fauna |
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Owen
Utente nuovo
Città: Barcelona
3 Messaggi
Biologia Marina |
 Inserito il - 20 maggio 2011 : 19:14:25
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Salve,
You can easily measure the exact age of a dead Paracentrotus by counting the annual growth rings in the test plates of dead specimens, after dehydrating them in a stove and immersing the plates in xylene. The procedure is described in Turon et al. Growth and population structure of Paracentrotus lividus (Echinodermata: Echinoidea) in two contrasting habitats. MARINE ECOLOGY PROGRESS SERIES, Vol. 122: 193-204 (1995). After you have done that procedure for many specimens in the same population, you can correlate the age with the test diameter, so you can have an estimation for the age in living sea urchins.
Here is an extract of the Materials & Methods in that paper:
Growth ring measurements. Samples of 20 individuals
of Paracentrotus lividus of all sizes were taken
every 2 wk at both localities. The samples were fixed
and preserved in formalin. Growth rings were studied
in 509 individuals from Tossa de Mar and 537 from
Cubelles [these were the same specimens as those used
in Lozano et al. (1995) for the study of biological cycles].
The maximum diameter of the indlvlduals was
measured to the nearest 0.1 mm in the laboratory.
The body was then oven dried at 120°C for 48 h and
weighed. The test was cleaned of spines and an
interambulacral series of plates was dissected and
used to count growth rings (Jensen 1969, Allain
1978, Azzolina 1988, Gage 1991). Within one corona1
series, the larger plates corresponding to the zone of
the ambitus were the most suitable for ring counting,
since in the older ones (near the peristomial membrane)
the distal bands were hardly distinct and
resorption phenomena were present (Smith 1980).
Interambulacral series were used because they were
free of podia orifices. The observation of the rings
was easy after drying, and the preparation procedure
of Jensen (1969) was not necessary. Rings were visualized
simply by immersing the plates in xylene and
observing them under a stereomicroscope. The number
of translucent rings (dark in reflected light) was
counted. They were narrower than the opaque ones
and easier to count.
The data on size and number of growth rings were
transformed to size-at-age under the assumptions of an
annual formation of the rings (see 'Discussion') and of
1 main settlement episode per year (Lozano et al.
1995). After trying different models (see 'Discussion'),
the Gompertz equation was used to fit a growth function
to these measurements. It has the form (we used
the same formulation as Cellario & Fenaux 1990):
Lt= Lm e^(-be^(-kt))
where Lt, is the test diameter at time t, Lm, is the maximum
test diameter, the scale parameter b = Ln (Lm/Lo),
where Lo is the diameter at t = 0 (settlement on
bottom), and k is a constant of the model.
The means of the sizes of each age-class were used
to fit the growth function. Parameter estimation was
performed using a nonlinear procedure (NONLIN
module of the SYSTAT program with the default
Quasi-Newton minimization algorithm).
I hope this works!
Greetings from Spain. |
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Informazione: età di Paracentrotus lividus...
