Growth model of the reared sea urchin Paracentrotus ... - SciViews

a. Choice of the growth model for sea urchins
General introduction
Von Bertalanffy 1 is the model most often used. Among 69 studies of
sea urchins (regardless of species), this model was used 32 times, the
Richards model 17 times, the Gompertz model 9 times and other models
11 times (Table 1). However, in 13 studies where several models were
tested in addition to von Bertalanffy 1, the latter was considered as being
the best one only twice. The reason invoked to reject the von Bertalanffy
model was the initial lag phase in growth that is correctly represented
solely by a sigmoid like in the Richards, Gompertz or logistic models
(Yamagushi, 1975). In many studies where no other model was tested, it
seems that the von Bertalanffy 1 curve was just a default choice: it
represents the model "usually" fitted on such kind of data.
The Richards model was first proposed by Ebert (1973) as a better
alternative to the von Bertalanffy 1 curve to fit echinoid growth data. It
was intensively used by the same author (Ebert, 1973, 1980a, 1982, 1999;
Ebert & Russell, 1992, 1993) as well as by some others (Gage & Tyler,
1985; Russell, 1987; Kenner, 1992; Turon et al, 1995; Lamare &
Mladenov, 2000). The Gompertz model is also a favorite when there seems
to be a lag phase in growth and it has been used in various studies (Gage et
al, 1986; Gage, 1987; Cellario & Fenaux, 1990; Dafni, 1992; Turon et al,
1995; Ebert, 1999). Each of these models (i.e., Richards or Gompertz) was
preferred in 50% of the multi-model studies which considered them. The
logistic curve, although also sigmoidal, was systematically rejected in
multi-models studies of sea urchins, except for the irregular echinoid
Echinocardium pennatifidum Norman (Gage, 1987).
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