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

Abstract
ABSTRACT
A rearing protocol for the edible European sea urchin Paracentrotus
lividus in a closed cycle (control of the whole life cycle of the echinoid)
and in a recirculating system (control of the environment around the
echinoid) is set up and tested at a pilot scale. This protocol is used to
experiment on growing postmetamorphics whose age and genetic origin
are perfectly known. Among the various measurements of size, we
determined that the test diameter is both rapid and accurate for quantifying
somatic growth. Causes and mechanisms of asymmetrical, or even
sometimes multimodal, size distributions among previously homogeneous
cohorts are studied. Results evidence the existence of a size-based
intraspecific competition, causing a reversible growth inhibition of smaller
individuals. A new growth model (called 'fuzzy-remanent'), including a
component of intraspecific competition, is elaborated by defuzzifying a
fuzzy model. Traditional least-square regression is abandoned in favor of
quantile regression to fit it. Both the model and the regression method are
adapted to include individual variations (we call this an 'envelope model').
This envelope model has functionally interpretable parameters. One of
them quantifies the degree of inhibition caused by intraspecific
competition. Since many similar fuzzy-remanent functions can be designed
and fitted with this method, this approach is promising to model growth of
other organisms in a functional way. This model rehabilitates von
Bertalanffy's theory on individual growth. Moreover, the latter theory is
now verified for Paracentrotus lividus, despite the observation of an initial
lag phase in growth. A functional classification of growth curves is
proposed.
Keywords: sea urchin, growth model, intraspecific competition, quantile
regression, fuzzy logic, aquaculture, Paracentrotus lividus.
5