Rate of gonad development in the ascidian Pyura praeputialis (Heller)

Abstract

Morphometric studies have been carried out on Pyura praeputialis. The relationships investigated were:

(a) weight of the visceral mass v, total body weight,

(b) total gonad weight v. weight of the visceral mass,

(c) weight of right gonad v. total gonad weight, and

(d) weight of right gonad v. weight of visceral mass.

There is evidence that spawning results in a significant decrease in gonad size and that there are two spawning seasons per year (spring and autumn), but evidence on the latter point is not conclusive.

It is shown that, within each of the populations studied, gonad weight bears a rectilinear relationship to body weight. It is also shown that the rate of gonad development is significantly lower in the littoral (i.e. intertidal) population than in the sublittoral (i.e. permanently immersed) population. The different rates of gonad development in the two populations are taken to indicate that the littoral is a less favourable environment, for this species, than the sublittoral. The implications of this finding are discussed.