Notes on oviposition and demography of a shallow water population of the edible snail Zidona dufresnei (Caenogastropoda: Volutidae) living in San Antonio Bay (northern Patagonia, Argentina)

Abstract

Zidona dufresnei (Donovan, 1823) is a big-sized and long-lived snail endemic to the south-western Atlantic where it dwells in sandy bottoms between five and 115 m; females lay big egg capsules from which crawling juveniles emerge. An unusual population of Z. dufresnei inhabits the low intertidal and shallow subtidal zone of San Antonio Bay, the southernmost location of the species, where it faces many threats. The aim of this study is to describe some of the demographic and reproductive characteristics of this population and to compare them to those located in northern zones. Monthly samples of adults and egg capsules were obtained from October to April and their position was recorded; snails and capsules were gathered for examination in the laboratory. Sex-ratio was near 1:1 for the whole sampling period and the size–frequency distributions were similar for both sexes; females were wider and heavier than males at the same shell length. Maximum shell length was 120.5 mm in our study and so no female reached the minimum size at first gonadal maturity reported for other populations (128 mm); female size seems to limit the capsule diameter and the number and size of embryos that are lower than in other populations. Egg capsule and adult densities in the intertidal zone peaked in February and March respectively, averaging 1.34 capsules and 1.91 snails by 100 m2 during the sampling period; egg capsule deposition elapsed from November to March and peaked in December; females select cobble by size to lay egg capsules. Due to its restricted distribution and the low juvenile and adult dispersal, the unusual Z. dufresnei population dwelling in San Antonio Bay seems to be quite vulnerable to diverse anthropogenic impacts.

Reproductive cycle and oviposition inZidona dufresnei(Caenogastropoda: Volutidae) from northern Patagonia, Argentina

“…The numbers of egg capsules present were recorded and their developmental stages classified according to Pereyra et al (2009) (Table II). In those areas of the bay where egg capsules were in the intertidal zone, similar transects were performed.…”

“…Previous studies on Z. dufresnei in the area of Mar del Plata show that individuals may reach up to 210 mm (in shell length) and that the oldest individuals can live for more than 17 years, attaining sexual maturity at 128 and 120 mm for females and males, respectively (Giménez & Penchaszadeh 2003;Giménez et al 2004). In San Matías Gulf, individuals from the intertidal population from SAB can reach a maximum size of 120 mm for males and 110 mm for females (Pereyra et al 2009). Moreover, the females from the intertidal population were found to have wider and heavier shells than males (Pereyra et al 2009).…”

“…In the San Matías Gulf there are two distinct populations of this species, one in the intertidal area inside San Antonio Bay (SAB, 40°45′ S, 64°56′W) (Pereyra et al 2009;Roche et al 2011Roche et al , 2013a and another inhabiting deeper water (up to 120 m) (Medina 2013). In San Antonio Bay this species is found in a small and shallow channel (4 m maximum depth during low tide), on sandy substrates mixed with boulders and sponges (Roche et al 2011(Roche et al , 2013a(Roche et al , 2013b.…”

“…In San Antonio Bay this species is found in a small and shallow channel (4 m maximum depth during low tide), on sandy substrates mixed with boulders and sponges (Roche et al 2011(Roche et al , 2013a(Roche et al , 2013b. Both sexes reach a similar maximum size (120 mm in shell length, Pereyra et al 2009) and share the same habitat. Zidona dufresnei has direct development and a low dispersal ability (Penchaszadeh & de Mahieu 1976;Giménez & Penchaszadeh 2003), which could result in different population enclaves being locally adapted.…”

“…In San Matías Gulf, individuals from the intertidal population from SAB can reach a maximum size of 120 mm for males and 110 mm for females (Pereyra et al 2009). Moreover, the females from the intertidal population were found to have wider and heavier shells than males (Pereyra et al 2009). However, there is no information about the gonadal cycle and size at sexual maturity either for the intertidal or shallow subtidal populations in SAB.…”