Andrés Averbuj

REPRODUCTIVE SEASONALITY AND OVIPOSITION INDUCTION IN TROPHON GEVERSIANUS (GASTROPODA: MURICIDAE) FROM GOLFO NUEVO, ARGENTINA

ABSTRACT The reproductive biology of a population of the edible muricid Trophon geversianus inhabiting an intertidal rocky shore in Golfo Nuevo (Chubut, Argentina) was studied regarding the seasonality of oviposition and oviposition induction under laboratory conditions. Sex ratio in the population differed from 1:1 (female biased). The mean shell length was 22 mm for males and 24 mm for females, although the females presented significantly larger maximum sizes. No external sexual dimorphism was evident, whereas the female snails differed internally by the presence of the albumin and capsule gland and by gonad color. Although the population under study inhabits an area with marine traffic and a concentration of 1.9 ng Sn/g, it did not present signs of imposex, in contrast with other sympatric species. T. geversianus presented a marked reproductive seasonality during the study period. Oviposition started in May and concluded in November, when hatching of crawling embryos was registered up to January. This seasonality coincided with changes in water surface temperature, ambient temperature, and photoperiod. Reproductive activities were registered when the environmental stress was minimum. In the aquarium, each female laid an average of 12 egg capsules (range, 6–26) per oviposition event, and needed a total of 25 h (range, 12–57 h) to complete attachment of a single egg capsule. Data presented here could be useful for culture of the species.

On the reproductive biology and impact of imposex in a population of Buccinanops monilifer from Mar del Plata, Argentina

The populations of Buccinanops monilifer (Gastropoda: Nassariidae) from two different sites, Mar del Plata (Buenos Aires province) and a close non-polluted locality (Mar Chiquita), are compared in their imposex indices and reproductive parameters. In Mar del Plata, a beach nourishment (sand filling) remobilized sediment from the harbour area during 1999; our results show high imposex percentage and an increase in relative penis size index during and after this beach filling event, in contrast with the Mar Chiquita population that showed nil values during this study. Comparisons of reproductive parameters between both populations showed significantly higher frequency of spawning females and number of egg capsules per female in Mar Chiquita, while female size and number of eggs per capsule did not differ. Females from Mar del Plata that did not succeed in spawning showed higher imposex values than spawning ones. Sex-ratio was not significantly different from 1:1 in any of the sites (although male-biased in Mar del Plata and the opposite in Mar Chiquita). We found no malformations or abnormalities during intracapsular development in the imposexed population. Alternatively, we found evidence that suggests that B. monilifer intracapsular development includes the occurrence of intracapsular embryonic cannibalism of other smaller embryos, which was not previously known in this genus, and that complements adelphophagy (feeding on nurse eggs feeding).

Embryonic development and reproductive seasonality of Buccinanops globulosus (Nassariidae) (Kiener, 1834) in Patagonia, Argentina

Buccinanops globulosus mated all year round, with higher frequency from May to September, prior to spawning months. Gravid females were found between October and March. Oviposition peaked during rising temperatures and longest daylength while hatching peaked with high water temperature and declining daylength. Gravid females measured between 20 and 41 mm in shell length. The spawn consisted on average of 31 egg capsules, each containing 1266 eggs. Embryos usually completed development within each egg capsule by ingesting small fragments of the uncleaved nurse eggs, which were not a limiting resource. Egg capsules with more than one embryo were not common; in those cases, the embryos had different sizes probably related to intracapsular competition for nutrients, and were on average smaller than solitary embryos in the other capsules. Embryos hatched as crawling juveniles with a mean hatchling shell length of ~3.4 mm. In a few cases, malformed embryos were found, but it was not a common phenomenon. The information recorded in this study, as the minimum reproductive size and spawning season, is valuable for fisheries management.

ON THE EGG MASSES, EGGS AND EMBRYOS OF NOTOCOCHLIS ISABELLEANA (D'ORBIGNY, 1840) (GASTROPODA: NATICIDAE) FROM NORTHERN PATAGONIA

Naticids are common predators in sandy bottoms of shallow waters around the world. Probably due to their infaunal habitat, they are hard to find alive, particularly in the Patagonian waters of Argentina. Nevertheless, their presence is confirmed by the typical predation boreholes that can be seen on their bivalve prey along the coast (e.g., Bromley, 1981; Carriker, 1981; Pastorino & Ivanov, 1996; Signorelli et al., 2006). These boreholes record information on predators without actually seeing them. Paleontologists have exploited this field, analyzing the behavior and producing models of predator-prey relationships in ancient and recent communities (Kabat, 1990, and citations herein). Studies on the spawn of naticids are scarce in modern literature, despite its common presence in sandy bottoms. The typical sand collars were recognized several decades ago as belonging to this family. Ankel (1930) and Thorson (1935, 1940, 1946), among others, described these characteristic egg masses from different areas around the world. An accurate account of the morphology of the collar and capsules, including the way the gastropod builds them, was described by Giglioli (1955) and Ziegelmeier (1961). An interesting approach was recently published by Huelsken et al. (2008), who reviewed the naticids from Giglio, an Italian island off the coast of Tuscany. They compared mitochondrial and nuclear gene fragments (COI, 16S, H3, 18S) from adults and embryos from the egg masses, leaving no doubt about the mother species of each egg mass. During the past few years, several papers were published in which egg capsules of various gastropods from the southwestern Atlantic were described (Pastorino & Penchaszadeh, 1999, 2002; Pastorino et al., 2007; reviewed in Gallardo & Penchaszadeh, 2001). However, there is no published information about naticids MALACOLOGIA, 2009, 51(2): 395−402

Reproductive biology in the South Western Atlantic genus Buccinanops (Nassariidae): the case of Buccinanops paytensis

ABSTRACT The reproductive biology of the nassariid Buccinanops paytensis is considered and compared with the other species in the genus. In B. paytensis an average of 42 egg capsules were attached to the shell of each female. A mean of 2738 eggs (246 µm in diameter) occurred per capsule and generally only one embryo developed inside, measuring c. 5 mm in shell length when hatching; eggs at pre-hatching stage are still abundant. Four percent of the egg capsules contained two pre-hatching embryos of unequal size, in which nurse eggs were totally consumed. ‘Larval kidneys’ were recorded at advanced developmental stages (‘pediveliger’). Adaptations to reproduction in soft substrates involve a great amount of energy being invested by the females (nurse eggs and maternal care of the capsules), which enhance the survival of juveniles. Buccinanops paytensis had the highest number of nurse eggs per embryo (c. 2600), but B. cochlidium had more eggs and embryos per female (c. 3100 and c. 800, respectively). Hatching of crawling juveniles occurred in about 4 months in all species. When multiple embryos occur in an egg capsule, food becomes limiting, hatching size is reduced and unequal. Evidence of sibling cannibalism was observed in B. monilifer. Major differences are related to the spawn size, and the amount of nurse eggs and feeding modality of each species, which impact on the reproductive output (number and size of the juveniles) per female. The South African nassariid genus Bullia differs in egg capsule morphology and attachment, but is similar in having nurse eggs and direct development.

Age estimation methods in the marine gastropod Buccinanops globulosus comparing shell marks and opercula growth rings

ABSTRACT Age determination in gastropods is an essential tool for understanding the main aspects of population dynamics that allow for the formation of fisheries policies. Small-scale fisheries of the nassariid gastropod Buccinanops globulosus from northern Patagonia are not yet regulated, although it is locally consumed while an incipient commercialization is taking place. The aim of this study was to show the suitability of opercula readings for age estimation in B. globulosus, compared with shell marks, previously validated by the analysis of the stable isotope of oxygen. The individual age estimated by the opercula rings reading method did not match the estimation made by the shell marks reading method. Stable isotope analyses confirmed that shell marks were deposited annually. Proper age estimation for B. globulosus, based on recognizable external shell marks, reached up to 9 years.

Variability of imposex development and reproductive alterations in the Patagonian gastropod Buccinanops globulosus inhabiting a polluted harbour area

El objetivo de este trabajo fue estudiar parametros reproductivos y desarrollo de imposex en el caenogasteropodo Buccinanops globulosus que habita en una zona portuaria de alto trafico maritimo y con presencia de contaminantes. Los resultados mostraron una mayor incidencia de imposex en hembras sin ovicapsulas que en hembras con ovicapsulas. Entre las hembras con imposex, el desarrollo del pene fue significativamente mayor en aquellas sin ovicapsulas (3.4 mm) que en las hembras con ovicapsulas (1.5 mm). En B. globulosus comunmente un solo juvenil eclosiona por cada capsula, sin embargo, en este estudio se registraron capsulas con multiples embriones. Todos estos resultados sugieren una relacion entre el desarrollo de imposex y alteraciones en los parametros reproductivos de las hembras de B. globulosus que habitan en sitios con condiciones ambientales adversas (area contaminada).

Diet of the invasive sea slug Pleurobranchaea maculata in Patagonian coastal waters

ABSTRACT High densities of the invasive sea slug, Pleurobranchaea maculata, have been detected on the Argentinean coast, but studies on the species’ adaptation have been absent until now. Stomach contents of P. maculata in two sampling sites located at Golfo Nuevo, Patagonia Argentina, revealed animals as a major prey, but surprisingly algae ingestion on both sampling sites was abundant. This fact was not reported in previous studies that described opportunistic carnivorous feeding habits of species belonging to the genus Pleurobranchaea. Significant differences in the species prey items were found between sampling sites; however, sedentary polychaetes were the main consumed group at both sites. These results are useful to understand the adaptation of this invasive species in Argentinean waters and to monitor future changes in the benthic communities colonised by P. maculata.

Acute toxicity of tributyltin to encapsulated embryos of a marine gastropod

ABSTRACT The marine gastropod Buccinanops globulosus is known to have high imposex incidence in areas moderately polluted by tributyltin (TBT). Acute toxicity was previously studied in adults but no information is known about embryonic intracapsular development. To estimate the potential effects of organotin pollution on the progeny of B. globulosus, acute toxicity tests were conducted on encapsulated and excapsulated pre-hatching embryos. The lethal median concentration estimated for 96 h (LC50 96 h) in B. globulosus excapsulated embryos was 196.70 µg TBTCl L−1, while in encapsulated embryos it was 2951.28 µg TBTCl L−1. The LC50 96 h was 15-fold higher for encapsulated embryos compared to excapsulated embryos, denoting egg capsule protection against pollutants from the external environment. Our results show that TBT pollution can have significant effects in molluscs other than the chronic effect of imposex.

Age and growth differences in two populations of the edible marine gastropod Buccinanops globulosus

ABSTRACT Buccinanops globulosus is an edible marine gastropod that is being captured by artisanal fishermen without management regulations. As basic knowledge on population features is required in case a sustained commercial exploitation of this species is established, we estimated and compared the age and growth of B. globulosus in two populations separated by 16 km, inhabiting similar physical environments but different anthropic influence. Our results, based on stable oxygen isotope analysis and best fitted models by likelihood ratio tests, detected differences in age and growth between both samplings. Maximum shell marks suggest one year difference between populations. Richards was chosen as the best fitting model for both sampling sites and significant differences were observed between them. Human activities could be causing the age reduction among other irreversible effects on the population under anthropic influence. This should be considered when developing sustainable management regulations for this fishery resource, especially those based on shell/age size.