María Soledad Avaca

Shell shape variation in the Nassariid Buccinanops globulosus in northern Patagonia

Morphological variation among natural populations is a phenomenon commonly observed in marine invertebrates and well studied, particularly, in shelled gastropods. The nassariid Buccinanops globulosus is interesting to study shell shape variation because it exhibits strong interpopulation differences in life history features, including maximum size, fecundity and growth rate. In this study, we examined the pattern of variation in size and shell shape among populations and between sexes of B. globulosus (Bahía San Antonio 40°29′S 63°01′W, Playa Villarino 40°45′S 64°40′W and Bahía Nueva 42°46′S 65°02′W). In particular, we used geometric morphometric techniques to test: (1) whether the two components of shell morphology (size and shape) are independent and (2) whether shape differences between sexes are consistently found among populations, regardless of their body sizes. Our results show shell shape variation between the populations of B. globulosus of northern Patagonia. Intra-specific shell shape variation is affected by body size, indicating allometry. Regardless of the size differences, individuals from Playa Villarino have high-spired shells, and shorter apertures and wider columellar area than individuals from the other populations. Also, sex-related shape differences were consistently found at each population, thus suggesting a common sexual dimorphism in shell morphology for this species. The functional significance of the variability found is discussed in terms of the flexibility of developmental programmes for morphology as well as the evolution of phenotypic plasticity.

Age, growth and mortality in Buccinanops globulosus (Gastropoda: Nassariidae) from Golfo Nuevo (Argentina)

Abstract Buccinanops globulosus is a commercially exploited gastropod common in coastal waters of the Southwestern Atlantic Ocean. We determined the age and estimated growth and mortality rates of B. globulosus in a population from Golfo Nuevo (Patagonia, Argentina). Age was determined by counting opercular rings and growth was described by the von Bertalanffy function fitted to data of length-at-age. Mortality rate (Z) was estimated by the linearized catch curve method. The maximum age was determined at 8 years. Growth parameters estimated for the whole population were TSL ∞ =37.87 mm, k=0.33 year−1 and t 0=−0.65 year. Likelihood ratio tests indicated significant differences in asymptotic length and fitted growth models between sexes. Annual mortality rate (the first reported for the species) was estimated to be 0.34 year−1 (0.49–0.20). Information on growth parameters of B. globulosus showed that TSL ∞ and the index of overall growth performance of the population studied here were intermediate compared to previously studied populations, thus indicating site-specific growth differences. Taking into account that the most common management strategy in gastropod fisheries is the use of a minimum size limit (MSL), we suggest that fishery measurements such as MSL for this species should be established only for small geographical scales.

Short term impact of artisanal dredges in a Patagonian mussel fishery: Comparisons with commercial diving and control sites

Mussels in the San Matías Gulf fishery are targeted using artisanal dredges and diving. The main objective of this study was to assess the direct impact of artisanal dredging on the biota and sediments, and to compare the composition of the catches and the individual damage induced by fishing between dredging and commercial diving. The experimental design included samplings from dredge catches, dredge tracks, control sites and commercial diving. According to their damage level, individuals were scored as undamaged, lightly damaged and severely damaged. Sediment characteristics were analyzed using coring samples and traps. Damage of mussels, mostly corresponding to the severely damaged category, was less than 5% both in samples from dredging and diving. Conversely, mean damage of the main bycatch species (sea urchins and ophiuroids) was 75 and 65% in samples from dredging and diving respectively, being most of the individuals lightly damaged. Considering also the catch sample composition of both fishing methods, dredging affected relatively more individuals than diving. Although sediment removal in dredged areas was three times higher than that in non-dredged ones, mean grain size and gravel percentage of sea floor sediments showed subtle differences between them.

Variability in size and age at maturity in the marine scavenger Buccinanops globulosus (Gastropoda: Nassariidae) from Patagonia

Fil: Avaca, Maria Soledad. Universidad Nacional del Comahue. Instituto de Biologia Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Beyond imposex: other sexual alterations in a nassariid snail from Patagonia

ABSTRACT The occurrence of a penis in female gastropods has commonly been accepted as an indicator of tributyltin (TBT) pollution. During the surveys performed in Patagonian waters between 2002 and 2010, individuals of Buccinanops deformis with a short penis and an external vas deferens were initially considered as showing imposex. Doubt arose when different manifestations of the phenomenon were identified at the two sites with the densest populations of the species (San Antonio Bay, SAB, and Villarino). This led us to search at both locations for: (a) histological confirmation of sex, (b) butyltin measurements in sediments and snail tissues, and (c) incidence of trematode infestation. We found that both populations have individuals with a short penis. While all the inspected individuals from SAB were histologically identified as females (imposex), those from Villarino were identified as males. Trematodes were absent in individuals from SAB and showed very low prevalence in those from Villarino, with metacercariae found in the digestive gland. In snail tissues, butyltins were found mainly in the form of dibutyltin (DBT) in SAB and at negligible levels in Villarino. In sediments, butyltins were found only in the form of TBT, at higher levels in SAB than in Villarino. Thus, it became clear that our finding of a short penis is a manifestation of imposex on females from SAB related to the high TBT levels, whereas in Villarino it is a male trait, which is not related to TBT or a trematode infestation but may be a Dumpton syndrome-like abnormality.