Maite Narvarte

Comparison of AVHRR and SeaWiFS imagery with fishing activity and in situ data in San Matías Gulf, Argentina

Seven years (January 2000 to December 2006) of AVHRR and SeaWiFS data were used to estimate monthly climatological means and to present SST and chlorophyll-a seasonal evolution in San Matías Gulf, located between 40° 47′ S and 42° 13′ S on the Argentine coast. SST and chlorophyll-a satellite maps corresponding to spring–summer showed two well differentiable sectors: the southern zone presented colder waters and higher chlorophyll-a concentration while the northern one showed warm water and lower chlorophyll-a. Hake (Merluccius hubbsi) is the most important resource in terms of landings and economic revenues of the San Matías Gulf. Fishing activity data gathered by a Vessel Monitoring System (2004–2006) were linked with SST and chlorophyll-a maps showing that the fishing vessels operated on the thermal front from November to March and had the maximum hake yields. In addition, AVHRR-SST and SeaWiFS-chlorophyll-a data were compared with temperature and chlorophyll-a measured in oceanographic surveys carried out in 2007.

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.

Spatial patterns of the Argentine hake Merluccius hubbsi and oceanographic processes in a semi-enclosed Patagonian ecosystem

Abstract Time-series of fishing position, landings, satellite-derived sea-surface temperature and chlorophyll a concentrations were used to relate the spatial–temporal distribution of the Argentine hake Merluccius hubbsi with seasonal oceanographic processes in San Matías Gulf. Also, the seasonal effect of fishing on the hake population structure was analysed. During summer the fleet was concentrated over the area of the frontal system, obtaining the best catch-per-unit-effort (CPUE) of hake in relatively deep waters. In autumn, the dispersion of the fleet due to a reduction in CPUE coincided with the dissipation of the front, suggesting that the distribution and shoaling of the Argentine hake is associated with seasonal thermal structures. In spring, the thermal structure of the waters and the chlorophyll a blooms seem to modulate the timing of spawning of hake, which occurs mainly in October–November. In addition, the fleet captured a higher proportion of females in the gonadal recovery stage during warm months (November–April). While winter catches (May–October) consisted mainly of males, the intense summer fishing may result in a high impact on the female population. This information is relevant to design of spatial management tools intended to provide biological sustainability to the hake fishery.

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.

Reproductive traits of the small Patagonian octopus Octopus tehuelchus

This study evaluated the reproductive features of Octopus tehuelchus in three coastal environments of San Matías Gulf (Patagonia). Monthly samples of O. tehuelchus were used to estimate size at maturity, compare seasonal changes in oocyte size frequency distributions between sites as well as oocyte number and size between female maturity stage and sites. Females in Islote Lobos had a smaller size at maturity than females in San Antonio Bay and El Fuerte, probably as a consequence of a generally smaller body size. Males in San Antonio Bay were smaller at maturity than females. O. tehuelchus is a simultaneous terminal spawner. Fecundity (expressed as number of vitellogenic oocytes in ovary) was lower in Islote Lobos, and an increase in oocyte number in relation to female total weight was found. Females in San Antonio Bay had the largest oocytes, which may indicate higher energy reserves for the embryo and therefore higher juvenile survival. There was a close relationship between reproduction, growth and condition, represented as size at maturity, number and size of vitellogenic oocytes and period of maturity and spawning. Given the local variation in some reproductive features of O. tehuelchus, studies should focus on the environmental factors, which bring about this variation, and on how it affects the dynamics of local populations.

Organotin compounds in sediments of three coastal environments from the Patagonian shore, Argentina

One of the most toxic compounds that have been introduced into the marine environment is Tributyltin (TBT) used as a biocide in antifouling paints. The aim of this study was to obtain the first information of TBT pollution in sediments of three environments of the Argentinean coastline. Sediments from the Bahia Blanca estuary, San Antonio Bay and Ushuaia Bay were sampled to determine TBT and dibutyltin (DBT) concentration. The butyltin compounds were identified and quantified by gas chromatography and mass spectrometry (GC?MS). The different amount of organotin compounds detected shows dissimilar pollution levels and degradation processes along the Argentinean coasts.

Attachment features of mytilids in ecosystems with mobile substrate: Brachidontes rodriguezii in San Antonio Bay (Patagonia, Argentina)

The force required to dislodge mussels from the substrate is known as attachment strength. This feature has been mostly studied in mytilids inhabiting the intertidal of consolidated rocky substrates, whereas it has been less studied in sedimentary substrates. The aim of this study was to evaluate the attachment strength and the number of byssal threads of Brachidontes rodriguezii in two sites with mobile substrates in San Antonio Bay, Argentina [Punta Verde (PV) and Punta Delgado (PD)]. PV has relatively higher current velocities and coarser grain size than PD. Along coastal line transects at two different levels of the mid-intertidal of each site, the attachment strength was measured. The number of byssal threads in collected mytilids and the weight of the sediment adhered to them were recorded in the lab. The attachment strength, the number of byssal threads and the sediment adhered to the byssus differed significantly between levels and sites. Mytilids from the mid-level of both sites where the density was relatively lower, had a significantly greater number of byssal threads and higher weight of sediment adhered. This study reveals that a high amount of coarse sediment adhered to the byssus affects the attachment strength of B. rodriguezii in ecosystems relative to unstable substrates. We underline the importance of mobile substrates in understanding attachment features (attachment strength and byssal threads) of mytilids in this unstable ecosystem.

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)

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 otherpopulations (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 m 2 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.

Duration of Intracapsular Development of Zidona dufresnei (Gastropoda: Volutidae) at its Southern Distributional Limit

Abstract. Zidona dufresnei Donovan, 1823 is an endemic snail of the southwestern Atlantic Ocean. In San Antonio Bay, Río Negro Province, it is commonly found in the intertidal zone all year round and from October to April the females deposit planoconvex egg capsules attached to hard substrates. The population of Z. dufresnei studied is an exception because it is unique in that inhabits shallow waters. The main goal of this study was to determine the duration of the direct intracapsular development of Z. dufresnei in the field. Results show that the intracapsular development takes 34.5 ± 3.8 days. In late developmental stages, a mean of three embryos per capsule was observed. Developmental duration under natural conditions was shorter than in lab conditions previously studied. The shorter developmental period than that reported for other temperate neogastropods may be related to the high summer water temperatures and high salinity at the location studied. Shorter embryonic duration would be important for this population of Z. dufresnei which inhabits an environment of high predation pressure on egg capsules.

Ecological impacts of the austral-most population of Crassostrea gigas in South America: a matter of time?

Abstract The Pacific oyster Crassostrea gigas is one of the most invasive species worldwide. This oyster has a preponderant ecological role in the invaded environments, for example structuring the benthic community through the provision of micro-habitats. Twenty-five years after its introduction in Argentina, the species is colonizing new areas along the coast, extending northwards and southwards its local distribution. In this study, we provide the first ecological characterization of the southern-most population of C. gigas; where the composition, density, richness and diversity of the macroinvertebrate assemblages associated with zones with oysters were compared with zones where it is absent at four different times of the year. Additionally, the main epibionts taxa settled on the oyster shells were studied. Our results showed differences in the assemblage composition between zones. However, these differences were not consistent throughout the year. Furthermore, density, richness and diversity were higher in the zones with oysters only in one of the surveys and the parameters did not differ between zones in the remaining months. Moreover, the majority of oysters were used as settlement substrate by the sessile common species present in the area. Thus, our work provides new information about the ecology of C. gigas in recently invaded areas that enhance our understanding of the role that facilitation plays in physically stressful ecosystems and the importance that density and time since the invasion may have in the engineering effects of the species.