Claudia Bremec

Feeding habits and prey selection by the skate Dipturus chilensis (Elasmobranchii: Rajidae) from the south-western Atlantic

The diet of Dipturus chilensis was composed mainly of the nototheniid fish Patagonotothen ramsayi , squid Illex argentinus , hake Merluccius hubbsi , serolid isopods, and crustaceans. Our results suggest that D. chilensis feeds selectively on some teleosts and rejects eel-like fishes. Total length of consumed P. ramsayi was significantly correlated with the skates mouth width.

Benthic richness in the Argentine continental shelf: the role of Zygochlamys patagonica (Mollusca: Bivalvia: Pectinidae) as settlement substrate

In this study we present results on epibionts on Zygochlamys patagonica from material collected during monitoring cruises in different areas in the Argentine Sea. We update the checklist of epibionts increasing the number of taxa from 19 to 41 and considering two species closely associated with the shells. The demosponge Iophon proximum was the most frequent and abundant epibiont (% presence and coverage). Polydora sp. was registered as a parasite of Z. patagonica in shells from the Beagle Channel, but it did not infest scallops from the commercial beds. Zygochlamys patagonica shells constitute conspicuous hard substrate available for the settlement of sessile organisms. This fact leads to an increased benthic richness in the continental soft-bottom areas of the Argentine Sea, where scallop beds are located.

THE INVASIVE RAPA WHELK RAPANA VENOSA (VALENCIENNES 1846): STATUS AND POTENTIAL ECOLOGICAL IMPACTS IN THE RÍO DE LA PLATA ESTUARY, ARGENTINA-URUGUAY

Abstract Recent range extensions of the invasive rapa whelk Rapana venosa, biological data of the population and possible ecological impacts on the food webs of the Río de la Plata estuary are presented. A total of 41 rapa whelks and 21 egg capsules were collected between February 2004 and March 2006. Specimens were found all over the mixohaline waters of the estuary, with records off Montevideo, Samborombón Bay and off Punta Rasa. Specimens ranged between 28 and 120 mm shell length. Almost all R. venosa presented epibionts all over the shell, suggesting an exposed lifestyle. Egg-masses were attached to specimens of R. venosa, debris and plastic garbage. The spatial distribution of R. venosa within the estuary was coupled with the spatial distribution of Mactra isabelleana, a typical subtidal bivalve of mixohaline waters. The implications for the food webs of the estuary, including possible predators, are discussed. The presence of R. venosa in muddy sediments together with the finding of egg-capsules over the specimens, and the low salinity values at which it is found in the Río de la Plata estuary, confirmed the high plasticity of R. venosa and the potential capability of successfully invading novel environments.

Polychaetes from a southwestern shallow shelf Atlantic area (Argentina, 38 S) affected by sewage discharge

Un programa de muestreo bentonico fue llevado a cabo en la ciudad de Mar del Plata con el fin de examinar la composicion y distribucion de los poliquetos infaunales de los sustratos submareales afectados por el vertido cloacal. Los fondos arenosos muestran heterogeneidad en su composicion de sedimentos y un bajo contenido de materia organica. Se identifico un total de 33 especies de poliquetos en el rango de profundidades comprendido entre 6,5 y 12,5 m. En este trabajo se presenta una comparacion de estos datos con datos de 30 anos atras provenientes de fondos de mas de 12 m de profundidad. El patron de distribucion de los poliquetos se relaciona tanto con el tipo sedimentario como con el contenido de materia organica. Owenia fusiformis Delle Chiaje fue la especie dominante en las estaciones mas cercanas al efluente. Dicha area estuvo caracterizada por la presencia de poliquetos de tamano pequeno. Una explicacion probable para la composicion faunistica en estos ambientes bentonicos cercanos a descargas es que los procesos hidrodinamicos perturban frecuentemente el area, y la fauna bentonica se encontraria permanentemente en un estado de desarrollo inicial. El efecto del efluente cloacal parece estar limitado al area submareal somera alrededor de la descarga

Primary Settlement Substrate of Scallop, Zygochlamys patagonica (King and Broderip, 1832) (Mollusca: Pectinidae) in Fishing Grounds in the Argentine Sea

Abstract The Patagonian scallop (Zygochlamys patagonica) fishery started in the Argentine Sea after exploratory cruises developed during 1995. Knowledge concerning the habitat requirements involved in the settlement processes of the target species was lacking. The main objectives of this study are to find Z. patagonica spat and to assess the characteristics and distribution of its primary settlement substrate (PSS). We observed under binocular microscope different invertebrate species (potential PSS) collected during 2006 from 125 sampling sites between 37° to 44°S and 83–133 m depth. Spat were found on the hydroid Symplectoscyphus subdichotomus (n = 215) and on adult Patagonian scallops (n = 51, attached to the encrusting sponge Iophon proximum, amphipod, and polychaete tubes in nearly half of the cases). To analyze possible interactions between the benthic assemblage and scallop spat throughout the study area, we performed a faunal analysis including the species considered potential PSS (hydroids and scallops) and potential predators. The analysis showed a unique cluster of species closely associated, with variable abundance of hydroids (higher in samples with spat), scallops, and predators. A particular study in MDQ Area (38°S) shows that the sites where spat was collected presented lower density of potential predators and had been scarcely fished in comparison with the other sites within the area. The availability of PSS should be monitored and areas with dense patches of dichotomous hydroids should be protected from trawling.

Survival of Patagonian scallop (Zygochlamys patagonica, King and Broderip, 1832) after the size selection process on commercial fishing vessels

Commercial catches of Patagonian scallops (Zygochlamys patagonica) are automatically processed on board the fishing vessel and frozen adductor muscles are landed. During the factory process, the first step sorts commercial sizes (>55 mm shell height) and lasts about 30 min before scallops <55 mm are returned to the sea. This paper deals with the results of a field experiment carried out to investigate the survival of scallops as a consequence of time exposure to air, before and after the factory size selection process on board. The results show high survival in Patagonian scallops subjected to 30 min aerial exposure, and no significant differences between specimens collected before and after the mechanical size selection process.

Porifera from the Argentine Sea: Diversity in Patagonian scallop beds

Porifera are a frequently collected taxon in the invertebrate by‐catch of the Patagonian scallop Zygochlamys patagonica (King & Broderip 1832) fishery. In order to prevent the destruction of the exploited environments in the Argentine Sea, it is important to know in detail the taxonomic composition of the benthic assemblages. We present here the first study on the sponge assemblage associated with the mollusc species exploited. Thirteen species of Demospongiae (four of which are new records for the Argentine Sea) have been identified, confirming the importance of this phylum as a major component of the scallop bed community.

Chapter 26 Argentina

Publisher Summary This chapter discusses the two species, Aequipecten tehuelchus (Tehuelche scallop) and Zygochlamys patagonica (Patagonic scallop), their fisheries, and experimental results that have significance in the future development of aquaculture. The fisheries supported by these two species are radically different from each other. The Tehuelche scallop is the target of small inshore fisheries in the gulfs of northern Patagonia, and involves dredging and commercial diving. In spite of the small volumes landed, these fisheries are of considerable significance for the local economies. The Patagonic scallop fishery is an industrial operation conducted by three or four factory trawlers that process the catch at sea. Catches in the order of 50,000 tons yr -1 now rank this species among the most important scallop fisheries in the World. The Tehuelche scallop is a simultaneous hermaphrodite and is iteroparous. The Tehuelche scallop may do quick and brief swimming movements as an escape response to the predators or other disturbances.

The feeding ecology of Mustelus schmitti in the southwestern Atlantic: geographic variations and dietary shifts

The feeding ecology of Mustelus schmitti was studied based on analysis of stomach contents of 525 specimens collected from three research cruises carried out during October 2008 to March 2009 on the Argentinean continental shelf (34º45′S–41ºS). Generalized Linear Models were used to test the effects of Geographic location, Total Length, Sex and Maturity stage on the diet. The most commonly occurring major prey groups differed between Geographic locations. In Río de la Plata (RLP) deep M. schmitti feed on Crustaceans, Fish and Polychaetes, whereas Crustaceans, Polychaetes and Fishes were the main prey in RLP coast, Rincón (RIN) coast and RIN deep, respectively. Moreover, models showed dietary shift related to total length in each Geographic location. In coastal nursery areas Polychaetes decreased and Fishes increased in importance as M. schmitti grew in size; while Crustaceans increased in importance from small to medium size, and then decreased in the large specimens. Deeper areas also show dietary changes related to growth. The trophic level of M. schmitti showed lower values in coastal Geographic locations (3.48–3.53) than in deeper Geographic locations (3.56–3.77). The higher trophic role in deeper communities could be related to the size of M. schmitti which increases with depth. Finally, total vacuity index was 2.47 (the lowest in the literature) indicating an intense and continuous feeding activity of the species.

Opheliidae (Polychaeta) from the Southwestern Atlantic ocean, with the description of Travisia amadoi n. sp., Ophelina gaucha n. sp. and Ophelina alata n. sp

Opheliid polychaetes belonging to the genera Armandia, Ophelia, Ophelina, and Travisia, collected along the Southwestern Atlantic coast off Brazil and Argentina, are recorded or given extended descriptions. Travisia amadoi sp. n., Ophelina gaucha sp. n. and Ophelina alata sp. n. are described.