In this study, we analyse spatial patterns of macrobenthic communities of the Río de la Plata system, and assess the species turnover or beta diversity and its relationship with environmental gradients. Macrobenthic samples and physico-chemical parameters were collected from 20 sampling sites along a transect of 560 km, including the freshwater (FW), estuarine (ES) and marine (MA) sectors. Three main assemblages corresponding to the above mentioned sectors were defined with multivariate analysis (cluster, MDS). In total 134 taxa were recorded, 81 in MA, 33 in FW and 38 in ES, represented mainly by polychaete, mollusc and crustacean species. Depth, salinity and %clay showed the strongest correlation with the observed faunal patterns (ρw=0.62; BIO-ENV analysis). Beta diversity varied between dominant taxonomic groups and was positively correlated with changes in salinity. The high variability in the composition of assemblages was reflected in beta diversity, reaching its highest values at the boundaries between the defined sectors. This study suggests that beta diversity represents a useful tool to define ecological boundaries for benthic communities in the Río de la Plata.

This study deals with the spatial distribution of macrobenthic communities (biomass and abundance) in the Rı́o de la Plata estuary, Argentina–Uruguay, and the adjacent shelf waters. The benthic invertebrates were caught with an epibenthic dredge (41 samples). Multivariate analysis (cluster, MDS), SIMPER and BIO-ENV analyses were applied to analyze benthic community structure and their relationships with environmental variables. A consistent large-scale diversity pattern was found: a distinctive estuarine zone could be distinguished, with muddy sediments and a wide range of salinity, characterized by higher abundance of fauna and lower diversity, dominated by the deposit-feeding bivalve Mactra isabelleana; and a marine zone, with sandy-shell debris sediments and higher and less variable salinity values, with higher values of diversity. Major presence of deposit feeders was related to higher particulate organic matter in the estuarine area. Bottom type, salinity and the presence of a turbidity front are considered the main physical variables in structuring benthic communities of the Rı́o de la Plata estuary.

The present paper reports the occurrence of Ebalia rotundata (A. Milne-Edwards, 1880) in marine waters off Argentina and Uruguay, and thus extends its known geographical distribution in the Argentinean Zoogeographical Province more than 700 km northwards. Feasible dispersal mechanisms of this species are discussed. Este trabajo reporta la ocurrencia de Ebalia rotundata (A. Milne-Edwards, 1880) en aguas marinas de Argentina y Uruguay, extendiendo su distribucion geografica en la Provincia Zoogeografica Argentina mas de 700 km hacia el norte. Se discuten los posibles mecanismos de dispersion de esta especie.

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 (>55mm shell height) and lasts about 30min before scallops <55mm 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 30min aerial exposure, and no significant differences between specimens collected before and after the mechanical size selection process.

By-catch samples were taken in Patagonian scallop (Zygochlamys patagonica King and Broderip, 1832) beds during a survey evaluation on the Argentinian continental shelf between 38-46degreesS in 1995, prior to the development of the present commercial fishery. The invertebrate epibenthic fauna was identified and the community structure was analyzed using univariate and multivariate methods. Patagonian scallop was dominant in weight. In four geographical areas a characteristic assemblage of associated species (sponge Tedania sp., anemone Actinostola crassicornis, echinoderns Ophiactis asperula, Ophiacanta vivipara, Ophiuroglypa lymani, Sterechinus agassizii, Austrocidaris canaliculata, Cosmasterias lurida, Ctenodiscus australis, Psolus patagonicus and Pseudocnus dubiosus leoninus) could be defined by cluster analysis. Areas differed in biomass of scallops and by-catch and also in the relative presence of scallop epibionts. This study gives baseline information on the undisturbed condition of natural communities and will permit future evaluation of structural changes due to fishery impact, since commercial fishing has taken place on the beds since 1996.

This article deals with the diet of the Patagonian scallop, Zygochlamys patagonica, during a yearly period at Reclutas bed (39degreesS-55degreesW), Argentine Sea, and relates the results with the oceanographic conditions and the growth pattern known for this species. Scallops (n = 180) from six samples were dissected and the gut contents were identified and counted. Results showed a predominance of diatoms in the diet and maximum food ingestion in spring. Maximum somatic (muscle) growth for this species at the same study site was also found during spring. It is suggested that after the spring phytoplanktome bloom, oceanographic conditions (thermocline in development) allow the sedimentation of food particles to the bottom; this input of energy could produce the somatic growth documented for this filter-feeding species.

A benthos-samp ling program was carried out in the coastal area of Mar del Plata city in order to know the composition and distribution of infaunal polychaetes living on a subtidal soft-bottom substrate affected by the sewage discharge. Sandy bottoms showed heterogeneous sediment composition and very low organic matter content. Thirty three polychaete species were identified in a range depth between 6.5 to 12.5 m. A comparison with data from 30 years ago from adjacent areas deeper than 12 m is herein presented. Polychaete distribution was related both to the type of sediment and to the content of organic matter. Owenia fusiformis Delle Chiaje was dominant and peaked at stations near the sewage effluent. Small-sized polychaetes were abundant in the sampling area. A possible explanation to the faunal composition of sites near sewage effluents is that hydrodynamic forces frequently disturb the area, and benthic fauna is permanently in an early stage of development. The effect of sewage appeared to be restricted to the shallower subtidal area around the outfall.

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 skate's mouth width.

The hawkfish (castaneta) Cheilodactylus bergi Norman, 1937 is distributed in the Atlantic Ocean, from southern Brazil (22 degreesS) to the Gulf of San Jorge in Argentina (47 degreesS), between 50 and 150 m depth, and constitutes a fishing resource of commercial value. Previous studies indicated that polychaetes constitute its main food. The contribution of different families of worms to the diet of hawkfish and the relationships between those taxa and the benthic fauna of the feeding grounds are presented in this paper. A total of 522 specimens of fish was measured, weighed and the gut contents analyzed. Polychaete families, mainly Onuphidae, Lumbrineridae and Eunicidae, were the most important feeding items in specimens from 28 to 51 cm total length, both in percent of frequence (%F) and percent of weight (%W). Occasional presence of Aphroditidae, Arabellidae, Palmyridae, Lysaretidae and Dorvilleidae was recorded. Bibliographic data on faunistic composition of feeding grounds indicate that polychaetes constitute between 12 to 21% of number of taxa of macroinvertebrates. C, bergi feed upon 25-38% of species of polychaetes present in the area. It is concluded that C, bergi feed on polychaetes which are mandibulated, implying mobility over the benthic surface.

Terebellides lanai is recorded from shallow subtropical waters off Brazil, and two new species of Terebellides are described from cold-temperate waters off Argentina: T. totae from Blanca Bay and T. malvinensis from the continental shelf off Argentina.

This paper gives information associated with the development of a new fishery of patagonian scallop (Zygochlamys patagonica King and Broderip 1832) in the Argentine Continental Shelf. A joint State-Industry research program was performed during 1995 with a 56 m scalloper FN (Erin Bruce). A total of 7,134 trawl shots were performed over 246 days. Seven new beds with commercial potential were found between 38 degrees 50' S and 42 degrees 30' S, largely along the 100 m isobath. Beds were discrete, ranging from 42.7 to 353.8 km(2). Proportions of scallops and invertebrate by-catch and population size structure varied between beds. CPUE varied from 291 to 4,927 (kg of commercial size scallops towing h(-1)) in different beds. Lame differences were found between muscle yield estimated at laboratory (12.07% and 23.65% in Sea Bay and MdQ beds, respectively). On the basis of CPUE and muscle yield, the average landing per unit of effort ranged from 65.5 to 1,037.6 (kg of muscle towing h(-1)). During the study period a total of 1,315 t of muscle (160-240 pieces . kg(-1)) was landed. Total scallop catch and commercial scallop catch were 13,580 and 10,592 t, respectively. We suggest that management of this new developing fishery should be based on the application of a rotation and reserves areas criteria.

This paper summarizes the effects of pollution on the composition and spatial distribution of benthic communities in Blanca Bay, Argentina. Monitored fish species of commercial interest that feed on benthos have high heavy metal concentrations, in two cases up to the legal limit for human consumption. The composition and patterns of spatial distribution, both of the benthic and bacterial communities, are related to the enrichment of organic matter in sediments of the inner region of the bay. The need for a pollution control program for the bay is emphasized.