María Gabriela Liuzzi

Non-indigenous bryozoans are frequent components of biofouling assemblages in harbour environments worldwide. We performed a survey of artificial hard substrates in six harbours spanning 16 degrees of latitude along the coast of Argentina, from Ingeniero White (38º47′ S) to Ushuaia (54º48′ S). Microeciella argentina n. sp., distributed in warm-temperate waters of northern Patagonia and Buenos Aires Province, is described. The non-indigenous species (NIS) Callopora dumerilii, Smittoidea spinigera and Stephanollona boreopacifica are recorded here for the first time in the Southwest Atlantic. Their occurrence in fouling assemblages of warm-temperate harbours and their previous absence in these areas suggest that they probably arrived in Argentina by international shipping traffic. Callopora dumerilii is native to Europe and the northeast Atlantic. Smittoidea spinigera and Stephanollona boreopacifica are native to China and Korea, respectively. The morphological differences between S. spinigera and the Californian species S. prolifera, which is invading European harbours in the North Sea, are discussed. Bugula neritina, Bugulina flabellata, Cryptosula pallasiana and Fenestrulina delicia, common in harbours of Buenos Aires Province, are here recorded in Patagonia, highlighting the importance of regional shipping traffic to secondary spread of NIS. Arachnidium fibrosum, Buskia socialis, Anguinella palmata, Aetea cultrata, Bicellariella edentata and Exochella moyanoi, previously known from Brazil, and Hippothoa divaricata, are here recorded in Argentina. This study shows that warm-temperate harbours in Buenos Aires Province and northern Patagonia are particularly prone to the introduction of non-indigenous bryozoans.

Hippomonavella charrua n. sp. is introduced based on material from the continental shelf off Uruguay. Bilaminar fragments of this species were also found in mid-Holocene deposits of Destacamento Río Salado Member, Canal de las Escobas Formation (Buenos Aires Province, Argentina), ca. 6,000 yr BP. Hippomonavella charrua n. sp. resembles H. brasiliensis Ramalho, Muricy & Taylor, 2008, but differs from this species in its more triangular and protruding avicularia occurring in just a small proportion of zooids. Hippomonavella charrua n. sp. is the third species of the genus with both fossil and Recent representatives. The tatiform ancestrula and the early astogeny are described for the first time in a species of Hippomonavella.

The clam Neilonella sulculata is the dominant bivalve on muddy bottoms along the Argentine continental shelf (Southwest Atlantic). The medusa stage of the hydroid Bougainvillia macloviana is one of the most abundant species in the gelatinous zooplankton of the Magellan region. Two benthic surveys carried out in 2007 and 2009 in San Jorge Gulf gave us the opportunity to analyse (1) the interaction between N. sulculata and its epibiont, B. macloviana, and (2) the role of the clam as hard substrate in a depositional area characterized by silt/clay sediments. Bougainvillia macloviana has a high prevalence on the posterior region of live clams. The presence of gonophores shows that these small colonies are able to reproduce there. Hydroid colonies are very rare on dead valves of N. sulculata and also on almost all other live bivalve species in the study area. Specimens of N. sulculata with hydroids were slightly but significantly larger than those without them, both in 2007 and 2009. The high prevalence of B. macloviana on live individuals of N. sulculata and its almost total absence on other clam species suggest that this association may be critical at least for the epibiont and not the result of chance alone.

Neilonella sulculata is a dominant bivalve on muddy bottoms of the continental shelf and gulfs off Argentina (Southwest Atlantic). Two benthic surveys performed in 2007 and 2009 in San Jorge Gulf, a depositional area characterized by silt/clay sediments, gave us the opportunity to test whether the population of this clam displays a significant spatial structure and to analyse if there is an inverse relationship between size and density. Density, biomass and size–frequency distribution displayed significant spatial structure, being positively autocorrelated at the smallest spatial scales (c. 1.7–14/17 km). Biomass also showed spatial contagion at scales of 25–33 km. A substantial increase in density and biomass occurred between 2007 and 2009. Empty valves in the sediment showed that the maximum size attained by the species may exhibit considerable variation at relatively short temporal scales. Regardless of temporal changes in density and biomass, the spatial structure of these variables remained stable. In densely populated areas, shell size decreased with increasing density, suggesting a density-dependent control of growth. A clear north–south increase in density and biomass was detected, which might be related to a gradient in food availability caused by a thermohaline frontal system associated with wind-related upwelling.