Climate Variability of the Northern Argentinean Shelf Circulation: Impact on Engraulis Anchoita

A high-resolution ocean model and hydrographic observations are used to characterize the shelf circulation of the northern Argentinean shelf during the study period (1993–2008) and ultimately to explore possible linkages among atmospheric, oceanic, and biological climatic variability. Abundance of larvae and eggs of the local anchovy species, Engraulis anchoita, exhibit a spatial and temporal variability similar to those stocks found in other parts of the world and that we interpret in the context of the particularities of the local circulation and hydrography. Two (statistically) coupled modes of wind stress-surface velocity are described and interpreted in terms of historical and new information. A complex picture emerges in which the intensity of both a thermal shelf front, the alongshore flow, and larvae abundance would be connected and forced by local wind stresses. For all areas examined on the shelf, the larvae/egg abundance would not be very sensitive to short-lived climatic fluctuations (e.g., year-to-year) but they would be indeed to regime shifts. The shallow shelf area bounded by the 39°S and 41°S parallels would expose a clearer linkage between physical and biological variables than that north of 39°S. We attribute this fact to the particular physical conditions found in the southernmost area, which would favor an increased habitat quality for Engraulis anchoita.

Climate Variability of the Northern Argentinean Shelf Circulation: Impact on Engraulis Anchoita

A high-resolution ocean model and hydrographic observations are used to characterize the shelf circulation of the northern Argentinean shelf during the study period (1993–2008) and ultimately to explore possible linkages among atmospheric, oceanic, and biological climatic variability. Abundance of larvae and eggs of the local anchovy species, Engraulis anchoita, exhibit a spatial and temporal variability similar to those stocks found in other parts of the world and that we interpret in the context of the particularities of the local circulation and hydrography. Two (statistically) coupled modes of wind stress-surface velocity are described and interpreted in terms of historical and new information. A complex picture emerges in which the intensity of both a thermal shelf front, the alongshore flow, and larvae abundance would be connected and forced by local wind stresses. For all areas examined on the shelf, the larvae/egg abundance would not be very sensitive to short-lived climatic fluctuations (e.g., year-to-year) but they would be indeed to regime shifts. The shallow shelf area bounded by the 39°S and 41°S parallels would expose a clearer linkage between physical and biological variables than that north of 39°S. We attribute this fact to the particular physical conditions found in the southernmost area, which would favor an increased habitat quality for Engraulis anchoita.

A new species of Hysterothylacium (Ascaridoidea, Anisakidae) parasitic in Zenopsis conchifer (Zeiformes, Zeidae) from Argentinean waters

A new species of parasitic nematode, Hysterothylacium spirale sp. nov. (Ascaridoidea, Anisakidae), is described based on specimens collected from the intestine and pyloric caeca of the silvery john dory Zenopsis conchifer (Lowe) (Zeiformes, Zeidae), from the Argentinean Shelf (35°05′–40°46′S, 53°03′–58°07′W). Among the 66 valid species described so far in the genus, the new species most closely resembles H. zenis (Baylis, 1929). Both species, apparently specific for fishes of the family Zeidae, share the shape of the dorsal lip, the long expanded lateral alae originating from subventral interlabia and the ornamentation of the tail tip, as well as general morphometry. The combination of these shared features distinguishes both species from all congeners so far known. However, the new species is distinguishable from H. zenis by having shorter interlabia, and consequently the lateral alae originating more posteriorly, shorter spicules, a smaller number of postcloacal papillae and the presence of two pairs of double postcloacal papillae.

Variability in epibiont colonization of shells of Fusitriton magellanicus (Gastropoda) on the Argentinean shelf

An inventory of the main epibiont organisms on living specimens, on empty shells and on pagurized shells of Fusitriton magellanicus collected in Zygochlamys patagonica fishing grounds off Argentina is provided here. Additionally, considering that the presence of the thick, hairy periostracum could be an inhibitor of boring and encrusting species, we analyse the presence of a periostracum in living F. magellanicus in relation to the presence of epibionts. More than 70% of all shells bore encrusting organisms (of at least 30 taxa) but only a small proportion of shells was heavily fouled, the majority of living, empty and pagurized shells being lightly or moderately fouled. Polychaetes were the most common epibiont group (present on more than 60% of shells) while sponges and ascidians were responsible for the majority of the heavily fouled living gastropods. In general, specimens had a moderate level of encrustation and, simultaneously, a low or medium coating of periostracum. Hairy gastropods (only 14% of the sampled specimens) had few or no epibionts. A relationship between the size of the shell and the level of encrustation was only found in living gastropods. Fusitriton magellanicus is the second species in importance (after the Patagonian scallop) for the provision of a hard settlement substrate in the shelf-break frontal area of the Argentine Sea.

Potential source regions of biogenic aerosol number concentration apportioning at King George Island, Antarctic Peninsula

Nowadays it is well accepted that background aerosols in the boundary layer over remote oceans are of marine origin and not aged continental. Particularly in the Atlantic sector of the Southern Ocean at least four main important regions exhibit significant ocean primary productivity. They are the Bellingshausen–Amundsen Sea, the Weddell Sea, the southern Argentinean shelf and the southern Chilean coast. In this work, we have combined ground-based continuous atmospheric sampling of aerosol number concentration (ANC), over-sea dimethyl sulphide (DMS) measurements, chlorophyll a (chl a) concentration provided by Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite images, in situ meteorological data and monthly regional NCEP-NCAR re-analysis wind fields in order to investigate the relative contribution of each of the above regions to the apportionment of the ANC at King George Island (KGI), South Shetland Islands. Our results suggest that, at least during the period from September 1998–December 1999, the southern Argentinean shelf acted as the main contributor to the ANC measured in KGI.