Claudia S. Bremec

Macrobenthos and multi-molecular markers as indicators of environmental contamination in a South American port (Mar del Plata, Southwest Atlantic).

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.

Sabellaria nanella (Sabellariidae): from solitary subtidal to intertidal reef-building worm at Monte Hermoso, Argentina (39°S, south-west Atlantic)

Fil: Bremec, Claudia Silvia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigacion y Desarrollo Pesquero; Argentina

BORING POLYCHAETES ASSOCIATED WITH PYCNODONTE (PHYGRAEA) VESICULARIS (LAMARCK) FROM THE UPPER CRETACEOUS OF PATAGONIA. A CASE OF COMMENSALISM

Abstract. The presence of the oyster Pycnodonte (Phygraea) vesicularis (Lamarck) is recorded in the Maastrichtian mudstones of the Jagüel Formation. This species was free-lying and inhabited muddy bottoms in a shallow marine shelf with a low sedimentation rate. Their shells supported a diverse community including fungi, algae, sponges, cirripedes, bryozoans, phoronids, polychaetes and mollusks. The most conspicuous components of this community are the boring polychaetes. The aim of this work is to assess possible paleoecological relationships between the oysters and polychaetes. Eighty-nine specimens of P. (Ph.) vesicularis were studied and presence/absence data were recorded. Most of the boring openings are located on the ventral margins and are perpendicular to the growth lines. Preferential distribution of borings on the external surface of valves and on the ventral margins suggests a syn-vivo colonization. The high density of polychaete traces on the valves is an evidence of aggregative behavior of these worms. Although the borings weakened the valve and reduced shell strength, this does not seem to have been lethal for the oysters because there is no evidence of borings opening on the external surface reaching the internal surface of the valve. This suggests that a symbiotic relationship probably existed between P. (Ph.) vesicularis and polychaetes and that this relationship could be classified as commensalism.

Byssal Attachment Etchings: A New Bioerosion Trace on Recent Oysters

Byssate bivalves can be attached to hard substrates by byssal threads. Dissolution of the substrate to which they are attached may leave superficial bioerosion traces. This study reports the scars produced by byssus of Mytilus edulis and Aulacomya atra recorded in shells of Ostrea puelchana. Oyster valves were cut and gold-sputtered prior to scanning electron microscope observation. Each byssal thread leaves a characteristic scar on shells substrate. They etch an irregular trace on the substrate which may reach a diameter of several centimeters. These etching-traces comprise shallow round/oval holes of variable number and placement. A bundle of pits corresponding to fibers that compose the thread core was identified in the interior of each hole. We suggest that this trace could be included in the ethological class Fixichnia. The description of this trace would allow adjusting the composition of fossil assemblages and therefore paleoenvironmental interpretations in those cases in which mytilid shells have not been preserved. The recognition of this trace along with other ones of tracemakers with reotaxis or positive phototaxis could be useful in inferring the life habit of fossil biogenic substrates and in reconstructing their taphonomic history.