CONICET | Buscador de Institutos y Recursos Humanos

INVESTIGADORES

BRUSCHETTI Carlos Martin

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Título:

Morphometric variations and internal shell growth patterns of the Patagonian scallops Zygochlamys patagonica across their SW Atlantic distribution range

Autor/es:

LOMOVASKY, B.; LASTA, M.; VALIÑAS, M.; BRUSCHETTI, C.M.; CAMPODONICO, S.; IRIBARNE, O.O

Lugar:

Mooloolaba. Australia

Reunión:

Workshop; 15th International Pectinid Workshop; 2005

Resumen:

Zygochlamys patagonica is widely represented (depth range between 40-200m; #6,9,13,20) in the extreme of South America (reaching 42ºS in the Pacific to Tierra del Fuego (55ºS) and 35º50S in the Atlantic), being an important economic resource in the Atlantic.In the Pacific, main grounds occur in relatively shallow waters (#1) while in the Atlantic they are located along the 100m (#12). Growth and age of Z. patagonica were determined from surface external rings (#18,7) and chondrophores (#20,19,5).However, more precise studies are needed to identify internal growth bands, such as acetate peels technique (#16), to validate the external growth rings avoiding misestimating individual age. Growth, production and, physiological activity of bivalves can be affected by environmental conditions (e.g., temperature, salinity, substrate, food-availability; #3,8,10,11). However, density-dependence (#21,8,9) and biological interactions could also have an important effect. Individuals from different beds along the Atlantic may have different growth pattern, maximum age and morphometric relationships.We evaluate this prediction comparing different beds along a latitudinal gradient in the Southwestern Atlantic. Material and methods Samplings of scallop (24 tows;n=2047) were performed in 4 beds (Uruguay:36º17S-53º49W; Reclutas:39°20S-56°W and 39°30S-55°52W; TangoB:42º30S-59º05W and Beagle: 55º10S-66º05W) between January 2000-October 2004. We measured shell height (H:umbo-ventral margin), length (L:anterior-posterior axis) and width (W;precision ±0.1mm), and total mass without epibionts (TM), shell mass (SM), shell free wet mass (SFWM), gonadal mass (GM), adductor muscle mass (AMM) and epibionts mass (EM;precision ±0.01g).Morphometric relationships were determined and log-log transformations were applied when necessary and compared with ANCOVA between beds.Unplanned comparisons (Tukey multiple comparison,TMC) were made when significant differences were found (#22,17). For growth and age analysis sub-samples were taken (n= 605).Growth pattern observation was inferred from internal shell growth bands using acetate peels technique to allow microscopic examination (#16). Results and Discussion The size-mass relationship between TM, SM, SFWM, AMM, GM and EM (dependent variables) and H (independent variable) was exponential in each bed and there was a linear relationships between L and W with H (p<0.01) for all beds. However, the slope of L-H relationship differed between beds (p<0.001); Uruguay and Reclutas beds were similar and differed of TangoB and Beagle (TMC, p<0.05). Similar results were observed for W-H and log(TM)-log(H) relationships.For log(SM) and log(SFWM) with log(H), the slopes differed between beds (p<0.001). All beds differed each other (TMC, p<0.05). There were no difference for the relationship log(EM)-log(H) between beds (ANCOVA:F=0.71;p=0.5446).There was an increase in all variables following a latitudinal gradient N to S. Under reflecting light, acetate-peels from the polished shell cuts showed a pattern of alternating broad opaque and narrow translucent growth bands. Growth pattern and maximum age differ between beds. There was a similar pattern of internal bands between Uruguay and Reclutas (maximum age of 13 and 14 years-old respectively).Internal growth bands in the umbo were clearly observed. It was possible to follow the translucent growth bands all the way along a cross section of the shell to the point where they cross the outer shell layer to form a ring on the exterior shell surface.The 2-3 first bands, difficult to observe along the shell section, showed a different pattern from other growths bands. Each growth break (i.e.,an external ring) of the recent bands was formed with a group of internal growth bands (cluster shape).Thus, these clusters were formed by a growth rate slowed down during some periods within a year, but not by a total interruption in growth.At the last portion of the valve (recent bands), the internal growth bands were closer to the shell edge and were proximate each other (individuals>50 mm H), clearly visible in acetate peels but difficult to identify on the exterior shell surface. Internal growth bands in the umbo and along the cross section were similar in TangoB but it was difficult to observe the point where the translucent bands cross the outer shell layer to form an exterior ring. The cluster shapes of these exits were less pronounced. Maximum age was 20 years-old. Beagle bed showed a higher shell thickness along the cross shell section, as was refluxed in a higher shell mass (see above), where was possible to see all the internal growth bands.The point where the translucent growth bands form an exterior ring did not have a cluster shape; they were a simple translucent growth band. Thus, a total interruption of growth appears to be the cause of this external ring.Maximum age was 21 years-old. Acetate-peels technique allows us to obtain new information on the maximum age across the latitudinal gradient. The presence of translucent growth bands indicate periods of very slow or even halted shell growth, possibly caused by low metabolic rates related to a lack of food (#4,3,11) or by a diversion of metabolic products into gamete production (#2,15,14).The influence of 1-2ºC annual variation in temperature in the studied areas seems to be negligible to explain variations detected by our study. However, other factor such as density-dependence, different biological interactions and, food availability could explain the differences found between populations inhabiting different latitudes.

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