Doldan M. S., Gimenez L.H., Morsan E.M.

In coastal ecosystems, the recruitment of bivalves is characterized by year-to-year variability. Annual cohorts often differ in the number of recruits, resulting in irregular pulses of high abundance (i.e., successful recruitment) followed by periods of scarcity (i.e., failing recruitment). Environmental forcing likely underlies these pulses as favourable conditions (i.e., temperature, food availability) determine whether larvae settle and whether new recruits survive. As a factor that operates in a large-scale, it can also result in a synchronic recruitment of populations of multiple species within the same area. Sessile organisms represent a continuous record of environmental variability for a given location as a result of changes in annual growth rates. These changes can be seen in the shells as wide and narrow growth increments, representing favourable and unfavourable environmental conditions, respectively. At San Matías Gulf (Northern Patagonia, Argentina) the clam Glycymeris longior offers an opportunity to assess the effects of environmental forcing on the recruitment of commercial bivalve species along coastal ecosystems of the Southwestern Atlantic based on the growth anomalies recorded on its shells. In this context, we generated a multi-decadal growth chronology (~60 years) using sclerochronological on G. longior live collected individuals. We assessed the relationship between annual standardized growth variability and environmental factors. We also analysed the coherence between G. longior growth and successful recruitments reported for three clam populations from the area (Panopea abbreviata, Ameghinomya antiqua and G. longior itself). We found a positive relationship between the sclerochronology and the mean sea surface temperature of autumn (Spearman correlation, ρ= 0.48, p= 0.04) and the Southern Annular Mode index for winter months (Spearman correlation, ρ= 0.54, p= 0.007). On the other hand, the successful annual recruitments corresponded to peak values of growth, particularly for the periods 1976-1979, 1982-1983, 1997-1998. Our findings support a geographic large-scale coherence in recruitment for bivalve populations.

Funding: Projects M025 and M026 from Universidad Nacional del Comahue.