Effects of El Nino-Southern oscillation on the population dynamics of the tropical bivalve Donax dentifer from Malaga bay, Colombian Pacific

The population dynamics of a Donax dentifer (Hanley, 1843) population from Malaga bay, Colombia, was studied during two periods (August 1997-July 1998 and November 1999-February 2002) in order to investigate the effects of El Nin (EN) 1997/1998 and La Nina (LN) 1998/2000. The EN-LN cycle was strongly associated to an interannual precipitation and salinity variability in Malaga bay. Additionally, these factors were highly correlated with the reproductive cycle. Results indicate that EN had negative effects on the reproductive cycle, leading to weak, abnormal spawning events. In contrast, good spawning events were recorded during LN and post-LN. Based on these findings, an opportunistic reproductive strategy is proposed for this species. Overall growth performance (P) was higher during LN (P=4.41) than during EN and post-LN (P=4.20, P=4.28, respectively). These results indicate that D. dentifer has a higher overall growth performance compared to several tropical species reported in the literature. Total mortality rate of small individuals was higher during LN whereas that of large individuals was higher during EN. These results are best explained by recruitment variability and spatial differences between recruits and adults. Individual production and productivity were higher during LN, although annual biomass was relatively low. This, together with the results regarding growth and reproduction, suggests that food availability was higher during LN, thus positive effects under LN may be concluded. In contrast, EN seems to have negative effects on growth, reproduction and somatic production for this surf clam.