Population and production parameters of the wedge clam Donax trunculus (Linnaeus, 1758) in intertidal areas on the southwest Spanish coast: Considerations in relation to protected areas

Abstract

The main objectives of this study were (i) to provide an updated age-length key for D. trunculus from Atlantic waters, and (ii) to evaluate population dynamics, the timing of recruitment and production parameters of the wedge clam Donax trunculus in two moderately exposed sandy beaches (the protected area of Doñana National Park and the tourist destination of Isla Canela) along the littoral of Huelva (SW Spain). First an in-depth analysis of the shell and updated estimation of growth parameters of the intertidal D. trunculus population were performed between January 2014 and July 2015 using two different methods i) thin-layer cross section (TL) (ii) length-frequency distributions (LFD). Von Bertalanffy growth functions provided an asymptotic length of 46 mm (LFD) and 46.7 mm (TL) and growth constants of 0.48 (LFD) and 0.47 yr−1 (TL) in Doñana beach. In addition, several deformities as well as signs of shell repair were observed. Population dynamics analyses through length-frequency distribution clarified the timing of recruitment (February–March and July). The mean annual biomass (B¯) of intertidal populations of D. trunculus ranged between 3.03 (Doñana) and 3.31 g ash-free dry mass (AFDW) m−2 yr−1 (Isla Canela). Individual production showed the highest value at 27 mm length (0.117 g AFDW m−2 yr−1) and annual production (P) ranged between 3.40 (Doñana) and 4.91 g (Isla Canela), resulting in renewal rate (P/B¯) values between 1.03 and 1.61, respectively. The present results, together with information on environmental parameters, revealed clear differences in population dynamics and production between beaches related to the presence or absence of a protection figure.