BEACH MORPHODYNAMICS AND CLAM (DONAX HANLEYANUS) DEN SITIES IN BUENOS AIRES) ARGENTINA

PENCHASZADEH, P. E.; MARCOMINI, S.; LOPEZ, R. A. ; LUZZATTO, D. C.

Florencia

Workshop; Beaches-What future? An Integrated approach to the Ecology and Evolution of Beaches and Sand Dunes; 2001

The scudied co asral ar ea is locared along the Arlanuc ccean, berween ehe: localieiesof Punca R.1.SJ and Vilb Gcsdl. Twclve monitoring sices \Vere tscJblished alongche shore. Thcy are: Punel R:¡sJ.. Sln Clemente del Tuyú. LJS ToninJs. Sanca TerTwo morphologic r)'pes of beach profiles were observed a!ong che srudied coast.One cype locared norrhward berween San Clemente and Nueva Arlanris is characrerizedby a linear configurarion profile with rncan slopes of 0.028 and beach widrhberwcen 40 re 70 m. The beach has no berrn developmenr and a swash bar is usuallyobserved afrer surge storrns. The grJ.in size of.'c~e sedirnenrs is fine: sand, The naruralbeach profiles berween Punta Médanos ant 'Villa Cesell prese:ne .:1: srable berrn -of abour 40 to 80 m width, and one or rwo ridal berms of 20 re 30 m. The rncanbeach slope is 0.014, the beach width varies from 90 'o 140 m and rhe rnean grainsize is medium ro fine: sand, The backshore continues landward wirh the forcdune.The rnean grain size of rhe beach sedirnenrs where the cockle Dona» hanleyanusoccurs varies from fine sand (2.10-2.80 phi) for the north sector to medium 'ocoarse sand (0.70-1.90 phi). Donax iJalllryanllJ is found in the lower ehird of theinrertidal zone in the tr ansverse pr'ofile. A permanenr absence of individuals W:J.Sobservedin Punta Iüsa and San Clernenre del Tuyú. The m ean densicy recognised wasabour 400 individuals per square meter and rhe highesr den sities were recorded forMar del Tuyú wirh 2254 individuals pe:r sqJ.t;¡re meter.The grain size of me: sedirnents analysed did noe insure the occurrence of Donaxhanleyanus, a!chough ir was observed that the presence of coarser she:~t! wich rneangrain size of 0.71 phi and standard deviarion of 1.07 :úfe:cc rhe burrowing capaciry ofDonax.The longeviry of Donax hanlryanJl! is greater in rhe south where rhey can liveup to three years. The growrh rates are similar for borh arcas alehough in thesourh a dccrease in rhe: groweh rares was observed during che winter rclare d re aseascnal effecr.