Population structure, growth and production of the yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) from a high-energy, temperate beach in northern Argentina

MARKO HERRMANN ; JOSE E. F. ALFAYA; MAURO L. LEPORE; PABLO E. PENCHASZADEH; WOLF E. ARNTZ

HELGOLAND MARINE RESEARCH

SPRINGER

Año: 2010 p. 285 - 297

1438-387X

 The yellow clam Mesodesma mactroides(Bivalvia: Mesodesmatidae) was once the most abundantintertidal species on the Atlantic coast of northern Argentinaand an important commercial resource in SouthAmerica. This study of a population inhabiting the intertidalzone of the sheltered-dissipative sandy beach SantaTeresita documents the species? population biology,including demographic structure, growth and productionduring December 2004 and December 2006, and adumbratesthe critical state of M. mactroides at present. A totalof 3,015 M. mactroides were collected and measured,whereas individuals were found with an anterior?posteriorshell length between 2 and 64 mm. A von Bertalanffygrowth function with an asymptotic length (L?) of 85 mmand a growth constant (K) of 0.47 year-1 was establishedfrom length?frequency distributions. The longevity of thespecies is estimated at approximately 6 years, and instantaneousmortality rate was about three times higher than 40 years ago. Besides, this study confirmed that the overallgrowth performance index (OGP) is habitat-specific andcan be used to group M. mactroides and M. donacium fromdifferent areas into temperate and upwelling species. Furthermore,OGP is inversely correlated with the latitudinaldistribution of Mesodesma populations. The intertidalbiomass ranged between 0.06 and 0.07 g AFDMm-2 year-1. Individual production was observed to behighest at 47 mm length (0.35 g AFDM m-2 year-1), andannual production ranged between 0.12 and 0.19 g AFDMm-2 year-1, resulting in productivity values (P/B) between1.84 and 2.93. The comparison of the results of the presentstudy with those of growth studies conducted on M. mactroides40 years ago revealed the following considerabledifferences in the population structure of M. mactroides,indicating the conservation status of this intertidal bivalveas endangered: (1) present growth rates are faster, but thatthe maximum length attained has decreased, (2) the numbersof individuals per square metre were many timeshigher in the past than in the present, (3) bivalves from thepresent work never reached the ?commercial size? of60 mm and (4) 40 years ago, the population of M. mactroideswas composed of up to three cohorts, whereas inthis study, there was only one single cohort visible.