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

The yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) was once the most abundant intertidal species on the Atlantic coast of northern Argentina and an important commercial resource in South America. This study of a population inhabiting the intertidal zone of the sheltered-dissipative sandy beach Santa Teresita documents the species' population biology, including demographic structure, growth and production during December 2004 and December 2006, and adumbrates the critical state of M. mactroides at present. A total of 3,015 M. mactroides were collected and measured, whereas individuals were found with an anterior-posterior shell length between 2 and 64 mm. A von Bertalanffy growth function with an asymptotic length (L∞) of 85 mm and a growth constant (K) of 0.47 year-1 was established from length-frequency distributions. The longevity of the species is estimated at approximately 6 years, and instantaneous mortality rate was about three times higher than 40 years ago. Besides, this study confirmed that the overall growth performance index (OGP) is habitat-specific and can be used to group M. mactroides and M. donacium from different areas into temperate and upwelling species. Furthermore, OGP is inversely correlated with the latitudinal distribution of Mesodesma populations. The intertidal biomass ranged between 0.06 and 0.07 g AFDM m-2 year-1. Individual production was observed to be highest at 47 mm length (0.35 g AFDM m-2 year-1), and annual production ranged between 0.12 and 0.19 g AFDM m-2 year-1, resulting in productivity values (P/B) between 1.84 and 2.93. The comparison of the results of the present study with those of growth studies conducted on M. mactroides 40 years ago revealed the following considerable differences in the population structure of M. mactroides, indicating the conservation status of this intertidal bivalve as endangered: (1) present growth rates are faster, but that the maximum length attained has decreased, (2) the numbers of individuals per square metre were many times higher in the past than in the present, (3) bivalves from the present work never reached the 'commercial size' of 60 mm and (4) 40 years ago, the population of M. mactroides was composed of up to three cohorts, whereas in this study, there was only one single cohort visible.Fil: Herrmann, Marko. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Johann Heinrich von Thünen Institute; AlemaniaFil: Fernandez Alfaya, Jose Elias. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Lepore, Mauro L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Arntz, Wolf E.. Institute for Polar and Marine Research; Alemani

Medium- and long-term temporal trends in the fish assemblage inhabiting a surf zone, analyzed by Bayesian generalized additive models

The present study characterizes the fish assemblage in the surf zone of Cassino Beach, Rio Grande, Brazil, and analyzes temporal fluctuations in richness and abundance of these species in medium (months) and long terms (years), associating them also with abiotic covariates. Data were collected monthly between 1996 and 2012 at two locations. Bayesian generalized additive models (GAMs) were used as statistical tool, placing this study among few that have used Bayesian GAMs in Ecology. Our results show a decrease in both species richness and abundance of the most representative species, over the last 16 years, but no significant distinction between locations. Water temperature and salinity along with seasonality were the statistically most influential explanatory covariates to describe fluctuations in richness and abundance. Higher discharge rates of the three main rivers that flow into Patos Lagoon (Jacuı´, Taquari, Camaqua˜) were associated with increased richness and abundance of some species in the assemblage. Hence, our findings show that medium- and long-term fluctuations in richness and species abundance are controlled by abiotic factors related to seasonal cycles (temperature) and productivity of the ecosystem. Long-term changes seem to be also related to man-induced factors and climate change; but further research is needed

A review on macrobenthic trophic relationships along subtropical sandy shores in southernmost Brazil

Main trophic relationships that occur along the exposed sandy shores in southernmost Brazil (,336 S) are established taking into account several biological compartments operating at morphodynamically distinct environments. Beaches are predominantly of the intermediate type but some stretches of coastline are truly dissipative (Cassino Beach) or tending-to-reflective (Concheiros Beach), presenting thus diverse biological compartments and inhabitant macrobenthic assemblages. Dense concentrations of the surf-zone diatom Asterionellopsis glacialis are responsible - at least for the intermediate shorelines - for the most year-round primary production, sustaining several consumers up to tertiary level. Among them, bivalves Amarilladesma mactroides, Donax hanleyanus and the hippid crab Emerita brasiliensis can account for more than 95% of all the surf-zone secondary production, in addition to the elevated biomass of the suspension-feeder polychaete Spio gaucha and the scavenger isopod Excirolana armata. Crabs, whelks, carnivorous polychaetes, seabirds and surf-zone fishes may also be present and occupy superior trophic levels depending on the beach morphodynamics. Based on the high species richness, abundance and the role of macrobenthic fauna in transferring matter and energy to seabirds and the surf-zone fish assemblages, we address this important issue on the Southwestern Atlantic ecology. Conservation efforts should be implemented for the southernmost Brazilian sandy shores, at least for those non urbanized areas.As principais relac¸o˜ es tro´ ficas observadas ao longo da costa arenosa exposta do extremo sul do Brasil (,336 S) sa˜o estabelecidas levando-se em considerac¸a˜o os va´ rios compartimentos biolo´ gicos que operam em ambientes morfodinamicamente distintos. Estas praias sa˜o predominantemente do tipo intermedia´ rio, embora alguns trechos sejam dissipativos (Praia do Cassino) ou apresentem tendeˆncias reflectivas (Praia dos Concheiros), possuindo compartimentos biolo´ gicos diversificados e associac¸o˜es macrobentoˆnicas residentes. Densas concentrac¸o˜ es da diatoma´cea Asterionellopsis glacialis sa˜o responsa´ veis - pelo menos para as praias intermedia´ rias - por grande parte da produtividade prima´ ria anual, sustentando va´ rios consumidores ate´ o nı´vel tercia´ rio. Entre estes, os bivalves Amarilladesma mactroides, Donax hanleyanus e o crusta´ceo Emerita brasiliensis sa˜o responsa´ veis por mais de 95% de toda a produc¸a˜o secunda´ ria da zona de surfe, em adic¸a˜o a` elevada biomassa do poliqueta suspensı´voro Spio gaucha e do iso´pode necro´fago Excirolana armata. Caranguejos, gastro´ podes, poliquetas carnı´voros, aves marinhas e peixes da zona de surfe tambe´m podem estar presentes, ocupando nı´veis tro´ ficos superiores dependendo da morfodinaˆmica praial. Baseado na alta riqueza de espe´cies, na abundaˆncia e no papel da macrofauna bentoˆ nica em transferir mate´ria e energia para as aves marinhas e as assemble´ias de peixes da zona de surfe, esta importante questa˜o ecolo´ gica do Atlaˆntico Sudoeste foi investigada. Esforc¸os de conservac¸a˜o devem ser implementados nas praias arenosas do extremo sul do Brasil, pelo menos naquelas a´ reas na˜o urbanizadas