Assessing sandy beach macrofaunal assemblages across geographically diverse morphodynamic environments.

While the physical characteristics of sandy beaches play a significant role in shaping the macrofaunal community features through morphodynamics, regional environmental factors may also account for deviations from the expected patterns. Here, we assess the concurrent effects of local morphodynamic factors and regional variables, such as sea surface temperature (SST), salinity, and chlorophyll-a (chl-a), on species richness and abundance of intertidal macrofaunal assemblages in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP) in the southwestern Atlantic Ocean. Species richness was higher in dissipative beaches compared to intermediate ones, consistent with the predictions of the Swash Exclusion Hypothesis. However, this trend was not observed for total abundance, which significantly increased with chl-a. Both local and regional-scale environmental factors, such as salinity and chl-a, proved to be significant predictors in the arrangement of these communities. These results further support previous findings that highlight the critical role of the estuarine gradient of the RdlP in shaping life-history traits, population structure, and abundance of the resident intertidal macrofauna at both local and regional scales. The study underscores the importance of integrating environmental factors operating at different spatial scales to decipher community patterns in these physically-controlled environments.

Disentangling patterns in population parameters of the wedge clam Donax hanleyanus from sandy beaches of Argentina: The role of environmental variability.

The concurrent role of morphodynamics and estuarine gradients in shaping population patterns in sandy beach macrofauna has not been adequately assessed. Here, we analyze the effects of beach morphodynamics, salinity, sea surface temperature, and chlorophyll-a (chl-a) on life-history traits of the wedge clam Donax hanleyanus in four sandy beaches located along the estuarine gradient generated by the Río de la Plata (RdlP, Argentina) over a 13-month period. A general linear model showed that chl-a and salinity were positively correlated with the abundance of D. hanleyanus, whereas between-beach differences in individual size, population structure, and growth performance were mainly explained by salinity fluctuations. These results indicate that the estuarine gradient of the RdlP plays a critical role in shaping life-history traits, population structure, and abundance of D. hanleyanus at local to regional scales, overriding the effects of local characteristics of the habitat. The study highlights the importance of conducting multi-scale studies that integrate environmental factors to elucidate the main physical drivers of population patterns in sandy beach ecosystems.

Contrasting patterns of morphological variation with dietary preferences in Micropogonias furnieri: insights from stable-isotope and digestive-trait analyses.

The dietary preferences of populations of whitemouth croaker Micropogonias furnieri, which commonly inhabit estuarine and oceanic environments of the south-western Atlantic Ocean, were investigated using stable-isotope analysis and digestive traits, and compared with previous genetic and morphometric surveys of this species. Isotopic and C:N-derived data suggested that individuals from coastal lagoons are the most differentiated from the remaining localities surveyed. In contrast, the analysis of the digestive traits did not show the same differentiation pattern. The overall correlation between isotopic, molecular and morphological variations suggests that genetic and phenotypic differences among populations are accompanied by differential resource use, supporting the idea that selective forces could be playing an important role in population differentiation.

Differences in coprophilous beetle communities structure in Sierra de Minas (Uruguay): a mosaic landscape.

Coprophilous beetles represent an abundant and rich group with critical importance in the functioning of terrestrial ecosystems. Most coprophagous beetles have a stenotopic distribution in relation to vegetation types. Because of this, they are usually very sensitive to environmental changes and are considered well suited as bioindicator organisms. The aim of this study was to analyze variations in coprophilous beetle assemblages in natural and anthropogenic habitats. Coprophilous beetle communities were sampled monthly for 1 year using pitfall traps baited with cow dung, in native xeric upland forests, 15-years-old plantations of Pinus elliottii and pastures in Sierra de Minas, Lavalleja, Uruguay. A total of 7,436 beetles were caught and identified to species or morphospecies level. The most abundant families were Aphodiidae, Scarabaeidae, and Staphylinidae. Differences in species richness, abundance, Shannon index, evenness, and dominance were detected between habitats. Abundances of most frequent families were significantly higher in both kinds of forests. Species richness and diversity of Aphodiidae and Staphylinidae were higher in forests, while Scarabaeidae showed the highest richness and diversity in pine plantations. Species composition significantly differed between habitats. Uroxys terminalis Waterhouse and Ataenius perforatus Harold typified the assemblages in native forests and pine plantations and also discriminated both communities because of their differential pattern of abundance between habitats. Typifying species in pastures were Onthophagus hirculus, Ateuchus robustus (Harold), and Ataenius platensis Blanchard. Habitat type had a strong effect on the coprophilous beetle community structure and composition.

[Growth of Octopus maya (Mollusca: Cephalopoda) of the Yucatan coast, Mexico: a long-term analysis]. / Crecimiento del pulpo Octopus maya (Mollusca: Cephalopoda) de la costa de Yucatán, México: un análisis de largo plazo.

Growth of the octopus (Octopus maya) off Yucatan (Mexico) was estimated from a long-term study (seven years) by the length-based methods ELEFAN, PROJMAT and SLCA. Some 19,251 octopuses with a range of mantle length between 50 and 240 mm were sampled from commercial landings in 1983-1987, 1989 and 1992. The jackknife technique was applied to deal with uncertainty in growth estimates resulting from chance variations in sampling design. The growth index phi' was used for comparative purposes. Results differed markedly among methods: ELEFAN produced parameter estimates within the range reported in the literature, whereas PROJMAT and SLCA showed problems to converge in an optimum combination of parameters, and tended to underestimate them. Jackknife analysis revealed very low intraannual variability in phi' but high variability among years, especially when applying PROJMAT. No significant differences were found in precision parameters--percent error and coefficient of variation--among methods. Estimates of phi' derived by ELEFAN varied between 4.19 and 5.23 and agreed with those reported in the literature (between 4.25 and 4.91), whereas PROJMAT and SLCA estimates were significantly lower. We suggest the use of ELEFAN, together with jackknife, to estimate growth parameters of Octopus maya.