Revista de Biología Tropical

Introduction: Chironomidae (Diptera) is the most widespread and abundant aquatic insect family in freshwater ecosystems. Chironomids are considered good indicators of water quality but are seldom identified at the genus level in broad spatial scale studies. Objective: To identify environmental conditions associated with chironomids in an altitudinal gradient. Methods: We compared ecoregions, river types, and seasons, for chironomids in neotropical streams and rivers (18 river sites; 2014-2018; Yungas rainforest and Western Chaco dry forest, Argentina). We used non-metric multidimensional scaling, dissimilarity, envfit analysis and rank-abundance curves. Results: Chironomic “assemblages” matched both ecoregions and river types. However, ecoregions presented a better fit with species composition. The stenothermal taxa of Orthocladiinae were dominant at high elevations and the eurythermal Chironominae in lowland rivers. Altitude, water temperature and conductivity were important. Seasonal differences were smaller than ecoregional differences. Conclusions: Ecoregions, altitude, water temperature and conductivity correlated with chironomid communities. Orthocladiinae were dominant at high elevations and Chironominae in lowland rivers.

Introduction: Defined seasonality in savanna species can stimulate physiological responses that maximize photosynthetic metabolism and productivity. However, those physiological responses are also linked to the phenological status of the whole plant, including leaf phenophases. Objective: To study how physiological traits influence phenophase timing among congeneric and co-occurring savanna species. Methods: We evaluated the leaf phenology and physiological traits of populations of Byrsonima intermedia, B. coccolobifolia, and B. verbascifolia. Physiological measurements were performed at the onset of the dry and rainy seasons and again late in the season. Results: B. intermedia and B. coccolobifolia were classified as brevideciduous and B. verbascifolia as evergreen. The maximum quantum yield for B. intermedia and B. coccolobifolia were lowest during the dry season. At the onset of the dry period, the highest chloroplastidic pigment levels were observed, which decreased as the season advanced, total chlorophyll/carotenoid ratios were lowest, and carotenoid contents were highest. We detected low starch content values at the start of the rainy season, coinciding with the resumption of plant growth. Two months into this season, the leaves were at their peak structural and functional maturity, with high water-soluble polysaccharide values and photosynthetic rates, and were storing large amounts of starch. Conclusions: Physiological and leaf phenological strategies of the Byrsonima species were related to drought resistance and acclimatization to the seasonality of savanna water resources. The oscillations of the parameters quantified during the year indicated a strong relationship with water seasonality and with the phenological status of the leaves. Objective: We studied how physiological traits, and not only seasonality, influence phenophase timing among congeneric and co-occurring savanna species. Methods: We followed the leaf phenologies and physiological traits of populations of Byrsonima intermedia, B. coccolobifolia, and B. verbascifolia native to the Brazilian savanna. Analyses of specific leaf mass, relative water content, leaf phenology, leaf carbohydrate content, chloroplastidic pigments, and photosynthetic efficiency were performed at different times during both the dry and rainy seasons. Physiological measurements were performed at the onset of the dry season and again late in that season, as well as at the onset of the rainy season and again late in the rainy season. Results: Byrsonima intermedia and B. coccolobifolia were classified here as brevideciduous and B. verbascifolia as evergreen. Few variations in chlorophyll a fluorescence values were detected over the full year, with the lowest maximum quantum yield values (Fv/Fm) for B. intermedia and B. coccolobifolia occurring during the dry season. The deciduous species (B. verbascifolia) evidenced higher photosynthetic yields during periods of abundant water availability, mainly after its complete recovery after the start of the prolonged rainy period. The highest chloroplastidic pigment levels were observed at the onset of the dry period, although chlorophyll levels decreased as the dry season advanced. The lowest total chlorophyll/carotenoid ratios and the highest carotenoid contents observed at the onset of the dry season indicated that Byrsonima plants were still investing in mechanisms of photoprotection and the dissipation of excess energy from their photosynthetic systems even under water deficit conditions. We detected low starch content values at the onset of the rainy season, which coincides with the resumption of plant growth. At two months into the rainy season, the leaves were at their peak structural and functional maturity, exhibiting high water-soluble polysaccharide values and high photosynthetic rates, and were storing large amounts of starch. Conclusions: Our data evidenced that the physiological and foliar phenological strategies of the Byrsonima species studied here were related to drought resistance and to acclimatization to the seasonality of savanna water resources. The oscillations of the parameters quantified during the year in the three studied species indicated not only a strong relationship with water seasonality, but also with the phenological statuses of the leaves.

Introduction: Pollution by microplastics is a global problem in marine environments, and impacts microorganisms and ecosystems at several spatial levels. Sandy beaches are depositional environments where microplastics tend to accumulate in large quantities. The co-occurrence of interstitial meiofauna and microplastics in sand grains raises the question on whether the accumulation of microplastics in the sediments affects the abundance and composition of the meiofaunal communities. Objective: To test the hypothesis that microplastics affect the meiofauna of urban sandy beaches. Methods: We studied the three main urban sandy beaches of Santa Marta, Colombia: El Rodadero, Santa Marta Bay, and Taganga. All are similar in morphology and external pressures and differ from other beaches in the region. In April 2019 we collected 81 sand samples, equally distributed in the intertidal zone (upper, mid, and lower intertidal levels). We applied generalized linear models to abundance, and multivariate permutational tests to community composition. Results: We identified 17 taxonomic groups of meiofauna, and microplastic particles (mainly 45-500 micron fibres) evenly distributed across beaches and intertidal levels. There was more meiofauna at the mid intertidal level, and in fine and medium grain sediment. At the lower intertidal level, sites with more microplastics had less meiofauna. Microplastics “explained” 39 % of the variation in meiofaunal communities at lower intertidal levels. Conclusions: The accumulation of microplastics has a negative impact on these meiofaunal interstitial communities. This is not surprising: microplastics occupy the same physical space as these animals, presumably modifying the structure of sediments and the composition of interstitial water. Objective: As a step forward on that direction, we have here analysed the distribution of the abundance of microdebris and major interstitial meiofaunal groups in three urban sandy beaches in Santa Marta region, Colombia, and possible relation among both factors. Methods: We selected the three main urban sandy beaches in Santa Marta, Northern Colombia: El Rodadero, Bahía de Santa Marta, and Taganga. All of them are very similar to each other due to its morfolophy and extern pressions, and differ starkly from other beaches in the region. Sampling was performed in April 2019 with a 81 samples in total equitably distributed in the supratidal zone, intertidal zone, and subtidal zone. In each point, we collected samples for microplastics quantification, meiofaunal community characterization, and granulometric analysis. Results: We extracted a total of 1131 debris particles, dominated by fibres ranging between 45-500 microns. Generalised linear models showed that microdebris were uniformly distributed across beaches and tidal levels, whereas meiofaunal abundances were significantly affected by the granulometry and tidal level. We detected a significant correlation between the abundance of microplastics and meiofauna at those levels, although with a very small estimate. Furthermore, our permutational multivariate tests showed that the abundance of microdebris significantly explained the 39.3% of the variation of the meiofaunal communities at the lowest tidal levels. Conclusions: Our result suggested that microdebris accumulating amongst the beach sand grains negatively impact meiofaunal diversity. This is not surprising, given that microdebris occupy the same physical space than these animals, presumably modifying the structure of the sediments and the composition of the interstitial water.