Spatial and temporal variation in the diet of the sandy beach gastropod Olivella minuta

Marine gastropods exert a strong influence on the structure of marine ecosystems through their foraging activities, yet little is known about how environmental differences in space and time may affect their feeding behavior. To enhance the knowledge about the trophic ecology of coastal benthic species, we investigated temporal and spatial variations in the diet of the sandy beach gastropod Olivella minuta. We collected individuals of O. minuta seasonally, over 1 year, at two sandy beaches with different morphodynamic characteristics (Araçá Bay, an ultra‐dissipative tidal flat, and Barequeçaba Beach, a dissipative beach) and analyzed the stomach contents of specimens of O. minuta. We identified approximately 15,000 food items, which we grouped into 14 categories. Thirteen food categories were found at each area, but significant differences in diet were observed between sites and sampling periods. Individuals from Araçá consumed an overall larger quantity and diversity of food items, which consisted mainly of foraminiferans, polychaetes, and crustaceans. At Barequeçaba, diatoms were the most important item, followed by crustaceans and polychaetes. Temporal variation depended on sites: the number of food items in the stomachs of individuals of O. minuta and dietary composition was roughly constant over time at Araçá, whereas larger variations were observed at Barequeçaba. Although O. minuta has been previously characterized as a carnivore/scavenger, our results show that the diet of this species varies in space and time and comprises a large variety of food resources. The species thus plays a role in the cycling of both vegetal and animal organic matter. This generalist behavior may allow individuals to shift their diet according to habitat alterations and food availability, thereby enhancing the persistence and resilience of O. minuta in different environments or future climate change scenarios.     

Evaluating the anesthetization and fixation efficacy of “soft” and “hard” freshwater benthic meiofauna: what is the best method for specimen preservation?

Sampling freshwater biological diversity is a challenge when it comes down to techniques for meiofauna fixation and preservation because this polyphyletic group of taxa is highly diverse. The aim of this study is to test the performance of three anesthetics (CO₂, MgCl₂ and low temperature) and three fixatives (formaldehyde 4 %; buffered formaldehyde 4 and 70 % ethanol) in the preservation of “soft” (gastrotrichs and rotifers) and “hard” (tardigrades and copepods) freshwater benthic meiofaunal assemblages. Due to these different morphological structures, we expected that treatment performance would vary among taxa in the quality of specimen fixation. Results revealed that the meiofaunal abundances of samples sorted alive or after the treatments with a coupling of anesthetics and fixatives were not different. However, preservation of specimens varied substantially among “soft” and “hard” meiofauna and among treatments. The use of 4 % buffered formaldehyde is highly recommended for freshwater meiofauna, while unbuffered formaldehyde should be avoided. Studies that have “soft” meiofauna as target organisms are recommended to use some type of anesthetic, although it is necessary to use a specific one for each taxon as they respond in different ways to different anesthetics.     

Fiddler crab (Crustacea: Ocypodidae) distribution and the relationship between habitat occupancy and mouth appendages

Sediment characteristics, especially grain size, are usually considered the most important variables affecting Uca distribution, mainly due to its close relationship with mouth appendage morphology. The aim of this study was to verify, from an assemblage perspective, if sediment is the most important variable affecting Uca species distribution, and if mouth appendage morphology (setae type and curvature) would be related to habitat occupancy. Niche metrics and null model approaches were used to assess and test the hypothesis. The relevance of spoon-tipped setae curvature to Uca distribution was verified for the first time. A fragmented mangrove area was divided into seven subareas, and sampling of crabs and environmental variables took place in June and November 2010. Of 10 species recorded for Brazil, seven were found in the study area: U. burgersi, U. cumulanta, U. leptodactyla, U. maracoani, U. rapax, U. thayeri and U. uruguayensis. Multivariate analysis showed that sediment grain size and the presence of vegetation were the most important variables explaining distribution, reinforcing results commonly obtained by univariate approaches. The overlap of habitat occupancy was generally low and no relationship between mouth appendages was found with breadth and overlap measures. Contrary to predictions, most non-random overlap values were lower than expected by chance, suggesting that interspecific competition might influence species distribution. Also, variables such as the presence of vegetation are important and influence crab distribution, limiting the potential distribution that would be predicted by mouth adaptations alone. Thus, the use of these adaptations as surrogates of fiddler crab distribution is not recommended.     

Parasitism by isopods in sandy beach fish assemblages: role of urbanization and environmental characteristics

Parasitism by isopods is a common phenomenon in marine fishes and may induce negative effects, especially in juvenile stages. The surf-zones of sandy beaches are an important nursery habitat for many fish species, including commercially important ones, and are structured by beach characteristics and human activities, which are suggested to influence the fishes’ susceptibility to parasitism. Here, we analyze the early infestation and prevalence of parasitism in surf zones fishes of 27 beaches in southeastern Brazil with different characteristics. Parasites were recorded in only seven of the beaches. A high infestation was found in a single site, the highly urbanized Itaguá beach, where the prevalence of parasitism on juveniles and early adults of the Atlantic anchoveta Cetengraulis edentulus was high (68.11%). Four species of parasitic isopods were found, all belonging to the Cymothoidae family, but Livoneca desterroensis was the most abundant (78.7%). No effects of parasitism were detected on the size, weight and physiological condition of fishes, but presence of parasites and prevalence of infestation were positively affected by urbanization. Overall, our results indicate that the surf-zones have low parasite infestation, yet, they suggest that anthropic effects such as urbanization may enhance the prevalence of isopod parasitism.

     

Cavity-nesting bee communities in areas with different levels of vegetation disturbance

ABSTRACT

The reasons for the decline of bee diversity and abundance include the destruction and loss of natural habitats. Protected areas are created for biodiversity conservation, but these areas vary strongly in their level of vegetation disturbance. Using trap-nests, we assessed changes in solitary bee abundance, richness, and composition in areas ranging from naturally conserved to degraded. Solitary bees were sampled during an 18-month period in three areas of southeastern Brazil: a preserved area in Rio Preto State Park – PERP; a restored/altered area with exotic plants at the Federal University of the Jequitinhonha and Mucuri Valleys – JK Campus; and a degraded area in Biribiri State Park – PEBi. A total of seven species of bees built 115 nests. In the degraded area, only two nests were built. Abundance of built nests was higher in the preserved area (PERP), but diversity was higher in the restored area (JK Campus). Our results show that the solitary bee population responds positively to habitat complexity (local scale). The presence of a diverse solitary bee fauna in the restored area indicates that altered areas should also be protected as suitable areas for re-colonization of cavity-nesting bees.