Gustavo Luis Hirose

Species distributions along environmental gradients may exhibit nestedness, turnover, or clumping patterns. In environments subject to strong environmental variability, such as continental shelves, environmental filters exert a decisive influence on community composition, which may alternate across seasonal periods, leading to temporal variations in the structure and diversity of marine communities. This study aimed to investigate the organizational patterns of the metacommunity at small (north, central, and south sectors) and large spatial scales (continental margin) during two seasonal periods along a depth gradient on the northeastern Brazilian continental margin. Taxonomic α-diversity was higher in the southern sector and during the rainy periods. β-Diversity did not differ among sectors, but species composition exhibited high dissimilarity, particularly between the northern–southern and central–southern sectors, reflecting stronger species turnover during the rainy season, whereas richness differences predominated in the dry period. The metacommunity structure along the environmental gradient was predominantly Gleasonian at smaller spatial scales, with individualistic species responses and gradual shifts in composition, whereas quasi-Clementsian patterns emerged at broader scales, revealing groups of species with similar distributional limits and abrupt compositional changes. The metacommunity was primarily structured by environmental filters, with depth and gravel as the main predictors. Spatial processes had a limited influence and were associated with dispersal limitation, whereas most of the variation remained unexplained by the measured variables. Overall, the results indicate that environmental filtering (depth and gravel) constitutes the primary structuring mechanism, acting in conjunction with large-scale spatial effects associated with dispersal limitation and mass effects acting at smaller-scales.

This study investigated the population dynamics of the symbiotic pea crab Austinixa aidae and its non-obligate host, the ghost shrimp Callichirus corruptus , on a sandy beach in Northeast Brazil, assessing the influence of the symbiotic relationship and environmental conditions on population traits. Monthly collections were conducted over 1 year at Cinelândia Beach, Aracaju, Sergipe, and specimens of both sexes were sexed and measured from individual burrows. We analysed size–frequency distributions, sex ratios, and reproductive periods, correlating them with each other and with environmental factors. A. aidae showed continuous seasonal reproduction, with peaks between June and August and in April, positively influenced by precipitation (the rainy season). Conversely, the host, C. corruptus , exhibited seasonal reproduction, peaking in February, which was correlated with higher temperatures (the dry season). This antagonistic reproductive pattern between the symbiont and host was confirmed by a significant negative correlation between their respective percentages of ovigerous females. Furthermore, a significant positive correlation was found between the number and size of crabs and the size of their host. Both species displayed smaller sizes than populations at higher latitudes, suggesting a latitudinal influence. This reproductive asynchrony may represent a coevolved strategy for the symbiont to avoid competition for resources during the host’s reproductive peak.

The aim of the present study is to document a morphological abnormality in specimens of Macrobrachium amazonicum (Heller, 1862) based on specimens sampled in Jequitinhonha River, Bahia State, Brazil. Samples were collected at Itapebi Hydroelectric Power Plant using a cylindrical trap and a hand-drawn seine net. The morphologically altered telson was measured, characterized, and compared among specimens. Symmetrical or asymmetrical bifurcations were observed in the telson of four female specimens. Morphological abnormalities in decapod crustaceans can happen due to several reasons, and in M. amazonicum, it is mainly polluted rivers or failed wound healing; perhaps caused by excess fishing pressure in stocks bred in the dam reservoir. The present results add information about abnormalities in decapod crustaceans, besides being the second report on such features in this species.

Invasive corals of the genus Tubastraea exhibit early maturity, rapid growth, and plasticity regarding the substrate they use, which has enabled the genus to quickly become successful and expand its non-native range. For the state of Sergipe there are 23 records of Tubastraea spp. on oil platforms; here we report the first records of the sun coral T. coccinea on the coast in the estuarine zone of the Vaza-Barris River, expanding its invasive range from offshore to onshore. Contaminated oil platforms, vessels, and shipwrecks may have provided a pathway as vectors, acting as stepping stones that connect oceanic regions to the coast. Dispersal may also occur through currents responsible for transporting organisms from the continental shelf to the coast, although this seems unlikely. Thus, we reinforce the importance of constant monitoring of vectors and the coast to minimize the adverse effects of invasive corals on native fauna.

Male morphotypes in a population may lead to the development of social dominance hierarchies in crustacean species. Currently, Macrobrachium is the decapod crustacean genus with the largest record of species that present the development of hierarchies. Macrobrachium olfersii has morphological characteristics that indicate the presence of male social dominance within its populations. Thus, the present study tested the hypothesis of the occurrence of male morphotypes in M. olfersii through morphometric and morphological analysis of the chelipeds. Sampling was carried out from March 2018 to October 2021 in seven points along the Jequitinhonha River, Northeast Brazil. A total of 264 males were collected with carapace length (CL) ranging from 4.01 to 23.70 mm. Morphological sexual maturity size was estimated at 8.95 mm CL. The morphometric and morphological analysis confirmed the presence of three adult male morphotypes: M1, M2, and M3. The characterization of the different morphotypes was mainly due to the variation in size, shape, and morphology of the largest cheliped of the second pair of pereopods. Most morphometric relationships differed significantly ( p < 0.01) among the three morphotypes, mainly between M3 against M1 and M2. The variation in the propodus shape was also evident. This trait and the angulation of the spines differed significantly between morphotypes ( p < 0.01), with the propodus of morphotype M3 being more robust and carrying a greater number of spines than the others. The occurrence of social dominance and the exaggerated development of a cheliped (weapon) can be advantageous for dominant individuals when they need to compete for resources. This morphological trait can provide these individuals with advantages during fights and guarantee access to the best resources, whether they are shelter, food, or sexual partners. Our results add new information to the biology of M. olfersii , as well as the genus Macrobrachium , and the occurrence of social dominance in species of this group. In addition, by describing these morphotypes in detail, using a set of complementary morphological and morphometric techniques, it is possible to access the differential morphology along the M. olfersii males, as well as confirm a life history trait found in several Macrobrachium species.

The complete larval development of Amphithrax hemphilli was described, illustrated, and compared with that of the previously described larvae of the genus Mithrax sensu lato. Specimens of A. hemphilli were sampled from the northeastern Brazilian coast. The larval development of A. hemphilli consisted of two zoeal stages and one megalopa. Amphithrax hemphilli shows morphological features in all stages of larval development that differ from those observed in other species of Amphithrax, Mithrax, and Maguimithrax. In the first larval stage, A. hemphilli was the only species with two aesthetascs on the antennule and the coxal endite of the maxillule with five setae. In the second larval stage, A. hemphilli was distinguished from the other species of the genus Mithrax sensu lato by the presence of five setae on the basial endite of the maxilla and 26 setae in the scaphognathite of the maxilla. Finally, the megalopa stage of A. hemphilli is characterized by the number of aesthetascs on the three-segmented exopod of the antennule, the setation of both the endopod of the third maxilliped, and pleonites 1–6. Based on the results obtained in the present study, we verified that the more advanced the larval stage, the more distinct characteristics are observed among species of the genus Mithrax sensu lato, facilitating the identification of species through later larval stages.

This study tested the hypothesis of the existence of male morphotypes in Macrobrachium acanthurus, a species of recognized economic potential, with an extensive geographic distribution. The collections occurred on eight occasions between July 2016 and March 2018 at seven points along the Jequitinhonha River, state of Bahia, Brazil. The identification of male morphotypes occurred through morphological and morphometric analyses. In total, 297 males were collected. The carapace length (CL) ranged from 4.6 to 41.81 mm, with a size at onset of maturity estimated at 11.85 mm. The morphological and morphometric analyses confirmed our hypothesis with the distinction of three morphotypes: M1, M2, and M3. M1 was characterized by males with chelipeds similar to those of females: relatively small, with tiny spines and without pubescence in the dactylus; M2 males had chelipeds larger than those of M1, as well as larger and denser spines, with little pubescence in the dactylus; and M3 individuals had considerably more robust chelipeds, very prominent spines and a thick layer of pubescence when compared to those of the previous morphotype. Our results suggest a social hierarchy where M1 is subordinate, M2 subdominant, and M3 the dominant morphotype. However, behavioural studies are needed to confirm this.

Considering the environmental impacts to rivers caused by the exploitation of water resources and the consequences of these impacts upon fauna, the objective of this study was to evaluate the population biology of the shrimp Atya scabra (Leach, 1816) in the final stretch of the major river of South America. This species was assessed as “Near Threatened” in the red book of Brazilian crustaceans. Specimens were sampled monthly from February 2015 to January 2016 in a region of the lower São Francisco River, Brazil. A total of 233 individuals of A. scabra were collected, including 120 males and 113 females (71 non-ovigerous and 42 ovigerous). Atya scabra abundance was higher when water flow values increased. A decrease in abundance was observed over the one year of sampling, indicating a decline of about 90 % in this population in this region of the São Francisco River. We suggest that this decline was caused by the reduction of water flow in the São Francisco River, due to a policy that authorized retaining more water behind dams and releasing less water into the river in April and June 2015. In light of this, other studies should monitor the population dynamics of this species, while legislative actions are also needed to protect this fragile ecosystem.