Tropical Bay In Southeastern Brazil Research Articles

Polychaetes and fish in a tropical bay in southeastern Brazil: Community concordance and influence of environmental variables

AbstractThe distribution of species depends on the relationship with other species and the influence of abiotic factors, modulated by long‐term evolutionary and biogeographic processes. Polychaetes and fish are important components of the biota that inhabit estuarine systems, coexisting in various habitats, although the relationship between these groups and their responses to environmental variables is poorly understood. This study aimed to assess the concordance between fish and polychaete communities in three zones (inner, middle, and outer) of a tropical bay and to determine environmental influences on these communities. The raised hypothesis is that benthic fish is associated with polychaetes and that these taxonomic groups respond differently to environmental conditions. Environmental characteristics were the main drivers determining the occurrence of fish species and polychaetes families; however, no consistent relationship was observed between fish and polychaetes. Sediment granulometry seems to be an essential driver in determining polychaetes and fish distribution while turbidity and phosphorus were also important for fish. The three zones differed in both water physicochemical and sediment (nutrients and granulometry) variables, which determined their uses by different fish and polychaetes species. Only one fish species, the gerreid Eucinostomus argenteus showed a weak but significant association with the Goniadidae and Spionidae polychaetes, which may be associated with similar environmental preferences of both taxa. The lack of a consistent relationship between benthic fish and their likely invertebrate prey may be associated with the small spatial scale of this study and the early fish life stages. Most fish in shallow coastal areas are still in their early life, feeding mainly on polychaetes and other benthic macroinvertebrates, and as the area is shallow, planktonic organisms may be included in their diet, thus relieving predation pressure on benthic organisms. These findings are important to unveil relationships among different taxonomical groups and their environment.

Do closely related species share of feeding niche along growth? Diets of three sympatric species of the mojarras (Actinopterygii: Gerreidae) in a tropical bay in southeastern Brazil

Understanding the trophic relationships among closely related species is a way to obtain subsidies for their management and conservation of their habitats. The diets of three co-occurring abundant fish species of the Gerreidae family (Diapterus rhombeus, Eucinostomus argenteus and Eucinostomus gula) in a tropical bay were described. The tested hypothesis was that the three sympatric species present shifts in their use of resource during the ontogenetic development to facilitate their coexistence. Size groups for each species were categorized according to breakpoints in the morphological structures determined by piecewise regression models. Significant overlapping in diets was found for all size classes of D. rhombeus but not for size classes of the Eucinostomus genus. Furthermore, different size classes of D. rhombeus did not overlap diet with size classes of the Eucinostomus genus. The specialization in feeding niches corresponding to growth seems to bring benefits for this group of fish rather than a generalist feeding strategy. The hypothesis of the available resources partitioning was accepted only between the two genera (Diapterus and Eucinostomus), and among size classes of the Eucinostomus genus that seemed to follow the principle of limiting similarity. However, different size classes of D. rhombeus exhibited strong evidence of an intraspecific overlapping of the trophic niche. It seems that different processes related to use of the trophic niche dimension are structuring these closely related fish species.

Inter-annual changes in fish communities of a tropical bay in southeastern Brazil: What can be inferred from anthropogenic activities?

We assessed inter-annual changes in fish assemblages of a tropical bay which experienced a heavily industrialized process in the last decades. A highly significant difference in community structure among the bay zones, and a decrease in fish richness and abundance over time were found. Changes in fish richness and abundance between the two first (1987–1988 and 1993–1995) and the two latter time periods (1998–2001 and 2012–2013) were sharpest in the inner bay zone, the most impacted bay area, and in the middle zone, whereas the outer zone remained comparatively stable over time. These changes coincided with increased metal pollution (mainly, Zn and Cd) in the bay and with the enlargement of the Sepetiba Port. Spatial changes in the fish community structure among the bay zones were related to differences in salinity, transparency and depth with this latter variable acting as a buffer stabilizing temporal community changes.

Metal bioaccumulation in edible target tissues of mullet (Mugil liza) from a tropical bay in Southeastern Brazil

The present study aimed to investigate metal bioaccumulation in mullet (M. liza) from a tropical bay located in Southeastern Brazil, comparing a previously considered reference site to a known contaminated area of the bay, as well as to conduct human health risk assessments with regard to the consumption of this species. The metal concentrations were compared to the maximum residue level (MRL) in foods established by the different national and international regulatory agencies, and the Provisional Tolerable Daily Intake (PTDI) was determined and compared to reference values. Chromium (Cr), Zinc (Zn), Copper (Cu), Manganese (Mn), Nickel (Ni), Cadmium (Cd) and Lead (Pb) concentrations were determined in the gills, muscle and liver of 28 mullet by ICP-MS after acid digestion. Certain metals exceeded MRL guidelines established by different regulatory agencies, indicating human health risks associated to these metals. PTDI values, however, did not exceed corresponding metal values proposed by the World Health Organization. The metal concentrations found in the mullet samples indicate that the previously considered reference site is now showing signs of anthropogenic contamination.

Gonadal development and fecundity of the smooth weakfish Cynoscion leiarchus (Teleostei: Perciformes: Sciaenidae) in a tropical Brazilian bay

Cynoscion leiarchus (Cuvier, 1830) is a coastal fish species that is widely distributed along the Western Atlantic coast, from Belize to Southern Brazil. In Brazil, C. leiarchus It is an important resource for commercial and artisanal fisheries. Our objective was to describe the oogenesis and spermatogenesis stages of the species and to estimate batch size and relative fecundity of a population at a tropical bay in southeastern Brazil. The examined specimens were obtained from artisanal catches that took place from July 2013 to June 2014. A total of 18 individuals (11 females and 7 males) were examined for histological analysis and 20 spawning-capable females were used to estimate fecundity. Five stages of oocyte development (primary growth, pre-vitellogenic, vitellogenic, oocyte maturation and atresia) and four stages of spermatocytes (spermatogonia, spermatocytes, spermatids, spermatozoa) were described in different phases of gonad development (immature, developing, spawning capable and regenerating), suggesting that spawning happens in batches, oocyte development is asynchronic and fecundity is indeterminate. Batch fecundity ranged from 100 × 103 to 866 × 103 oocytes undergoing final oocyte maturation, and relative fecundity ranged from 232 to 1,225 oocytes, averaging 467 oocytes per gram of ovary-free body weight. Fecundity tended to increase linearly with gonadal weight, total weight, total length, and age, but the highest linear correlation obtained was between fecundity and gonadal weight. This study provides the first information on the gonadal development of C. leiarchus from the Brazilian coast and is a baseline to compare with other populations and/or congeneric species.

Inter-decadal changes in fish communities of a tropical bay in southeastern Brazil

Long-term evaluations of coastal fish communities worldwide have in many cases showed a decrease in the species richness and abundance as a result of anthropogenic impacts. Fish communities in two zones (inner and outer) of a tropical bay in southeastern Brazil were sampled monthly during six years over two decades (1983–1985, 1993–1995, 1999–2001) using identical sampling methods. Over time, an increase in temperature and a decrease in water transparency were detected, while salinity remained stable. Fish assemblage was dominated by benthivorous species both migrant and resident species. The fish assemblage structure differed significantly between the two bay zones. Significant decreases in the fish richness, abundance and biomass were detected over time. The highest decreases in the species richness was recorded between 1983–1985 and 1993–1995 for the marine migrants in both bay zones and for the resident and marine straggler species in the outer zone. Dominant species such as the clupeoids Anchoajanuaria, Anchoa tricolor,Harengula clupeola, the gerreid Eucinostomos argenteus,the sciaenid Micropogonias furnieri, the atherinopsid Atherinella brasiliensis and the ariid Genidens barbus decreased over time, whereas the mugilid Mugil liza increased. Persistent differences in the fish assemblage structure between the two bay zones over the three periods can be attributed at least in part to differences in environmental variables between the zones and seem to be a key ecological element to maintenance of biodiversity. This is the first study to examine long-term changes in the fish community of a tropical bay in Brazil.

Partitioning of the feeding niche along spatial, seasonal and size dimensions by the fish community in a tropical Bay in Southeastern Brazil

Feeding guilds and spatial, seasonal and ontogenetic changes in the diets of 24 fish species in a tropical bay in Southeastern Brazil were examined. The hypotheses tested were that groups of species form specific trophic guilds and that the feeding partitioning differs along the niche dimensions. Five trophic guilds (Polychaeta, Copepoda, Teleostei, Teleostei/Crustacea and Polychaeta/ Crustacea) and two species with specialised feeding, one teleost (Aspistor luniscutis) and one bivalvia (Sphoeroides testudineus), were found. Polychaeta was the most important resource for nine fish species, followed by Copepoda (6 spp.), Teleostei (5 spp.) and Caprelidae Amphipoda (3 spp.). Polychaeta was the most used resource for species in the inner bay zone, and Crustaceans in the outer bay zone. We detected a predominance of Polychaeta between the spring and autumn, whereas crustaceans were consumed at a greater rate in the winter. The most conspicuous changes in diet occurred along the spatial and seasonal dimensions, rather than the size dimensions. The hypotheses tested were accepted. Identifying and incorporating information about the bay food web is a first step towards developing management strategies that are sensitive to this particular ecosystem.

Shifts of the feeding niche along the size dimension of three juvenile fish species in a tidal mudflat in southeastern Brazil

The diet of three cooccurring abundant fish species (Eucinostomus argenteus, Diapterus rhombeus and Micropogonias furnieri) and its ontogenetic changes in a mudflat area of a tropical bay in southeastern Brazil were described. The working hypothesis is that these three species shift the use of the available resources throughout their growth. Early juveniles of D. rhombeus and M. furnieri fed mainly on Cyclopoida copepods, shifting to Nematoda (D. rhombeus) and errant Polychaeta (M. furnieri) as they increased in size. In contrast, the early life stages of E. argenteus fed mainly on errant Polychaeta and Calanoida copepods, with increasing niche breadth as they grew. The relative degree of individual specialisation in resource use indicated specialism for M. furnieri and E. argenteus, and generalism for D. rhombeus. The largest intraspecific overlap was found for the smallest size classes. Niche breadth increased during ontogeny, with a higher average niche breadth at lower prey length/predator length ratios. Therefore, species-specific differences in diet across the resource gradient and increased niche breadth during ontogeny characterised the shifts of resource use, and probably account for the coexistence of these species in zones of sympatry in mudflat areas of southeastern Brazil.

Spawning season, recruitment and early life distribution of Anchoa tricolor (Spix and Agassiz, 1829) in a tropical bay in southeastern Brazil

The pattern of the use of the Sepetiba Bay, a semi-closed 450 km(2) area in southeastern Brazil, by Anchoa tricolor was investigated to assess spawning period, recruitment and to detect spatial-temporal patterns of this major fishery resource. Fishes were sampled by seine nets, from spring, 1998 to winter, 1999 and by beach seine, from spring, 1998 to winter, 2000. Reproductive season, measured in terms of GSI, gonad development and appearance of recruits, indicate that reproduction occurs from August to March, when they reach the best condition. Recruitment peaks in winter/spring at sandy beaches where they stay until late summer, moving toward deeper bay areas during autumn. After that, they join adults and perform movements between the bay and the adjacent continental shelf to reproduce.

Inter-annual variability of planktonic copepods in a tropical bay in southeastern Brazil

The aim of this work was to study the structure of the copepod community in relation to hydrographic conditions in Espírito Santo Bay, from 1993 to 1997. Zooplankton samples were obtained in the horizontal tows four times a year, using a 200 µm net. Temperature, salinity and dissolved oxygen were determined in the water samples. The overall mean density of the copepods was 9,085 ind.m-3 with the peaks exceeding 15,000 ind.m-3 in the summer and autumn during the first three years (1993 - 1995). The PCA analysis was used to relate the environmental conditions with the distribution of the copepods. The increases in the abundant species, namely Acartia lilljeborgi, Oithona hebes, Oithona oculata, Paracalanus quasimodo, Parvocalanus crassirostris and Euterpina acutifrons, were related to the decreases in the diversity. The spatial and temporal variations of the temperature and salinity influenced the abundance of the species during the five years of the sampling and the dominant species alternated in abundance.

Demersal fishes in a tropical bay in southeastern Brazil: Partitioning the spatial, temporal and environmental components of ecological variation

This study analyzed the factors structuring demersal fish community in a tropical bay in southeastern Brazil. The results were used to quantify the partitioning of ecological variation among the environmental, spatial and temporal components molding the fish community. Three bay zones (inner, middle and outer) were defined according to depth and salinity gradient. Monthly samplings were conducted by bottom trawl tows during daylight hours, between October 1998 and September 1999. In each zone, three replicate samples were taken. Ninety-three fish species from 73 genera and 37 families were recorded in the 108 samples. Two demersal fish assemblages were evidenced, one in the inner and the other in the outer zone. These assemblages were characterized by changes in species composition and relative abundance. Depth, followed by transparency and salinity, influenced spatial pattern of fish assemblages. The largest part of the explained variation occurred as a result of the spatial structure of environmental variables, which means that both species and environmental variables presented similar spatial structure. The spatial effect, not the seasonal, explained the highest part of species variations. The amount of unexplained variation was relatively high (76%), even assuming that part of it is due to nondeterministic fluctuation, which could be due to local effects of unmeasured (biotic and abiotic) controlling variables. Knowing the relative importance of these factors can be of decisive importance when applying casual hypotheses in the framework of some precise ecological theory and should facilitate management, planning, and usage of bay resources.

Co-occurrence of demersal fishes in a tropical bay in southeastern Brazil: A null model analysis

Co-occurrence of demersal fishes was assessed in a tropical bay in southeastern Brazil along an environmental gradient (inner, middle, and outer zones), defined according to depth and salinity. The aim was to test whether fish species are distributed randomly and independently of one another in accordance with a null model. The unconstrained null hypothesis for occurrence of a given species by chance in relation to other species was accepted for each zone separately, and rejected for the bay as a whole, for the full year and for each season separately, except summer. Findings of the environmentally constrained null models, which predict species presence or absence as a function of environmental conditions, were not significant, suggesting that the environmental variables we chose are not key factors for these species and that biotic interactions between species are not strong when species–environment relationships are considered. The partition of available resources inside each zone and fish movements along the three zones during summer may have contributed to higher fish species co-occurrence. Habitat segregation in the bay during the remaining seasons could explain the pattern of reduced co-occurrence, indicating the presence of two fish assemblages associated with different environmental characteristics.

Use of a tropical bay in southeastern Brazil by juvenile and subadult Micropogonias furnieri (Perciformes, Sciaenidae)

Abstract The white croaker Micropogonias furnieri is a commercially important marine fish that uses bays and other semi-closed coastal areas early in its life. A sampling programme, using beach-seine and otter trawl, was carried out in Sepetiba Bay (22°54′–23°04′S, 43°34′–44°10′W), southern Brazil, from October 1998 to September 1999, with the objective of assessing the patterns of temporal and spatial usage of the bay by white croaker during its early life. Early recruits (total length, TL, 10–50 mm) appear off beaches of the inner bay between October and December, move away from them during late summer and early autumn (January–April), and are caught by trawl offshore from May to September at a TL of 70–150 mm. From May to August, new recruits (10–50 mm) are again found inshore. Fish grow from 10–40 to 70–150 mm during the first year of life in the shallows of the bay, before moving offshore. They cross the deeper waters of the bay as they migrate towards the open ocean. Juveniles (TL 70–150 mm) are most abundant in the inner bay, and subadults (TL 150–200 mm) in the outer and central bay. M. furnieri use semi-closed coastal areas as nursery grounds, before moving out over the continental shelf, where they spawn.