SOME ASPECTS OF THE POPULATION ECOLOGY OF THE EXOTIC AMPHIPOD, TALITROIDES TOPITOTUM, IN AN ATLANTIC FOREST RESERVE IN BRAZIL

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SEASONAL AND SPATIAL-DISTRIBUTION OF KALLIAPSEUDES-SCHUBARTI MANE-GARZON, (TANAIDACEA, CRUSTACEA) IN THE ARACA REGION, SAO-SEBASTIAO (SP)

Information on the seasonal density and spatial contribution of Kalliapseudes schubarti Mane-Garzon. 1949, common tanaidacean along southeastern mud-flats and estuaries of Brazil, was obtained by a mensal sampling of 0,05m(2) of sediment in the Araca region, Sao Sebastiao (SP), along 14 stations. High densities of K.schubarti were obtained throughout the year in sts. 3 to 8, specially in the spring. At these sites very fine sand occurred, with high organic matter due to the contribution of some mangrove vegetation and rocky coast vicinity. The carbonate was specially conspicuous in sts. 1 and 2 because of the introduction of shell fragments carried from Pernambuco Island. However in sts. 9 to 14 a compact, well sorted, very fine sand was obtained with a few interstitial water during low tide, where occasional occurrence and low density of K. schubarti was verified. There is indication that this tanaidacean has a preference for fine sediment with high organic matter and is adapted to a wide range of salinity and temperature.38260561

Shell-size selection by intertidal sympatric hermit crabs

This study evaluated selection for shell size by three species of tropical intertidal hermit crabs, Clibanarius antillensis,C. sclopetarius, and C. vittatus, from species of shells which are frequently used in nature. Crab size and weight were strongly and significantly related to all measured parameters of the selected shells. The strength of these relationships (r(2) values) depended neither on the crab nor on the shell variables taken into account. The relationships between crab size and the dimensions of the selected shells showed higher r(2) values than the corresponding relationships with the shells that the crabs had occupied when they were collected (0.482-0.903 in comparison to 0.091-0.652, respectively), indicating that the crabs were occupying sub-optimal shells in nature. Negative allometry was frequently found in the relationships between crab and shell variables, indicating that large crabs select and use proportionally lighter shells than do small crabs. This negative allometry was stronger for the shells used in nature (except for C. antillensis), i.e. larger crabs tended to select heavier shells in the laboratory than in nature. Different allometric relationships were also recorded among the dimensions of shells used in nature and those selected by the hermit crabs in free-access experiments: as shell length increased, the selected shells were heavier and had larger apertures than the shells used in nature. The relationships between crab size and the length and weight of the selected shells did not depend on the species of crab or species of shell, but only on crab size. Therefore, analyses using these variables can be performed without taking the species of crab or shell into account, i.e. data from different crab or shell species can be pooled. The influence of crab and/or shell species was recorded only in the models fitted for aperture length and width, variables which were more related to shell architecture than did shell length or weight. In contrast, if crab weight is used as an independent variable, different crab or shell species can be analyzed together independently of the particular shell parameter. This indicates that crab weight may be less susceptible than crab shield length to shell morphological constraints. Finally, the results indicate that the preferred size of a given shell type chosen by a given hermit crab will depend more on crab size or weight, than on the crab or shell species under consideration, i.e. crab shell-size relationships are not species specific.145225125

Population structure and fecundity of the hermit crab Clibanarius antillensis Stimpson 1862 (Anomura, Diogenidae) in southeastern Brazil

The population structure and fecundity of Clibanarius antillensis at the rocky shore of Praia Grande, Sao Sebastiao, Sao Paulo State, southeastern Brazil, was studied. Sexual dimorphism was verified, with males reaching larger sizes than females. Population sex ratio was skewed for females, which predominated in the smallest size classes, while males predominated in the largest ones. Size frequency distribution revealed a bimodal pattern correlated with seasonal differences in crab size. Reproductive season was continuous, with a peak of reproductive activity from November to March. Fecundity was positively correlated with crabs shield length and larger broods were found to be produced in relatively heavier (larger) shells. Thus, shells influenced both crab and consequently, brood size, probably by regulating individual growth and reproductive activity of females.64228128

Population biology of ampitholdae species (Crustacea,Amphipoda) associated with Sargassum filipendula (Phaeophyta, Fucales), at Fortaleza beach, Ubatuba, Sao Paulo, Brazil

The population biology of three species of the family Ampithoidae (Ampithoe ramondi, Cymadusa filosa e Sunampithoe pelagica) associated with Sargassum filipendula at Fortaleza beach, northern coast of Sao Paulo state was investigated from June 2000 to May 2001. The amphipods were identified, counted and separated in size classes through a nested sieve-set. Month hystograms were obtained for juveniles, males and females. The ampithoid sex ratio was determined monthly The reproductive biology of the species was evaluated by the relative frequency of ovigerous females, fecundity, average egg volume and correlation analysis between head lengh of ovigerous females and number of eggs in its brood pouch. Ampithoe ramondi was the most abundant species. The higher densities of the three species occurred in spring and summer. The sex ratio presented a significant difference from 1:1 only for A ramondi (1:1.2; X-2 = 4.37; g.l. = 1; p < 0.05). Ovigerous females were registered for almost all the sampling periods. A positive correlation between the female head lengh and the number of eggs were only registered for A ramondi (r(2) = 0.27; p < 0.05; n = 33). Cymadusa filosa showed the greatest fecundity and egg volume.2341207121

Spatial scaling in the distribution of macrofauna associated with Sargassum stenophyllum (Mertens) Martius: analyses of faunal groups, gammarid life habits, and assemblage structure

Benthic communities can vary greatly at a range of temporal and spatial scales, due to different ecological processes that operate at each scale. Characteristics of the natural history of the organisms, Such as mobility and behavior, can influence their distribution, mainly at smaller scales. In this study, the spatial distribution of the macrofauna associated with Sargassum stenophyllum in SE Brazil was documented using a hierarchical sampling design, repeated four times throughout I year. We found differences in the density of the main macrofaunal groups at spatial scales ranging from meters to kilometers, sometimes with greater differences at smaller scales than between shores. We then analysed whether life habits influenced the distribution of gammarid amphipods, the dominant. Group. The distribution of tube-building amphipods was generally more patchy than that of free-living animals, although some variation among species was found within each category. Multivariate analyses indicated distinct gammarid assemblages a few meters distance from each other. Similarity among assemblages was reduced when comparing more distant assemblages, whereas faunal density influenced similarity in one of the four sampling dates. Factors that may influence the small-scale patchiness found in phytal communities include differences in physical conditions created by the spatial distribution of the substrate, habitat complexity as a result of epiphyte colonization, and aggregations caused by colonization of algal patches by organisms with direct development. Differences in reproductive and dispersal strategies of the animals can influence small-scale distribution of these assemblages, suggesting that effective descriptions of phylal communities should include more than one spatial scale. (C) 2003 Elsevier B.V. All rights reserved.293112

The effect of sieve mesh size on the abundance and composition of macrophyte-associated macrofaunal assemblages

Sampling efficiency of several sieve mesh sizes (2, 1, 0.5, 0.2 and 0.1 mm) was tested in invertebrate assemblages associated to Sargassum stenophyllum. Samples of this brown algae were collected in southeastern Brazil to determine whether different sampling devices resulted in differences on the abundance and composition of the macrofauna. The 1 and 2 mm mesh sizes sampled less organisms, resulting in smaller abundances, densities, number of species and diversity, when compared to the other three mesh sizes, that achieved similar results. The most efficient sieve was the 0.5 mm mesh, sampling 85.8% and 94.5% of gammaridean and caprellidean amphipods, respectively, and 93.1% of gastropods. However, polychaetes and isopods were best sampled with the 0.2 mm sieve. Our results suggest that caution should be exercised when deciding on which sieve to use, as mesh sizes commonly used in benthic studies (1 and 0.5 mm) may result in very different estimates of diversity and abundance, as well as community structure patterns.38941699212

The molding hypothesis: linking shell use with hermit crab growth, morphology, and shell-species selection

The 'molding hypothesis' (Elwood et al. 1979. Anim Behav 27:940-946) predicts that shell-species selection by hermit crabs may be influenced by past experience in shell use through shell-imposed alterations in crab morphology. The present study was designed to test this hypothesis and to further the understanding of plasticity in the shell-species selection in hermit crabs. Shell use was demonstrated to influence crab growth and morphology. Individuals reared in shells of Tegula viridula attained larger sizes than individuals in shells of Morula nodulosa. Crab growth was also dependent on crab sex, since males reached larger sizes and presented longer intermolt periods than females. The most conspicuous influence of shell utilization on crab morphology was in dorso-ventral flattening, which occurred on a decreasing scale with the shell species, as follows: M nodulosa > Cerithium atratum > T. viridula. Crabs from all treatments and those collected in nature in shells of Olivella minuta chose mainly shells of C atratum, but the previous experience of crabs strongly influenced their shell-species selection pattern. Individuals maintained in M. nodulosa shells selected M nodulosa shells more frequently than individuals reared in T viridula or C. atratum. The influence of past experience was demonstrated to depend on shell type, since patterns of shell-species selection of individuals reared in T viridula or C. atratum were identical. These differences in the shell-species selection pattern directly reflected the differences in crab dorso-ventral flattening, i.e. dorso-ventrally compressed individuals (those in shells of M. nodulosa or O. minuta) showed a higher probability of selecting narrow-aperture shells than did 'rounded' individuals (those in shells of T viridula or C. atratum). The weight of the selected shells at the end of the experiment depended on crab size instead of previous experience with different shell architectures.o TEXTO COMPLETO DESTE ARTIGO, ESTARÁ DISPONÍVEL À PARTIR DE AGOSTO DE 2015.26515516