Fosca Pedini Pereira Leite

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 1 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 phytal communities should include more than one spatial scale.

Population biology and growth of three sympatric species of intertidal hermit crabs in south-eastern Brazil

Hermit crab populations have been described in different habitats and latitudes but few studies focused on coexisting populations. Such information is especially important to evaluate the effect of coexistence in the population biology of such organisms. This study was done in the intertidal region of Pernambuco Islet, Sao Sebastiao Channel, south-eastern Brazil. Random samples of crabs were taken monthly during one year to evaluate their size and sex. The three coexisting Clibanarius populations ( C. antillensis , C. sclopetarius , and C. vittatus ) showed similar patterns of sex ratio (skewed for females), sexual dimorphism (males larger than females), recruitment (February to June) and population growth but differed in size structure ( Cs > Cv > Ca ) and reproductive activity over the year. Population growth was estimated using the von Bertalanffy growth function (VBGF) and revealed that the growth of these three populations was strongly reduced from August to January and that longevity varied from 42 to 48 months. Clibanarius antillensis showed continuous reproduction with high frequency of ovigerous females over the year while C. sclopetarius and C. vittatus had a reproductive peak in April and absence of ovigerous females in August/September. Coexistence seemed to influence population biology of these hermit crabs, given the relationship of their reproductive periods and growth patterns to the shell adequacy to the crabs. The overlap in reproductive peaks and recruitment periods may strengthen competition for shells. Comparisons of the reproductive patterns of the hermit crab populations recorded to date emphasize that reproduction and, consequently, life strategies of hermit crabs are not directly dependent on taxonomic or geographical proximity, but on their evolutionary histories and on local processes acting on each assemblage or population.

Gammaridean and caprellidean fauna from Brazil

This review of Brazilian Amphipod works is arranged in a chronological list and points out the significant works for each one of the four arbitrary periods. Besides that, this paper deals with the distribution of 83 species of Brazilian Gammaridea and Caprellidea in relation to bathymetry, substrate, latitude and thermal region.

Shell utilization patterns of a tropical intertidal hermit crab assemblage

The shell selection and utilization patterns of three sympatric hermit crab populations (Clibanarius antillensis, C. sclopetarius, and C. vittatus) and shell availability were studied in a tropical intertidal low energy area. Shell availability (except for C. antillensis) was low and the hermit crabs showed overlap in size (mainly C. sclopetarius and C. vittatus). The influence of shell availability and selection on shell use was dependent on crab species. Clibanarius antillensis used mainly shells of Cerithium atratum, the most available shell species, while Clibanarius sclopetarius and C. vittatus occupied shells with lower availability in the studied area such as Chicoreus senegalensis, Stramonita haemastoma, Leucozonia nassa and Cymatium parthenopeum. The three species selected different gastropod shells with only Clibanarius antillensis using almost exclusively its preferred shell species in nature. The relationship between shield length and the weight of the used shell was not dependent on crab species or shell species, indicating that the size (not species) of the shells defines what size (not species) of crabs will occupy them.

Temporal variation in Sargassum Biomass, Hypnea epiphytism and associated fauna

Studies were carried out to investigate the temporal variation in Sargassum biomass, Hypnea epiphytism and associated fauna. There was a marked variation in the biomass of Sargassum and Hypnea among various sampling periods. Low values for Sargassum were recorded in August and November, while the lower value for Hypnea biomass was recorded in August. An inverse relationship was found between Sargassum biomass and the intensity of Hypnea epiphytism. The density of the total fauna associated to Sargassum showed a marked reduction in May. This variation was influenced by the variation patterns of the dominant faunistic groups (Gastropoda, Gammaridea, Isopoda and Caridea). Significant positive relationships were found between the biomass of Sargassum and Sargassum+Hypnea with the total density of all faunistic groups (per macroalgae biomass unit). However, the influence of Hypnea epiphytism on the phytal organisms was not evidenced.

Population biology and distribution of the tanaid Kalliapseudes schubarti Mañé-Garzon, 1949, in an intertidal flat in southeastern Brazil.

The population biology and the spatial and temporal distribution of Kalliapseudes schubarti Mañé-Garzon, 1949, a common tanaidacean in mud flats and estuaries in southern and southeastern Brazil, was studied in the Araçá region, São Sebastião (SP), Brazil. This species showed a clustered dispersion in the area and the individuals were concentrated in the superficial sediment layer (5 cm). Higher densities of K. schubarti were recorded in areas characterized by moderately sorted fine sediment. Multiple regression analysis revealed a positive influence of the organic matter contents and a negative effect of the silt-clay contents on the abundance of K. schubarti. This species showed a marked temporal variation with very low abundance in winter and fall (March to August). Sexual dimorphism was evidenced with males being larger than females. Ovigerous females were also larger than pre-ovigerous ones. Sex ratio was skewed towards females. Seven cohorts were identified during the sampling period, the estimated longevity was 12 months, and no seasonal oscillation in growth was evidenced. The continuous reproduction, as evidenced by the presence of larval phases (manca II and neutron) and reproductive females throughout the year, and high fecundity among the tanaids associated with fast growth and limited longevity support the case for the opportunistic life strategy suggested for this species in the literature.

Hermit crabs (Crustacea: Decapoda: Anomura), gastropod shells and environmental structure: their relationship in southeastern Brazil

Species composition and the pattern of shell utilization by hermit crabs were studied in five areas of Sao Sebastiao Channel. Habitat characteristics were evaluated and related to the presence and relative abundance of crabs. Nine species of hermit crab were found: Clibanarius antillensis, Clibanarius vittatus, Clibanarius sclopetarius, Calcinus tibicen, Paguristes tortugae, Paguristes erythrops, Petrochirus diogenes, Pagurus criniticornis and Pagurus brevidactylus. Habitat complexity, moisture, rocky shore slope and hydrodynamism were the major characteristics influencing hermit crab presence, relative abundance and distribution in these areas. Shell utilization and availability varied among sites and shell utilization seemed to be dependent on differences in local shell supply (size and abundance of living snails) and preferences of the hermit crabs for certain shell types.

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.

Temporal variation of amphipod assemblages associated with Sargassum filipendula (Phaeophyta) and its epiphytes in a subtropical shore

The phytal assemblages change in response to variation in biological and environmental conditions. In the present study, we evaluated the temporal variation of amphipod assemblages associated with a Sargassum filipendula bed in a subtropical shore, in relation to variation of the host alga, its epiphytes and local environmental conditions. Samples of S. filipendula with associated amphipods, water temperature, water movement and suspended solids were obtained monthly from June 2000 to May 2001. We recorded 24 species of amphipods associated with S. filipendula. Species richness varied throughout the year, with maximum values in October 2000 and minimum in April 2001. Total amphipod density gradually increased during the sampling period, with the highest value in March 2001. Amphipod diversity and evenness were both positively influenced by epiphyte load and negatively by temperature, with higher values during summer months. Total density and tube-builder density were also positively influenced by temperature, whereas nestler density was influenced by epiphyte load. Individual amphipod species showed significant density fluctuations over the year. The canonical correspondence analysis performed explained 88.2% of the variation, with a strong correlation of water movement, temperature and suspended solids with the first axis, and a strong effect of epiphyte load on both the first and the second axes. The temporal structural variation of the studied algal bed strongly influenced amphipod diversity and assemblage composition, possibly through direct and indirect effects.

Distribuição vertical e flutuação sazonal da macrofauna vágil associada a Sargassum cymosum C. Agardh, na praia do Lázaro, Ubatuba, São Paulo, Brasil

Seasonal fluctuations and depth distribution of the vagile macrofauna associated with Sargassum cymosum at Lazaro beach, Ubatuba, Sao Paulo State, were evaluated through density comparison of higher taxonomic groups among three depth intervals in four periods of the year. Ten groups were identified and among them gammarid and caprellid amphipods were numerically dominant in all sampling periods and did not show any consistent zonation trend. Gastropods, polychaetes and ophiuroids ocurred in lower densities and tended to dominate as depth increased, Wet weight algae variation did not explain the observed spatial and temporal patterns. Biotic interactions, recruitment and environmental parameters are probably involved in seasonal density variation of the faunal groups studied but it was evident that the depth gradient play an important role in vagile macrofauna vertical distribution.