11 research outputs found
Influence of the tidal and rainfall cycles on the population structure and density of Mesacanthion hirsutum gerlach (nematoda, thoracostomopsidae) on a tropical sandy beach (Tamandaré Bay, Pernambuco, Brazil)
The population structure (males, females and juveniles) and density of Mesacanthion hirsutum Gerlach were studied during the tides (low, flood, high and ebb) of two consecutive tidal cycles in four different months of the year (May, July, September and November). Mesacanthion hirsutum density variations showed association with the rainfall cycle, with lower densities during July and September and significantly higher values in May and November. The population structure was constituted mostly by juveniles indicating a continuous reproduction during all the studied period. There were no significant differences between light and dark periods of the day, however, the higher densities detected during the high and ebb tidal stages demonstrate that this species could be dispersing through the water column and/or migrating within the sediment.<br>A estrutura populacional (machos, fêmeas e juvenis) e densidade de Mesacanthion hirsutum Gerlach foram estudadas durante as marés (baixa, enchente, alta e vazante) de dois ciclos de maré consecutivos, em quatro meses diferentes do ano (Maio, Julho, Setembro e Novembro). As variações de densidade de Mesacanthion hirsutum mostraram associação com o ciclo de chuvas, com densidades mais baixas durante Julho e Setembro e significativamente maiores em Maio e Novembro. A estrutura populacional constituiu-se em sua maior parte por juvenis indicando uma reprodução continua durante todo o perÃodo de estudo. Não foram encontradas diferenças significativas entre os perÃodos claros e escuros do dia, contudo maiores densidades foram detectadas durante as marés altas e vazantes demonstrando que a espécie pode estar se dispersando através da coluna d'água e/ou migrando dentro do sedimento
Species richness of the genus Molgolaimus (Nematoda) from local- to ocean-scale along continental slopes
This study investigated the distribution of Molgolaimus species (Nematoda) at different hierarchical spatial scales and observed the turnover of species along bathymetrical transects and among transects in two separate geographical regions. Samples from six transects (200-2000 m) from the Southern Oceans (SO) and four bathymetric transects (50-2000 m) from the Western Indian Ocean (WIO) were compared. Of the 30 species recorded, only one was common to both regions. WIO had higher local species richness than the SO. In both regions, the local scale was the greatest contributor to the total species richness. In the SO, there was no difference between species turnover at the different spatial scales, however, in the WIO, the turnover along bathymetrical transects was higher than among separated transects. For the particular genus studied, the evidence suggests that the study area in WIO has more widespread species and was better sampled, while the SO has many restricted species and it is most probably characterized by different biogeographical provinces. At the ocean scale (i.e. WIO versus SO), evolutionary histories may have strongly influenced nematodes species composition, while at local and regional scales, ecological processes are probably promoting species co-existence and speciation. The high co-existence of certain species at local scale is partially explained by species preference for different sediment layers
Stress-induced selection of a single species from an entire meiobenthic nematode assemblage: is this possible using iron enrichment and does pre-exposure affect the ease of the process?
The present work proposes a new experimental
design using iron enrichment to select a single species from
an entire meiobenthic nematode community. The high diversity
of nematodes makes it impossible to study their responses
to stressors in terms of chemical biomarkers, as this kind of
research demands a single species as a form of biological
material. Two assemblages, one from a control site (Canal)
and one from an iron-contaminated site (Fouledh) in Bizerte
Lagoon (Tunisia), were used to validate the protocol and to
study whether pre-exposure to iron could affect the ease of the
selection process. Analyses of variance suggested that the
abundance and species number of nematodes from the Canal
and Fouledh sites decreased discernibly with exposure to iron.
Multivariate analyses performed on nematode abundances
revealed that Oncholaimus campylocercoides, Sabatieria
granifer, Sabatieria punctata and Theristus flevensis were
the most tolerant species, probably due to their depositfeeding
behaviour. Species with a restricted feeding spectrum
showed a low tolerance potential. At the end of the experiment,
O. campylocercoides became the unique component of
the nematode community from both sites. The complete alteration
of the community was achieved with more difficulty for
nematodes from Fouledh than for those from Canal. The
identity of the selected species was confirmed at both the
morphological levels and by sequencing the nuclear small
subunit ribosomal DNA (18S rDNA)