Community differentiation of bacterioplankton in the epipelagic layer in the South China Sea

The South China Sea (SCS) is the largest marginal sea in the western tropical Pacific Ocean and is characterized by complex physicochemical environments. To date, the biogeographic patterns of the microbial communities have rarely been reported at a basin scale in the SCS. In this study, the bacterial assemblages inhabiting the epipelagic zone across 110°E to 119°E along 14°N latitude were uncovered. The vertical stratification of both bacterial taxa and their potential functions were revealed. These results suggest that the water depth-specific environment is a driver of the vertical bacterioplankton distribution. Moreover, the bacterial communities were different between the eastern stations and the western stations, where the environmental conditions were distinct. However, the mesoscale eddy did not show an obvious effect on the bacterial community due to the large distance between the sampling site and the center of the eddy. In addition to the water depth and longitudinal location of the samples, the heterogeneity of the phosphate and salinity concentrations also significantly contributed to the variance in the epipelagic bacterial community in the SCS. To the best of our knowledge, this study is the first to report that the variability in epipelagic bacterioplankton is driven by the physicochemical environment at the basin scale in the SCS. Our results emphasize that the ecological significance of bacterioplankton can be better understood by considering the relationship between the biogeographic distribution of bacteria and the oceanic dynamics processes.

Distribution of Holtodrilus truncatus, a Branchiobdellidan Ectosymbiotic on Atyid Shrimps in the Kii Peninsula, Western Japan, with Reference to Salinity Tolerance and Host Preference

The distribution of the branchiobdellidan Holtodrilus truncatus (Liang, 1963), which is symbiotic on atyid shrimps, was surveyed in 26 river catchments, covering almost all of the Kii Peninsula, western Japan. Holtodrilus truncatus has been recorded in 10 rivers located from the southwest to northeast regions of the peninsula. Paratya compressa was the dominant host species in all rivers, with a lower prevalence on Caridina leucosticta, C. multidentata, C. typus, and Neocaridina denticulata. The longitudinal distribution of H. truncatus was limited to the middle and upper reaches, while its main host P. compressa occurred widely from the lower to the upper reaches. The numbers of H. truncatus and their cocoons per host increased in summer and decreased in winter, in accordance with the abundance of the host P. compressa. The body size of P. compressa was larger in individuals with H. truncatus than those without H. truncatus in some rivers, while in another river, sizes of the two groups were not different. A salinity tolerance experiment revealed that the threshold of salinity tolerance of H. truncatus occurred between 0-0.5%. A choice experiment between two host species showed that H. truncatus preferred C. leucosticta to C. multidentata, P. compressa to C. multidentata, and P. compressa to C. leucosticta.

Emergence patterns and ecological associations of some haematophagous blackfly species along an oligotrophic hydrosystem

Emergence patterns of blackflies (Diptera: Simuliidae) were investigated for 2 years at nine sites in the Plitvice Lakes area of Croatia, using pyramid-type traps. A total of 38 012 specimens representing 10 haematophagous species were collected. The dominant species was Simulium angustipes Edwards, 1915, a vector transmitting avian trypanosomes. Water temperature, alkalinity, conductivity and habitat type represented the factors with the greatest degree of influence on blackfly species composition, structure and distribution along a longitudinal gradient of this oligotrophic karstic hydrosystem. Simulium angustipes was highly associated with lake outlets. The blackfly communities at all sites were dominated by species typical of the rhithral zone, but there was a shift in species composition along a longitudinal gradient from the hypocrenal-epirhithral to the epirhithral-metarhithral zone. Multiple generations per year were detected in S. angustipes, whereas in Simulium costatum Friederichs, 1920, the number of generations differed between sites with constant and those with variable water temperature.