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991.
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Spatial distribution of surgeonfish and parrotfish in the north sector of the Mesoamerican Barrier Reef System
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Roberto C. Hernández‐Landa Gilberto Acosta‐González Enrique Núñez‐Lara Jesús E Arias‐González 《Marine Ecology》2015,36(3):432-446
Surgeonfish and parrotfish play an important role in structuring the benthic communities of coral reefs. However, despite their importance, little is known about their distribution patterns in the north sector of the Mesoamerican Reef System. This study evaluated the distribution of these fish in 34 sites in four habitats (lagoon, front, slopes and terrace) along a depth gradient (c 0.5–20 m). These herbivorous fish were assessed by visual censuses. Species dominance was evaluated for each habitat using SIMPER analysis. Habitat characteristics data were collected to determine the relationship between habitat conditions and spatial variations in herbivorous fish (using abundance and biomass as a proxy) via redundancy analysis. The herbivorous fish assemblage had a low density (fish per 100 m2) and biomass (g·100 m?2) in comparison with assemblages in similar studies. In contrast, species richness was high compared with other studies in the Caribbean. Spatial variation of the abundance, biomass and size of herbivorous fish was strongly related to coral and seagrass cover, as well as to depth and rugosity. These four variables were critical in controlling the distribution patterns of the herbivorous fish assemblages. No associations were found between fish and macroalgae or any other benthic group. The present study indicates that the species richness of surgeonfish and parrotfish was not regionally affected by the dominance of macroalgae in the habitats studied. Seagrass beds and the coral reef matrix need to be preserved for the herbivorous fish assemblages to remain healthy and capable of controlling excess macroalgae growth. 相似文献
994.
The influence of environmental variability of a coastal lagoon ecosystem on genetic diversity and structure of white seabream [Diplodus sargus (Linnaeus 1758)] populations
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Raquel Hernández‐García Irene Muñoz Antonio López‐Capel Concepción Marcos Ángel Pérez‐Ruzafa 《Marine Ecology》2015,36(4):1144-1154
As coastal lagoons serve as nursery areas for some marine and estuarine fish, selective pressures of these brackish or hypersaline lagoons may influence the genetic structure of species and populations. We examined spatial and temporal genetic patterns at eight microsatellite loci in white seabream [Diplodus sargus (Linnaeus 1758)] recruits from the Mar Menor (Southeast Spain) and compared these loci with those in coastal populations from the open sea, observing a high degree of genetic diversity and spatio‐temporal genetic stability. However, the results suggest the presence of subpopulations or genetic substructures in the Mar Menor D. sargus population that could be interpreted as a homogeneous mixture of individuals from three differentiated subpopulations in the Mediterranean and evidence of the Wahlund effect. It also suggests that D. sargus adults return to their original spawning habitat, thus conserving the genetic differences among the respective populations over time. Overall, this study demonstrates the importance of the Mar Menor coastal lagoon as a nursery area for the conservation of genetic diversity of D. sargus populations. 相似文献
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D. Pérez-Ramírez J. R. Sánchez-Sutil A. Muñoz-Arjonilla J. Martí J. L. Garrido P. Luque-Escamilla 《Astrophysics and Space Science》2007,309(1-4):147-150
Ultraluminous X-ray sources (ULXs) are the most luminous discrete X-ray sources (excluding AGNs) in the local Universe with observed luminosities above, and in many cases in excess of, 1039 erg?s?1. Their physical nature is still uncertain, and many models have been proposed to explain their unusual luminosities. Some of them favour the possible nature of these objects as extragalactic microquasars with strong beaming effects. Others, instead, rely on accretion onto intermediate-mass black holes. In any case, both interpretations offer perspectives for possible gamma-ray detections by future space missions. In order to help to constrain at present the ULX physical nature, we provide here an account of our search for radio counterparts to ULXs located in nearby galaxies, based on a systematic cross-identification of the most recent, available and extensive ULX catalogues and radio archival data. Although we ended up with 70 positional coincidences, most of them were located within the nuclear regions of these galaxies, and thus, they do not represent true ULXs. However, among these sources we identify 11 remarkable cases not previously reported of ULX and radio emission coincidence. Future follow up of these promising cases with a multi-wavelength approach could be useful to improve our understanding of the ULX phenomenon. 相似文献
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J.A. Segovia-Zavala M.L. Lares F. Delgadillo-Hinojosa A. Tovar-Sánchez S.A. Sañudo-Wilhelmy 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):53-64
We report dissolved iron (Fed) concentrations measured in the upper 600 m in the central region of the Gulf of California (GC) under spring conditions. Our results showed the complex nature of Fe cycling within the GC. In the northern region of the study area, surface waters were relatively enriched, with Fed concentrations >5.0 nM, which can be partially explained by an atmospheric source. These concentrations are 12 times higher than those found in the adjacent Pacific Ocean. In contrast, Fed depth profiles in the southern region did not show any Fed surface enrichment (concentrations <1.5 nM) because of particle scavenging and higher stratification of the water-column. The most southern station in our area of study was the most stratified and showed an excess Fed and PO4 with respect to NO3, conditions favorable for nitrogen fixation. This station also showed the least negative surface value of N* of all stations. However, despite the adequate levels of Fed and PO4 at that location, the surface temperature (22.6 °C) was probably not high enough for diazotrophs to develop. A slight increase in Fed levels in intermediate waters at the southern region was associated with the oxygen minimum zone. Finally, our results suggest that remineralization of organic matter is probably the major source of Fed in subsurface waters of the GC. 相似文献
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Earth, Moon, and Planets - 相似文献