排序方式： 共有15条查询结果，搜索用时 15 毫秒
11.
Influence of habitat and host morphology on macrofaunal assemblages associated with the sponge Halichondria melanadocia in an estuarine system of the southern Gulf of Mexico 
下载免费PDF全文
下载免费PDF全文 Sponges are inhabited by a wide variety of organisms and have been regarded as one of the richest biotopes in tropical seas. The aim of this study was to assess the influence of the host morphology and selected environmental conditions on macrofaunal assemblages associated with the sponge Halichondria melanadocia in an estuarine system of the southern Gulf of Mexico. This sponge exhibits different growth forms when it inhabits mangrove prop roots of Rhizophora mangle (thickly encrusting form) and adjacent seagrass beds (massive, amorphous or ramose form). From a total of 50 sponge specimens collected in each habitat, a total of eight taxa (of epi‐ and endobionts) was found associated with this sponge, with polychaetes, echinoderms and crustaceans the most abundant groups. In both morphotypes (thickly‐encrusting and massive‐ramose forms), taxon richness was positively related to sponge volume and oscular diameter. The overall mean abundance of associated fauna was also positively related to sponge volume in both morphotypes and with the oscular diameter (in the seagrass morphotype only). These findings suggest that H. melanadocia constitutes an important microhabitat for a wide variety of fauna, independent of its morphology and habitat type. However, when comparing the two morphotypes, the mangrove individuals, despite having smaller sizes, smaller oscular diameter and less structural complexity, displayed an overall mean abundance of fauna 17 times higher [0.36 ± 0.18 individuals (ind.)·ml·sponge?1] than that recorded in the seagrass individuals (0.021 ± 0.01 ind.·ml·sponge?1). There were also marked differences in the proportions of the major taxonomic groups; in fact, some of them were found exclusively in one morphotype. The variability recorded in the composition and abundance of associated fauna between the morphotypes seems to be influenced by differences in sponge morphology, environmental conditions (e.g. sedimentation rate and light intensity), substrate orientation and the fauna inhabiting the surrounding area. 相似文献
12.
There has evolved, as of late, a strong interest in decentralized modes of governance over fisheries and other marine resources, particularly that of community-based resource management (CBRM). However, analysis of this institutional model is hindered by simplistic, typological depictions of CBRM. We use organizational theory to argue how, within the broad category of CBRM, there exists a rich variation of institutional forms. We illustrate the analysis by showing how two ostensibly similar fishers’ organizations in Batangas, Philippines, differ in important ways and, furthermore, how these differences respond to particular challenges and opportunities found in their respective contexts. We also discuss implications of this research for program evaluation. 相似文献
13.
Filipe Galiforni Silva Kathelijne M. Wijnberg Alma V. de Groot Suzanne J. M. H. Hulscher 《Ocean Dynamics》2018,68(7):885-897
A cellular automata model is used to analyze the effects of groundwater levels and sediment supply on aeolian dune development occurring on sand flats close to inlets. The model considers, in a schematized and probabilistic way, aeolian transport processes, groundwater influence, vegetation development, and combined effects of waves and tides that can both erode and accrete the sand flat. Next to three idealized cases, a sand flat adjoining the barrier island of Texel, the Netherlands, was chosen as a case study. Elevation data from 18 annual LIDAR surveys was used to characterize sand flat and dune development. Additionally, a field survey was carried out to map the spatial variation in capillary fringe depth across the sand flat. Results show that for high groundwater situations, sediment supply became limited inducing formation of Coppice-like dunes, even though aeolian losses were regularly replenished by marine import during sand flat flooding. Long dune rows developed for high sediment supply scenarios which occurred for deep groundwater levels. Furthermore, a threshold depth appears to exist at which the groundwater level starts to affect dune development on the inlet sand flat. The threshold can vary spatially depending on external conditions such as topography. On sand flats close to inlets, groundwater is capable of introducing spatial variability in dune growth, which is consistent with dune development patterns found on the Texel sand flat. 相似文献
14.
Martín?A.?Montes-Hugo Saúl?Alvarez-BorregoEmail author Alma?D.?Giles-Guzmán 《Estuaries and Coasts》2003,26(5):1302-1309
Attenuation of photosynthetically available radiation (PAR) measured using a light meter, was related to Secchi disk, horizontal
black disk and horizontal sighting ranges observed in a coastal lagoon of the Southern California Current System. Vertical
attenuation coefficient (KPAR) was calculated from radiometric PAR profiles. Vertical (ZD) and horizontal (HS) sighting ranges were measured with white (Secchi depth or ZSD, HS
W
) and black (Z
BD, HS
B
) targets. Empirical power models for the KPAR-ZSD (KPAR=1.47 ZSD
−1.13), KPAR-Z
BD (KPAR=0.98 Z
BD
−1.26), KPAR-HS
W
(KPAR=1.22 HS
W
−1.14) and KPAR-HS
B
(KPAR=0.73 HS
B
−1.07) relationships were developed. The parameters of these models may not apply to other water bodies because their values depend
on the range of water reflectance in each case, as reported in the literature. This is the first contribution reporting KPAR-HS empirical relations in an estuarine environment but their application may be limited to this coastal lagoon. While this
approach may be universal, more data are needed to explore the variability of the parameters between different water bodies. 相似文献
15.
David A. Hodell Mark Brenner Roger Medina-González Alma Albornaz-Pat 《Quaternary Research》2005,63(2):109-121
We studied a 5.1-m sediment core from Aguada X'caamal (20° 36.6′N, 89° 42.9′W), a small sinkhole lake in northwest Yucatan, Mexico. Between 1400 and 1500 A.D., oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2.2‰ and the benthic foraminifer Ammonia beccarii parkinsoniana appeared in the sediment profile, indicating a hydrologic change that included increased lake water salinity. Pollen from a core in nearby Cenote San José Chulchacá showed a decrease in mesic forest taxa during the same period. Oxygen isotopes of shell carbonate in sediment cores from Lakes Chichancanab (19° 53.0′N, 88° 46.0′W) and Salpeten (16° 58.6′N, 89° 40.5′W) to the south also increased in the mid-15th century, but less so than in Aguada X'caamal. Climate change in the 15th century is also supported by historical accounts of cold and famine described in Maya and Aztec chronicles. We conclude that climate became drier on the Yucatan Peninsula in the 15th century A.D. near the onset of the Little Ice Age (LIA). Comparison of results from the Yucatan Peninsula with other circum-Caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the LIA. At that time, sea surface temperatures cooled and aridity in the circum-Caribbean region increased. 相似文献