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701.
砂质海滩是最变化莫测和脆弱的海岸带类型之一。众所周知,海滩在高能环境中会被侵蚀,但海滩上不同位置点对于极端事件的抵御能力则大不相同。而且,侵蚀速率通常受控于海滩状况、机械结构和前期补给。 相似文献
702.
The introduction of exotic marine species has caused considerable economic and ecological damage around the world. Some of these species possess adaptations such as secondary metabolites which facilitate their successful invasion into new areas. In this study we tested two hypotheses: (i) crude extracts produced by two invasive hard corals Tubastraea coccinea and Tubastraea tagusensis, introduced to the southwest Atlantic, inhibit predation by generalist fish; (ii) substances found in the crude extracts of both species reduce or enhance the settlement of other organisms. In an in situ palatability bioassay the extract of T. tagusensis reduced predation by generalist fish. The extracts of both species of coral showed species‐specific effects on fouling organisms in in situ gel plate bioassays. Control and extract plates had similar total cover, although plates with extracts had significantly fewer Cladophora sp., and Lithophyllum sp. was only detected on control gels. In contrast, a hydrozoan was only found on plates with extracts and overall community ordination demonstrated clear differences in the fouling communities between treatments. These results demonstrate that both coral species have chemical substances which can bring about a negative interaction with potential fish predators and competitors such as algal and invertebrate foulers and the advantage gained could explain their success in invading new regions to the detriment of local fauna and flora. 相似文献
703.
Aurélia Mouret Pierre Anschutz Pascal Lecroart Gwénaëlle Chaillou Christelle Hyacinthe Jonathan Deborde Frans J. Jorissen Bruno Deflandre Sabine Schmidt Jean-Marie Jouanneau 《Geo-Marine Letters》2009,29(3):133-149
Manganese is a major redox reactive element of benthic metabolism. We have built a database of existing knowledge on the benthic
geochemistry of Mn in the Bay of Biscay, in order to comprehensively assess the behaviour of Mn in a variety of environments
during early diagenesis. The database contains vertical profiles of particulate and dissolved Mn species of 59 cores collected
during 17 cruises between 1997 and 2006 at nine stations positioned between 140 and 4,800 m water depths. At all studied stations,
Mn species follow the conventional distribution, where Mn(III,IV) species are enriched in the oxic layer, and dissolved Mn
is present in the anoxic sediments. A minor part of Mn-oxides originates from sedimenting particles. The major part is of
diagenetic origin, and derives from the oxidation of upward-diffusing dissolved Mn(II). Mn-oxide inventories are higher at
the deeper stations than at the shallower ones. This difference cannot be attributed to different sources of sedimenting particles,
but it must depend on sedimentation rate and diagenetic processes. At depth, dissolved Mn(II) concentrations are constant.
This probably reflects equilibrium with an authigenic Mn(II) phase, which is the ultimate phase into which Mn is fossilized.
The Mn content of deeper anoxic sediments is similarly low in all the cores studied, associated with corresponding trends
of Mn content in sedimenting particles of the Bay of Biscay. Bioturbation, rather than redox oscillations, can convey Mn(III,IV)
species downwards into the anoxic sediments where they are reduced, associated with a peak of dissolved Mn. Because dissolved
Mn(II) is re-oxidized when it diffuses towards the oxic layer, the inventory of the diagenetic Mn(III,IV) phase remains at
steady state, especially at stations where the oxic layer is thick. It then becomes possible to calculate the residence time
of diagenetic Mn(III,IV) particles within the oxic layer, using the upward-directed flux of pore water Mn(II). By applying
this residence time to the accumulation of sediments within the oxic layer, we obtain the sediment mass accumulation rate.
The values calculated for the sediments of the Bay of Biscay fit well with accumulation rates obtained from radionuclides
or sediment traps. The method has also been validated with data collected in other marine sedimentary environments.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献