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SA Mwachireya M Carreiro-Silva BE Hartwick TR McClanahan 《African Journal of Marine Science》2018,40(1):25-42
Microbioerosion rates and microbioeroder community structure were studied in four Kenyan protected coral-reef lagoons using shell fragments of Tridacna giant clams to determine their response to the influence of terrestrial run-off. Fourteen different microbioeroder traces from seven cyanobacteria, three green algae and four fungi species were identified. The river discharge-impacted reef and ‘pristine’ reef showed similar composition but higher microbioeroder abundance and total cyanobacteria- and chlorophyte-bioeroded areas when compared with the other study reefs. Cyanobacteria dominated during the north-east monsoon (NEM) relative to the south-east monsoon (SEM) season, with algae and cyanobacteria being major microbioeroders in the river-impacted and pristine reefs. The rate of microbioerosion varied between 4.3 g CaCO3 m?2 y?1 (SEM) and 134.7 g CaCO3 m?2 y?1 (NEM), and was highest in the river-impacted reef (127.6 g CaCO3 m?2 y?1), which was almost double that in the pristine reef (69.5 g CaCO3 m?2 y?1) and the mangrove-fringed reef (56.2 g CaCO3 m?2 y?1). The microbioerosion rates measured in this study may not be high enough to cause concern with regard to the health and net carbonate production of Kenya’s coral reefs. Nevertheless, predicted increases in the frequency and severity of stresses related to global climate change (e.g. increased sea surface temperature, acidification), as well as interactions with local disturbances and their influence on bioerosion, may be increasingly important in the future. 相似文献
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In deep-sea environments, plant remains of several origins are found, including branches, twigs, leaves, and wood pieces, among others. As most of the deep-sea bottoms are oligotrophic and nutrient-limited, plant remains provide an oasis of localized organic enrichment and a substrate for colonization. Sunken wood was suggested to play an important evolutionary role in the diversification of chemosynthetic ecosystems, possibly representing stepping stones for the colonization between vent and seep ecosystems. In order to understand colonization processes of the Pacific Costa Rican meio-epifaunal assemblages associated with sunken wood, a field experiment was conducted on Mound 12 (8°55.778′N, 84°18.730′W) at ~1,000 m water depth. Woodblocks were placed in four different habitats (Mussel beds, tube worms, near mussel beds, rubble bottoms), and different local environmental conditions (seepage-active and seepage-inactive sites). Seven experimental Douglas fir woodblocks (each 1,047 cm2 in surface area) were deployed from the R/V Atlantis using the manned submersible Alvin in February 2009 and recovered after 10.5 months in January 2010. Sample processing and analyses led to a data set of abundance (total 9,951 individuals) and spatial distribution of nine meio-epifaunal higher taxa/groups. Meio-epifaunal densities on individual woodblocks ranged from 3 to 26 ind.10 cm2. Copepods accounted for the highest abundances (75.1%), followed by nauplii larvae (11.7%) and nematodes (9.8%). The maximum number of individuals (26.3 ind.10 cm−2) was found in blocks placed in seepage-inactive areas (near active mussel beds) in contrast to 2.9 ind.10 cm−2 in active areas (within a mussel bed). A hierarchical cluster analysis grouped blocks according to seepage activity and not to habitat, but tests of similarity showed no significant differences in higher taxon composition and abundances, probably owing either to substrate homogeneity or low sample size. Copepods were the most abundant representatives, suggesting that this group is one of the most successful in colonizing in the early stage of succession, in this case while hardwood substrates are not yet decomposed or bored by bivalves. 相似文献
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During the late Paleozoic, the intracratonic Paraná Basin, Brazil, in central Gondwanaland, was covered by a huge (>1.600.000 km2), shallow and isolated epeiric sea. Within the Permian succession, oxygen-deficient facies are commonly recorded in the Mesosaurus-bearing Irati Formation (Cisuralian, Artinskian/Kungurian) and the overlaying Serra Alta Formation (Guadalupian, Wordian/Capitanian). Barren, dark-grey mudstones are the main facies preserved in this last unit, which has usually discouraged extensive and detailed stratigraphical and paleontological investigations. However, exhaustive sedimentological, taphonomic and paleontological surveys in those deposits reveal a dynamic and complex depositonal history. Based on sedimentary fabric, autochthonous to parautochthonous occurrences of shelly benthic invertebrates (bivalves) and the presence/absence of concretion-bearing and phosphate-rich layers, we report variations in the oxygen levels of bottom and pore waters, in bathymetry, sedimentation rates, and changes in benthic colonization. Our data indicate that the deposition of this “apparently barren” mudstone-dominated succession was driven by a complex interplay of variations in sedimentation rate and oxygen pulses tied to tectonic and climate changes. Three distinct populations or invertebrate paleocommunities were recorded, which were adapted to (a) normal background low-oxygen (dysoxic) conditions (i.e., minute infaunal suspension-feeding bivalves associated with the trace fossil Planolites), (b) chemically toxic (anoxic/extreme dysoxic) substrates, including gigantic burrowing bivalves (probable chemosymbiotic taxa), and (c) oxic/dysoxic substrates following short-term bottom disruptions. 相似文献
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The passage of jet boats through spawning areas can kill salmon eggs buried in the river bed. By using a jet boat on the Ashley River the pressure gradients created in a redd were determined. At the maximum boat speed investigated (11 m.s‐1) gradients up to 9.32 kPa.m‐1 were recorded. The induced water velocities through the gravel were then estimated from the equation of motion and reproduced in a gravel‐filled tube in the laboratory. For the test conditions discharge velocities ranged from 0.18–0.3 m.s‐1. Studies of the effect of these flows on salmon eggs revealed fatality rates of up to 40% at their most critical stage on the ninth day of development. 相似文献
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Because offshore wind energy development is fast growing in Europe it is important to investigate the changes in the marine environment and how these may influence local biodiversity and ecosystem functioning. One of the species affected by these ecosystem changes is Atlantic cod (Gadus morhua), a heavily exploited, commercially important fish species. In this research we investigated the residency, site fidelity and habitat use of Atlantic cod on a temporal scale at windmill artificial reefs in the Belgian part of the North Sea. Acoustic telemetry was used and the Vemco VR2W position system was deployed to quantify the movement behaviour. In total, 22 Atlantic cod were tagged and monitored for up to one year. Many fish were present near the artificial reefs during summer and autumn, and demonstrated strong residency and high individual detection rates. When present within the study area, Atlantic cod also showed distinct habitat selectivity. We identified aggregation near the artificial hard substrates of the wind turbines. In addition, a clear seasonal pattern in presence was observed. The high number of fish present in summer and autumn alternated with a period of very low densities during the winter period. 相似文献
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Pre-weighed packets of Spartina alterniflora and of plastic (polypropylene) twine were placed in a salt marsh pool and recovered on 40 dates spanning 14 months. New packets were placed out regularly to provide a contrast with ageing material. Twelve species of copepods were extracted, counted, and identified. Dry weight and Kjeldahl-nitrogen were determined for Spartina packets.Eight species of copepods, Amphiascus pallidus, Onychocamptus mohammed, Cletocamptus deitersei, Halicyclops sp., Harpacticus chelifer, Mesochra lilljeborgii, Metis jousseaumei and Nitocra sp. were found in higher densities on old grass or plastic packets than on new. The quantity of material was important in that the relative attractiveness of old grass was much lower early in the second year when 7–15% dw and 0·7% nitrogen remained than early in the first year when over 60% dw and 2·0% nitrogen remained. Old plastic polypropylene was equally or more attractive than old grass to 7 of 8 species, therefore, nitrogen decline in old grass was not the factor making it less attractive. Once aged, the quantity of substrate was more important than its quality. Apparently, this is due to colonization by microflora or settlement of detritus but these were not studied. The four clear exceptions to these trends were Darcythompsonia fairliensis and Eurytemora affinis which showed highest densities 72% and 50% of the time in new grass, Apocyclops spartinus with 70% in grass and equal numbers between old and new packets and Acartia tonsa a bay calanoid with 82% of highest densities in the water column and only two occurrences out of 40 dates in the packets. 相似文献
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古代深海底质氧控的遗迹化石群落 总被引：1，自引：2，他引：1
通过中国 9个深海沉积区近 2 0条研究剖面的沉积地质学和古遗迹学的研究 ,获得了判别深海底质遗迹化石群落与含氧量关系的几点认识 :1深海贫氧的底质中因相对含氧量的差异 ,其代表性的遗迹化石组合也不尽相同。以Megagrapton,Paleodictyon和 Protopaleodictyon为代表的 A组合 ,以 Scalarituba和 Phycosiphon为代表的 B组合 ,和以 Chondrites和 Zoophyeos为代表的 C组合 ,所指示贫氧底质中的溶解氧含量 ,是随组合的不同而依次降低 ;2遗迹化石潜穴的粗细通常与底质含氧量呈正相关 ,即潜穴直径随含氧量降低而变细 ;3遗迹化石的分异度随底质含氧量降低而变低 ;4应用个别遗迹化石属判识贫氧环境要慎重 ,如 Chondrites或者 Zoophycos,不能不加分析地视为贫氧环境的遗迹化石标志 ,应结合多种因素综合分析后 ,才能得出更符合客观实际的认识。 相似文献
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New and important roles for DMSP in marine microbial communities 总被引：4，自引：0，他引：4
The algal osmolyte dimethylsulfoniopropionate (DMSP) is recognised as the major precursor of marine dimethylsulfide (DMS), a volatile sulfur compound that affects atmospheric chemistry and global climate. Recent studies, using 35S-DMSP tracer techniques, suggest that DMSP may play additional very important roles in the microbial ecology and biogeochemistry of the surface ocean. DMSP may serve as an intracellular osmolyte in bacteria that take up phytoplankton-derived DMSP from seawater. In addition, DMSP appears to support from 1 to 13% of the bacterial carbon demand in surface waters, making it one of the most significant single substrates for bacterioplankton so far identified. Furthermore, the sulfur from DMSP is efficiently incorporated into bacterial proteins (mostly into methionine) and DMSP appears to be a major source of sulfur for marine bacterioplankton. Assimilatory metabolism of DMSP is via methanethiol (MeSH) that is produced by a demethylation/demethiolation pathway which dominates DMSP degradation in situ. Based on the linkage between assimilatory metabolism of DMSP and bacterial growth, we offer a hypothesis whereby DMSP availability to bacteria controls the production of DMS by the competing DMSP lyase pathway. Also linked with the assimilatory metabolism of DMSP is the production of excess MeSH which, if not assimilated into protein, reacts to form dissolved non-volatile compounds. These include sulfate and DOM–metal–MeSH complexes, both of which represent major short-term end-products of DMSP degradation. Because production rates of MeSH in seawater are high (3–90 nM d−1), reaction of MeSH with trace metals could affect metal availability and chemistry in seawater. Overall, results of recent studies provide evidence that DMSP plays important roles in the carbon, sulfur and perhaps metal and DOM cycles in marine microbial communities. These findings, coupled with the fact that the small fraction of DMSP converted to DMS may influence atmospheric chemistry and climate dynamics, draws attention to DMSP as a molecule of central importance to marine biogeochemical and ecological processes. 相似文献
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