Experimental Investigation of Local Scour Around Artificial Reefs in Steady Currents

Artificial reef is a man-made object that is deployed purposefully on the seafloor to restore the offshore fishery resources and the ecological environment.To secure its ecological effects,it is important to study the possible instability of artificial reefs,like drifting and reversing caused by burial and scour in different seafloor conditions.In the present study,experiments of local scour around an artificial reef are carried out in steady currents.The effect of the open-area ratios and the open-hole heights of the cubic reefs,and the bottom angles of the triangular reefs on the time-scale of the scour process and the equilibrium scour depth are investigated.The results indicate that for the cubic artificial reef,the scour depth decreases with the increasing open-area ratios,and increases with the increasing open-hole heights.In the present study,the optimal prototype of the cubic reef with an open-area ratio of 0.49 and open-height of 0.7 m produces the minimum scour depth.For the triangular reef,the scour depth increases when the bottom angle increases.Moreover,based on the experimental results,empirical equations of the effects of the cut-opening and the bottom angle on the maximum equilibrium scour depth are proposed.The formulas will provide theoretical support and practical guidance for the optimized design and construction of artificial reefs.     

基于GEBCO的海底热液区地形复杂度分析方法研究

海底热液区地形复杂度是热液活动场的重要指标数据,获取地形复杂度指标数据,为系统研究全球海底热液区分布特征具有重要意义。阐述了地形复杂度和GEBCO数据的基本应用情况,介绍了基于数字地形模型数据进行地形复杂度计算的基本方法,提出了海底热液区地形复杂度计算的窗口序列分析法和基本步骤,实例分析了伊豆—小笠原海底热液活动亚带的地形复杂度情况。     

舟山本岛北部大麦秆礁海域地形诱发的小尺度涡

在舟山附近北至南汇嘴附近,南至象山港附近,东至-60 m等深线附近海域建立了二维潮流模型,通过多个验潮站和实测潮流资料的验证,潮流、潮位计算结果与实测结果符合良好。在此基础上,通过数值模拟,研究了舟山北部大麦秆礁附近海域地形诱发的小尺度涡,Lagrange质点漂移实验也很好地验证了数模的结果。为了研究大麦秆礁的地形对小尺度涡的影响,在数值模型中将大麦秆礁的东北部的岛礁去除,结果显示:涨潮时,大麦秆礁西侧两个小尺度涡减少为一个;落潮时,大麦秆礁东北岛礁东侧两个小尺度涡消失,表明地形是大麦秆礁附近小尺度涡生成的主要原因。     

Genetic connectivity of the coral‐eating sea star Acanthaster planci during the severe outbreak of 2006–2009 in the Society Islands,French Polynesia

Occasional population outbreaks of the crown‐of‐thorns sea star, Acanthaster planci, are a major threat to coral reefs across the Indo‐Pacific. The presumed association between the serial nature of these outbreaks and the long larval dispersal phase makes it important to estimate larval dispersal; many studies have examined the population genetic structure of A. planci for this purpose using different genetic markers. However, only a few have focused on reef‐scale as well as archipelago‐scale genetic structure and none has used a combination of different genetic markers with different effective population sizes. In our study, we used both mtDNA and microsatellite loci to examine A. planci population genetic structure at multiple spatial scales (from <2 km to almost 300 km) within and among four islands of the Society Archipelago, French Polynesia. Our analysis detected no significant genetic structure based on mtDNA (global F_ST = ?0.007, P = 0.997) and low levels of genetic structure using microsatellite loci (global F_ST = 0.006, P = 0.005). We found no significant isolation by distance patterns within the study area for either genetic marker. The overall genetically homogenized pattern found in both the mitochondrial and nuclear loci of A. planci in the Society Archipelago underscores the significant role of larval dispersal that may cause secondary outbreaks, as well as possible recent colonization in this area.     

Climate change and warm‐water species at the north‐western boundary of the Mediterranean Sea

The effects of global change are particularly serious in areas where range shifts of species are physically constrained such as the Ligurian Sea, which is one of the coldest sectors of the Mediterranean. In this basin, historical information on water temperature (from the sea surface down to 75 m depth) dates back to the 1950s. Early studies also recorded warm‐water species occurrence. Thanks to these data we provide the first detailed characterization of water temperature variation from 1958 up to 2010 in the layer 0–75 m depth. We coupled this analysis with the available information on rocky reef epibenthic communities (literature review from 1955 to 1964 and field data from 1980 to 2010). The analysis of water temperature revealed several patterns of variation: a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to 1990 and a phase of slower warming from 1990 to 2010. Inter‐annual variation in temperature increased over the entire period for the water layer down to 20 m. Warm‐water native and alien species richness increased during the warming phases. Literature estimates suggest a decrease in warm‐water native species richness during the cooling phase. The analysis of quantitative data collected in the early 1990s and late 2000s indicated a decrease in the cover of warm‐water native species on shallow rocky reefs and an increase in deeper waters. We argue that increased inter‐annual variation in water temperature may disadvantage native warm‐water species in shallow waters. Our results indicate that the effect of temperature rises in cold, constrained basins may be more complex than the simple prediction of species changing their geographical range according to their thermal limits.     

风作用下孤立波在珊瑚礁上传播变形机制数值模拟研究

基于二维不可压缩两相流模型建立了数值风浪水槽,采用SST k-ω雷诺时均湍流模型,研究了风作用下孤立波在珊瑚礁上的传播变形规律。将计算结果与实验数据对比,证明了该两相流模型计算孤立波在珊瑚礁上传播的准确性,并进一步分析了不同风速对珊瑚礁上孤立波传播变形的影响。结果表明：风的作用会使波面发生随机脉动特征。当地波高随风速的增大而增大;当地波高关于风速的变化梯度随入射波高的增大而增大。风的作用会加快孤立波的传播并且使孤立波提前发生破碎;孤立波开始破碎的位置随风速的增大向远离礁坪的方向移动。反射系数随风速的增大而增大;反射系数关于风速的变化梯度随入射波高的增大而减小;透射系数随风速的增大呈增大趋势。平底区波峰剖面同一水深处的水平流速随风速的增大而增大;且一定的风速不改变水平流速沿水深的变化梯度。有风时波面上方的矢量密度和大小均明显高于无风时且与风速呈正相关,并且波峰上方气流不再循环。随着风速的增大,水气交界面附近的正涡量和负湍流剪应力减小,负涡量和正湍流剪应力增大。水体动能、势能和总能达到高值的时间随风速的增大而减少;水体动能、势能和总能随风速的增大而增大,并且风速对水体动能的相对影响大于势能。     

广西田林浪平地区晚石炭世生物礁古生态特征

广西田林县浪平地区发育了几处黄龙期生物格架礁。这些发育在海百合碎屑滩上的礁体规模普遍不大,造礁和附礁生物种类多样,礁生物群落成熟度低,造礁方式单一,具有斑块式分布特点。浪平地区黄龙期点礁是在缺乏全球性主要后生骨架造礁动物的背景下发育的,没有明显优势造礁生物出现;点礁受研究区内大规模发育的碎屑滩影响显著,成礁环境多变、高能水体与碎屑选择作用明显、固结和硬质基底分布不广泛、水体能量频繁变化与适应环境的海百合繁盛、藻类在研究区内不发育,这些使得浪平地区点礁具有典型的"碎屑滩点礁模式"特征;造礁生物的生态特点对点礁的具体面貌具有重要影响。晚石炭世碎屑滩后生动物骨架点礁的发现,有助于进一步加强生物礁古生态系统研究。     

Architecture and composition of the Upper Burdigalian z-coral build-ups of southern Corsica (Mediterranean)

In southern Corsica, three successive Upper Burdigalian coral reef episodes (R1, R2 subdivided into R2A and R2B subunits, and R3) developed within the Cala di Labra Formation. Tabular corals dominated under high water energy and siliciclastic input conditions. The R1 reefs show the highest coral diversity with 16 species described for the first time. A coral impoverishment was recorded in the R2 and R3 reefal episodes. The reefs did not reach a climax growth stage, except the R1 ones. Analogous to North Sardinian reefs, they reflect local vanishing conditions in the Corsican–Sardinian block through Upper Burdigalian because of constant siliciclastic inputs and deepening of the Bonifacio straight.     

The Diagenesis of Coral Reefs

Coral reefs are often constrained by diagenesis as a sound environmental archive. The correct understanding and evaluation of diagenesis is the key to the paleoenvironmental reconstruction of coral reefs. The diagenesis of coral reefs mainly includes cementation, dissolution, neomorphism and dolomitization etc. On the one hand, the diagenesis itself can record the paleoenvironment that coral reefs underwent, such as sea-level fluctuation, climate change, change of sea water, hydrothermal alteration, microbial activity and so on. The diagenetic evolution thus can be used for the reconstruction of paleoenvironment change. On the other hand, diagenesis also destroys the original environmental information which recorded of coral reefs recard, and it is necessary to know the degree of the impact of diagenesis. In the future, we should pay more attention to the study on the relationships among diagenesis, modern climate, sea-level change, atmospheric water transformation and microbial activity. It can provide more accurate and longer time series of paleoenvironmental information that coral reefs recorded.     

Assessment of the distribution of sponge chips in the sediment of East Pacific Ocean reefs

Sponges are one of the principal agents of bioerosion and sediment production in coral reefs. They generate small carbonate chips that can be found in the sediments, and we investigated whether these could provide a means for assessment of bioerosion applicable to reef monitoring. We tested this hypothesis on samples from 12 Mexican coral reefs distributed along the Pacific coast, where boring sponges were particularly abundant, and quantified the amount of chips in samples of superficial sediment in three grain‐size fractions: fine (<44 μm), medium (44–210 μm) and coarse (>210 μm). The grain‐size distribution varied among reefs, with the majority of the sediment of most reefs being composed of coarse sands, and the medium and fine fractions dominating only at La Entrega and Playa Blanca. All the reefs presented clear evidence of bioerosion by sponges, with the characteristic chips present in the sediment, although at most sites the percentage of chips was very low (from 1% to 3% of the total sediment). Only at La Entrega and Playa Blanca did they constitute a significant fraction of the total sediment (18% and 16%, respectively). While not statistically significant, there was an interesting trend between sponge chips versus sponge abundance that suggests that quantification of the chips in the sediment could be used as a proxy for sponge erosion of the entire community, which cannot be estimated in by laboratory experiments. However, while this methodology could provide an integrated approach to monitor sponge bioerosion, more studies are necessary due to the influence of environmental factors on the transport and deposition of these chips.