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661.
Angela Dikou Colin Ackerman Carly Banks Alex Dempsey Michael Fox Meagan Gins Patricia Hester Adam Parnes Stephanie Roach Jessica Rohde Cliff Spital Mackai Tapleshay Luke Thomas 《Marine Ecology》2009,30(4):425-436
Coral reefs of the Turks and Caicos Islands (TCIs) (Caribbean Sea) constitute some of the few pristine coral reef systems in the world and play a crucial role in the islands’ economy because they support rich fisheries catches and tourism development. Ambitious development plans involving increase in fishing and tourism pressures are about to bring changes in coastal zone resources of the TCIs associated with increased sediments and nutrients and reduced predation by herbivorous fish on coral reefs. Understanding change is critical when attempting to protect the resources that these coral reefs support and to adopt proper management strategies. Yet, an environmental assessment program to detect imminent human‐induced changes on the surrounding reefs of the TCIs is lacking. Thus, (i) we obtained baseline data on benthic composition and coral community structure at seven reef sites of representative reefs of the TCIs within the Admiral Cockburn Land and Sea National Park (ACLSNP) of South Caicos Island and (ii) performed a priori statistical power analysis to calculate replication requirements for safely and confidently detecting small (δ = 0.1), medium (δ = 0.3), and large (δ = 0.5) effect sizes for a number of relevant to anticipated changes, univariate, benthic indices and for power β = 0.95. The platforms of the margin reefs studied (9–12 m depth) appeared rather variable regarding benthic composition but quite homogeneous regarding hard coral community structure. Mean percent cover of algal functional groups was 0.1 ± 0.3 (mean ± sd) percent for coralline algae and Halimeda, 0.1 ± 0.6 (mean ± sd) percent for macroalgae, 21.7 ± 33 (mean ± sd) percent for turf algae and 4.8 ± 4.0 (mean ± sd) percent for hard coral cover. The dominant benthic component, however, was carbonate substrate (mean ± sd = 30.4 ± 34.3), thus indicating an accreting reef framework. Mean hard coral density, colony size and recruit density were 5.5 ± 1.8 (mean ± sd) corals per 20‐m line transect, 13.0 ± 2.3 (mean ± sd) cm maximum colony diameter, and 1.3 ± 1.4 (mean ± sd) recruits per square foot, respectively. Due to high natural variance, hard coral colony size and density were practically the most sensitive indices in detecting even small size changes on benthos. Also, the geometric mean of log‐transformed colony size‐frequency distributions of the most abundant hard coral taxa, i.e. Montastrea annularis, Agaricia spp., Siderastrea spp. and Porites asteroides were practically sensitive for the same purpose. We hope that the study will optimize the spatial component of a necessary environmental impact assessment program on coral reefs of the TCIs once the natural spatial variability of the system has been assessed and sensitive, benthic, univariate indices have been identified for representative reference coral reef sites of the TCIs. 相似文献
662.
Erik Mrk Gustaf Lillieskld Sj Nils Kautsky Tim R. McClanahan 《Estuarine, Coastal and Shelf Science》2009,84(3):331-336
Top–down and bottom–up regulation in the form of grazing by herbivores and nutrient availability are important factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenic activities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, are altering the interaction of these two structuring forces. The present study was conducted in Kenya and investigates the relative importance of herbivory and nutrient loading on macroalgal community dynamics, by looking at alterations in macroalgal functional groups, species diversity (H′) and biomass within experimental quadrats. The experiment was conducted in situ for 42 days during the dry season. Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition was conducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory is generally low and nutrient levels are relatively high for the region. Nutrient addition increased tissue nutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivore exclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticated forms. These results are in accordance with similar studies in other regions, but are unique in that they indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure is relatively low, continued anthropogenic disturbance results in further ecological responses and increased reef degradation. 相似文献
663.
The present study explored ontogenetic shifts in habitat associations by coral reef fishes between recently settled juvenile and adult life stages (Moorea Island: Tiahura and Papetoai sites). Visual censuses highlighted four ontogenetic patterns in habitat associations: (1) no change in habitat associations between the juvenile and adult stages; (2) a decrease in the number of habitats used by adults compared to juveniles; (3) an increase in the number of habitats used during the adult stage; and (4) use of nursery areas by juveniles followed by an extensive movement to an entirely different adult habitat. The comparative analysis of spatial distribution of fish at Tiahura and Papetoai highlighted no-spatial variability in ontogenetic patterns (i.e., 10 of the 15 recorded species have spatial consistency in ontogenetic patterns). Overall, the shifts in habitat associations are of interest in the perspective of understanding flexibility and adaptation capability of coral reef fish, at least at the settlement time. 相似文献
664.
Geochemical tracers, including Ba, Co, Th, 7Be, 137Cs and 210Pb, and magnetic properties were used to characterize terrestrial runoff collected in nearshore time-series sediment traps in Hanalei Bay, Kauai, during flood and dry conditions in summer 2006, and to fingerprint possible runoff sources in the lower watershed. In combination, the tracers indicate that runoff during a flood in August could have come from cultivated taro fields bordering the lower reach of the river. Land-based runoff associated with summer floods may have a greater impact on coral reef communities in Hanalei Bay than in winter because sediment persists for several months. During dry periods, sediment carried by the Hanalei River appears to have been mobilized primarily by undercutting of low 7Be, low 137Cs riverbanks composed of soil weathered from tholeiitic basalt with low Ba and Co concentrations. Following a moderate rainfall event in September, high 7Be sediment carried by the Hanalei River was probably mobilized by overland flow in the upper watershed. Ba-desorption in low-salinity coastal water limited its use to a qualitative runoff tracer in nearshore sediment. 210Pb had limited usefulness as a terrestrial tracer in the nearshore due to a large dissolved oceanic source and scavenging onto resuspended bottom sediment. 210Pb-scavenging does, however, illustrate the role resuspension could play in the accumulation of particle-reactive contaminants in nearshore sediment. Co and 137Cs were not affected by desorption or geochemical scavenging and showed the greatest potential as quantitative sediment provenance indicators in material collected in nearshore sediment traps. 相似文献
665.
中国珊瑚礁资源状况及其药用研究调查 Ⅱ.资源衰退状况、保护与管理 总被引:1,自引:0,他引:1
对中国珊瑚礁资源衰退状况和原因进行了调查和分析.结果表明,中国南海珊瑚礁资源衰退状况严重,珊瑚礁破坏率高达 90%以上,其中,占全国珊瑚礁总面积98%的海南,80%~95%的珊瑚礁受到破坏.除自然因素外,对珊瑚礁资源的不当的、过度的开发利用,社会经济发展带来的海洋环境污染等人为因素,是珊瑚礁资源衰退的主要原因.建立南中国海珊瑚礁生态系统保护与管理国际合作机制,正确评估珊瑚礁的生态功能与价值,建立珊瑚礁自然保护区及监测网络系统,是中国珊瑚礁资源保护性开发利用的可行对策. 相似文献
666.
南海北部造礁珊瑚碳同位素的时空变化及其影响因素 总被引:2,自引:1,他引:1
海南岛东岸和南岸两个礁区采集了3个活体滨珊瑚,沿珊瑚生长轴线切样进行月分辨率的氧碳同位素分析,目的是研究珊瑚碳同位素组成在季节、年际和年代际3个时间尺度上的变化与季风气候的联系.结果表明,珊瑚的δ18O值的季节性变化和年际变化在全年都基本上受表层海温的控制,基于这一相关变化可以建立同位素序列的时间标尺.在同位素的时间序列上,珊瑚δ13C值季节性变化与日照基本同步.由于日照变化主要受大气顶部太阳理论日照和云量变化的控制,而理论日照在某一地点随时间的变化是规律的,所以,云量变化是珊瑚碳同位素组成季节变化的主要因素.过去30年珊瑚δ13C值最明显的年代际变化特征是1986~1987年δ13C值的突然减小事件,这一事件与日照的变化在时间和统计特征上都有一致性,但与云量变化关系不大,可能与其他因素引起的日照变化有关.现代滨珊瑚碳同位素组成普遍存在着变小的趋势,这种年代际变化与大气CO2同位素变化一致,两者在机理上成因关系也说明,近代珊瑚碳同位素组成变小的趋势与大气CO2的变化有关.不同海区的珊瑚同位素记录对比显示,海水及其中的有机物的碳同位素组成决定着珊瑚δ13C值季节变化性在空间上的分异特征,它们在很大程度上受淡水注入量的影响;同时,日照起主要作用的光合作用也对珊瑚δ13C值的变化在空间上的分异有一定的贡献. 相似文献
667.
针对我国南海某岛礁珊瑚砂地基上的圆形桩基础,采用N-S方程k-ε模型、双向耦合方式跟踪流场中颗粒运动轨迹的方法,对桩周珊瑚砂的冲刷规律进行了求解,分析了桩体周围流体的速度场以及桩体表面剪应力场的分布规律,同时对桩周珊瑚砂冲刷坑的形成过程进行了模拟。计算结果表明,在桩体周围形成的马蹄形漩涡和桩柱后方的尾涡作用下,桩周土体出现了较为明显的冲刷现象,涡旋的释放显著地影响着珊瑚砂地基上桩基的冲刷坑形状;而且,由于珊瑚砂颗粒密度较石英砂小,水动力作用下桩周冲刷坑更容易形成,所以实际工程中需要考虑有效的防护措施。 相似文献
668.
669.