Persistent alternate abundance states in the coral reef sea urchin Diadema savignyi: evidence of alternate attractors          下载免费PDF全文

Xueying Han 《Marine Ecology》2016,37(6):1179-1189

Alternate attractors have been shown to exist in a variety of terrestrial and aquatic systems, e.g. temperate forests, savannas, shallow lakes, wetlands, coral reefs, kelp forests. The shift from one attractor to another, also referred to as a regime shift, is thought to occur when a system passes some critical threshold such that the trajectory of the system changes direction. Alternate attractors in population dynamics can also exist, leading to alternate stable states in the population abundance of a species. This study explored alternate attractors in the population dynamics of the Indo‐Pacific sea urchin Diadema savignyi and the potential underlying mechanisms that promote its bi‐stability. In Moorea, French Polynesia, the local abundance of D. savignyi, a functionally important herbivore in lagoon habitats, occurs in two states: (i) solitary individuals that occupy crevices in low densities and (ii) aggregations of tens to hundreds of individuals. These different states are temporally stable and are not explained by spatial differences in recruitment rates of juveniles. A field experiment revealed that the per capita mortality rate of adult D. savignyi was substantially lower at sites where urchins occurred in aggregations compared with sites at which they were solitary individuals. An additional experiment showed that per capita mortality decreased with increasing aggregation size. Individuals in high‐density aggregations, however, had significantly smaller test diameters than solitary individuals, indicating that individuals in aggregations may be food limited. Collectively, the evidence suggests that the two different local abundance states of D. savignyi result from negative feedback loops where high local density can be maintained by aggregative behavior that greatly reduces per capita risk of predation when the local number of adult sea urchins is sufficiently large; sites with few sea urchins remain at low density because individuals are more susceptible to predation when crevices are occupied but there are not enough individuals to form large aggregations. Thus, there may be alternate attractors in the population dynamics of D. savignyi that can produce either persistently low or high local population densities.  相似文献   

Spatial distribution of crustaceans associated with shallow soft‐bottom habitats in a coral reef lagoon          下载免费PDF全文

Carlos Navarro‐Barranco  José M. Guerra‐García 《Marine Ecology》2016,37(1):77-87

The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats.  相似文献   

全珊瑚骨料海水混凝土力学性能试验研究   总被引：3，自引：1，他引：2       下载免费PDF全文

糜人杰  余红发  麻海燕  达波  袁银峰  张小平  朱海威  窦雪梅 《海洋工程》2016,34(4):47-54

为了探讨全珊瑚骨料海水混凝土的基本力学性能,并比较其与普通混凝土和轻集料混凝土的差异,通过实验系统测定了珊瑚混凝土的基本力学性能,建立了其轴心抗压强度(f_(c,m))、劈裂抗拉强度(f_(sp,m))、抗折强度(f_(t,m))与立方体抗压强度(f_(cu,m))之间的线性关系与计算公式。结果表明:在强度等级C20~C50的范围内,珊瑚混凝土的f_(c,m)和f_(sp,m)分别比普通混凝土的f_(c,m)和f_(sp,m)高出10%~48%和9%~33%,随着强度等级的提高,两种混凝土之间的差距在减小。珊瑚混凝土的f_(t,m)与普通混凝土的ft,m之间的差异规律与强度等级有关,较低强度等级的C30珊瑚混凝土ft,m比普通混凝土的f_(t,m)要高4%,而较高强度等级的C55珊瑚混凝土f_(t,m)比普通混凝土的f_(t,m)低13%。较高强度等级的C50珊瑚混凝土f_(c,m)、f_(sp,m)和f_(t,m)分别比页岩陶粒轻集料混凝土的f_(c,m)、f_(sp,m)和f_(t,m)低11%、0.9%和4%。  相似文献   

Sublittoral seaweed communities on natural and artificial substrata in a high-latitude coral community in South Africa     

L Gersun  JR Hart  GW Maneveldt  JJ Bolton 《African Journal of Marine Science》2016,38(3):303-316

Coral mortality may result in macroalgal proliferation or a phase shift into an alga-dominated state. Subtidal, high-latitude western Indian Ocean coral communities at Sodwana Bay on the KwaZulu-Natal coast, South Africa, have experienced some mortality because of warm-water anomalies, storms and other causes, but the response of the macroalgae is unknown. We investigated the abundance and diversity of benthic algae on different hard natural substrata (dead digitate, brain and plate corals and beach rock) on Two-Mile Reef, Sodwana Bay. We also compared algal communities colonising ceramic, marble and pretreated ceramic tiles placed on the reef for six months. We identified 95 algae (14 Chlorophyta, 11 Phaeophyceae, 69 Rhodophyta and one cyanobacterium). Assemblages on natural and artificial substrata were dominated by the brown alga Lobophora variegata (Lamouroux) Womersley ex Oliveira and non-geniculate corallines (Rhodophyta, Corallinaceae). Cluster and ordination analyses revealed that the algae showed no affinity for particular substrata, whether natural or artificial. Algal cover was occasionally higher on rougher tiles and crustose corallines were significantly more abundant on marble than ceramic tiles. Two-Mile Reef had 23.1% dead and 48.4% live scleractinian coral cover, where dead corals were colonised indiscriminately by many small algal species, but there was no evidence of algal proliferation. The results provide a baseline for monitoring this high-latitude reef system.  相似文献   

广西田林县石炭纪礁内海百合生态功能分析   总被引：1，自引：0，他引：1  

陈晓红  巩恩普  王铁晖  关长庆  张永利  杨大勇  王会敏 《地质论评》2013,59(3):446-453

本文以石炭纪的后生动物格架礁为例,从礁体生长过程和群落竞争关系的角度,对赋存于造礁生物群落中的海百合与造架珊瑚之间的关系,以及其在礁体发育过程中的作用进行详细探讨,揭示了礁生态系统内的生物因子之间的关系。研究发现：在礁体发育初期,以海百合为主的群落是造架珊瑚定殖的初始条件;在礁体的生长过程中,海百合与造架珊瑚之间存在一种受环境控制的竞争关系,两者在数量上呈现此消彼长的关系。当环境变化导致造架珊瑚死亡,礁体停止生长,海百合仍存活并不间断地为礁体提供沉积物,对已停止发育的珊瑚格架起到覆盖作用,从一定程度上保护了礁体  相似文献   

Storm‐dominated sedimentation in a protected basin fringed by coral reefs,Nara Inlet,Whitsunday Islands,Great Barrier Reef,Australia     

A. D. Heap  P. Larcombe  K. J. Woolfe 《Australian Journal of Earth Sciences》2013,60(3):443-451

Hydrodynamic data and samples of bed sediment were collected from Nara Inlet, a small incised embayment in the Whitsunday Islands, central Great Barrier Reef. Measured tidal currents in the inlet do not exceed 0.2 ms^–1 even at spring tides. Swell waves dominate much of the inner shelf of the Great Barrier Reef but are absent from in the inlet due to the presence of a fringing reef at the inlet mouth. On the silty sand floor of the inlet, particle size decreases towards the inlet head. Most of the bed is too coarse to be remobilised by fair‐weather wave and tides, and we predict that bedload sediment transport thresholds are only exceeded in the inlet during cyclones. The observed distribution of bed sediments is consistent with landward dispersal of sediment under storm conditions. Over 20 m of (presumably Holocene) sediments occurs in the inlet and the seismic character of the infill is consistent with the observed textural variation of the modern sediments. We infer that sediment accumulation on the floor of the inlet has been storm dominated throughout much of the Holocene.  相似文献   

The Enya mounds: a lost mound-drift competition     

D. Van Rooij  V. A. I. Huvenne  D. Blamart  J.-P. Henriet  A. Wheeler  H. de Haas 《International Journal of Earth Sciences》2009,98(4):849-863

The genesis and evolution of cold-water coral banks along the Northeastern Atlantic margin is known to be influenced by several factors, among which the palaeotopography and nature of the coral settling surface, the presence of bottom currents and sediment supply. In this paper, a case study is presented of the Enya mound cluster, located in the southernmost tip of the Belgica mound province, west of Ireland. Below this mound cluster, seismic stratigraphy revealed a yet unmapped local unconformity RD1b, being part of a composite erosion event (RD1). As such, from the Late Miocene to Late Pliocene, at least two erosional events have incised the margin, ending with the final RD1a “moundbase” unconformity, acting as a base for the Enya mounds. During the Quaternary the mounds became outgrown and were covered by a mounded contourite drift. In addition, they are closely associated with a cluster of seabed pockmarks. The bottom current regime which became active since the Middle Pleistocene has certainly influenced the fate of this mound cluster. The occurrence of the pockmarks seems to be related to relatively recent fluid migration processes, however leaving an open question if any previous seepage phases were involved in the growth or initiation of the coral banks.  相似文献   

南海北部晚全新世高海平面及其波动的海滩沉积证据          下载免费PDF全文

余克服  陈特固 《地学前缘》2009,16(6):138

揭示晚全新世以来的海平面变化过程对于理解海平面所处的现状和变化的趋势等具有重要意义。构造活动相对稳定的雷州半岛珊瑚礁区蕴藏着丰富的海平面变化信息,文中对该区晚全新世发育的海滩沉积序列研究表明,距今约1.7～1.2Cal.kaBP(14C年代为2.1～1.7kaBP)期间总体上是一个海平面持续上升的时期,其中在距今约1.5Cal.kaBP时海平面有过短暂的下降波动,约1.2Cal.kaBP时的海平面比现在的至少高128cm;之后海平面开始下降,至今海岸线后退了约210m,形成现代海滩-沙堤地貌体系。结合本区珊瑚礁记录的全新世其他时段海平面的变化特征,本文认为全新世海平面与气候变化一样,也存在千年、百年、年代际尺度的波动特征。  相似文献   

西沙群岛珊瑚礁海域浮游动物群落结构初步分析*     

李开枝  柯志新  王军星  谭烨辉 《热带海洋学报》2022,41(2):121-131

为了解西沙群岛珊瑚礁海域浮游动物的群落特征, 于2015年5月末至7月初在西沙群岛8个岛礁(七连屿、永兴岛和东岛3个岛屿以及浪花礁、盘石屿、玉琢礁、华光礁和北礁5个环礁)进行了浮游动物采样, 分析了浮游动物的多样性、丰度和群落结构特征, 并比较了5个环礁潟湖内和向海礁坡区浮游动物群落组成的差异。调查海域共鉴定浮游动物180种(包括浮游幼虫13个类群), 其中桡足类最多, 达83种, 其次是水母类(38种)、浮游软体类(14种)、毛颚类(11种)和浮游被囊类(7种); 浮游动物平均丰度为256.4±117.8个·m^-3, 桡足类占总丰度的51.08%, 其次是浮游幼虫(16.30%)、浮游被囊类(13.22%)和毛颚类(7.70%)。浮游动物种数、多样性和均匀度指数、丰度在岛屿和环礁之间以及环礁的潟湖区和向海礁坡区均存在差异; 浮游动物多样性和丰度在东岛、玉琢礁和华光礁较高, 而在七连屿和北礁较低; 5个环礁向海礁坡区的浮游动物多样性和丰度皆高于潟湖区的。多元统计分析结果表明调查岛礁的浮游动物可划分两个聚群(相似水平85%); 岛屿近岸及环礁的潟湖群落(Ⅰ)和岛屿远岸及环礁的向海礁坡群落(Ⅱ); 两个聚群浮游动物组成差异较显著(r=0.832, p<0.001); 前者的种数、多样性指数、总丰度和主要浮游动物类群如桡足类、毛颚类和浮游幼虫的丰度显著低于后者。环礁潟湖区和向海礁坡区的空间异质性和生态环境差异可能是导致浮游动物群落结构呈现不同特征的主要因素。  相似文献   

Are catch-up reefs an artefact of coring?     

Paul Blanchon  David Blakeway† 《Sedimentology》2003,50(6):1271-1282

Drill cores through modern coral reefs commonly show a time lag in reef initiation followed by a phase of rapid accretion to sea level from submerged foundations – the so-called ‘catch-up response’. But because of the difficulty of drilling in these environments, core distribution is usually restricted to accessible areas that may not fully represent reef history, especially if the reef initiated in patches or developed with a prograde or retrograde geometry. As a consequence, core data have the potential to give a misleading impression of reef development, particularly with respect to the timing of initiation and response to sea-level rise. Here, we use computer models to simulate keep-up reef development and, from them, quantify variations in the timing of reef initiation and accretion rate using mock cores taken through the completed simulations. The results demonstrate that cores consistently underestimate the timing of reef initiation and overestimate the reef accretion rate so that, statistically, a core through a keep-up reef will most likely produce a catch-up pattern – an initiation lag followed by a phase of rapid accretion to sea level. This implies that catch-up signatures may be an artefact of coring and that keep-up reefs are significantly more common than previous core studies claim.  相似文献