On the small-scale fractal geometrical structure of a living coral reef barrier

The topographical complexity of coral reefs is of primary importance for a number of hydrodynamical and ecological processes. The present study is based on a series of high-resolution seabottom elevation measurements along the Maupiti Barrier Reef, French Polynesia. Several statistical metrics and spectral analysis are used to characterize the spatial evolution of the coral geometrical structure from the reef crest to the backreef. A consistent fractal-like power law exists in the spectral density of bottom elevation for length scales between 0.1 and 7 m, while at larger scale, the reef structure shows a different pattern. Such a fine characterization of the reef geometrical structure provides key elements to reconstruct the reef history, to improve the representation of reef roughness in hydrodynamical models and to monitor the evolution of coral reef systems in the context of global change. © 2020 John Wiley & Sons, Ltd.     

Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs.     

The 1997/1998 mass mortality of corals: effects on fish communities on a Tanzanian coral reef

The abnormally high surface temperatures in the world's oceans during 1997/1998 resulted in widespread coral bleaching and subsequent coral mortality. An experiment was performed to study the effects of this coral mortality as well as the influence of the structural complexity on fish communities on a Tanzanian coral reef. Changes in fish communities were investigated on plots of transplanted corals after 88% of these corals had died. A distinct shift in fish community composition was found, although diversity was not affected. Fish abundance rose by 39% mostly due to an increase in herbivores, which seemed to benefit from enhanced algal growth on the dead corals. Fish abundance, species diversity and community composition were also strongly influenced by the structural complexity provided by the live and dead corals. This suggests that a coral reef can support abundant and diverse fish populations also after the corals have died as long as the reef structure is sustained.     

Spatial and temporal variance of river discharge on Okinawa (Japan): inferring the temporal impact on adjacent coral reefs.

Land-use changes and associated river discharges in coastal tropical regions present a global threat to coral reef environments. This study investigated the temporal variation in biological oxygen demand (BOD5) and suspended particulate matter (SPM) at the mouths of seven rivers on Okinawa Island (Japan) over 20 years. We report strong positive relationships between human population densities within river catchment areas and both average BOD5 concentration (r2 = 0.968; p < 0.001) and SPM (r2 = 0.659; p < 0.003) at the mouths of the rivers. At the reef adjacent to one river (Hija River, 50.2 km2 catchment area) we applied moving window analysis to assess an optimal sampling strategy for elucidating transitional boundaries in coral composition from the river mouth to a point where the effect of river discharge was minimal. The optimal window width for Okinawan rivers was five 1 m2 quadrats spaced over 5 m intervals. This sampling strategy clearly showed dissimilarity spikes in coral community composition up to 400 m from the Hija River mouth, beyond which no significant differences in coral composition were detected using analysis of similarities (ANOSIM). We developed a simple diffusion model linking the rivers' maximum discharge rate, and the average concentration of BOD5 and SPM with the spatial impact on the coral communities. The diffusion model can aid in predicting negative shifts in coral communities expected to result from detrimental land-use changes and is an important tool for monitoring coral reefs.     

The influence of pearl oyster farming on reef fish abundance and diversity in Ahe,French Polynesia

Many cultured pearl farms are located in areas of the Pacific that have thriving, highly diverse fish communities but the impacts of farming on these communities are poorly understood. We studied the effects of pearl oyster farming on shore fish abundance and diversity in the lagoon of Ahe, French Polynesia by adapting roving diver census methods to the coral reef bommies of the lagoon and compared 16 sites with high pearl farming impact to others with no direct impact. Pearl farming has a slightly positive effect on reef fish abundance (N) and no significant impact on fish diversity (H) or community composition. This is important when considering the ecological sustainability of pearl farming in French Polynesia and suggests that a potential synergy between pearl farms and marine conservation should be further explored.     

Environmental determinants of species turnover of aquatic Heteroptera in freshwater ecosystems of the Western Ghats,India

Partitioning beta diversity into its two components of spatial turnover and nestedness is a more robust method for checking spatial variability in biological communities than calculating the total beta diversity alone. The relative contribution of spatial turnover and nestedness has been used to test the effects of climatic, environmental, spatial and temporal variables on community composition. In this study, we tested the effects of environmental factors and microhabitat features on total beta diversity and its spatial turnover and nestedness components using a comprehensive dataset of aquatic Heteroptera collected from four types of permanent freshwater habitats (i.e. streams, ponds, rock tanks and reservoirs) in the Western Ghats of India. We observed that communities in all four types of habitats were predominantly shaped by dissimilarity caused due to spatial turnover (>85 %). Each type of habitat showed the presence of one or more species uniquely associated with it, which might contribute to the turnover between communities. The abiotic environment (climatic factors, topological factors, soil characteristics and microhabitat features) as well as assemblage structure differed significantly between habitat types. Communities in each type of habitat were affected by different environmental factors, such as precipitation and temperature patterns for streams, altitude and rocky substrate for rock tanks, and soil characteristics and the presence of aquatic macrophytes for ponds and reservoirs. Assemblages observed in the four types of permanent habitats are thus compositionally distinct due to species replacements between local communities, which in turn are strongly influenced by environmental variables. Similar to previous studies, our results show that spatial turnover largely measures the same phenomenon as total beta diversity on a regional scale.     

The next step in shallow coral reef monitoring: Combining remote sensing and in situ approaches

Most current coral reef management is supported by mapping and monitoring limited in record length and spatial extent. These deficiencies were addressed in a multidisciplinary study of cyclone impacts on Aboré Reef, New-Caledonia. Local knowledge, high thematic-resolution maps, and time-series satellite imagery complemented classical in situ monitoring methods. Field survey stations were selected from examination of pre- and post-cyclone images and their post-cyclone coral communities documented in terms of substrata, coral morphologies, live coral cover, and taxonomy. Time-series maps of hierarchically defined coral communities created at spatial scales documenting the variability among communities (29-45 classes) and suggesting the processes that affected them. The increased spatial coverage and repeatability of this approach significantly improved the recognition and interpretation of coral communities’ spatio-temporal variability. It identified precise locations of impacted areas and those exhibiting coral recovery and resilience. The approach provides a comprehensive suite of information on which to base reef-scale conservation actions.     

Remote sensing of coral reefs and their physical environment

There has been a vast improvement in access to remotely sensed data in just a few recent years. This revolution of information is the result of heavy investment in new technology by governments and industry, rapid developments in computing power and storage, and easy dissemination of data over the internet. Today, remotely sensed data are available to virtually anyone with a desktop computer. Here, we review the status of one of the most popular areas of marine remote sensing research: coral reefs. Previous reviews have focused on the ability of remote sensing to map the structure and habitat composition of coral reefs, but have neglected to consider the physical environment in which reefs occur. We provide a holistic review of what can, might, and cannot be mapped using remote sensing at this time. We cover aspects of reef structure and health but also discuss the diversity of physical environmental data such as temperature, winds, solar radiation and water quality. There have been numerous recent advances in the remote sensing of reefs and we hope that this paper enhances awareness of the diverse data sources available, and helps practitioners identify realistic objectives for remote sensing in coral reef areas.     

低头坝养鱼对上下游局域栖息地和鱼类群落时空格局的影响

河流鱼类的群落特征会随栖息地环境的变化而发生变化.为了解鱼类群落对低头坝养鱼的响应程度,2013—2014年共6次调查了乌龙河(长江下游支流)两个可涉水河段样点(上游坝和下游坝)的环境因子、鱼类多样性及其群落结构.共采集到5目10科21属24种鱼类,以鲤形目鲤科最多,占总数的58.3%.通过解析时空动态变化与局域栖息地条件对鱼类群落的影响,发现季节因素对鱼类群落结构无显著影响,而鱼类群落所在空间位置(上游坝,下游坝)对群落结构差异具有较显著影响,其中上游中华鳑鲏(Rhodeus sinensis)、(Hemiculter leucisculus)、棒花鱼(Abbottina rivularis)、大鳍鱊(Acheilognathus macropterus),下游食蚊鱼(Gambusia affinis)的多度决定了这种差异;而3个栖息地变量(溶解氧浓度、电导率和流速)均对鱼类群落特征具有显著性影响.栖息地环境差异对河流上、下游鱼类群落的影响较大,具体体现在下游样点鱼类的捕获重量、捕获数量、密度、多样性明显下降,推测利用低头坝养鱼是造成这些现象的重要原因.     

Benthic status of near-shore fishing grounds in the central Philippines and associated seahorse densities

Benthic status of 28 near-shore, artisanal, coral reef fishing grounds in the central Philippines was assessed (2000-2002) together with surveys of the seahorse, Hippocampus comes. Our measures of benthic quality and seahorse densities reveal some of the most degraded coral reefs in the world. Abiotic structure dominated the fishing grounds: 69% of the benthos comprised rubble (32%), sand/silt (28%) and dead coral (9%). Predominant biotic structure included live coral (12%) and Sargassum (11%). Rubble cover increased with increasing distance from municipal enforcement centers and coincided with substantial blast fishing in this region of the Philippines. Over 2 years, we measured a significant decrease in benthic 'heterogeneity' and a 16% increase in rubble cover. Poor benthic quality was concomitant with extremely low seahorse densities (524 fish per km(2)). Spatial management, such as marine reserves, may help to minimize habitat damage and to rebuild depleted populations of seahorses and other reef fauna.     

Coral reef health and effects of socio-economic factors in Fiji and Cook Islands

This research focuses on coral reef health in the South Pacific region, an area of high global coral diversity. Coral reef health surrounding four island case studies in the Cook Islands and Fiji have been assessed in areas that have not been previously surveyed. This study compares four islands with barrier and fringing reefs that have different levels of economic development, population pressure, land-use practices, and marine management practices. This interdisciplinary research methodology includes both ecological and social data collection to further understanding of human environment interactions. In comparing the reefs with different socio-economic factors, this research shows that reefs with traditional systems of resources management are healthier, population pressure is not the main factor causing the demise of the reefs and agro-industry is the main industry causing the degradation of the reef in these four South Pacific Islands. In addition, researchers need to use a whole reef perspective to examine coral reef health.     

Baseline study of the spatio-temporal patterns of reef fish assemblages prior to a major mining project in New Caledonia (South Pacific)

From 2008 onwards, the coral reefs of Koné (New Caledonia) will be subjected to a major anthropogenic perturbation linked to development of a nickel mine. Dredging and sediment runoff may directly damage the reef environment whereas job creation should generate a large demographic increase and thus a rise in fishing activities. This study analyzed reef fish assemblages between 2002 and 2007 with a focus on spatio-temporal variability. Our results indicate strong spatial structure of fish assemblages through time. Total species richness, density and biomass were highly variable between years but temporal variations were consistent among biotopes. A remarkable spatio-temporal stability was observed for trophic (mean 4.6% piscivores, 53.1% carnivores, 30.8% herbivores and 11.4% planktivores) and home range structures of species abundance contributions. These results are discussed and compared with others sites of the South Pacific. For monitoring perspectives, some indicators related to expected disturbances are proposed.     

Can dynamite-blasted reefs recover? A novel, low-tech approach to stimulating natural recovery in fish and coral populations

Throughout Southeast Asia, blast fishing creates persistent rubble fields with low coral cover and depauperate fish communities. We stabilized a 20-year-old rubble field in a Marine Protected Area in the Philippines, using plastic mesh and rock piles in replicated 17.5m(2) plots, thereby increasing topographic complexity, fish habitat, and recruitment substrate surface area. Multivariate analysis revealed fish community shifts within the rehabilitated area from that characteristic of rubble fields to one similar to the adjacent healthy reef within three years, as measured by changes in fish abundance and body size. Coral recruitment and percent cover increased over time, with 63.5% recruit survivorship within plots, compared with 6% on rubble. Our low-cost approach created a stable substrate favoring natural recovery processes. Both rehabilitation and the elimination of poaching were integral to success, emphasizing the synergism between the two and the need to incorporate both when considering mitigation.     

River discharge reduces reef coral diversity in Palau

Coral community structure is often governed by a suite of processes that are becoming increasingly influenced by land-use changes and related terrestrial discharges. We studied sites along a watershed gradient to examine both the physical environment and the associated biological communities. Transplanted corals showed no differences in growth rates and mortality along the watershed gradient. However, coral cover, coral richness, and coral colony density increased with increasing distance from the mouth of the bay. There was a negative relationship between coral cover and mean suspended solids concentration. Negative relationships were also found between terrigenous sedimentation rates and the richness of adult and juvenile corals. These results have major implications not only for Pacific islands but for all countries with reef systems downstream of rivers. Land development very often leads to increases in river runoff and suspended solids concentrations that reduce coral cover and coral diversity on adjacent reefs.     

Fatty acid profiles of benthic environment associated with artificial reefs in subtropical Hong Kong

Artificial reefs can enhance habitat heterogeneity, especially in seabed degraded by bottom-dredging and trawling. However, the trophodynamics of such reef systems are not well understood. This study provided baseline data on trophic relationships in the benthic environment associated with artificial reefs in late spring and mid summer of subtropical Hong Kong, using fatty acid profiles as an indicator. Data from sediments collected at the reef base, materials from sediment traps deployed on top and bottom of the reefs, total particulate matter from the water column and oyster tissues from reef surface were subjected to principal component analysis. Results showed variations of fatty acid profiles in the total particulate matter, upper sediment trap and oyster tissue samples collected in the two samplings, indicating seasonal, trophodynamic changes within the reef system. The wastes produced by fish aggregating at the reefs can also contribute a source of biodeposits to the nearby benthic environment.     

Effects of habitat structural complexity on diversity patterns of neotropical fish assemblages in the Bita River Basin,Colombia

Several studies have shown that fish assemblages are structured by habitat features, most of them have proposed that there is a positive relationship between habitat structural complexity and species diversity. In this study, we aimed to test this positive-relationship idea in three habitats types (creeks, oxbow lakes and river sandbanks) distributed along the Bita River Basin in South America. Standardized surveys were conducted during January and February of 2016 (low water period) in 30 sites distributed along the entire basin. We recorded 23,092 individuals representing 191 species. To investigate possible relationships between habitat structural complexity and species diversity, we calculated the first three Hill’s numbers, and performed a Non-metric Multidimensional Scaling (NMDS), a Principal Component Analysis (PCA) and a Canonical Correspondence Analysis (CCA). Our results showed that river sandbanks and creeks had the highest species richness. Results from the NMDS analysis (stress = 0.19) showed that fish community composition was different in the assessed habitats (ANOSIM < p = 0.001). According to the results of the principal component analysis, sand percentage, dissolved oxygen, and vegetation width separated river sandbanks from the other habitats. Results from the Hill’s numbers, forward selection procedure, and canonical correspondence analysis suggested that species composition and diversity were significantly influenced by the habitat structural complexity index and conductivity.     

The influence of land use patterns on water quality at multiple spatial scales in a river system

The influence of land use patterns on water quality in a river system is scale‐dependent. In this study, a four‐order hierarchical arrangement method was used to select water sampling sites and to delineate sub‐basins in the Daliao River Basin, China. The 20 sub‐basins were classified into four spatial scales that represented four different stream orders. Pearson correlation analysis was used to quantify relationships between land use composition and the river's physical‐chemical variables for all samples collected. This analysis showed that the presence of forest cover was associated with higher water quality at the scale of the whole basin. The scale effects of land use patterns on water quality were then examined using stepwise multiple regression analysis that compared different land use types with water quality variables. The results from this analysis showed that urban areas, as opposed to forest areas, became the most significant contributors of water pollutants when scale effects were considered. The influence of urban land cover on water pollution was significantly higher at larger scales. The lack of a significant regression correlation for the forest land use type at smaller scales revealed that forest located upstream of the Daliao River Basin did not provide a buffer for improved water quality. Further analysis showed that this result could be because of disproportionate spatial distributions for forest and urban land use types. The topographic characteristics of sub‐basins, such as average slope (S) and size (A), were determined to be secondary explanatory variables that affected land use impacts on stream water quality. Areas with steep slopes were associated with increased water oxygenation, whereas areas with flatter slopes were associated with higher concentrations of pollutants. These results are significant because they can provide a better understanding of the appropriate spatial scale required for effective river basin management in the future. Copyright © 2013 John Wiley & Sons, Ltd.     

鄱阳湖水位变化对候鸟栖息地的影响

鄱阳湖越冬候鸟保护最重要的环节是保护栖息地,候鸟栖息地的面积和空间分布随水位过程而变化.在分析认定鄱阳湖湿地景观分类中水陆过渡带及其上下摆动区(稀疏草滩区和浅水区)为越冬候鸟主要栖息地的基础上,选择不同水位的遥感影像资料,经解译定量分析不同水位水陆过渡带面积及其空间分布,从而分析不同水位条件对候鸟柄息地的影响.进而分析...