Anthropogenic factors and habitat complexity influence biodiversity but wave exposure drives species turnover of a subtropical rocky inter‐tidal metacommunity

Coastal ecosystems are complex and species rich, but are vulnerable to degradation from a variety of anthropogenic activities. Nevertheless, information on inter‐tidal community composition in the Caribbean Basin and at other oceanic sites is lacking. Such information is essential to developing a more comprehensive understanding of rocky inter‐tidal systems and their responses to global change. The goals of this study were to determine the relative importance of environmental (wave power density, wave height), habitat (e.g. algal cover, slope, complexity of rock surfaces) and anthropogenic (distance to roads, population density) factors associated with the structure of local assemblages at multiple shore heights and the regional metacommunity of mobile invertebrates on oceanic rocky inter‐tidal habitats. Environmental characteristics associated with habitat complexity (algal cover, rock surface complexity) and human population density were most strongly associated with abundance and biodiversity of invertebrates. Species richness was positively correlated with surface complexity, but abundance was negatively correlated with both surface complexity and per cent algal cover. By contrast, abundance of invertebrates was positively correlated with human population density, and diversity was negatively correlated with human population density. Abundance of invertebrates was greatest in the mid inter‐tidal zone, whereas diversity was greatest in the lower inter‐tidal zone. Metacommunity structure was Gleasonian, but the gradient along which species turnover occurred was correlated with measures of wave exposure, rather than anthropogenic activity. Unlike in previous studies, mostly at mainland sites, human activity primarily altered dominance patterns of communities, while having relatively little effect on species richness or composition.     

Spatio‐temporal dynamics of the surf‐zone faunal assemblages at a Southern Oregon sandy beach

Sandy beach/surf‐zone ecosystems are unique environments that, despite the harsh and highly variable hydrodynamic conditions, present a diverse and heterogeneous fauna. However, the dynamics of these ecosystems are currently poorly understood. In this study we tested the hypothesis that surf‐zone assemblages vary with temporal factors such as time of day, tide and tidal height. To test this hypothesis, the surf‐zone community of Bastendorff, a Southern Oregon sandy beach was sampled during the summer of 2006. Samples were collected to (i) describe the smaller, benthic and larger swimming assemblages, (ii) determine whether assemblage compositions, densities, species richness and diversity vary with time of day, tide and tidal height, (iii) explore potential reasons for the variation by correlating environmental factors to the assemblages, and (iv) identify particular species that most strongly exhibit these variations. A hyperbenthic sledge, a sediment corer and a beach seine were used to collect the smaller swimming, benthic and larger swimming fauna, respectively. Sampling occurred during day and night, spring and neap tide, and high, mid and low tide. A total of 76,743 individuals belonging to 105 species were collected. Ninety‐one invertebrate (72,904 individuals), 15 invertebrates (2234 individuals), and 19 invertebrate and vertebrate species (1605 individuals) were collected with the sledge, corer and seine, respectively. Nine species of fish were caught, 98% of which were juveniles. The smaller and larger swimming assemblages varied most strongly with the time of day, suggesting certain species will actively move to the shallow surf‐zone at night. The three assemblages also varied with the tide, potentially due to the larger waves and higher abundance of detached macrophytes observed during spring tides when compared to neap tides, which could push individuals into the surf zone. The benthic assemblage most strongly varied with tidal height and sand grain size, confirming the presence of different faunal zones within Oregon sandy beaches. Finally, several variables of the swimming assemblages varied with temperature and salinity, suggesting that downwelling favorable conditions may have transported species close to shore. Bastendorff presents a complex and diverse surf‐zone community that appears to be influenced by diel species movements, environmental variables such as wave height and abundance of detached macrophytes, and regional oceanographic conditions.     

Diurnal and tidal patterns of carbon uptake and calcification in geniculate inter‐tidal coralline algae

Research on coralline algal responses to ocean acidification and other environmental stressors has increased in recent years as coralline algae is thought to stand a higher chance of being affected by acidification stress than other macroalgae. To provide context and enhance the existing eco‐physiological framework for climate change studies, it is important to understand the effects of non‐extreme stressors experienced regularly by inter‐tidal coralline algae. In this study, we tested the potentially interacting effects of diurnal and tidal treatments on calcification in the geniculate coralline algae Corallina frondescens and Corallina vancouveriensis using ¹³C‐labeled bicarbonate. Both species deposited more calcium carbonate during the day than at night, and also when submerged (high tide) compared with when emerged (low tide) in their apical and mature segments (intergenicula). These results indicate that inter‐tidal coralline algae do in fact pay a cost for living inter‐tidally at the edge of an adaptive zone.     

琼州海峡南岸海岸动力地貌研究

岬湾相间的琼州海峡南岸在海岸动力条件作用下,岸滩发生侵蚀或堆积,特别是南岸中部的南渡江三角洲沿岸岸滩演变剧烈。该文从海岸动力地貌的角度,对琼州海峡南岸的海岸动力特征、泥沙运动以及岸滩演变进行分析。根据海峡南部三维潮流场数值模拟结果,结合经验公式初步分析潮流引起的泥沙运移速率和方向,得到岸外水域总的泥沙运移趋势为从西向东。根据波浪动力计算分析沿岸泥沙运移,探讨沙质岸滩的动态与地貌演变之间的关系,得出海峡南岸海岸地貌演变与盛行的NE和NNE向风浪有密切关系,岸滩的演变过程主要受制于这两个方向的风浪及其引起的泥沙沿岸运移。     

淤泥质海床相邻的岬湾沙滩剖面特征研究

通过对浙江沿海岬角海湾沙滩多处典型剖面的调查,结果表明沙滩与淤泥质海床存在较明显的沙泥分界线,滩面物质自北至南,粒径差别不大,中值粒径在0.15~0.25mm之间,滩面基本呈现单一坡度,坡度为1∶15~1∶30,沙滩坡度与波浪动力相关,沙滩前沿波浪动力强,滩面较缓,反之滩面较陡。沙滩退化表现为滩面的截断、粗化和泥化,滩面截断导致沙滩面积减少,中、细沙供给不足;细沙采挖或局部工程导致的沿岸输沙动力条件的改变会使滩面物质变粗;岬湾的水动力条件减弱,易使沙泥分界线抬升,局部泥化;过度挖沙会导致沙滩消失成为泥滩。     

Influence of rock‐pool characteristics on the distribution and abundance of inter‐tidal fishes

Rock pools can be found in inter‐tidal marine environments worldwide; however, there have been few studies exploring what drives their, fish species composition, especially in Australia. The rock‐pool environment is highly dynamic and offers a unique natural laboratory to study the habitat choices, physiological limitations and adaptations of inter‐tidal fish species. In this study rock pools of the Sydney region were sampled to determine how the physical (volume, depth, rock cover and vertical position) and biological (algal cover and predator presence) parameters of pools influence fish distribution and abundance. A total of 27 fish species representing 14 families was observed in tide pools at the four study locations. The five most abundant species were Bathygobius cocosensis, Centropogon australis, Enneapterygius atrogulare, Lepidoblennius haplodactylus and Microcanthus strigatus, which together represented 71% of the total number of fish recorded. Larger rock pools containing more algal and rock ledge cover hosted a larger and more diverse population of fish. Furthermore, certain species were only found in pools with specific characteristics, such as the presence of loose shells, a variety algae or rock cover, suggesting a high degree of habitat specificity. By contrast, some species were ubiquitous and thus can likely tolerate a wide variety of physical conditions.     

Community structure and functional traits of mollusks associated with coastal reef macroalgae in Northeastern Brazil

This study investigated the community structure and functional traits of the mollusk fauna associated with macroalgae with different thallus morphologies in a reef environment in Northeastern Brazil. A total of 15 individuals of each species of macroalgae adhered to natural substrate and 15 individuals of Padina gymnospora detached from the substrate were collected. The structural complexity of algal habitats was measured and the associated malacofauna screened and identified. All three macroalgae differed significantly in the complexity of their habitat, with Sargassum polyceratium being the most complex. A total of 823 specimens of mollusks belonging to 22 species and 11 families were recorded, of which Columbellidae was the most represented with six species. The functional trait “size” revealed that micromollusks smaller than 10 millimeters were predominant in the community; however, individuals of larger sizes (up to 24.54 millimeters) belonging to young stages of other species were also present. Eight functional trophic groups were identified, of which “carnivorous” stood out with seven species. Six functional groups of microhabitats were identified, with intra‐specific variation in habitats, while habitat expansion was documented for species not yet recorded in association with macroalgae. The structure of the molluskan community differed among the three algae species with the greatest richness, abundance, and diversity of mollusks and functional traits occurring with S. polyceratium. Community structure differed between algae adhered to natural substrate and detached algae, with the latter having lower mollusk richness and diversity, but with greater abundance of some species that remained on algal fronds after release from the reef environment. This study reinforces the importance of algal habitat for marine invertebrate fauna, especially for micromollusks that spend their entire life cycle, or part of it, in association with macroalgae.     

潮汐汊道及其沙滩的安全风险和动力机制

为提高海水浴场的安全性,避免发生溺水事故,文章以潮汐汊道及其沙滩的动力地貌结构和发育演变为基础,研究青岛市灵山湾城市阳台海水浴场沙滩的安全风险和动力机制,并提出风险防范建议。研究结果表明:河口潮汐汊道落潮流三角洲的潮汐水道延伸至沙滩滩面,高潮时淹没,落急时水流集中,形成流向外海的高速水流,极易引发海水浴场安全事故;区域落潮流与汊道落潮流相叠加、落潮流三角洲阻挡沿岸输沙造成下游局部岸段侵蚀以及沿岸输沙变化导致水道迁移摆动等因素进一步加大潮汐汊道附近沙滩的安全风险;安全风险最大的地点位于沿岸输沙下游与区域落潮流流向一致的潮汐水道末端附近沙滩,且该位置不稳定,随波浪场发生年际和季节变化;在潮汐汊道沙滩岸段设置海水浴场前应研究其动力地貌和发育演变,划分危险区和安全区,浴场设置后定期监测并确定危险区的位置,并在沙滩安全维护和质量评价等方面将潮汐汊道作为重要判定指标。     

Macrobenthic surf zone communities of temperate sandy beaches: spatial and temporal patterns

The spatial and temporal patterns within the surf zone epibenthic assemblages were studied in a coastal fringe of Argentina to determine whether assemblage compositions, abundance, species richness and diversity vary spatially and temporarily. Sampling was conducted seasonally in two sandy beaches over 2 years with a benthic sledge used to collect the fauna in the upper centimeters of soft bottom sediments and the epifauna on the sediment surface. Physical variables were measured in the same coastal sites where biological sampling was conducted. A total of 58 morphospecies were collected. Peracarid crustaceans were the most abundant group. The mysid Pseudobranchiomysis arenae (new genus–new species) (29.73 ± 17.79 ind. per sample) and the isopod Leptoserolis bonaerensis (51.54 ± 22.35 ind. per sample) were the most abundant and common species and were present regularly throughout the sampling period. Differences in the surf zone community composition were found between the beaches; these differences could be related to variation in physical parameters such as sand grain size and wave climate, indicating the possible influence of the morphodynamic state of the beaches on the epibenthic assemblages. A seasonal abundance trend was detected, reflecting the changes in abundance of the two dominant species; the richness pattern was not easily detectable due to the sporadic appearance of non‐resident species in the surf zone, probably due to different causes, including dispersion by entry of water from surrounding areas, littoral currents and storms. The surf zone studied presents a complex and dynamic epibenthic community that appears to be influenced by the morphodynamic state of the beach and the dynamic of non‐resident species.     

东海岛东北部砂质岸滩年度冲淤变化及沉积物运移分析

东海岛是全国第五大岛,其东部长达28km的海滩是"中国第一长滩"。近年来因海平面上升和人类开发,该海滩局部出现较为严重的海岸侵蚀。基于高精度GPS监测结果及表层沉积物粒度测试结果,使用GSTA趋势分析模型,研究了东海岛东北部砂质岸滩的季节性冲淤变化及沉积物运移趋势,探讨了海岸侵蚀机制。结果表明,研究区岸滩沉积物的运移主要受潮流的控制,以沿岸向北运移为主。研究区南部岸滩紧邻低滩灯塔形成的波影区,沉积物供应较少,岸滩以侵蚀为主;研究区北部沿岸流搬运的沉积物能从南侧得到补给,加之向岸运移的沉积物,岸滩多处于淤积状态。     

琼州海峡白沙门海滩冲淤的遥感分析

琼州海峡白沙门海滩是海口市重要旅游资源,历史研究表明自20世纪60年代以来其一直处于侵蚀退化状态。本文选取1994—2015年的19景Landsat遥感影像提取白沙门海滩水边线并计算海滩坡度,分析海滩冲淤,结果表明:1994—2008年海滩处于冲刷状态,高潮位的水边线平均向岸回退了104.71 m, 低潮位的水边线平均向岸回退了95.49 m,但是2000年附近时段的人工补沙弥补了海滩侵蚀退化;2008—2015年海滩转为淤积状态,高潮位的水边线平均向海前进了34.17 m,低潮位的水边线平均向海前进了25.52 m,海滩淤积可能是海滩东侧的新埠岛围填海工程造成的。     

Beach nourishment effects on sand porosity variability

A standard assumption in coastal engineering is that the porosity of natural beach sand (non-cohesive) is 40%. However, is this assumption correct for all beach sand? This paper proposes an accurate and simplified method to assess changes in sand porosity after beach nourishment by means of in-situ density surveys through a nuclear densimeter. This novel application has been applied to different beaches in the southwest of Spain according to the tidal range, grain size and beach morphology in several terms. General results show that sand porosities range from 25.6% to 43.4% after beach nourishment works. This research can be considered a support tool in coastal engineering to find shifting sand volumes as a result of sand porosity variability after beach nourishment and later marine influence.     

设计彩沙示踪法研究滨海沙滩底沙运动--以厦门大学滨海沙滩为例

本文设计彩沙示踪法于厦大滨海沙滩东段进行试验 ,取得了沙粒运动方向、最大运移速度、扩散范围、沿岸输沙率及粒度分异运移状态等定量数据 ,弥补了以往示踪法难以定量分析的缺陷。结果表明 :调查期间 ,厦大滨海沙滩东段沙粒运动是构成厦门岛南岸岸滩在偏东向波浪作用下形成的西南向沿岸漂沙之一个环节 :沙粒大体平行岸线向北运动 ;沙粒沿岸最大运移速度为 2 0 0m/d ;经一个潮周期 ,沙粒向两侧的最大横向扩散距离为 2 0m ,最大垂直扩散深度达 7cm ;岸滩横断面沿岸输沙率为 42 5t/d ;在该岸段沿岸漂沙中 ,粗粒沙偏向低潮带一侧 ,而细粒沙偏向高潮带。     

Appraisal of storm beach buffer width for cyclonic waves

The loss of beach sand from berm and dune due to high waves and surge is a universal phenomenon associated with sporadic storm activities. To protect the development in a coastal hazard zone, hard structures or coastal setback have been established in many countries around the world. In this paper, the requirement of a storm beach buffer, being a lesser extent landward comparing with the coastal setback to ensure the safety of infrastructures, is numerically assessed using the SBEACH model for three categories of wave conditions in terms of storm return period, median sand grain size, berm width, and design water level. Two of the key outputs from the numerical calculations, berm retreat and bar formation offshore, are then analysed, as well as beach profile change. After having performed a series of numerical studies on selected large wave tank (LWT) test results with monochromatic waves using SBEACH, we may conclude that: (1) Berm erosion increases and submerged bar develops further offshore as the storm return period increases for beach with a specific sand grain size, or as the sand grain reduces on a beach under the action of identical wave condition; (2) Higher storm waves yield a large bar to form quicker and subsequently cause wave breaking on the bar crest, which can reduce the wave energy and limit the extent of the eroding berm; (3) A larger buffer width is required for a beach comprising small sand grain, in order to effectively absorb storm wave energy; and (4) Empirical relationships can be tentatively proposed to estimate the storm beach buffer width, from the input of wave conditions and sediment grain size. These results would benefit a beach nourishment project for shore protection or design of a recreational beach.     

Material type and roughness influence structure of inter‐tidal communities on coastal defenses

On a global scale, urbanization has resulted in substantial proportions of coasts being replaced by artificial structures such as marinas, breakwaters and seawalls. There is broad consensus that coastal defense structures are poor surrogates of the natural habitats that they replace. Here we investigated the effects of the type and roughness of materials used for the construction of artificial structures on the surrounding biota by comparing abundances and distribution of key inter‐tidal taxa between natural shores and coastal defenses. Lower abundances of gastropods and barnacles were found on artificial coastal defense structures (regardless of the material type). At small spatial scales, abundances of key taxa increased with increasing roughness. Our results suggest that the choice of materials used for the construction of coastal defense structures has little effect on community structure per se, but that enhanced roughness could make coastal defenses better surrogates of natural habitats by supporting assemblages that are more similar to those found on natural shores.     

Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington

Anomalous morphological features within large estuaries may be: (1) recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes, and (2) possible predictors of cycles of future coastal change. At the entrance to Willapa Bay, Washington, chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of Cape Shoalwater. Northward channel migration since the late 1800s conforms to the long-term net sediment transport direction. What requires explanation is periodic southward relocation of the trunk channel by as much as 5 km, and attendant construction of moderately large sand spits on the north side of the bay such as Kindred Island, Tokeland Peninsula, and Cape Shoalwater.Both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition. Channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges. Under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of El Niño winter storms. However, co-seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition. Unless external forcing changes sand supply and predominant sediment transport directions in the future, the relative rise in sea level, frequent winter storms, and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary.     

近岸波、流作用下结构物附近海岸演变的数值模拟

针对与砂质海岸在波浪作用下的演变有关的波浪、近岸流及输沙问题进行了系统的研究,并对结构物附近海岸演变进行了数值模拟。考虑了波浪折射-绕射及波浪破碎的综合作用,在近岸流场的模拟中用沿水深积分形成的K方程模型确定涡粘系数。计算岸滩地形变化时,综合波浪、近岸流作用的底沙和悬沙输沙率,并考虑波浪对泥沙作用的影响。模型对防波堤和近岸沉船附近地形变化进行了模拟,效果良好。     

Assembly processes in upper subtidal macroalgae: The effect of wave exposure

The structure and diversity of sixteen macroalgal assemblages originating from two coastal locations in the Northern (Kavala gulf) and Central (Maliakos gulf) Aegean in Greece were explored by examining their relative abundance distributions (RADs) and fitting five stochastic niche-based models. A mechanistic interpretation of the underpinning assembly processes was attempted by relating the assumptions of the fitted models with available abiotic data corresponding to each assemblage. The random fraction niche-based model, assuming a random niche apportionment to species, was fitted to the majority of Maliakos assemblages characterized by more evenly distributed and speciose RADs, whereas the random assortment model, assuming no relationship among species abundance and niche size, was fitted to most of the Kavala assemblages characterized by steeper RADs with fewer species. Among the possible underlying mechanisms, wave exposure seems to play a key role in macroalgal assembly processes; however factors such as biogeography and hard substrate availability must be also taken into consideration. Short-term processes as changes in resource availability (nutrients and light), known as drivers of assembly rules in other primary producers (e.g. phytoplankton), do not considerably affect macroalgae in the oligotrophic Eastern Mediterranean, possibly due to their longer life spans.     

Numerical modelling of sand beach evolution around coastal structures

I~crIOWIn the coastal area, especially at the sandy seashore, wave and nearshore current are the major factors which affect sediment transPOrt and the motyhChdynamics.The numerical models of predicting the beach evolution can be classified intO the medi~term and long-term models according to their space and time scales (De Briend et al., 1993;Watanabe, 1990; Watanabe et al., 1986; Tao, 1996). In the medium-term model the effects ofwave, nearshore current and sediment transport are conside…     

Tidal variation in a rocky inter‐tidal fish population: the case of white seabream Diplodus sargus juveniles

The rocky inter‐tidal habitat is a harsh and fluctuating environment, subject to frequent disturbances. Field observations of juvenile white seabream Diplodus sargus in inter‐tidal rocky habitats were conducted to analyse the spatial distribution and feeding activity of this species in relation to the tidal cycle. The depth at which fish were observed did not change in most tidal phases while feeding activity changed with tidal level, showing the occurrence of tidal migrations and that feeding may be limited by habitat availability in shallow waters and thus be dependent on tidal changes. The present results show the exploitation of available feeding areas in the rocky inter‐tidal by juvenile white seabream, which corroborates the importance of these habitats for the first developmental stages of this fish species.