Sandy beach macrofaunal assemblages as indicators of anthropogenic impacts on coastal dunes

Ocean sandy beaches are iconic recreational assets to society and have undergone rapid degradation caused by both natural and anthropogenic pressures. A major effect of urbanisation on biota stems from artificial structures placed in aquatic systems. While the installation of these structures has been widespread, our understanding of how they impact shoreline habitats and fauna is relatively limited. On the sandy Leirosa Beach, on the European Atlantic coast (Portugal), a decade of cumulative impacts was recorded, with disruption of the frontal dune, dune nourishment and the incorporation of geotextiles to reconstruct the dune and maintain it as an artificial structure. Two years after the dune rehabilitation process at Leirosa Beach, seasonal sampling campaigns (from spring 2010 to winter 2011) were carried out to assess the effects of the artificial dune (and the first signs of its eventual disruption) on macrofauna compared to a natural dune on the same beach. During the study period, the rehabilitated foredune maintained the average slope, with similar sediment characteristics (finer sediments) when compared with the natural dune system, with no physical significant differences being appreciated between the two sites. The macrofaunal assemblages were represented especially by crustaceans (amphipods and isopods), with similar mean total density, taxon richness and diversity between sites. Special attention was given to the supralittoral species, and the results revealed that the natural zone harboured a significantly higher density of sandhopper Talitrus saltator with respect to the artificial zone. PERMANOVA results detailed the significant difference that occurred, particularly during the warmer seasons (spring and summer 2010), the recruitment period described for this species along this coast. In fact, SIMPER analysis revealed that T. saltator accounted for 46% of the dissimilarities between the natural and artificial dune sites. The presence of geotextiles extending across the supralittoral zone appeared, on the one hand, to allow for the presence of talitrids, but the application of textiles around the area prevented them from burrowing, thus causing them to avoid the rehabilitated area. The results highlighted the potentially negative effects of this artificial dune system if textile disruption continues, and the usefulness of T. saltator as an effective and reliable ecological indicator for these ecosystems. Thus, evaluating the risks and magnitude of human interventions is a major challenge for sandy beach ecologists, and baseline information is required if we are to better understand how resident macrofaunal species deal with future impact scenarios.     

Variation of the Locomotor Activity Rhythms in Three Species of Talitrid Amphipods,Talitrus saltator,Orchestia montagui,and O. gammarellus,from Various Habitats

The expression of biological rhythms was investigated in five populations of three different species of talitrid amphipods from various habitats in the Maremma Regional Park, Grosseto, Italy: Talitrus saltator (from a sandy beach and a canal), Orchestia montagui (form a Posidonia banquette), and O. gammarellus (from a cave entrance and a river bank). Locomotor activity rhythms were recorded in individual animals over 21 days in constant dark at a temperature of 18°±1°C. A high variability in rhythm expression was evident, not only among species and populations but also within populations and the activity pattern of individuals. Activity rhythms of T. saltator and O. montagui were similar, with a good definition and precise circadian periodicity, whereas O. gammarellus showed a high variability and low definition of the circadian rhythm. Significant differences were also observed between two populations of O. gammarellus and T. saltator from different habitats. Within the O. gammarellus species, a significantly higher percentage of active animals (p<0.001) was observed in the cave than the river‐bank population; within T. saltator, a significantly lower percentage of active animals (p<0.01) and higher percentage of periodic animals (p<0.05) was found in the canal than the sandy beach population. With reference to environmental stability and variability, the differences observed are explained as a need for plasticity to adapt to environmental changes.     

On the role of Posidonia oceanica beach wrack for macroinvertebrates of a Tyrrhenian sandy shore

The use of Posidonia oceanica beach wrack by macroinvertebrates of the sandy beach at Burano (Tuscany, Italy) was assessed by following the colonisation dynamics of the wrack and analysing the stable isotopes ‘scenario’ of the main local carbon and nitrogen sources and consumers. One-hundred experimental cylinders, filled with P. oceanica wrack, were placed on the beach and sampled over a 1-month period. Abundance and species richness of macroinvertebrates in wracks varied through time. Wrack was colonised by crustaceans almost immediately after deployment of the experimental cylinders. The amphipod Talitrus saltator largely dominated the faunal assembly and, together with the isopod Tylos europaeus, occupied the wracks closer to the sealine. These were followed by dipterans, staphylinids, pselaphids and tenebrionids that occurred in drier wracks higher up on the eulittoral. Moisture content of the wrack and sand decreased through space and time. This was the primary factor explaining the spatial and temporal changes observed in macroinvertebrate abundance, with species colonising or abandoning wracks according to thresholds of environmental parameters. Isotopic analysis clearly established the absence of any direct dietary link between P. oceanica wrack and macroinvertebrates. Terrestrial food sources were also discarded. Both our experimental data and a literature search showed that the organic matter from seston as filtered by the sand is the most plausible carbon and nitrogen source for beach food webs. Even if P. oceanica wrack is not a trophic source for macroinvertebrates, it is vitally important as a physical structure that provides detritivorous and predatory species with refuge from environmentally stressful conditions.     

Comparison of the epifauna spatial distribution in Posidonia oceanica,Cymodocea nodosa and unvegetated bottoms: Importance of meadow edges

In order to detect the influence of seagrass, the most important habitats of shallow soft-bottom along the Mediterranean coast, on spatial distribution of epifauna, four different types of habitat were sampled: Posidonia oceanica, Cymodocea nodosa, edge of Posidonia meadow and sandy bottoms. Sampling was carried out, using the hand net method, in various random sites and at different times (April 95, August 95 and February 96) on the Alicante coast (SE Spain). A double taxonomic approach was used in order to detect spatial and temporal changes in the abundance of the main taxonomic groups and amphipod species. The differences among habitats were detected by non-parametric multidimensional scaling (MDS) for community structure and by analysis of variance for groups and amphipod populations. The community structure defined by the abundance of taxonomic groups was not significantly modified by the habitats. Single abundance of taxonomic groups also had no significant preference for the type of habitat except in the case of Acari, a group linked to Posidonia. However, certain trends of preference, such as mysids on Posidonia edge and isopods on Cymodocea, were detectable. On other hand, the amphipod assemblage showed important differences among habitats. Some species changed significantly in abundance depending on the habitat considered, e.g. Dexamine spiniventris and Perioculodes longimanus. It was possible to conclude that there is an important influence of Posidonia and Cymodocea on epifauna distribution by diversification of habitat structure on sandy bottoms, but it was more important at the species level than when considering taxonomic groups. Furthermore, sandy bottoms and the meadow edges had a relatively high importance on fauna distribution, depending on taxa and the period of the year.     

Donax trunculus (Bivalvia: Donacidae) as a potential biological indicator of grain-size variations in beach sediment

Donax trunculus (Linnaeus, 1758) is one of the most common bivalve molluscs inhabiting the sandy shores of the Mediterranean Sea. This species, which is preferentially distributed on sediments at depths between 0 and about 2 m, is considered to be a substrate-sensitive organism because of its sensitivity to sediment grain size variations during its life cycle, in particular during its early growth stages. This study aims at investigating the relationship between D. trunculus’ density distributions and sediment grain size, in order to evaluate its use as a biological indicator of grain-size variations in beach sediment. For this purpose, a specific environmental study was performed by ISPRA (Italian National Institute for Environmental Protection and Research) along six beaches located in the Central Tyrrhenian Sea between Ladispoli and Anzio (Rome, Italy). On each beach, samples of D. trunculus and superficial sediments were collected in the infra-littoral zone at 3 different depths (0, 0.5, and 1 m) between June 2002 and March 2004. The results pointed out that the distribution of D. trunculus populations is strongly influenced by the sediment's grain size variations. A significant positive correlation was found between species density and the 2.00-phi and 2.50-phi grain size classes; but, in particular, the predominance of the 2.00-phi grain size class in the beach's sediment seems to positively influence the species density and distribution.This study suggests that sediment grain size is the chief factor controlling the distribution of D. trunculus populations; suitable grain sizes allow the settlement and the subsequent growth of well-structured populations. Generally, species density declined in areas subjected to grain-size variations in beach sediments, suggesting a predictable biological response to both natural and human-caused stressors. The present study also highlighted that where nourishment was carried out using suitable sediments, the species reappears on the beach after a few months, as it finds an optimal substrate for settlement. In this case, finding D. trunculus specimens a few months after replenishment indicates that the nourishment operations have been successful from an environmental point of view. As reported by Carignan and Villard (2002), a species that is strongly associated with particular habitat features could be a useful indicator; in particular, a species – like D. trunculus – that is negatively associated with human disturbances could be considered a “positive” indicator of ecological integrity.Long-term monitoring of D. trunculus abundance or density on sandy beaches (adequately carried out during the species’ recruitment period, e.g. between July and September), could help pinpoint the presence of natural or human-made phenomena that are leading to grain-size variations in the sediment. In conclusion, we can assume that D. trunculus can be used as a practical biological indicator to detect grain size variations on sandy beaches in coastal monitoring programmes; it could be a useful tool for researchers, managers and administrators to assess erosion phenomena while minimizing times and costs, also in view of an integrated coastal zone management.     

Effects of nourishment on the form and function of an estuarine beach

Beach nourishment programs in estuaries can enhance shore protection, but they decrease habitat suitability by creating higher berms and wider backshores than would occur under natural conditions. Use of sediment sources from outside the area can result in sedimentary characteristics that differ from native sediments on the surface and at depth, altering conditions for both aeolian transport to dunes and interstitial fauna. Field data were gathered on an estuarine beach to determine differences in beach profile change, depth of sediment reworking, and potential for aeolian transport due to nourishment. Data were gathered over a 20-month period 6 months prior to nourishment, 3 days after nourishment, 6 months after nourishment, and 14 months after nourishment when the beach was mechanically graded to eliminate a vertical scarp in the foreshore. The nourishment consisted of 87,900 m³ of sediment emplaced to create a 1.34-km-long, 30-m-wide berm 2.3 m above mean tide level. Seven percent of the fill was removed from the profile within 6 months after nourishment, accompanied by 7 m in horizontal retreat of the artificial berm. The fill on the backshore remained above the zone of wave influence over a winter storm season and was separated from the active foreshore by the scarp. Nourished sediments on the intertidal foreshore were significantly different from native sediments to a depth of 0.20 m below the surface. A lag surface of coarse sediment formed by deflation on the backshore, resulting in a rate of aeolian transport <2% of the rate on the wave-reworked foreshore.Nourishing a beach to a level higher than would be created by natural processes can create a profile that compartmentalizes and restricts transport of sediment and movement of fauna between the foreshore and backshore. Mechanical grading can eliminate the scarp, allow for faunal interaction, and reestablish wave reworking of the backshore that will facilitate aeolian transport. Using an initial design to nourish the backshore at a lower elevation and allowing a dune to provide protection against flooding during major storms could prevent a scarp from forming and eliminate the need for follow-up grading.     

Estimating the Effect of Beach Nourishment on Caretta caretta (Loggerhead Sea Turtle) Nesting

Caretta caretta (loggerhead sea turtle) nesting activity was recorded daily during three seasons prior to and two seasons immediately following a beach nourishment (replenishment) project in Palm Beach County, Florida. Surveys were done at the nourished beach (Jupiter/Carlin) and at two natural beaches (Juno and Tequesta). The size of the nourishment effect on nesting activity was estimated using Before‐After‐Control‐Impact Paired Series (BACIPS) models. Nesting declined by 4.4 to 5.4 nests km ^{? 1} day ^{? 1} on the nourished beach compared to the two natural beaches in the first season after nourishment. At the same time, false crawls (FC, non‐nesting crawls) increased by 5.0 to 5.6 FC km ^{? 1} day ^{? 1} on the nourished beach. In the second season following nourishment, nesting was reduced by 0.5 to 1.6 nests km ^{? 1} day ^{? 1} on the nourished beach compared to the two natural beaches. The increase in false crawl frequency in the second season following nourishment was 0.7 to 0.9 FC km ^{? 1} day ^{? 1}.These results suggest that beach nourishment significantly decreased loggerhead sea turtle nesting during the first season following the project. However, the size of the effect, in terms of nesting frequency and false crawl frequency, was much reduced by the second season following nourishment.     

Crustaceans as ecological indicators of metropolitan sandy beaches health

We have investigated how indices of beach health perform in predicting the abundances of the crustaceans Emerita brasiliensis and Atlantorchestoidea brasiliensis from 22 metropolitan beaches in the cities of Rio de Janeiro and Niterói. Urbanization, Recreation and Conservation indices were used to assess sandy beaches health. Grain size and beach slope were used as morphodynamics indicators. Diagram from the principal component analysis clearly separated beaches with different urbanization and conservation levels. Generalized additive models (GAM's) were adjusted for species abundance using the indices and morphodynamic parameters as explanatory variables. Lower abundances were predicted for beaches with high levels of urbanization, whereas predictions of higher abundances occurred on beaches with high conservation levels. Using theoretic inference we showed that the urbanization index was the most important predictor for abundance of A. brasiliensis and the conservation index was the most important predictor for E. brasiliensis, reflecting different responses by upper tidal and intertidal species. A. brasiliensis occupies the intermediate and upper beach zones and E. brasiliensis is a swash zone filter-feeder that is more abundant in pristine beaches. Both species are highly subject to the impact of bathers and coastal modification. Unexpected, the recreation index did not show a negative effect on abundance predictions. Urbanization and conservation indices can be suitable metrics to measure anthropogenic effects on macrobenthic species. Moreover, mole crabs and sandhoppers species can be easily monitored. Coastal urbanization is a global phenomenon and we used the diagram of urbanization and conservation levels to expose possible directions for management strategies of metropolitan sandy beaches.     

Modifications of the specific diversity and feeding guilds in an intertidal sediment colonized by an eelgrass meadow (Zostera marina) (Brittany,France)

A sandy beach located in a bay of north Brittany (France) is partly colonized by an eelgrass meadow. The overall macrobenthic fauna, i.e. epifauna, endofauna and fish, living in this seagrass and in non-vegetated sands was compared in terms of species, abundance and biomass in the different feeding guilds. Seagrass makes this habitat more complex by increasing both its surface by 5.45–fold and volume by 4.79–fold. Eighteen species among the 23 living in the non-vegetated sands were observed in the seagrass assemblage. Their abundance and biomass were increased by 7.33–fold and 3.54–fold, respectively. The occurrence of Zostera was associated with the presence of 124 new species and 34 new feeding guilds. In the Zostera meadow, a spatial segregation exists among the taxa from the different microhabitats explored for food-quest. The balanced distribution of biomass within the various microhabitats may suggest that an optimization in the exploitation of feeding resources goes hand in hand with a higher complexity of the trophic web. It looks as if the architecturally increasing complexity of the habitat resulting from the development of a seagrass meadow on sediment both stimulates the abundance and biomass of the indigenous macrobenthic assemblage, increases the specific and functional biodiversity and favours the specialization of feeding guilds.     

Experimental Change of the Orientation of Two Populations of Talitrus saltator (Crustacea Amphipoda Talitridae) from Cap Bon (North‐Eastern Tunisia)

The orientation of sandhopper populations is adapted to the direction of the shoreline of the sandy beaches where they live; this behaviour was shown to be inherited in some Mediterranean populations. The question was open whether this behaviour could be adaptively modified in case of changing shoreline or passive transfer to a new differently oriented shoreline. The Cap Bon beaches in north‐eastern Tunisia are particularly interesting because they belong to two different Mediterranean Basins, the central and the eastern one, and their supra‐tidal populations do not come together. This work verified the effect of experimental change of the shoreline direction in two populations of Talitrus saltator from Cap Bon (north‐eastern Tunisia) through a displacement experiment. We transferred samples of T. saltator from two different localities (Korba and Ratiba) from their original beach to the familiar one and tested their solar and landscape orientation on the new beach that had an almost opposite direction with respect to the previous one. The comparisons of the results on the home beach and the new one confirmed the use of the solar compass in both populations, as well as the importance of landscape view and optical local sky factor in adjusting the escape direction. In both populations, an increase of scatter was observed on the new beach, especially when individuals could see the landscape. Also, a clear behavioural difference between the two populations was recorded, being Ratiba population not significantly oriented to the shoreline when tested on the unfamiliar beach, while Korba population maintained its home direction also on the new beach.     

枸杞岛潮下带沙地生境鱼类群落结构和季节变化

为了解岛礁水域沙地生境的鱼类群落结构特征,评估该生境对鱼类资源养护的潜在作用,于2009年采用多网目组合刺网对枸杞岛潮下带沙质区域进行了逐月采样,同步设置岩礁为对照生境.应用α和β多样性指数结合相对重要性指数、相对渔获率、ABC曲线和聚类排序方法对两种生境中的鱼类组成、多样性变化和群落格局与变化进行了全面探讨.全年在沙地和岩礁生境共采集鱼类63种,隶属11目38科56属,2种生境各自出现的鱼类皆为46种.受暖水种频繁出现在沙地生境的影响,潮下带沙质区域鱼类区系比岩礁生境略显丰富,且春夏季的渔获量普遍高于岩礁生境;由于种类组成均匀度较低,沙地生境各季节的α多样性普遍较低,夏季显著低于岩礁生境.日本须鳎是沙地生境的指示种,为早春、夏末和秋冬季沙地底层优势鱼种.5-7月鳀、多数月份鲻和10月份鳗鲇等种类对沙地生境的阶段性利用,使其形成了区别于以趋礁性鱼类为优势类群的岩礁生境的群落格局和季节动态.沙地是多种鱼类幼鱼阶段的庇护所和饵料场,是鲆鲽类的良好栖息地.沙地生境在维持鱼类区系和养护鱼类资源方面具有重要作用.     

Recovery of sandy beach and maritime forest vegetation on Phuket Island (Thailand) after the major Indian Ocean tsunami of 2004

Question: How rapidly has the sandy beach and maritime forest vegetation on Phuket recovered and regenerated after the impact of the major Indian Ocean tsunami of 2004? What are the characteristics of sandy beach species for regenerating their populations and the invasion patterns of originally non-sandy beach species or other newcomers after the tsunami? Location: Phuket Island, southern Thailand. Methods: Species composition of beaches was studied on the same research plots 6 months before and 9 months after the tsunami. The changes in individual species cover before and after the tsunami were determined by χ² tests. Change in community composition was analysed by detrended correspondence analysis. The relationship between species and environmental factors was analysed by canonical correspondence analysis. Results: The sites disturbed by the tsunami were often invaded by annuals, especially grasses and asteraceous plants, rather than by perennials. In contrast, species with clonal growth by stolons decreased significantly. Factors determining the species habitat differences were soil hardness (penetration resistance of sandy soil), per cent silt content, soil water content and beach management. Habitat differences among originally non-sandy beach herbaceous species that expanded their population or moved to the coast after the disaster were defined by sand accretion or erosion caused by the tsunami. Many sandy beach herbaceous communities changed into Dactyloctenium aegyptium communities because of the tsunami were originally constituted by non-sandy beach D. aegyptium with Cenchrus echinatus. Although the forest floors of most maritime forests were invaded by originally non-sandy beach Tridax procumbens, Eleusine indica or D. aegyptium because of the tsunami, this did not result in a change in the vegetation unit, because species' loss was restricted to the understorey. In time, these forests will recover their previous community composition. Conclusions: Our results suggest that originally non-sandy beach native species invaded the disturbed beaches rapidly after the tsunami but their habitats differ. Sites where sand accumulated on a beach because of the tsunami were invaded by D. aegyptium and E. indica, whereas soil erosion permitted invasion by Digitania adscendens. Tridax procumbens establishes rapidly on wet sites with hard soil, high per cent silt content and low beach management pressure. Sandy beach species with subterranean long rhizomes are strongly tolerant of such disasters. We concluded that the species composition of the beaches disturbed by a temporary large disaster is determined by dormancy and growth forms, with radicoid form being influential.     

Fish community structure and food chain dynamics in the surf-zone of sandy beaches: The role of detached macrophyte detritus

The surf-zones of sandy beaches near Perth, Western Australia often harbour huge accumulations of detached macrophyte detritus. During 2.5 yr sampling, 29 species of fishes were captured over two sandy beaches in this region and the fish community was dominated by juveniles. There was a highly significant positive relationship between the number of fishes and the quantity of detached macrophytes taken in each surf-zone netting. Comparisons of total fish abundance on beaches with and without surf-zone accumulations of detached plants, showed that fishes were two to 10 times more abundant on the beach with weed accumulations, depending on the time of day, and date of sampling. However, despite the overall lower abundance of fishes on the open sandy beach, there was a significant increase in the number of fishes captured over the sandy beach at night. There were also two to five times the number of species over the beach with weed during the day, as opposed to equal numbers of species at night. Seven fish species made up >95% of the total catch and these species fell into two groups with regard to diurnal distribution patterns; those that were equally abundant in weed dominated or open surf-zones, and those that were weed-associated. Analyses of the diets of these fishes and the daytime distribution of an important avian piscivore in the surf-zone suggested that the large quantities of weed in the surf-zone of sandy beaches in this region provide both a rich feeding site for fishes, as well as a refuge from diurnal predators. At night, when visual feeding predators are absent, some fish species move to open sandy areas to feed. Because the majority of fishes in this surf-zone community feed on weed-associated prey, and the input of macrophyte detritus is the major source of primary production in the surf-zone, we argue that the food chain dynamics in the surf-zone in this region are fundamentally different to those of sandy beaches that have been studied previously.     

Spatial and Temporal Variation in Enterococcal Abundance and Its Relationship to the Microbial Community in Hawaii Beach Sand and Water

Recent studies have reported high levels of fecal indicator enterococci in marine beach sand. This study aimed to determine the spatial and temporal variation of enterococcal abundance and to evaluate its relationships with microbial community parameters in Hawaii beach sand and water. Sampling at 23 beaches on the Island of Oahu detected higher levels of enterococci in beach foreshore sand than in beach water on a mass unit basis. Subsequent 8-week consecutive samplings at two selected beaches (Waialae and Kualoa) consistently detected significantly higher levels of enterococci in backshore sand than in foreshore/nearshore sand and beach water. Comparison between the abundance of enterococci and the microbial communities showed that enterococci correlated significantly with total Vibrio in all beach zones but less significantly with total bacterial density and Escherichia coli. Samples from the different zones of Waialae beach were sequenced by 16S rRNA gene pyrosequencing to determine the microbial community structure and diversity. The backshore sand had a significantly more diverse community and contained different major bacterial populations than the other beach zones, which corresponded to the spatial distribution pattern of enterococcal abundance. Taken together, multiple lines of evidence support the possibility of enterococci as autochthonous members of the microbial community in Hawaii beach sand.     

The Effects of Artificial Beach Nourishment on Marine Turtles: Differences between Loggerhead and Green Turtles

Marine turtle reproductive success is correlated with the stability and quality of the nesting environment. Female marine turtles show fidelity to nesting beaches, making artificial beach nourishment practices directly relevant to their recovery. We evaluated the impacts of artificial beach nourishment on Loggerhead ( Caretta caretta ) and Green turtles ( Chelonia mydas ) between artificially nourished and nonnourished beaches. We observed reduced nesting success (ratio of nesting emergences to emergences not resulting in nest deposition) for both species. This negative effect lasted for one season in Loggerheads and for at least one season in Green turtles. Physical attributes of the fill sand did not impede nesting attempts. We argue that the decrease in nesting success resulted from an altered beach profile not favorable for nest deposition, which subsequently improved in later seasons as the beach equilibrated to a more natural slope. We observed a 52.2% decrease in reproductive output (hatchlings km⁻¹ yr⁻¹) for Loggerheads one year postnourishment, with a 44.1% increase observed the two seasons postnourishment. In Green turtles, a 0.8% reduction was observed the first season postnourishment, despite a 13% increase in the nonnourished area. The reduction in reproductive output in both cases was primarily a consequence of decreased nesting success, lowering nest numbers. These results reveal stronger negative effects of beach nourishment on Loggerheads compared to Green turtles and the importance of minimizing excessive nonnesting emergences associated with artificial beach nourishment. Nourished areas also experienced more than 600% increase in the number of Loggerhead hatchlings disoriented by artificial lighting over two years postnourishment.     

Assessment of site specific benthic impact of floating cage farming in the eastern Hios island, Eastern Aegean Sea, Greece

The site specific impact on the benthic fauna was assessed within a 4.64 km² area of intensive aquaculture situated on the eastern side of Hios island (Aegean Sea, Greece) at 11 stations seasonally between November 2000 and October 2001. The benthic fauna showed marked changes in species numbers, diversity and faunal abundance between farm and control sites. The polychaetes Nereis diversicolor, Scolelepis fuliginosa and Capitella capitata were the most dominant species at the farm sites (35% of the total abundance), whilst the most dominant species at the control sites were the polychaete Hyalinoecia brementi and the sipunculid Aspidosiphon muelleri (23% of the total abundance). Species richness, diversity and evenness were higher at the control sites whereas numerical abundance was higher at the farm sites. K-dominance curves suggest a minor impact on the benthic community at the farm sites and temporal changes on macrobenthic assemblages.     

三沙湾浮游动物生态类群演替特征

根据2010年6月-2011年5月三沙湾海域5个航次海洋综合调查资料,对三沙湾浮游动物种群特征进行分析,并与我国不同纬度海湾生态类群结构进行比较.探讨三沙湾海域浮游动物生态类群季节变化特征及其受水团季节变化的影响.研究结果表明:4月和5月三沙湾海域主要受到浙闽沿岸流影响,生物多样性H'指数分别为2.03和2.02;种类数分别仅为17种和19种,明显低于6月、8月和10月;浮游动物生态类群以暖温带近海种为主;优势种种类数少,单一优势种优势性明显,4月中华哲水蚤丰度占浮游动物总丰度的65.03％;群落结构特征与同期我国长江口浮游动物区系特征相似.6月三沙湾海域受到浙闽沿岸流和台湾暖流共同影响,同时因闽北雨季导致大量大陆径流汇入,使得该月浮游动物种群结构复杂,生物多样性指数和种类数全年最高,为3.12和45种,与5月相比,种类更替明显,物种更替率为69.39％;亚热带近海种丰度百分比最高(73.03％),亚热带外海种种类数百分比次之(48.89％),是海域浮游动物生态类群由以暖温带近海种为主向以亚热带外海种为主的过渡时期.8月和10月浙闽沿岸流消失,三沙湾海域受台湾暖流控制,海水温度和盐度升高,生物多样性指数和种类数均略低于6月;生态类群结构以亚热带外海种为主;优势种特征表现为种类数多而各个优势种丰度较低;浮游动物群落结构特征与南海北部海域浮游动物组成极为相似.     

Soil disturbance favours threatened beetle species in sandy grasslands

Soil disturbance is recognised as an important restoration measure for conserving biodiversity in sandy soils. We used a soil disturbance (ploughing) experiment in a sandy grassland as well as a semi-natural disturbance (slope erosion enhanced by cattle trampling) gradient on a sandy slope to test the soil disturbance effects on the ground-living beetle community. Both experimental disturbance and semi-natural disturbance favoured sandy grassland specialists, but there was no overall effect on beetle richness and abundance. Amara lucida and Harpalus spp. were favoured by disturbance while Calathus melanocephalus was disfavoured. Experimental ploughing significantly increased the proportion of red-listed species in disturbed plots compared to non-disturbed controls. In the semi-natural disturbance gradient we found that the beetle community on the disturbed slope differed from that of the flat areas, and there were tendencies for a higher proportion of red-listed species on the slope. We conclude that increasing the area of bare sand in sandy grasslands can have positive effects on many threatened species. Soil disturbance should thus be included as a regular measure in sandy grasslands under conservation management and as a measure to restore high biodiversity in areas where bare sand is rare.