Temporal Variation In Community Structure Research Articles

Temporal Variations in Community Structure and Function of Root-associated Fungi Associated with Pinus sylvestris var. mongholica Plantations in the Mu Us Sandy Land

To illuminate the temporal variations in the structure and functional groups of the root-associated fungal community associated with Mongolian pine Pinus sylvestris var. mongholica plantations in the Mu Us Sandy Land, P. sylvestris var. mongholica plantations with different stand ages （23, 33, and 44 a） were targeted. The community compositions and main drivers of root-associated fungi at different months and stand ages were identified using the Illumina high-throughput sequencing method. The results indicated that： ① There was a distinct temporal distribution in the root-associated fungal community, the sampling month had a significant effect on the diversity of root-associated fungi （P<0.05）, and the values were higher in May and July. The stand age had no significant effect on the diversity of root-associated fungi （P&gt;0.05） and decreased gradually with increasing stand age. ② The dominant phylum of the root-associated fungal community was Ascomycota. The relative abundance of fungal function groups was different within each month and stand age, and the dominant groups were saprotroph-symbiotroph, undefined saprotroph, and ectomycorrhizal fungi. The indicator genera of ectomycorrhizal fungi in May, July, and September were Melanoleuca, Amphinema, and Tricholoma, respectively. ③ The temporal distribution of the root-associated fungal community was significantly affected by annual relative humidity, annual precipitation, soil porosity, ammonia nitrogen, annual sunshine duration, annual temperature, and soil water content （P<0.05）. Soil organic carbon content, soil porosity, annual precipitation, and annual relative humidity were the main factors that significantly affected the indicator genus of the root-associated fungal community. Our results demonstrated that the temporal distribution of the root-associated fungal community was shaped by climate and soil properties, whereas stand age contributed less. This improved information will provide a theoretical basis for the sustainable management of P. sylvestris var mongholica plantations.

Temporal variation in community structure of Dragnet (Pukat Tarik) fishery in relation to ecological variables in an inshore area of Sarawak, Malaysia

Temporal variation in community structure of Dragnet (Pukat Tarik) fishery in relation to ecological variables in an inshore area of Sarawak, Malaysia

Temporal variation in community structure of zoosporic fungi in Lake Biwa, Japan

Zoosporic fungi play an important role in aquatic environments, but their diversity, especially that of parasitic fungi of phytoplankton, has still not been fully revealed. We conducted monthly analyses of the community structure of zoosporic fungi at a pelagic site in Lake Biwa, Japan, from May to December 2016. Metabarcoding analysis, targeted to a large subunit region of ribosomal DNA in the nano-size fraction of particles (2-20 µm), was carried out on the samples. We also counted large phytoplankton and chytrid sporangia attached to the hosts. We detected 3 zoosporic fungal phyla (Blastocladiomycota, Chytridiomycota and Cryptomycota) within 107 operational taxonomic units (OTUs), in which Chytridiomycota was the most diverse and abundant phylum. Few fungal OTUs overlapped between months, and specific communities were detected in each month. These results showed that diverse zoosporic fungi with high temporal variability inhabited the lake. Five large phytoplankton species were found to be infected by chytrids: Staurastrum dorsidentiferum, S. rotula, Closterium aciculare, Asterionella formosa and Aulacoseira granulata. Some chytrids were detected by metabarcoding analysis: Zygophlyctis asterionellae infecting A. formosa, Staurastromyces oculus infecting S. dorsidentiferum and Pendulichytrium sphaericum infecting A. granulata. One OTU detected in association with infected C. aciculare by microscopic counting might have been an obligate parasitic chytrid of C. aciculare. The results indicated that a combination of metabarcoding and microscopic analysis revealed more information on zoosporic fungi, including those that are parasitic.

Structuring forces and β-diversity of benthic diatom metacommunities in soda pans of the Carpathian Basin

ABSTRACTSmall soda lakes represent one of the most vulnerable ecosystem types due to their high hydrological sensitivity to climate change and anthropogenic interventions. Since diatoms are excellent bioindicators, determining the β-diversity and the structuring dynamics of diatom metacommunities can provide valuable information for conservation planning for soda pans. In this study, two diatom metacommunities were surveyed monthly during a one-year period from distinct regions of the Carpathian basin: the Fertő-Hanság National Park (FH) between 2013 and 2014, and the Danube-Tisza Interfluve (DT) between 2014 and 2015. We explored whether β-diversity of diatom assemblages in the two regions is enhanced by species turnover or nestedness (related to richness differences) and investigated the role of deterministic and stochastic processes in shaping β-diversity patterns. Furthermore, we evaluated the contribution of environmental variables, geographic distance and temporal variation to community structure. High β-diversity (>90%) was revealed for both metacommunities, and was maintained primarily by species turnover. Within the metacommunity of the DT where the natural hydrological cycle of soda pans is not disturbed, diatom communities assembled mainly due to the selection force of environment at a spatiotemporal scale. In the soda pans located in the habitat reconstruction area of the FH, besides species-sorting, significant temporal variation in community structure appeared as a result of water management and periodic water supply. Our results point to the need for a conservation management strategy which maintains the natural hydrological regime of small saline lakes, and therefore their habitat heterogeneity which is of high conservation value.

不同时间和空间尺度上台湾水青冈群落谱系结构动态变化

PDF HTML阅读 XML下载 导出引用 引用提醒 不同时间和空间尺度上台湾水青冈群落谱系结构动态变化 DOI: 10.5846/stxb201612302712 作者: 作者单位: 浙江理工大学,浙江理工大学,浙江大学,浙江清凉峰国家级自然保护区管理局,浙江清凉峰国家级自然保护区管理局,浙江大学,浙江理工大学 作者简介: 通讯作者: 中图分类号: 基金项目: 浙江理工大学科研启动项目（13052168-Y）；浙江理工大学"521"人才项目 Dynamics of phylogenetic structure in Fagus hayatae communities vary across temporal and spatial scales Author: Affiliation: Zhejiang Sci-Tech University,Zhejiang Sci-Tech University,,,,,Zhejiang Sci-Tech University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:群落谱系结构是了解群落聚群过程的一个基础研究内容。但是现有大部分研究内容集中在群落组成和结构的时空差异，对谱系结构的动态变化研究较少。以浙江省清凉峰国家级自然保护区的国家二级保护植物台湾水青冈（Fagus hayatae）林为研究对象，利用2006年、2011年、2016年3次群落动态调查数据，从10、20、50m的3个空间尺度上研究该群落在10a间的谱系结构动态变化，分析时空尺度对台湾水青冈群落谱系结构的影响，探究调控台湾水青冈群落动态变化的主要因子，为后期台湾水青冈林的保护提供理论基础。研究发现（1）在10a森林动态变化过程中，群落的MPD指数下降，MNTD指数增加。NRI和NTI指数在大尺度上随时间显著增加，但在小尺度上无显著变化。（2）随着空间尺度的增加，上述指数的动态变化趋势均不断增强。以上结果表明，2006-2016年间台湾水青冈群落总体谱系结构表现出不断聚集的趋势，而近缘种的谱系关系则不断疏远；群落谱系结构的聚集趋势随空间尺度的增加而增强。大尺度上的环境过滤和小尺度上的随机过程和种间竞争作用可能是导致该地区台湾水青冈群落谱系结构动态变化的主要生态学过程。 Abstract:The phylogenetic structure of communities is a fundamental component in our ability to understand community assembly processes and species coexistence. However, although there have been many studies of the spatial and temporal variation in community structure, few have applied these observations to the dynamics of phylogenetic structure. Here, we performed such an analysis to study temporal and spatial variations in the phylogenetic structure of Fagus hayatae communities, Class Ⅱ protected plant, in China. In 2006, all free-standing woody stems with a diameter at breast height (DBH) ≥ 1cm were tagged, mapped, identified, and measured for DBH, and height in a 1 hm2 forest dynamic plot in Qingliangfeng National Nature Reserve, China. This was followed by re-censuses in 2011 and 2016, in which we recorded the survival status and DBH for previously recorded stems and documented new stems with DBH ≥ 1cm. On the basis of these three censuses spread across a decade (2006, 2011, 2016), we measured the dynamics of the phylogenetic structure at three spatial scales (10m, 20m, and 50m). We used global seed plant phylogenetic data to construct a phylogenetic tree of F. hayatae communities, and selected the mean phylogenetic distance (MPD), mean nearest taxon distance (MNTD), net relatedness index (NRI), and nearest taxon index (NTI) to describe the phylogenetic structure of F. hayatae communities. Additionally, we randomly resampled 999 plots at 10m, 20m, 50m scales using a moving split-window technique to create plots at different spatial scales. Analysis across spatial and temporal scales produced the following results. (1) On decadal time scales, the species richness and abundance of F. hayatae communities both decreased. MPD decreased, whereas MNTD increased. NRI and NTI both significantly positively increased at large scales, but did not change at small scales. (2) As the spatial extent of analyses increased, so did the strength of the trends observed. Thus, the phylogenetic structure of F. hayatae communities showed a clustering pattern and was spatial scale dependent. The largest variation in the phylogenetic structure across time was found at the 50m scale. We concluded that from 2006 to 2016, the phylogenetic structure of F. hayatae communities was clustering, whereas the phylogenetic relationships between nearest species became more distant. Moreover, the effects of environmental filtering dominated the phylogenetic structure dynamics of F. hayatae communities at large scales. This is in contrast to the effects of stochastic processes and interspecific competition, which dominated at small scales. Against a background of global climate change and forest degradation, further studies on scale dependence are needed to gain a better understanding of the mechanisms of community assembly, and to protect these endangered species. 参考文献 相似文献 引证文献

How do seasonality, substrate, and management history influence macrofungal fruiting assemblages in a central Amazonian Forest?

AbstractWorldwide, fungal richness peaks in tropical forest biomes where they are the primary drivers of decomposition. Understanding how environmental and anthropogenic factors influence tropical macrofungal fruiting patterns should provide insight as to how, for example, climate change and deforestation may impact their long‐term demographic stability and evolutionary potential. However, in Amazonia no studies have yet to disentangle the effects of substrate, seasonality and forest history on phenology. Here, we quantitate spatial and temporal variation in community structure of fruiting macrofungi in relation to these factors at a long‐term forest management research site in central Amazonia: the Biomass and Nutrients of Tropical Rain Forest (BIONTE's). Basidiome surveys of four substrate classes (leaves, soil, branches and trunks) were conducted along 250 m2 transects in primary and secondary (managed) forests, between 2012–13. From the 669 basidiomes collected, 290 taxa were identified of which 44 percent were restricted to primary and 36 percent to secondary forests. Although species‐accumulation curves did not asymptote, rarefaction analyses and Fisher's alpha indicate contrasting differences in richness among forests in relation to substrate type. For example, leaf litter basidiome richness was higher in secondary forests, whereas the contrary was observed for soil communities, suggesting that variation in fruiting patterns in relation to disturbance is substrate‐dependent possibly due to differences in necromass quality and/or understory micro‐climates. Furthermore, secondary forests harbored significantly lower basidiome richness and abundance in dry months, suggesting synergistic impacts of seasonality and management history on fruiting regimes.

Amphibian skin microbiota exhibits temporal variation in community structure but stability of predicted Bd-inhibitory function.

Host-associated microbiomes are increasingly recognized to contribute to host disease resistance; the temporal dynamics of their community structure and function, however, are poorly understood. We investigated the cutaneous bacterial communities of three newt species, Ichthyosaura alpestris, Lissotriton vulgaris and Triturus cristatus, at approximately weekly intervals for 3 months using 16S ribosomal RNA amplicon sequencing. We hypothesized cutaneous microbiota would vary across time, and that such variation would be linked to changes in predicted fungal-inhibitory function. We observed significant temporal variation within the aquatic phase, and also between aquatic and terrestrial phase newts. By keeping T. cristatus in mesocosms, we demonstrated that structural changes occurred similarly across individuals, highlighting the non-stochastic nature of the bacterial community succession. Temporal changes were mainly associated with fluctuations in relative abundance rather than full turnover of bacterial operational taxonomic units (OTUs). Newt skin microbe fluctuations were not correlated with that of pond microbiota; however, a portion of community variation was explained by environmental temperature. Using a database of amphibian skin bacteria that inhibit the pathogen Batrachochytrium dendrobatidis (Bd), we found that the proportion of reads associated with 'potentially' Bd-inhibitory OTUs did not vary temporally for two of three newt species, suggesting that protective function may be maintained despite temporal variation in community structure.

Three decades of coral reef community dynamics in St. John, USVI: a contrast of scleractinians and octocorals

AbstractTo better understand phase shifts on Caribbean reefs, we quantified community structure on shallow reefs over 27 yr in St. John, U.S. Virgin Islands, contrasted the community dynamics of scleractinians and octocorals, and evaluated the extent to which community structure was associated with rainfall, temperature, and hurricanes. To gain insight into the likely abundance of octocorals on future reefs with low scleractinian cover, we compared two sites dominated by the major Caribbean reef‐building coral Orbicella annularis. Between 1987 and 2013, scleractinian cover declined from 45% to 6% at Yawzi Point, but remained at ~30% at Tektite. We compared changes in community structure using four benthic assemblage constructs—“scleractinian‐focused” (cover of scleractinians, macroalgae, and CTB i.e. crustose coralline algae, algal turf, and bare space), “octocoral‐focused” (abundance of octocorals, cover of macroalgae, and CTB), “octocoral genera” (abundance by genus), and a “complete” approach (all taxa)—to reveal how a consideration of octocoral abundance influenced the interpretation of coral reef community dynamics. Overall, temporal variation in community structure differed among the four assemblage constructs at both sites and was associated with rainfall and mean seawater temperature. These results suggest that: (1) scleractinian‐ and octocoral‐focused communities in the same location responded differentially to the same environmental conditions, (2) their communities generally were influenced more by the chronic effects of rainfall and temperature than acute effects of storms, and (3) octocoral‐focused communities were more resilient to environmental conditions than scleractinian‐focused communities. With further declines in cover of scleractinians, octocoral communities are likely to become more common throughout the Caribbean.

Cryptic regime shift in benthic community structure on shallow reefs in St. John, US Virgin Islands

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 559:1-12 (2016) - DOI: https://doi.org/10.3354/meps11900 FEATURE ARTICLE Cryptic regime shift in benthic community structure on shallow reefs in St. John, US Virgin Islands Peter J. Edmunds1,*, Howard R. Lasker2 1Department of Biology, California State University, 18111 Nordhoff Street, Northridge, CA 91330-8303, USA 2Department of Geology, University at Buffalo, State University of New York, 411 Cooke Hall, Buffalo, NY 14260, USA *Corresponding author: peter.edmunds@csun.edu ABSTRACT: We evaluated whether long-term changes on fringing reefs (7-9 m depth) around St. John, US Virgin Islands, conformed to the ‘coral reef crisis’ involving ongoing collapse of community structure. Annual photoquadrats at 6 sites were used to measure octocoral abundance (by genus) and the cover of scleractinians (by species), macroalgae, crustose coralline algae, algal turf, and bare space. Community structure changed between 1992 and 2014, but did not correspond to large changes in response to pulse disturbances; octocoral abundance declined from 1992 to 2002, but increased to 2014, scleractinians remained uncommon (~4.5% cover), and macroalgae became more abundant. Richness and diversity of octocorals and scleractinians increased following 2000, and together defined 2 communities characterized by distinct taxonomic assemblages and temporally segregated to 1992-2001 versus 2002-2014. Smoothed temporal variation in community structure assessed at generic (Octocorallia) and species (Scleractinia) level was associated most strongly with rainfall, and to a lesser extent with hurricane intensity, thereby underscoring the roles of chronic disturbances in driving gradual changes in community structure. Together, these changes did not conform to the typical coral reef crisis construct, and instead summed to cryptic regime change that has escaped attention by researchers focused on scleractinians and macroalgae. KEY WORDS: Scleractinia · Octocorallia · Ecology · Caribbean · Coral Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Edmunds PJ, Lasker HR (2016) Cryptic regime shift in benthic community structure on shallow reefs in St. John, US Virgin Islands. Mar Ecol Prog Ser 559:1-12. https://doi.org/10.3354/meps11900 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 559. Online publication date: November 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Temporal, regional and geochemical drivers of microbial community variation in the melt ponds of the Ross Sea region, Antarctica

To expand the understanding of the poorly described planktonic bacterial communities inhabiting Antarctic meltwater ponds, this study characterized the community composition and identified environmental drivers influencing community structure from a total of 41 meltwater ponds: 37 from the McMurdo Ice Shelf (Bratina Island) and four from a terrestrial locale (Miers Valley) during three austral summers. DNA fingerprinting coupled with in situ pH and conductivity was utilized to select ponds for in-depth nutrient and chemical analysis and high-throughput sequencing of the bacterial 16S rRNA gene V5–V6 hypervariable region. Conductivity was the strongest driver of community structure across all ponds and for all time points; however, other influential factors (pH, climatological, Hg, Fe, and PO4) were also identified. Unique members of communities (sequences absent in at least one pond) represented a small percentage of total reads but also represented a large proportion of pond biodiversity that was strongly driven by differing environmental variables (Si, B and S). Significant temporal variation in community structure was also identified within the same ponds although major taxa remained present. Miers Valley ponds exhibit greater similarity to Bratina Island ponds rather than between each other, thereby suggesting regional movement of microorganisms. In summary, these data provide the first in-depth investigation of the intra-seasonal and regional variation of the microbial communities inhabiting these ponds and proved that a total of ten cosmopolitan OTUs were the dominant components of ponds throughout all sampling times and locations, their variable relative abundances driving the major dissimilarities in community structure.

Temporal variation in community structure and lipid composition of Thaumarchaeota from subtropical soil: Insight into proposing a new soil pH proxy

Crenarchaeol is a unique glycerol dialkyl glycerol tetraether (GDGT) lipid specific to Thaumarchaeota, which play an important role in the global C and N cycles. GDGTs from Thaumarchaeota have been used to develop proxies for paleoclimate or paleoenvironment studies in aquatic environments. However, our understanding of their response to environmental change in soil remains poor. We addressed this question by investigating the change in archaeal lipid composition and community structure in the context of other environmental variables over a period of 12months in a subtropical soil from Chongming Island, China. The results showed that Nitrososphaera spp. were the dominant archaeal population producing crenarchaeol in the soil. The relative abundance of GDGTs with one and three cyclopentane moieties, and crenarchaeol and its isomer in the core lipid (CL) fraction correlated with seasonal pH change in the soil. We therefore propose a molecular fossil proxy, the thaumarchaeota index (TI), which significantly related to pH in not only Chongming Island soil (R2 0.56, RMSE 0.14, P<0.05), but also global soils (R2 0.51, RMSE 1.39, P<0.001) and five thaumarchaeotal enrichments (R2 0.99, RMSE 0.04, P<0.001). This suggests that TI could be a useful proxy for soil pH, which may corroborate the use of the bacterial GDGT proxy for soil pH, the cyclisation ratio of branched tetraethers (CBT).

Response of benthic macrofauna to an oil pollution: Lessons from the “Prestige” oil spill on the rocky shore of Guéthary (south of the Bay of Biscay, France)

The benthic community on the rocky foreshore of Guéthary (France) has been monitored since 2002. The standardized and quantitative monitoring method counts 20 geographically referenced quadrats spread on three littoral zones: upper mediolittoral, lower mediolittoral and infralittoral zones. The setting up of this monitoring occurred when the “Prestige” sunk close to the Finistere Cape in Galicia (Spain). The oil slick following the shipwreck impacted the Guéthary foreshore in early 2003.After the “Prestige” oil spill, the taxonomic richness decreased in the studied area with a loss of 16 species – from 57 in 2002 (before the shipwreck) to 41 species in 2004. Two or 3 years later, taxonomic richness increased to a level observed prior to the oil spill.Along the years, temporal variations in community structure of benthic macrofauna are revealed by detailed analysis. Some polluo-sensitive species disappeared after 2002 and have not reappeared yet (e.g.: Hymeniacidon perlevis). Some others reappeared two or three years after the spill or even later (e.g.: Amphipholis squamata, Botryllus schlosseri, Calliostoma zizyphinum, Echinus esculentus, etc.). Noteworthy changes were found in 2004 driven by the sudden increase in abundance of grazers. The following years, these abundances went back to a stable level. The benthic community seemed to recover almost 5 years later, although a new composition of macrofauna populations was observed.In overall aspect, the complexity of the benthic ecosystem response to oil spills confirms the need of regularly updated baselines to assess the impact of pollutions and more generally to maintain marine biodiversity.

Assessing biodiversity with sound: Do acoustic diversity indices reflect phylogenetic and functional diversities of bird communities?

Measuring biodiversity is a challenging task for research in taxonomy, ecology and conservation. Biodiversity is commonly measured using metrics related to species richness, phylogenetic-, or functional-trait diversity of species assemblages. Because these metrics are not always correlated with each other, they have to be considered separately. A descriptor of animal diversity based on the diversity of sounds produced by animal communities, named here the Community Acoustic Diversity (CAD), was recently proposed. In many cases, the CAD could be easier to measure than other metrics. Although previous analyses have revealed that acoustic diversity might increase as species richness increases, the ability of CAD to reflect other components of biodiversity has not been formally investigated. The aim of this study is to test theoretically whether functional and phylogenetic diversities could be reflected by acoustic diversity indices in bird communities. Data on species assemblages were collated by the French Breeding Bird Survey describing spatial and temporal variation in community structure and composition across France since 2001. Phylogenetic and functional data were compiled from literature. Acoustic data were obtained from sound libraries. For each of the 19,420 sites sampled, indices of phylogenetic, functional and acoustic diversity of bird communities were calculated based on species’ pair-wise distance matrices and species’ abundances. The different aspects of biodiversity were compared through correlation analyses. The results showed that acoustic diversity was correlated with phylogenetic diversity, when the branch lengths of the tree were considered, and to functional diversity, especially body mass and reproduction. Correlations between phylogenetic, functional and acoustic distances among species did not entirely explain the correlations between phylogenetic, functional and acoustic diversity within communities. This result was interpreted as an effect of local ecological processes underpinning how bird communities assemble. Comparing the diversity patterns with a null model, phylogenetic and functional diversities were significantly clustered whereas acoustic diversity was not different from what was expected by chance. A comparison between acoustic indices showed that spectral component of acoustic diversity seems more appropriate to reveal bird phylogenetic diversity whereas temporal component seems more adapted to reveal functional diversity of a bird community. Overall, even if the processes at the origin of the different facets of biodiversity are different, CAD reveals part of phylogenetic diversity and some extent of functional diversity.

Picophytoplankton community from tropical marine biofilms

Although the importance of picophytoplankton (<3μm) as the major primary producers is well established in the oceanic and coastal marine environment, occurrence of this community in the marine biofilms is not explored. Considering their small size and high abundance which is next to bacteria, the initial heterotrophic colonizers, it was hypothesized that picophytoplankton are the first autotrophic colonizers in marine biofilms. In this study biofilms were developed by immersing glass slides in the tropical waters of the Dona Paula Bay up to a period of 192h. The presence of picophytoplankton and the temporal variations in community structure was investigated flow cytometrically after every 24h. Biofilms were also developed in the laboratory by immersing the glass slides in fresh natural seawater and the sequence of appearance of the microorganisms was assessed with high frequency samplings. Field observations showed the presence of three groups of picophytoplankton, two prokaryotes, Prochlorococcus-like organisms (PRO), Synechococcus (SYN) and the picoeukaryotes (PEUK). Nanoeukaryotes, which are mostly represented by diatoms were also monitored. In the total biofilm community, prokaryotes were dominant throughout the study period wherein contribution of SYN was highest (50%) in the earlier stages which were later overtaken by PRO-like cells. The contribution of PEUK and nanoeukaryotes was always below 20%. Picophytoplankton contribution to the total photosynthetic biomass was >60% in the initial period of biofilm formation, both in terms of numbers and biomass with PEUK as the major contributors. However, after 2days of incubation, their contribution to total chlorophyll declined thus revealing that although their numbers were increasing, picophytoplankton were succeeded by nanoeukaryotes in terms of biomass. Laboratory experiments revealed that heterotrophic bacteria and picophytoplankton appeared within 5min in the biofilms which were followed by the nanoeukaryotes after 5h. This study shows that picophytoplankton are the pioneer autotrophic colonizers in the tropical marine biofilms, suggesting an essential role in the biofilm food web dynamics, especially in the initial stages.

Intra-Annual Variation in Fish Communities and Habitat Associations in a Chihuahua Desert Reach of the Rio Grande/Rio Bravo Del Norte

Anthropogenic alterations to lotic systems are often implicated in global declines among stream-dwelling fishes. A primary step toward mediating fish declines is improving our understanding of species—environment relationships; unfortunately, such information is limited. The goal of this study was to assess relationships between fish communities and environmental variables in a relatively intact portion of the Rio Grande/Rio Bravo del Norte in the southwestern United States and northern Mexico. We quantified the relationship between riverine habitats and local fish communities at 7 sites in the Big Bend reach of the Rio Grande/Rio Bravo del Norte during 2006. Monthly collections yielded 10,565 individuals representing 20 species, including 6 species listed as threatened or otherwise at risk. Species richness varied among sites (range 13–19) as did diversity (1 - D: 0.49–0.72) and density (16–45 fish · 100 m-2). Fish community composition indicated spatial and temporal variations, but habitat characteristics indicated more variation among sampling sites than among months. Spatial variation in community structure correlated with site-specific habitat characteristics, and most threatened or at risk species were associated with run or riffle geomorphic units containing higher current velocities and gravel to cobble substrates. Temporal variation in community structure correlated with fall monsoonal flooding, during which composition of dominant species shifted from the habitat generalist red shiner (Cyprinella lutrensis) to the imperiled, regionally endemic Tamaulipas shiner (Notropis braytoni). Results from this study suggest that large flood pulses and maintenance of habitat heterogeneity are necessary for the persistence of both declining and intact local fish communities in the Rio Grande/Rio Bravo del Norte.

Spatial and temporal variations of meiofaunal communities from the western sector of the Gulf of Batabanó, Cuba: II. Seagrass systems

The meiofauna from seagrass meadows in the western sector of the Gulf of Batabanó, Cuba were studied to describe the spatial and temporal variations in community structure. Replicated cores were taken in three locations (arranged in m- and km-scales) and in two seasons (dry and wet). The meiofauna (metazoans between 500 and 45 microm) were identified to major taxa. Temporal changes in the meiofaunal communities could not be detected and they are not linked to the subtle seasonal changes in the water column. A larger variation in community structure was observed in the spatial m-scale (among cores in a station) probably accredited to heterogeneity of microenvironment and biological processes. A second source of variation in the km-scale (among locations) was identified relating to physical processes affecting seagrass meadows: marine currents and anthropogenic disturbances. Distribution patterns of meiofauna across locations coincide with one study from 20 years ago in seagrass beds (i.e. higher densities in area closer to break-shelf and diminution of fauna at southern of Pinar del Rio); however, cumulative anthropogenic disturbances on seagrass meadows would most likely explain the depletion of communities observed in our survey in comparison with decades ago. Estimates of meiofaunal density and richness of major taxa from our study (and other areas from the Cuban shelf) are consistently lower than other temperate and tropical sites; possibly caused by low primary productivity due to narrow tidal amplitude and oligotrophic waters.

The effect of mouth opening on the biomass and community structure of microphytobenthos in a small oligotrophic estuary

The relationship between microphytobenthic biomass, community structure and physico-chemical conditions was studied in the Van Stadens Estuary, South Africa. Quarterly sampling was conducted in 2003. Temporal variation in community structure was explained by the percentage contribution of very fine sand in the sediment and by porewater ammonium concentrations. Microphytobenthic biomass showed strong negative correlations with water column salinity and sediment redox potential, and a positive correlation with water column soluble reactive phosphorus concentration. Temporal variation in mouth condition, sediment structure and nutrient availability changed biomass and community structure but there was little spatial variability. During the quarterly sampling of this study, microphytobenthic biomass was higher during open mouth conditions (1.43 ± 0.14–3.64 ± 0.94 μg g −1 sediment) than under closed conditions (0.25 ± 0.08–1.88 ± 0.22 μg g −1 sediment). The estuary was sampled weekly immediately following a mouth breaching event, physico-chemical conditions and microphytobenthic biomass were measured. Biomass did not decrease following mouth breaching and ranged between 0.25 ± 0.02 and 0.56 ± 0.10 μg g −1 sediment. This is contrary to other studies on South African intermittently open estuaries and indicates the importance of site specific data and detailed descriptions of the opening event.

Factors influencing fish and macrocrustacean communities in the surf zone of sandy beaches in Belgium: temporal variation

Monthly samples were taken in the surf zone of sandy beaches along the Belgian coast from May 1996 until July 1997 at four selected stations. Temporal patterns of the macrocrustacean and fish species residing the surf zone were investigated, as well as the abiotic variables structuring the community. In total 34 species were recorded belonging to caridean shrimps (3), anomuran and brachyuran crabs (5), cephalopods (2) and fish (24). The brown shrimp Crangon crangon dominated almost all samples (>80%). Total densities often exceeded 400ind per 100m2, and if C. crangon was excluded 10ind per 100m2. Notwithstanding the harsh hydrodynamic conditions, the surf zone of Belgian sandy beaches is used intensively by a number of epibenthic macro-crustaceans and demersal fish species. Seven resident and ten migrant species were identified. As mainly juvenile fishes were present, the surf zone of the Belgian sandy beaches may act as a nursery for longer (e.g. plaice Pleuronectes platessa) or shorter (e.g. brill Scophthalmus rhombus) periods. However, its nursery function should be studied in more detail, since the highly dynamic circumstances and more specifically wave height and wind speed may be important structuring factors for the epibenthic communities. The surf zone of Belgian sandy beaches also seems to function as a transient area to other nurseries (e.g. bass Dicentrarchus labrax) or between a nursery and the true marine environment (e.g. dab Limanda limanda).Temporal variation in community structure was greatly masked by spatial differences between sites. Although variables such as salinity and hydrodynamic factors may have influenced the data, clear temperature-related, seasonal patterns occur. Most likely, extreme winter conditions and subsequent migration of organisms to deeper waters caused a decline in winter in both density and diversity.

Temporal variations in community structure in and around intertidal barnacle (Chthamalus challengeri Hoek) patches on a plebby shore in Japan

The community structure in and around two barnacle (Chthamalus challengeri Hoek) patches (sites A and B) which extended from the middle to the upper intertidal zone on a pebbly shore in Magarisaki (Amakusa, Kyushu, Japan), was studied during summer and winter of 1995 and 1996. The results show a significant decrease in the proportion of substrate covered by barnacles from January 1995 to July 1996. The number of species, number of individuals, and biomass also decreased in the patch areas through time. There were significant differences between inside and outside the patches for percentage of substrate covered by barnacles, number of individuals, number of species, and biomass during the first year. Numbers of some gastropods were significantly higher in the barnacle patches, suggesting that the presence of barnacles create favorable microhabitat for the other taxa.

SPATIALLY AND TEMPORALLY PREDICTABLE FISHCOMMUNITIES ON CORAL REEFS

Spatial and temporal variation in the distribution and abundance of site-attached fish species inhabiting small, isolated patches of coral reef has been attributed to variability in larval recruitment. However, the relative importance of settlement and postsettlement processes in determining the structure of fish communities in general, i.e., including non-site-attached species inhabiting large sections of contiguous reef, remains to be determined. Here, we examine the degree of spatial and temporal variation in community structure and population density of fish inhabiting sections of coral reef varying in size and connectivity. To investigate spatial variability in fish community structure and population density, we surveyed 36 sites on contiguous reef and 39 patch-reef sites varying in size and isolation from neighboring patches. Ordination and regression analyses indicated that the structure of fish assemblages inhabiting contiguous reef varied predictably along habitat gradients. In contrast, intrinsic habitat characteristics, such as the shelter availability and the composition of the substratum, were apparently unrelated to the structure of fish assemblages on patch reefs. For sites on contiguous reef, multiple regression models explained a significant proportion of spatial variation in the population density of 10 site-attached and vagile species (including 90% of variation in the density of Pomacentrus moluccensis, a site-attached damselfish). For patch-reef sites, models of spatial variation in population density were significant for six species, five of which were not site attached. The overall pattern across most species was that patch-reef models were characterized by a reduced r2 relative to corresponding models of contiguous-reef populations, but the reduction was substantially less for vagile species than for site-attached species. Ordination analysis of temporal variability in community structure over two years suggested that none of the fish communities at the sites examined was in a consistent state of community succession. For most sites, community structure varied randomly over time, although at some sites, the structure of resident fish communities tended towards a stable position in multivariate community space. Across all sites, temporal change in community structure was significantly higher during periods of recruitment than at other times of the year, although there was little evidence to suggest that recruitment was the sole source of temporal variation. At most sites, the structure of fish assemblages fluctuated considerably during nonrecruitment periods. Patterns of temporal variation in the population density of four site-attached species indicated that population increases corresponding with pulses of recruitment were modified by postsettlement processes. For site-attached and moderately vagile species, overall temporal variability in assemblage structure increased significantly as sites became smaller and more isolated. Temporal variability in assemblages of highly vagile species was unrelated to survey area and connectivity. Overall, the results of the analyses of spatial and temporal variability in fish community structure suggest that species' vagility and reef connectivity strongly influence the relative importance of recruitment and postrecruitment processes in determining local population density. Individuals of highly vagile species are able to move among isolated patches in response to habitat preferences or resource availability. Conversely, the continuous shelter provided by contiguous reef may allow sedentary species to migrate to more favorable areas. We suggest that for many fish species, including vagile species on patchy reef and site-attached species on contiguous reef, patterns in distribution and abundance established at recruitment are modified by postsettlement migration, which enhances the relationship between population density and habitat structure. Thus, while recruitment patterns may explain much of the spatial and temporal variation in populations of site-attached fish on small, isolated patch reefs, this result cannot necessarily be extrapolated to fish communities inhabiting large sections of contiguous reef.