Exploring macroinvertebrate species distributions at regional and local scales across a sandy beach geographic continuum

Exposed sandy beaches are highly dynamic ecosystems where macroinvertebrate species cope with extremely variable environmental conditions. The majority of the beach ecology studies present exposed beaches as physically dominated ecosystems where abiotic factors largely determine the structure and distribution of macrobenthic communities. However, beach species patterns at different scales can be modified by the interaction between different environmental variables, including biotic interactions. In this study, we examined the role of different environmental variables for describing the regional and local scale distributions of common macrobenthic species across 39 beaches along the North coast of Spain. The analyses were carried out using boosted regression trees, a relatively new technique from the field of machine learning. Our study showed that the macroinvertebrate community on exposed beaches is not structured by a single physical factor, but instead by a complex set of drivers including the biotic compound. Thus, at a regional scale the macrobenthic community, in terms of number of species and abundance, was mainly explained by surrogates of food availability, such as chlorophyll a. The results also revealed that the local scale is a feasible way to construct general predictive species-environmental models, since relationships derived from different beaches showed similar responses for most of the species. However, additional information on aspects of beach species distribution can be obtained with large scale models. This study showed that species-environmental models should be validated against changes in spatial extent, and also illustrates the utility of BRTs as a powerful analysis tool for ecology data insight.     

Competitive interactions in macroinfaunal animals of exposed sandy beaches

The influence of biotic interactions in structuring macroinfaunal communities of exposed sandy beaches, an unstable habitat characterized by strong physical forces, is generally considered negligible. We investigated the hypothesis that competitive interactions during burrowing could potentially affect the intertidal distribution and abundance of macroinfaunal animals of sandy beaches using two species of invertebrates, a hippid crab, Emerita analoga, and a bivalve, Mesodesma donacium, common along the coast of Chile. Spatial overlap in the intertidal distributions of these species was dynamic, varying with abundance, location, time of year and tide. Highest density zones of each species were often distinctly separated at low tide and spatial overlap in their distributions decreased significantly with increasing density, suggesting density dependence of the interactions. Negative relationships between densities of the two species at the smallest spatial scale examined also suggested active interactions among individuals. Over a tidal cycle, peak densities of the two species overlapped suggesting that interactions could occur frequently. Burrowing performance of E. analoga varied between size classes in three experimental densities of clams (5, 10 and 15 clams 0.008 m^-2) and in controls with no clams. Burrowing times of large crabs were significantly longer (~twofold) in all densities of clams than in controls, while those of small crabs did not differ significantly among treatments and controls. Large crabs also displaced clams from the sand while burrowing suggesting that two mechanisms of direct interference can occur, both of which could increase exposure of individuals involved to active swash and transport across or along the beach with potentially negative consequences. Our results suggest that competitive interactions capable of affecting zonation and population and community biology on a number of scales can occur among burrowing macroinfauna on exposed sandy beaches. Those interactions could be more ecologically significant than previously appreciated and may contribute to patterns observed in community structure and zonation on sandy beaches. Our results illustrate the potential importance of negative biological interactions in a physically stressful environment.     

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.     

Temporal patterns in the intertidal faunal community at the mouth of a tropical estuary

The use of intertidal sandy beaches by fish and macrocrustaceans was studied at different temporal scales at the mouth of a tropical estuary. Samples were taken along the lunar and diel cycles in the late dry and rainy seasons. Fish assemblage (number of species, density and biomass), crustaceans and wrack biomass, showed significant interactions among all studied factors, and the combination of moon phase and diel cycle, resulting in different patterns of environmental variables (depth, water temperature and dissolved oxygen), affected habitat use by the different species. Variances in faunal community were detected between seasons, stimulated by salinity fluctuations from freshwater input during the rainy season. These differences suggest an important cycling of habitats and an increase in connectivity between adjacent habitats (estuary and coastal waters). Moreover, the results showed that this intertidal sandy beach also provides an alternative nursery and protected shallow‐water area for the initial development phase of many marine and estuarine species. In addition, this intertidal habitat plays an important role in the maintenance of the ecological functioning of the estuarine–coastal ecosystem continuum.     

In depth review of the ecology of arenicolous marine fungi

As an ecotone, sandy beaches exist within a multi-dimensional mesh of environmental gradients, shaped by numerous parameters (e.g. temperature, humidity, wave action, sand particle size and salinity). These limit the proliferation of a narrow group of fungal species. Obligate arenicolous marine fungi are an ecological assemblage of sand-associated heterotrophs that inhabit sandy beaches. These organisms have evolved to cope with dynamic beach conditions, having a cosmopolitan distribution across tropical, subtropical and temperate regions. Herein we provide an overview of published works relating to the fungi of sandy beaches, focusing on the past half-century. We outline a broad range of topics in ecology including fungal adaptive traits to intertidal conditions at the morphological and genetic levels, temporal and spatial patterns in community structure, and species variations in substrate preference. Collectively, these concepts should encourage marine mycologists to embrace a holistic set of perspectives to shape the outlook for beach ecology.     

Disentangling diversity patterns in sandy beaches along environmental gradients

Species richness in sandy beaches is strongly affected by concurrent variations in morphodynamics and salinity. However, as in other ecosystems, different groups of species may exhibit contrasting patterns in response to these environmental variables, which would be obscured if only aggregate richness is considered. Deconstructing biodiversity, i.e. considering richness patterns separately for different groups of species according to their taxonomic affiliation, dispersal mode or mobility, could provide a more complete understanding about factors that drive species richness patterns. This study analyzed macroscale variations in species richness at 16 Uruguayan sandy beaches with different morphodynamics, distributed along the estuarine gradient generated by the Rio de la Plata over a 2 year period. Species richness estimates were deconstructed to discriminate among taxonomic groups, supralittoral and intertidal forms, and groups with different feeding habits and development modes. Species richness was lowest at intermediate salinities, increasing towards oceanic and inner estuarine conditions, mainly following the patterns shown for intertidal forms. Moreover, there was a differential tolerance to salinity changes according to the habitat occupied and development mode, which determines the degree of sensitivity of faunal groups to osmotic stress. Generalized (additive and linear) mixed models showed a clear increase of species richness towards dissipative beaches. All taxonomic categories exhibited the same trend, even though responses to grain size and beach slope were less marked for crustaceans and insects than for molluscs or polychaetes. However, supralittoral crustaceans exhibited the opposite trend. Feeding groups decreased from dissipative to reflective systems, deposit feeders being virtually absent in the latter. This deconstructive approach highlights the relevance of life history strategies in structuring communities, highlighting the relative importance that salinity and morphodynamic gradients have on macroscale diversity patterns in sandy beaches.     

Patterns and processes in abundance-body size relationships for marine benthic invertebrates

1. The nature of abundance-body size relationships in animal communities, and especially the drivers behind the observed patterns, have been a focus of persistent debate in animal ecology. In a recent review, Allen et al. (2006) categorized five mechanistic explanations behind the commonly observed polymodality in these relationships: energetic constraints; phylogenetic constraints; biogeographical determinants; habitat structure; and community interactions. Progress in understanding of these patterns and the processes underlying them have been hindered by the use of a range of methods that differ in their validity and robustness. 2. Here, we used data on invertebrate body sizes from a variety of sandy beaches in the UK to test the hypothesis that these communities display modality in their abundance-body size relationships. We quantified modality in the relationships using kernel density estimation and smoothed bootstrap resampling and then evaluated the competing explanations for this modality based on the patterns identified in conjunction with measurements of the physical beach environment. 3. We found bimodal distributions in the body size spectrum for benthic invertebrates at nine of 16 sites. There was a consistent trough in the spectrum at around 0·5-1 mm diameter, which reflected the traditional split between meiofauna and macrofauna. Beaches with finer particle sizes and more heterogeneous macrofauna hosted communities with more than two modes. 4. Our results suggest that modality in sandy beach benthic communities is unlikely to be explained by any single hypothesis. There will be an interplay between physical and biological factors, with different explanations accounting for modality at different scales.     

Bottom‐up control in the benthos of ocean‐exposed sandy beaches?

Bottom‐up control is a fundamental structuring force in food webs. Food webs of ocean‐exposed sandy beaches are predicted to be bottom‐up controlled systems, underpinned by imported organic matter rather than in situ primary production. This ecological model of resource‐based regulation of biological assemblages is juxtaposed against a prevailing paradigm built around a dominance of physical drivers in sandy beach ecosystems. Surprisingly, given the apparently ubiquitous energetic subsidies of beach food webs, the central premise of bottom‐up control has not been tested. Here we experimentally manipulated in situ nutrient levels on a sandy beach to test food web responses at the levels of primary producers (benthic microalgae) and their grazers (meiofauna). The meiofauna community as a whole appeared most strongly influenced by the local physical environment, particularly changes in sediment grain size – this supports the traditional ‘environmental control paradigm’. We also detected a significant, positive response of two consumer groups of the meiofauna (nematodes, ostracods) to nutrient enrichment that supports a model of biological, bottom‐up control. Although the predicted response of elevated producer biomass following nutrient enrichment was not detected, intense grazing pressure on new, stimulated production may have masked positive responses by the primary producers. Multichannel regulation of food webs is likely for many exposed sandy beaches, albeit an often lower importance of in situ bottom‐up forces compared with stronger environmental control.     

Interrelationships of bacteria,meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park,NW Italy)

Collelungo beach (Maremma Park, NW Italy), was sampled quantitatively for macrofauna, meiofauna and bacteria in May 2003; several physicochemical variables and variables associated with food availability and sediment structure were also measured. Replicated samples were collected from three sites representing natural conditions, an erosion regime, and the influence of the Ombrone River, respectively, as well as from four stations each located in the surf and sublittoral zones. Both uni- and multivariate techniques were used to assess the benthic community structure and the associated environmental variables. Different diversity indices revealed no pattern; in contrast, multivariate techniques applied on the macrobenthic fauna and the polychaete taxocommunity distinguished between the sites located in natural and eroding conditions from the one located nearby the discharges of the Ombrone river. Τhe community patterns deriving from meio- and macrofauna are clearly divergent. The overall benthic faunal community appears to be influenced by both groups of organisms. The patterns of the meio- and macrofaunal communities seem to be affected synergistically by a number of environmental variables, in accordance with the multicausal environmental severity hypothesis. Meiofaunal patterns are more often correlated with bacteria and the protein concentration than are macrofaunal patterns, indicating a potential utilization of bacteria as a food source by the meiofaunal organisms. Total bacterial numbers are associated with the macrofaunal pattern under the erosion regime, probably as a consequence of competition for food between macrofauna and meiofauna.     

Some physical,chemical, and microbiological characteristics of two beaches of anglesey

Observations during 1971 and 1972 of some of the physical, chemical, and microbiological characteristics of contrasting Anglesey beaches, Newborough and Llanddona, are reported. The fine sandy beach at Newborough was observed to be very unstable and topographical changes were recorded. In particular, the movement of a sand wave across the intertidal zone from low water to extinction at the foot of the dune system was observed. The more extensive fine sandy beach at Llanddona had greater stability.Chemically, each beach was variable both spatially and temporally, with ill-defined patterns of concentration changes. Sand from Newborough beach was low in organic carbon (0.07–0.40 mg C/g dry sand) and well aerated, and the soluble inorganic nitrogen in the ground water (up to 30 μg-at. N/l) was dominated by nitrate form (up to 22 μg NO₃-N/l). By contrast, Llanddona sand had a more variable organic carbon content (0.22–2.25 mg C/g dry sand), was wetter, and poorly aerated with consequent sulphide lenses; its dissolved inorganic nitrogen (over 70 μg-at. N/l) was completely dominated by the ammonium form.Microbiologically, the beaches possessed dissimilar bacterial floras, and sediment from Llanddona gave higher bacterial counts than that from Newborough. For both beaches it is shown that estimated bacterial numbers decreased with depth as well as down the intertidal zone.     

Latitudinal patterns in abundance and life-history traits of the mole crab Emerita brasiliensis on South American sandy beaches

Demographic and life‐history attributes of the mole crab Emerita brasiliensis were analysed along 2700 km of the Atlantic coast of South America, including sandy beaches at the southernmost limit (Uruguay) and at the core of its geographical range (Brazil). Population features varied markedly within this range and exhibited systematic geographical patterns of variation. Abundance significantly increased from temperate to subtropical beaches, and the same held true for the asymptotic weight of males. Conversely, length at maturity and asymptotic weight of females increased from subtropical to temperate beaches, being inversely related to sea water temperature. Macroecological patterns in abundance and body weight showed the first large‐scale evidence of scaling of population density to body size for a sandy beach population. Mortality rates (both sexes) followed a nonlinear increase from low‐density temperate beaches to high‐density subtropical beaches. The effect of habitat quality and availability could explain discontinuities in the species distribution within its range, and also differential responses in life‐history attributes at a local scale. Asymmetries and converse latitudinal trends between sexes suggest that there is not a single general factor determining large‐scale patterns in life‐history traits of this species. Our results reinforce the view that density‐dependent and environmental factors operating together regulate sandy beach populations. The need to develop macroecological studies in sandy beach ecology is highlighted, as knowledge acquired from local to large spatial scales throws light on population structure and regulation mechanisms.     

Community structure of macrobenthos in homestead ponds of Noakhali coast,Bangladesh

The integrity of the homestead pond supply depends on how various macrobenthic communities make their living more diversified and contribute to complex food webs. In addition, the macrobenthic community are significantly used as indicator organisms to detect the pollution impacts in aquatic ecosystems. In this study, we show the data about the diversity and community structure of macrobenthos and their relationship with environmental variables in homestead ponds of Noakhali coast from January 2019 to August 2019. The current study yielded 17 species belonging to seven taxonomic groups with a mean density of 3630 ind./m². The Nematode community, comprising 48.86% of the total taxonomic groups with Prionchulus sp. as the dominant macrobenthic species represented more than 31% of the total macrobenthic taxa, and showed a significant negative correlation with the value of salinity, DO, pH. The environmental variables and diversity indices were detected significant variations (P < 0.05) among stations by the Kruskal-Wallis ANOVA, whereas Shannon-Wiener Diversity Index (H´) assessed moderate pollution, Evenness index (J) assessed uniform distributions of macrobenthic community, and environmental variables showed acceptable condition for the productivity of ponds. Cluster analysis (CA) and Non-metric multidimensional scaling (nMDS) demonstrate demarcations in the community structure of macrobenthos between samples. Within macrobenthic communities, Canonical Correspondence Analysis (CCA) provided insights and interpretations of the relationships between species and environmental gradients. Macrobenthic community reached the most abundance at a lower temperature, transparency and a higher DO, pH and salinity.     

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.     

长江口潮沟大型底栖动物群落的初步研究

通过对长江口崇明东滩潮沟系统与大型底栖无脊椎动物进行取样调查 ,研究了潮沟不同生境的底栖动物群落及其多样性 ,分析了潮沟生境异质性与底栖动物群落的关系。研究发现 :①潮沟剖面中出现明显的动物群落分带现象 ,从潮沟底、潮沟边滩到草滩 ,底栖动物种类、生活型组成和生活类群比例反映了河口潮滩潮沟底栖动物生态系列 ;②密度和生物量的分布皆为潮沟边滩 >草滩 >潮沟底 ,但密度与生物量的面上群 /面下群值格局却有不同 ,说明了密度和生物量的优势生活型和生活类群随潮沟生境的差异而变化 ;③潮沟系统 3种生境的多样性指数D ,H′和J值均为草滩 >潮沟边滩 >潮沟底 ,是潮沟系统生境结构分化的结果。潮沟底和潮沟边滩等特殊生境的存在 ,提高了淤泥质河口潮滩的生境异质性 ,说明了潮沟系统在维持河口生态系统底栖动物物种多样性中的重要作用。     

Variable Importance of Macrofaunal Functional Biodiversity for Biogeochemical Cycling in Temperate Coastal Sediments

Coastal marine systems are currently subject to a variety of anthropogenic and climate-change-induced pressures. An important challenge is to predict how marine sediment communities and benthic biogeochemical cycling will be affected by these ongoing changes. To this end, it is of paramount importance to first better understand the natural variability in coastal benthic biogeochemical cycling and how this is influenced by local environmental conditions and faunal biodiversity. Here, we studied sedimentary biogeochemical cycling at ten coastal stations in the Southern North Sea on a monthly basis from February to October 2011. We explored the spatio-temporal variability in oxygen consumption, dissolved inorganic nitrogen and alkalinity fluxes, and estimated rates of nitrification and denitrification from a mass budget. In a next step, we statistically modeled their relation with environmental variables and structural and functional macrobenthic community characteristics. Our results show that the cohesive, muddy sediments were poor in functional macrobenthic diversity and displayed intermediate oxygen consumption rates, but the highest ammonium effluxes. These muddy sites also showed an elevated alkalinity release from the sediment, which can be explained by the elevated rate of anaerobic processes taking place. Fine sandy sediments were rich in functional macrobenthic diversity and had the maximum oxygen consumption and estimated denitrification rates. Permeable sediments were also poor in macrobenthic functional diversity and showed the lowest oxygen consumption rates and only small fluxes of ammonium and alkalinity. Macrobenthic functional biodiversity as estimated from bioturbation potential appeared a better variable than macrobenthic density in explaining oxygen consumption, ammonium and alkalinity fluxes, and estimated denitrification. However, this importance of functional biodiversity was manifested particularly in fine sandy sediments, to a lesser account in permeable sediments, but not in muddy sediments. The strong relationship between macrobenthic functional biodiversity and biogeochemical cycling in fine sandy sediments implies that a future loss of macrobenthic functional diversity will have important repercussions for benthic ecosystem functioning.     

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.     

Influence of Land Use,Nutrients, and Geography on Microbial Communities and Fecal Indicator Abundance at Lake Michigan Beaches

Microbial communities within beach sand play a key role in nutrient cycling and are important to the nearshore ecosystem function. Escherichia coli and enterococci, two common indicators of fecal pollution, have been shown to persist in the beach sand, but little is known about how microbial community assemblages are related to these fecal indicator bacteria (FIB) reservoirs. We examined eight beaches across a geographic gradient and range of land use types and characterized the indigenous community structure in the water and the backshore, berm, and submerged sands. FIB were found at similar levels in sand at beaches adjacent to urban, forested, and agricultural land and in both the berm and backshore. However, there were striking differences in the berm and backshore microbial communities, even within the same beach, reflecting the very different environmental conditions in these beach zones in which FIB can survive. In contrast, the microbial communities in a particular beach zone were similar among beaches, including at beaches on opposite shores of Lake Michigan. The differences in the microbial communities that did exist within a beach zone correlated to nutrient levels, which varied among geographic locations. Total organic carbon and total phosphorus were higher in Wisconsin beach sand than in beach sand from Michigan. Within predominate genera, fine-scale sequence differences could be found that distinguished the populations from the two states, suggesting a biogeographic effect. This work demonstrates that microbial communities are reflective of environmental conditions at freshwater beaches and are able to provide useful information regarding long-term anthropogenic stress.     

A Tale of Two Recent Spills—Comparison of 2014 Galveston Bay and 2010 Deepwater Horizon Oil Spill Residues

Managing oil spill residues washing onto sandy beaches is a common worldwide environmental problem. In this study, we have analyzed the first-arrival oil spill residues collected from two Gulf of Mexico (GOM) beach systems following two recent oil spills: the 2014 Galveston Bay (GB) oil spill, and the 2010 Deepwater Horizon (DWH) oil spill. This is the first study to provide field observations and chemical characterization data for the 2014 GB oil spill. Here we compare the physical and chemical characteristics of GB oil spill samples with DWH oil spill samples and present their similarities and differences. Our field observations indicate that both oil spills had similar shoreline deposition patterns; however, their physical and chemical characteristics differed considerably. We highlight these differences, discuss their implications, and interpret GB data in light of lessons learned from previously published DWH oil spill studies. These analyses are further used to assess the long-term fate of GB oil spill residues and their potential environmental impacts.