Differences In Assemblage Structure Research Articles

Crayfish assemblages correlate with dam‐induced effects on abiotic factors and predatory fish assemblages in Alabama streams

AbstractStream faunal assemblage structure is tied closely to hydrology and associated physiochemical properties. By altering natural flows, dams and their impoundments impact faunal assemblages over long distances. Although numerous studies have assessed the effect of dams on stream fauna, information is lacking for crayfishes. In this study, we characterized the effects of relatively large storage dams on crayfish assemblage structures. Over 2 years, we sampled three impounded and two unimpounded streams across two drainages in Alabama, United States, to identify biotic and abiotic factors correlated with crayfish assemblage metrics. Compared to impounded streams, unimpounded streams had greater habitat complexity (e.g., aquatic vegetation and woody debris), fewer predator fishes, lower minimum temperatures, and more variable discharges. These characteristics correlated with a higher density and diversity of crayfishes and smaller adults in impounded compared to unimpounded streams. Crayfish species assemblages differed between drainages, as did the biotic and abiotic factors affecting crayfish assemblages in each drainage, suggesting that these factors were species‐specific in their effects. Additionally, analysis of land uses suggested that factors other than dams may have also contributed to the observed differences in assemblage structures between impounded and unimpounded streams. For instance, in the more urbanized drainage, crayfish assemblages were more similar between up and downstream sections in all streams, regardless of impoundment. Our results indicate that large dams alter stream crayfish assemblage structure, with potentially cascading effects in trophic and organic matter dynamics both up and downstream.

Functional consequences of alder and oak loss in stream ecosystems

Abstract Alder (Alnus glutinosa) and oak (Quercus robur) are dominant tree species in European Atlantic mixed forests, and their leaf litter is a key resource for stream ecosystems. While alder litter has higher nutrient content and palatability than other species and is rapidly processed in the stream by detritivores and microorganisms, oak litter is a tougher and less nutritious but more persistent resource. Given that both species are declining due to the spread of the fungal pathogens Phytophthora alni and Phytophthora cinnamomi, respectively, we investigated how their reduction or loss might alter stream ecosystem functioning through changes in litter decomposition, invertebrate detritivore (Sericostoma pyrenaicum) growth and stoichiometry, and fungal decomposer assemblage characteristics. We conducted a microcosm experiment where we incubated litter mixtures representing different scenarios of alder and oak reduction or loss (and a concomitant increase in the other species), compared to a control that contained the four most common species in the study area (alder, oak, hazel [Corylus avellana] and willow [Salix atrocinerea]) in the same proportions as found in nature. The experiment lasted for 9 weeks, with the above variables measured every 3 weeks. Decomposition rates changed depending on which species was lost. Rates decreased as a result of alder loss and increased following oak loss. Sericostoma nutrient assimilation also responded to species loss, increasing and decreasing following alder and oak loss, respectively, possibly due to compensatory assimilation. Differences in Sericostoma nutrient concentrations among treatments decreased with time in the case of nitrogen, whereas they increased for phosphorus, probably due to microbial colonisation. The presence of oak also constrained microbial activity at the end of the experiment, reducing sporulation rates and causing differences in assemblage structure, probably due to inhibitory traits such as tannins or phenolic compounds. Treatments examining the loss of both species did not differ from the control, either in decomposition or sporulation rate, since loss of both alder and oak counteracted their effects. However, sporulation rates were higher for the scenario with loss of both species than for treatments with either alder reduction or loss, whereas sporulation rate and assemblage structure in the treatment with loss of both species were similar to the scenarios with oak reduction and loss, indicating that oak loss is more important for microbial activity. Changes in nutrient assimilation throughout the experiment suggested that effects of plant species reduction and loss can alter ecosystem functioning depending not only on litter palatability, but also on detritivore life stage. Overall, our results provide evidence for the importance of maintaining native riparian vegetation to preserve various ecosystem functions.

Same but different? Zoantharian assemblages (Anthozoa: Hexacorallia) in Bonaire and Curaçao, southern Caribbean

Marine community datasets are key to the effective management and conservation of marine ecosystems, including coral reefs, which are increasingly threatened by a myriad of stressors. Although community information exists for many comparatively well-studied taxa, other common groups remain to be examined for even such basic information. In this study, we report on the zoantharian communities (Cnidaria: Anthozoa: Hexacorallia: Zoantharia) on the reefs of Bonaire in the southern Caribbean, and compare current results from 30, 20, 10, and 5 m depths to recent similar surveys from nearby Curaçao. The surveys revealed a total of 17 zoantharian species and epibiotic associations on the reefs of Bonaire. Additionally, results showed that while zoantharian assemblages around Bonaire at shallow 5 and 10 m depths, dominated by Palythoa spp., were similar to those found on Curaçao, diversity and numbers of zoantharians were higher at 20 and 30 m due to more abundant epibiotic Parazoanthidae species associated with sponges. Differences in assemblage structure were seen in deeper 20 and 30 m depths between the two islands, implying that conservation of deeper reef slopes, or along depth gradients, may need to be independently considered and addressed for each location. Analyses with environmental parameters on the Bonaire dataset indicate the potential importance of coral reef rugosity and physical structure in shaping these zoantharian communities, aspects that should be focused on in more detail in future research.

Aggregated filter‐feeders govern the flux and stoichiometry of locally available energy and nutrients in rivers

Abstract Biogeochemical cycling has often been characterized by physical and microbial processes, yet animals can be essential mediators of energy and nutrients in ecosystems. Excretion by aggregated animals can be an important local source of inorganic nutrients in green food webs; however, whether animals are a source of dissolved energy that can support brown food webs is understudied. We tested whether animal aggregations are a substantial flux of bioavailable dissolved organic matter (DOM) by studying spatially stable, biogeochemical hotspots formed by filter‐feeding freshwater mussels. We used parallel‐factor analysis to quantify DOM fluorescent components composition of mussel excretion and expected digestive breakdown of particulate food sources would lead to excretion of labile DOM. Next, we combined measured excretion rates of DOM, ammonium (, N) and phosphorous (SRP; P) for 22 species with biomass estimates for 14 aggregations to quantify contributions of DOM, N and P to local availability. Because mussels occupy distinct stoichiometric niches, we anticipated that differences in species biomass and assemblage structure would elicit different flux and stoichiometries of aggregate excretion. Aggregate dissolved organic carbon (DOC) excretion was minor (1%–11%) compared to N (12%–2,860%) and P (1%–97%), yet generalities across assemblages emerged regarding organic matter transformation by mussels towards labile protein‐like compounds compared to abundant aromatic, humic compounds in ambient water. Aggregate excretion of labile DOM was a substantial pool of bioavailable energy, contributing 2%–114% of local labile DOM. Spatial differences in assemblage structure led to strong differences in aggregate flux and stoichiometry driven by biomass and stoichiometric trait expression of species with contrasting dominance patterns. Under the nutrient conditions of our study (high C:nutrient), biogeochemical hotspots associated with low‐trophic position animal biomass may indirectly control energy flow to the brown food web by shifting C:nutrient stoichiometry available to microbes or directly by increasing the flux of microbially available DOM. Collectively, our results highlight a potentially substantial flux of labile energy and nutrients to microbial communities through the transformation of ingested organic matter by aggregations of animals and emphasize that shared functional trait classification may not translate into shared ecological function. A free Plain Language Summary can be found within the Supporting Information of this article.

Spatio-temporal variability of amphipod assemblages associated with rhodolith seabeds

Rhodolith seabeds are habitats underpinned by free-living calcareous macroalgae. We partitioned the relevance of the scale of temporal (four seasons throughout two successive years) and spatial (three depth strata: 18, 25 and 40m) variation on the diversity, structure and abundance of amphipod assemblages living in rhodolith seabeds from Gran Canaria Island. In total, 3996 individuals, belonging to 32 taxa, were identified. Multivariate analyses showed consistent differences in assemblage structure among seasons and depths; more diverse and abundant amphipod assemblages were often observed during spring at 18- and 25-m than at 40-m depth. Ovigerous females of Gammaropsis ostroumowi and Ampithoe ramondi were observed mainly at 18 and 25m. Juveniles of both species were exclusively recorded at 18 and 25m, so denoting a clear segregation in their population structure with depth. In summary, this study has demonstrated that the ecological pattern of amphipods associated with rhodolith seabeds can vary greatly across both time (seasons) and space (depth).

The use of fatty acids to identify food sources of secondary consumers in wetland mesocosms

Increasing demand for freshwater during the last century has so severely degraded many wetland ecosystems that they are some of the most seriously impacted environments in the world. Environmental flows are used as a management tool to restore parts of the hydrological regime altered by human water use, to rehabilitate these wetlands. Research and monitoring to date has focused on understanding ‘flow-ecology’ relationships, without investigating the mechanisms underlying them. We sought to understand how different basal food sources are incorporated into fish tissue in temporary wetland systems. This study provides a necessary first step toward the development of mechanistic research that investigates the effects of variation in fatty acids (FA) within the food and prey base on top predators. We added different sources of fatty acids to wetland mesocosms by adding extra food sources including redgum leachate to increase planktonic bacteria populations, cyanobacteria, green algae and biofilm matrix to observe how they were incorporated into secondary consumers. Wetland soil and water was added to replicate mesocosms, left for 28 days to produce zooplankton and then Western carp gudgeons added. There was a clear shift in the invertebrate assemblage structure following the introduction of the gudgeons. There was also a clear difference in assemblage structure and nutritional value between benthic and planktonic invertebrates. However, the addition of extra food sources did not generate differing FA profiles between treatments in the substratum fractions, invertebrates or fish after 14 days. We suggest that food sources generated within the mesocosms themselves may have outweighed any treatment effects. Using flooded wetland mesocosms potentially would have provided more realistic knowledge of the food web mechanisms of wetland inundation rather than feeding zooplankton fed specific primary food sources to fish. However, future experiments attempting to identify the mechanisms of the transfer of basal food sources in wetlands to secondary consumers may wish to directly feed fish primary consumers raised on specific basal food sources.

Shoreline infrastructure degradation and increasing littoral naturalization accommodates juvenile fish and crab assemblages in heavily urbanized Upper New York Harbor

Many estuarine shorelines are influenced by urbanization. Extensive shoreline modification in Upper New York Harbor (UNYH) included port development, landfilling marshes, and armoring. Recent sedimentation in constructed shipping terminal embayments, abandonment of shoreline structure maintenance, subsequent recruitment of upland and intertidal vegetation, and restoration projects have naturalized some shorelines in this urban setting. We determined the species composition and relative abundance of fishes and crabs in shallow shoreline habitats in constructed embayments of UNYH with seine sampling to determine the potential for restoring similar isolated shallow water sites as functional habitats. Twenty‐seven identified species of fishes and crabs, including seasonally transient and resident marsh species, were represented in samples dominated by Menidia menidia, but marsh resident and coastal ocean species were also periodically abundant. Differences in assemblage structure among the sampled embayments as measured by principal components analysis were weak despite some differences in the slope and colonization of vegetation along shorelines. The mere presence of shallow shorelines was sufficient to recruit numerous species. Assemblage differences relative to a nearby relatively unaltered estuary revealed a lack of southern, warm affiliated species reflecting a natural clinal gradient. Marsh resident species dominated in UNYH, but not as strongly as at the reference estuary. Together with a previously published evaluation of life cycle connectivity for several sentinel species, this study shows that even small, isolated projects seeking to restore shallow shorelines add value to the estuarine landscape and are worth pursuing.

Short‐Term Distribution Patterns of Young‐of‐the‐Year Fish Assemblages between the Main Stem and Affiliated Lakes in the Middle Reaches of the Yangtze River, China

AbstractSurvival of fish in the first year is critical in determining the year‐class strength of fish populations. In river–floodplain ecosystems, affiliated lakes (i.e., floodplain lakes that are hydrologically connected to the river) play a crucial role as nursery habitats for young‐of‐the‐year (age‐0) fish. However, most lakes in the river–floodplain ecosystem of the Yangtze River, China, have been disconnected. Data on age‐0 fish distribution are important for developing appropriate strategies for management and conservation of fish populations in the river. We investigated the distribution patterns of age‐0 fish in the middle reaches of the Yangtze River. Overall, 33 species were collected from four main‐stem reaches (29 species) and two lakes (32 species) connected with the main stem from July to September in 2010 and 2011. The CPUE and species richness of age‐0 fish were higher in the lakes; age‐0 species richness showed an increasing trend in a downstream direction along the main stem. Analysis of similarities revealed that significant differences in assemblage structure of age‐0 fish occurred mainly among sampling sites. The higher CPUE and species richness of age‐0 fish in the lakes indicate the importance of connected lakes as age‐0 fish nursery habitats. We also found abundant age‐0 fish in the main stem and a relationship between spatial patterns of age‐0 fish with site proximity to the Three Gorges Dam, similar to previously observed spatial patterns in larval fishes. These results indicate the importance of the main stem as age‐0 fish nursery habitat and the effects of the dam on age‐0 fish distribution. This study presents the first data on age‐0 fish in the Yangtze River, thus providing a baseline for future age‐0 fish research. It also provides essential information for management and conservation measures, such as restoring the lateral connectivity between the main stem and disconnected lakes and guidelines for ecological operation of the dam.

The importance of oceanic atoll lagoons for coral reef predators

Predators on coral reefs play an important ecological role structuring reef fish communities and are important fishery targets. It is thought that reef predator assemblages increase in density and diversity from inner lagoonal to outer edge reefs. Oceanic atolls may differ though, as nutrients are available throughout. Reef predator populations are declining, but there is little known about how their distributions may vary across oceanic atolls. Using a combination of underwater visual census and baited remote underwater video, this study aimed to compare reef predator populations between inner and outer reefs of North Malé Atoll (Maldives) and determine which reef metrics may drive any differences in assemblage structure. We found that predator assemblages were significantly different between inner and outer atoll. Body sizes of several predator families were consistently larger in the outer atoll, however, abundance, biomass and species richness were similar between outer edge reefs and inner lagoonal reefs suggesting atoll lagoons may be undervalued habitats. Depth and complexity were consistently important predictors of the predator assemblage. Inner atoll lagoonal habitat is equally as important for reef predator assemblages as outer reef slopes, although the dominant species differ. This study provides important information on reef predator populations in the Maldives, where detailed assessments of the reef predator assemblage are lacking but the reef fishery is thriving and annual catch will continue to increase.

Oceanographic influence on coastal zooplankton assemblages at three IMOS National Reference Stations in Western Australia

Knowledge about the coastal zooplankton of the south-eastern Indian Ocean is limited, with few studies having compared assemblages across the latitudinal range of the western seaboard of Australia. The dominant oceanographic feature in this region is the Leeuwin Current, which transports warm, lower-salinity, tropical waters southward along the shelf-edge. This study examined data collected by Australia’s Integrated Marine Observing System at three coastal National Reference Stations located at 22°S 114°E, 32°S 115°E and 34°S 122°E. Spatial and temporal patterns in zooplankton abundance, composition and diversity were investigated, and differences in assemblage structure, particularly with respect to copepods, were related to oceanographic conditions. Clear dissimilarities among copepod assemblages were observed, becoming weaker in winter owing to enhanced connectivity of species driven by alongshore and cross-shelf transport in the Leeuwin Current. Both physical and biogeochemical factors were significant in structuring copepod assemblages, with seawater density, incorporating temperature and salinity, exerting the greatest influence. The results suggest that both broad-scale latitudinal gradients and mesoscale events contribute to variation in zooplankton assemblages in these waters. This study provides the first detailed comparison of zooplankton assemblages among the north-west, south-west and southern coastal waters of Western Australia, and enhances understanding of the processes influencing zooplankton distribution and structure.

Diatoms as indicators of the effects of river impoundment at multiple spatial scales.

River impoundment constitutes one of the most important anthropogenic impacts on the World's rivers. An increasing number of studies have tried to quantify the effects of river impoundment on riverine ecosystems over the past two decades, often focusing on the effects of individual large reservoirs. This study is one of the first to use a large-scale, multi-year diatom dataset from a routine biomonitoring network to analyse sample sites downstream of a large number of water supply reservoirs (n=77) and to compare them with paired unregulated control sites. We analysed benthic diatom assemblage structure and a set of derived indices, including ecological guilds, in tandem with multiple spatio-temporal variables to disclose patterns of ecological responses to reservoirs beyond the site-specific scale. Diatom assemblage structure at sites downstream of water supply reservoirs was significantly different to control sites, with the effect being most evident at the regional scale. We found that regional influences were important drivers of differences in assemblage structure at the national scale, although this effect was weaker at downstream sites, indicating the homogenising effect of river impoundment on diatom assemblages. Sites downstream of reservoirs typically exhibited a higher taxonomic richness, with the strongest increases found within the motile guild. In addition, Trophic Diatom Index (TDI) values were typically higher at downstream sites. Water quality gradients appeared to be an important driver of diatom assemblages, but the influence of other abiotic factors could not be ruled out and should be investigated further. Our results demonstrate the value of diatom assemblage data from national-scale biomonitoring networks to detect the effects of water supply reservoirs on instream communities at large spatial scales. This information may assist water resource managers with the future implementation of mitigation measures such as setting environmental flow targets.

Historical daytime vertical structure of larval fish assemblages in southeast Australian coastal waters: A benchmark for examining regional ecosystem change

Historical data are often used as benchmarks or reference points for assessing regional changes in ecosystem structure and function. For that purpose, we provide historical (1991–1992) data concerning the spatial and temporal consistency of vertical structuring of a diverse assemblage of larval fishes in inner continental shelf waters adjacent to Sydney, Australia. Daytime vertically stratified sampling at seven depths (0–65 m) across four stations and five sampling seasons yielded 35,772 individuals of 94 identifiable taxa from 81 families. Assemblages displayed consistent vertical stratification between surface (0 and 5 m) and subsurface (15 m and deeper) waters, with further spatio-temporal sub-structuring of subsurface assemblages between upper (15–30 m) and lower (45 m and deeper) water column. Differences in assemblage structure between surface and subsurface waters were primarily driven by several species that predominantly occurred in one depth zone and not the other. In contrast, differentiation between subsurface assemblages was dynamic and driven by taxa common across upper and lower subsurface depths but occurring in differing densities in certain depth strata that was spatially and temporally variable and not related to thermal stratification of the water column. Despite significant small-scale spatio-temporal variability, larval taxonomic diversity and total abundance was most often greatest in the upper and mid water column (15–30 m), potentially a response to light levels and prey concentrations. Nevertheless, the data show that all depths in the water column provide important habitat for larval fishes that need to be considered in ecosystem functioning and climate change projections.

Comparison of nematode assemblages associated with Sargassum muticum in its native range in South Korea and as an invasive species in the English Channel

Canopy-forming algae are important habitat providers in coastal ecosystems. Several canopy-forming species have spread outside their native geographic range. We investigated the role that these invasive non-native algae play in providing habitat for meiofaunal species. Sargassum muticum is a native species in East Asia and has been a successful invasive species of North American and European coasts. The nematode assemblages living in intertidal S. muticum on the English Channel coast in Europe, where it is an invasive species, were compared to those within its native range on the southern coasts of Korea. Nematode assemblages were sampled using a nested survey design (replicates nested within patches within shores within regions within coastlines in each country). Significant differences between countries were found in nematode assemblages in terms of both taxonomic composition and functional traits. Despite differences in assemblage structures between countries, some cosmopolitan nematode species were present in both countries. These nematode species may possibly have come from Asia to Europe with S. muticum.

Effects of deforestation on headwater stream fish assemblages in the Upper Xingu River Basin, Southeastern Amazonia

ABSTRACT The expansion of the Amazonian agricultural frontier represents the most extensive land cover change in the world, detrimentally affecting stream ecosystems which collectively harbor the greatest diversity of freshwater fish on the planet. Our goal was to test the hypotheses that deforestation affects the abundance, richness, and taxonomic structure of headwater stream fish assemblages in the Upper Xingu River Basin, in Southeastern Amazonia. Standardized sampling surveys in replicated first order streams demonstrated that deforestation strongly influences fish assemblage structure. Deforested stream reaches had twice the fish abundance than reference stream reaches in primary forests. These differences in assemblage structure were largely driven by increases in the abundance of a handful of species, as no influence of deforestation on species richness was observed. Stream canopy cover was the strongest predictor of assemblage structure, possibly by a combination of direct and indirect effects on the provision of forest detritus, food resources, channel morphology, and micro-climate regulation. Given the dynamic nature of change in land cover and use in the region, this article is an important contribution to the understanding of the effects of deforestation on Amazonian stream fish, and their conservation.

Diversity and community structure of rapids-dwelling fishes of the Xingu River: Implications for conservation amid large-scale hydroelectric development

A recent boom in hydroelectric development in the world's most diverse tropical river basins is currently threatening aquatic biodiversity on an unprecedented scale. Among the most controversial of these projects is the Belo Monte Hydroelectric Complex (BMHC) on the Xingu River, the Amazon's largest clear-water tributary. The design of the BMHC creates three distinctly altered segments: a flooded section upstream of the main dam, a middle section between the dam and the main powerhouse that will be dewatered, and a downstream section subject to flow alteration from powerhouse discharge. This region of the Xingu is notable for an extensive series of rapids known as the Volta Grande that hosts exceptional levels of endemic aquatic biodiversity; yet, patterns of temporal and spatial variation in community composition within this highly threatened habitat are not well documented. We surveyed fish assemblages within rapids in the three segments impacted by the BMHC prior to hydrologic alteration, and tested for differences in assemblage structure between segments and seasons. Fish species richness varied only slightly between segments, but there were significant differences in assemblage structure between segments and seasons. Most of the species thought to be highly dependent on rapids habitat, including several species listed as threatened in Brazil, were either restricted to or much more abundant within the upstream and middle segments. Our analysis identified the middle section of the Volta Grande as critically important for the conservation of this diverse, endemic fish fauna. Additional research is urgently needed to determine dam operations that may optimize energy production with an environmental flow regime that conserves the river's unique habitat and biodiversity.

Epibenthic and mobile species colonisation of a geotextile artificial surf reef on the south coast of England.

With increasing coastal infrastructure and use of novel materials there is a need to investigate the colonisation of assemblages associated with new structures, how these differ to natural and other artificial habitats and their potential impact on regional biodiversity. The colonisation of Europe’s first artificial surf reef (ASR) was investigated at Boscombe on the south coast of England (2009–2014) and compared with assemblages on existing natural and artificial habitats. The ASR consists of geotextile bags filled with sand located 220m offshore on a sandy sea bed at a depth of 0-5m. Successional changes in epibiota were recorded annually on differently orientated surfaces and depths using SCUBA diving and photography. Mobile faunal assemblages were sampled using Baited Remote Underwater Video (BRUV). Distinct stages in colonisation were observed, commencing with bryozoans and green algae which were replaced by red algae, hydroids and ascidians, however there were significant differences in assemblage structure with depth and orientation. The reef is being utilised by migratory, spawning and juvenile life-history stages of fish and invertebrates. The number of non-native species was larger than on natural reefs and other artificial habitats and some occupied a significant proportion of the structure. The accumulation of 180 benthic and mobile taxa, recorded to date, appears to have arisen from a locally rich and mixed pool of native and non-native species. Provided no negative invasive impacts are detected on nearby protected reefs the creation of novel yet diverse habitats may be considered a beneficial outcome.

Environmental characteristics drive variation in Amazonian understorey bird assemblages.

Tropical bird assemblages display patterns of high alpha and beta diversity and, as tropical birds exhibit strong habitat specificity, their spatial distributions are generally assumed to be driven primarily by environmental heterogeneity and interspecific interactions. However, spatial distributions of some Amazonian forest birds are also often restricted by large rivers and other large-scale topographic features, suggesting that dispersal limitation may also play a role in driving species’ turnover. In this study, we evaluated the effects of environmental characteristics, topographic and spatial variables on variation in local assemblage structure and diversity of birds in an old-growth forest in central Amazonia. Birds were mist-netted in 72 plots distributed systematically across a 10,000 ha reserve in each of three years. Alpha diversity remained stable through time, but species composition changed. Spatial variation in bird-assemblage structure was significantly related to environmental and topographic variables but not strongly related to spatial variables. At a broad scale, we found bird assemblages to be significantly distinct between two watersheds that are divided by a central ridgeline. We did not detect an effect of the ridgeline per se in driving these patterns, indicating that most birds are able to fly across it, and that differences in assemblage structure between watersheds may be due to unmeasured environmental variables or unique combinations of measured variables. Our study indicates that complex geography and landscape features can act together with environmental variables to drive changes in the diversity and composition of tropical bird assemblages at local scales, but highlights that we still know very little about what makes different parts of tropical forest suitable for different species.

Structure of mangrove meiofaunal assemblages associated with local sediment conditions in subtropical eastern australia

Meiofauna are ubiquitous but poorly-studied components of soft-bottom marine habitats around the world, including mangroves. The dynamic environmental conditions and heterogeneous sediments of mangroves present challenges to understanding the structure of mangrove meiofaunal assemblages at various spatial and temporal scales. In this study, we investigated the meiofaunal assemblage structure of sediments colonised by three mangrove species, namely, Avicennia marina, Rhizophora stylosa and Aegiceras corniculatum, at three locations in subtropical eastern Australia. Spatial and temporal variations were tested by sampling at the three mangrove locations (i.e. Tallebudgera, Currumbin and Terranora) in autumn, with samplings repeated at Tallebudgera at two other times broadly representing during dry/cool winter and wet/hot summer seasons. We examined the variability of the sediment environments within each of the different mangrove species, and investigated how meiofaunal assemblages would respond to the particular changes in their habitats to result in differences in assemblage structure between and within sites. Total meiofaunal density was highest in Tallebudgera and Currumbin and lowest in Terranora (mean density of 424, 393 and 239 ind.10 cm−2, respectively). In Tallebudgera, the density was higher in winter and summer (mean density of 546 and 530 ind.10 cm−2, respectively). The meiofaunal assemblage in this study shows a trend and association with the environmental variables. High availability of food proxies such phaeopigments, Chl a or TOC, with moderate tannin content and appropriate habitat structure (sediment particle size, belowground root biomass and/or moisture content provide the best condition for the meiofauna to achieve the highest density. However, given the complex dynamic habitats and the spatial heterogeneity of the mangrove environments across different locations and seasons, no clear generalization could be made regarding the key environmental variables that predominantly shape the meiofaunal assemblages’ structure.

Effects of proximity to stormwater on the sandy-beach macrofaunal assemblages of metropolitan Adelaide, South Australia

Stormwater run-off often enters coastal zones but its effects on sandy beaches are unknown. This study aimed to investigate associations between macrofaunal assemblages and proximity to stormwater outlets along Adelaide's beaches, comparing semi-natural creeks with concrete drains. Five positions along an increasing-salinity gradient were sampled in the intertidal zone of six stormwater outlets and also at corresponding control sites. There was no significant difference between the two forms of stormwater (semi-natural creeks with concrete drains). Only the largest outlet (Torrens) had a significant difference in assemblage structure and taxon richness compared to its control. Total abundances at this outlet followed a convex pattern across the salinity gradient, so it appears that flow there may have a spatially-limited positive effect on the macrofauna in terms of increasing abundance and richness. Therefore, the hypothesised detrimental effects of stormwater have not been found to be evident and these observed patterns warrant further investigation.

Effects of simulated human exploitation of a key grazer, Patella vulgata, on rocky shore assemblages

Exploitation of key consumers can have major consequences for community and ecosystem functioning. Limpets are key grazers exploited in regions such as Macaronesia, southern Africa, Chile and California. Here we describe a field experiment designed to simulate human exploitation of British limpets that are unexploited and used as model populations. Our aim was to evaluate the effects of size-selective harvesting on the composition of the rocky shore community of non-target species. Limpet populations were subjected to simulated exploitation of large size classes for 18 mo at 2 locations in the southwest of England, by systematic removal at 2 different intensities: low and high exploitation compared with unexploited plots. The exploitation of limpets led to establishment of Fucus spp. to differing degrees at each location, but while variation in percentage cover of Fucus spp. decreased over the course of the experiment in unmanipulated control plots, it increased in plots with either low or high exploitation. Multivariate analyses showed that communities at the 2 locations responded differently to the same intensity of exploitation: unmanipulated controls were similar to low-exploitation treatments at Constantine, while at Trevone low-exploitation treatments were similar to high-exploitation treatments. This was mainly due to increases in percentage cover of F. vesiculosus var. evesiculosus with exploitation, indicating that site-specific differences in assemblage structure and the size structure of the harvested populations will determine its assemblage-level responses. Therefore, reductions in density of grazers may have divergent consequences for different rocky shore communities.