1,721,167 research outputs found
Continuous benthic community change along a depth gradient in Antarctic shallows: evidence of patchiness but not zonation
No full textMany shallow water polar communities demonstrate considerable change along a bathymetric gradient. However, it is currently unclear whether community change is generally continuous or discrete. To determine the nature of community change with depth, extensive photographic surveys at three sites at Adelaide Island, West Antarctic Peninsula, were conducted along a bathymetric gradient of 5-35 m depth. Macroalgae were largely absent at the sites, so only distinguishable macrofauna were counted and analysed. Faunal abundance was greatest at the shallowest stations of the depth transects, whilst richness at both species and phylum level increased with depth. Variability in community structure between replicate transects decreased with depth, so that assemblages at > 25 m depth were more homogenous. Depth had a highly significant effect on total abundance, species richness and community structure, and it is likely that the frequency of ice disturbance, which also decreases with depth, drives this pattern. Overall, high variability between transects at each site was recorded, which suggested considerable patchiness at the scale of tens of meters. Community change along the bathymetric gradient was continuous and no evidence of discrete zones of assemblages was recorded
Spatial variability in the distribution of dominant shallow-water benthos at Adelaide Island, Antarctica
No full textStudies from temperate and tropical regions have shown that variability in the distribution of benthos exists at different spatial scales. There are very few similar studies from polar systems, the shallows of which represent some of the most intensely disturbed habitats on the planet. Variability in the abundances of the five most common macrofauna was examined at three spatial scales, metres, tens of metres and hundreds of metres, in the shallows (5-25 m depth) of Adelaide Island, West Antarctic Peninsula. Whilst significant community change occurs along a depth gradient at the study sites, not all of the common species studied showed clear depth-related patterns of distribution. Furthermore, although abundance patterns varied between the organisms, consistent depth-related trends in the spatial scale contributing most to the variability were observed for four of the five species. For four species the relative importance of large-scale variability (between sites) decreased from 5 to 25 in depth, whilst small-scale variability (between replicates) increased along the depth gradient. Variation between sites is probably largely driven by ice disturbance, which becomes less frequent with depth. Conversely, small-scale patchiness is promoted by biological interactions, which become relatively more influential as community complexity and species richness increase along the depth gradient
Ecological traits of benthic assemblages in shallow Antarctic waters: does ice scour disturbance select for small, mobile, secondary consumers with high dispersal potential?
No full textBenthic communities in nearshore habitats around Antarctica are strongly influenced by ice disturbance. It has been suggested that where ice scour disturbance is severe, the relative importance of certain ecological groups is elevated. I examined the relative contributions of mobility, size, feeding strategy and development mode groups to total faunal abundance and species richness in relation to ice disturbance at Adelaide Island, West Antarctic Peninsula. The contributions of ecological groups were assessed along a depth/disturbance gradient from 5 to 25 m depth at two sites. At one site, the relative abundance of the low mobility group was significantly greater at low disturbance levels, whilst the relative abundance of the high dispersal group (taxa with pelagic larvae) was elevated at high disturbance levels. At the other site, the relative abundance of secondary consumers was greater at high disturbance levels. Even over small spatial scales, certain ecological traits seem advantageous to a fauna shaped by intense, catastrophic ice scour
Extreme spatial variability in sessile assemblage development in subtidal habitats off southwest Australia (southeast Indian Ocean)
No full textThe development of marine benthic communities is strongly influenced by patterns of settlement, recruitment and survival, which may vary across multiple spatial scales in concordance with the scale-dependent processes that drive them. The temperate subtidal reefs off southwest Australia support highly diverse assemblages of macroalgae and sessile invertebrates, yet little is known about spatial variability in the structure of developing assemblages compared with established assemblages. Here, settlement panel arrays were deployed adjacent to subtidal rocky reefs, in 13–15 m depth, at 3 locations spanning 400 km of temperate coastline in Western Australia. Panel assemblages were allowed to develop for ~ 14 months before they were harvested. Variability in ecological pattern was analyzed at 4 spatial scales, spanning centimeters to 100 s of kilometers. The structure of sessile assemblages was vastly different between the 3 locations, in that one location (Geographe Bay) supported an impoverished assemblage comprising a single macrofaunal species whereas assemblages at the other two locations (Jurien Bay and Marmion Lagoon) supported fairly rich assemblages of macroalgae and sessile invertebrates. Multivariate assemblage structure, total richness and total cover varied significantly between the locations, although variability at the smallest spatial scale (centimeters) was consistently pronounced. Variability patterns for key taxa were less consistent across spatial scales. While explanations for the extreme between-location variability remain unclear, there was some evidence to suggest that herbivory by demersal fish may inhibit assemblage development at Geographe Bay, although local hydrodynamic factors (i.e. relatively lower water movement and influence of the dominant regional-scale oceanic current) could also be important
Multi-scale patterns of spatial variability in sessile assemblage structure do not alter predictably with development time
No full textPatterns of benthic community structure are driven by a range of biological and physical processes that act over multiple spatial and temporal scales. Settlement panels were deployed in relatively ‘pristine’ subtidal habitats off southwest Australia, to examine spatial variability in assemblage structure at multiple spatial scales, from centimetres to 100s of kilometres. Panel assemblages were harvested after 3, 9 and 14 months of maturation, to test the following hypotheses: (i) that the magnitude of variability at large spatial scales increases with assemblage development time, (ii) that variability at the smallest spatial scales is consistently high regardless of assemblage development time, and (iii) that patterns of spatio-temporal variability differ between taxa. No clear trends in the magnitude of variability at each spatial scale examined, in relation to assemblage development time, were recorded. Sessile assemblages were highly variable at all spatial scales examined, and variability at the smallest-spatial scale (cms) was consistently high. As predicted, the magnitude of variability at the largest spatial scales (i.e. between locations 100s of km apart) was lowest for immature assemblages, but overall patterns of large-scale variability did not alter predictably with maturation time. Subtidal sessile assemblages in southwest Australia, like elsewhere, are structured by a complex, interacting suite of biological and physical processes that vary in their relative importance throughout assemblage maturation. As such, understanding variability patterns is challenging, and requires greater appreciation of variability in physical processes across multiple spatial and temporal scales and improved knowledge of the life histories and population structures of key taxa
Ice disturbance intensity structures benthic communities in nearshore Antarctic waters
Full text linkIce scouring is one of the 5 most significant natural forces acting on ecosystems, yet very few data exist linking the intensity of ice disturbance with parameters of benthic community structure. The benthos at 2 nearshore sites on Adelaide Island, Antarctica, was sampled at 3 resolutions to make novel links between biological data and empirical disturbance data from the literature. A total of 125 taxa and > 70 000 individuals were recorded. A total of 8 parameters of community structure were measured; all of them were negatively correlated to disturbance intensity at one site, whilst 6 significant relationships were found at the other site. At 2 of the 3 sampling resolutions, disturbance, rather than depth or the percentage cover of major substratum types, was the environmental variable most correlated with the patterns in community structure. Furthermore, biological samples were divided into 3 categories based on the disturbance data (low, moderate and high). Each group was statistically dissimilar and the relative abundance of sessile fauna decreased as disturbance intensity increased. The intensity of disturbance was broadly correlated with depth, but small-scale differences in topography and substratum type created small-scale refugia, which supported richer assemblages. Overall, both study sites were disturbed frequently and no evidence of a peak in richness at the moderately disturbed locations was recorded
Spatial variation in the structure of overwintering, remnant <i>Saccorhiza polyschides </i>sporophytes and their associated assemblages
No full textUnderstanding the structure and richness of natural communities is a fundamental goal of marine ecology, and foundation species such as large macroalgae have a disproportionate role in structuring biodiversity. However, high-resolution information on assemblages associated with macroalgae is lacking for many species and regions. Saccorhiza polyschides is a warm-temperate kelp with a relatively short lifespan (12–18 months), large thallus and bulbous holdfast offering habitat for diverse assemblages. In the UK, S. polyschides populations are thought to have proliferated recently. Here, we quantified the density and habitat structure provided by S. polyschides along a gradient of wave exposure within Plymouth Sound, and examined the composition and diversity of associated faunal assemblages. Density varied significantly between sites but not by wave exposure, while biometric measurements were generally highly variable. Senescing holdfasts from sporophytes offered valuable habitat, with high abundance and richness of associated assemblages, although these varied markedly between sporophytes and sites. Faunal abundance, taxon richness and diversity were significantly higher at fully exposed sites than at moderately exposed sites. Internal volume of holdfasts was positively correlated with faunal abundance and taxon richness. We recorded more than 27 distinct taxa and up to ∼600 individuals within a single holdfast. Taxa included three fish species, including a novel observation of the pipefish Nerophis lumbriciformis. Further work is needed to examine seasonality in habitat structure and associated diversity patterns but our study demonstrates that even remnant holdfasts from decaying sporophytes represent a valuable microhabitat that may provide shelter, protection and food during winter
The occurrence of a widespread marine invader, Didemnum perlucidum (Tunicata, Ascidiacea) in Western Australia
No full textColonial ascidians of the genus Didemnum are emerging as potent invaders of coastal marine ecosystems. Here, we used taxonomic and phylogenetic approaches to confirm the presence of Didemnum perlucidum in Australia. D. perlucidum is widespread in tropical ports and is thought to be a recent introduction into Brazilian waters, where it has increased biofouling pressure and affected aquaculture practices. D. perlucidum was observed dominating fouling assemblages on settlement panels and jetty pylons at two study sites in the Perth metropolitan area, Western Australia. As identifying members of this genus based on morphological characteristics is difficult, analysis of mtDNA was conducted to verify the occurrence of D. perlucidum in Australia. Space occupation of artificial substrata was observed in summer and autumn, when D. perlucidum colonies overgrew other sessile organisms, including the commercially harvested Blue Mussel (Mytilus edulis ssp. planulatus). This represents the first confirmed record of this species in Australia, which should be considered cryptogenic until detailed biogeographical analyses are conducted. The distribution, biology, and economic and ecological implications of D. perlucidum in Australia are entirely unknown, and warrant urgent investigation
Climate-driven substitution of habitat-forming species leads to reduced biodiversity within a temperate marine community
No full textAim: In marine ecosystems, habitat-forming species (HFS) such as reef-building corals and canopy-forming macroalgae alter local environmental conditions and can promote biodiversity by providing biogenic living space for a vast array of associated organisms. We examined community-level impacts of observed climate-driven shifts in the relative abundances of two superficially similar HFS, the warm-water kelp Laminaria ochroleuca and the cool-water kelp Laminaria hyperborea. Location: Western English Channel, north-east Atlantic Methods: We compared algal and invertebrate assemblages associated with kelp stipes and holdfasts, across multiple sites and sampling events. Significant differences were recorded in the structure of assemblages between the host kelp species at each site and event. Results: Assemblages associated with stipes of the cool-water HFS were, on average, >12 times more diverse and supported >3600 times more biomass compared with the warm-water HFS. Holdfast assemblages also differed significantly between species, although to a lesser extent than those associated with stipes. Overall, assemblages associated with the warm-water HFS were markedly impoverished and comprised far fewer rare or unique taxa. Main conclusions: While previous research has shown how climate-driven loss of HFS can cause biodiversity loss, our study demonstrates that climate-driven substitutions of HFS can also lead to impoverished assemblages. The indirect effects of climate change remain poorly resolved, but shifts in the distributions and abundances of HFS may invoke widespread ecological change, especially in marine ecosystems where facilitative interactions are particularly strong.</p
Ecological observations associated with an anomalous warming event at the Houtman Abrolhos Islands, Western Australia
No full text- …
