Benthic functional diversity along small scale natural sediement gradients: do functional aspects vary synchronously with species composition?
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Abstract:
Benthic macrofauna in the North Sea is subjected to a wide variety of anthropogenic
stressors, which have a significant impact on community composition. In order to
understand how these communities react to anthropogenic influences, the effect of
natural environmental variation, such as temperature, salinity, or sediment
characteristics, must first be understood to disentangle these from potential human
pressures. This study determined changes in species and functional diversity of
benthic macrofaunal communities along natural sediment gradients on small spatial
scales (i.e. ~5 km). Soft-bottom assemblages including infauna and epifauna in the
Sylt outer reef area of the North Sea were examined, with functional diversity being
based on functional traits. Significant differences in infaunal species and functional
composition were observed. Traits changing most significantly from coarse to fine
sediment include longevity, age at maturity, movement type, length, and feeding
mode. Significant increases in species and functional diversity were found (Simpson
increasing from 0.40 to 0.83, Rao increasing from 0.10 to 0.20 from coarse to fine
sand. Changes in community metrics were linked most strongly to the median grain
size (MDGS) and organic content of sediments. No significant changes were found in
species nor functional composition and diversity for epifaunal communities. Positive
linear relationships were revealed between species and functional diversity in both
infaunal (R2 = 0.95) and epifaunal (R2 = 0.99) communities. The results deliver
valuable insight on the potential effects of community changes on ecosystem
functioning and process-driven changes in assemblages. Further, the outcomes
provide an important framework for ecological monitoring and impact assessments
for future North Sea projects.Keywords:
Functional Diversity
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Environmental gradient
Diversity index
Gamma diversity
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Dominance (genetics)
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Current concern about biodiversity change associated with human impacts has raised scientific interest in the role of biodiversity in ecosystem functioning. However, studies on this topic face the challenge of evaluating and separating the relative contributions of biodiversity and environment to ecosystem functioning in natural environments. To investigate this problem, we collected sediment cores at different seafloor locations in Saanich Inlet and the Strait of Georgia, British Columbia, Canada, and measured benthic fluxes of oxygen and five nutrients (ammonium, nitrate, nitrite, phosphate and silicate). We also measured 18 environmental variables at each location, identified macrofauna, and calculated a suite of species and functional diversity indices. Our results indicated that, examined separately, macrobenthic functional richness (FRic) predicted benthic flux better than species richness, explaining ~ 20% of the benthic flux variation at our sites. Environmental variables and functional diversity indices collectively explained 62.9% of benthic flux variation, with similar explanatory contributions from environmental variables (21.4%) and functional diversity indices (18.5%). The 22.9% shared variation between environmental variables and functional diversity indices demonstrate close linkages between species and environment. Finally, we also identified funnel feeding as a key functional group represented by a small number of species and individuals of maldanid and pectinariid polychaetes, which disproportionately affected benthic flux rates relative to their abundance. Our results indicate the primary importance of environment and functional diversity in controlling ecosystem functioning. Furthermore, these results illustrate the consequences of anthropogenic impacts, such as biodiversity loss and environmental changes, for ecosystem functioning.
Environmental change
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Macrobenthos
Benthos
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Life History Theory
Benthos
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Functional Diversity
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Macrofauna, an abundant and often patchy constituent of benthic soft sediments, alter important processes such as sediment oxygenation and nutrient fluxes. This study links spatial patterns in faunal biodiversity and ecosystem functions. I collected 39 sediment cores from 4 basins within the Gulf of Maine to characterize fauna and sedimentary characteristics. At coarse taxonomic levels (phyla and feeding guild), faunal composition was homogenous across the Gulf of Maine, whereas species-level taxonomy revealed heterogeneous composition and limited species turnover. Of the abiotic variables, all factors varied locally (across sites within basins) but only bottom depth differed significantly regionally. Ecosystem function varied significantly across and within basin, and additional analyses confirmed polychaete biodiversity, as well as abundance, were significant, positive predictors of secondary (microbial) production. Feeding guild biodiversity predicted more ecosystem functions than species or family level groupings, demonstrating that activity and behaviour better predict ecosystem functions in sediments than species diversity.
Guild
Marine ecosystem
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Abstract Community structure of many systems changes across space in many different ways (e.g., gradual, random or clumpiness). Accessing patterns of species spatial variation in ecosystems characterized by strong environmental gradients, such as estuaries, is essential to provide information on how species respond to them and for identification of potential underlying mechanisms. We investigated how environmental filters (i.e., strong environmental gradients that can include or exclude species in local communities), spatial predictors (i.e., geographical distance between communities) and temporal variations (e.g., different sampling periods) influence benthic macroinfaunal metacommunity structure along salinity gradients in tropical estuaries. We expected environmental filters to explain the highest proportion of total variation due to strong salinity and sediment gradients, and the main structure indicating species displaying individualistic response that yield a continuum of gradually changing composition (i.e., Gleasonian structure). First we identified benthic community structures in three estuaries at Todos os Santos Bay in Bahia, Brazil. Then we used variation partitioning to quantify the influences of environmental, spatial and temporal predictors on the structures identified. More frequently, the benthic metacommunity fitted a quasi-nested pattern with total variation explained by the shared influence of environmental and spatial predictors, probably because of ecological gradients (i.e., salinity decreases from sea to river). Estuarine benthic assemblages were quasi-nested likely for two reasons: first, nested subsets are common in communities subjected to disturbances such as one of our estuarine systems; second, because most of the estuarine species were of marine origin, and consequently sites closer to the sea would be richer while those more distant from the sea would be poorer subsets.
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Environmental gradient
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Current research revealed distinct changes in ecosystem functions, and thus in ecosystem stability and resilience, caused by changes in community structure and diversity loss. Benthic species play an important role in benthic-pelagic coupling, such as through the remineralization of deposited organic material, and changes to benthic community structure and diversity have associated with changes in ecosystem functioning, ecosystem stability and resilience. However, the long-term variability of traits and functions in benthic communities is largely unknown. By using abundance and bioturbation potential of macrofauna samples, taken along a transect from the German Bight towards the Dogger Bank in May 1990 and annually from 1995 to 2017, we analysed the taxonomic and trait-based macrofauna long-term community variability and diversity. Taxonomic and trait-based diversity remained stable over time, while three different regimes were found, characterised by changes in taxonomic and trait-based community structure. Min/max autocorrelation factor analysis revealed the climatic variables sea surface temperature (SST) and North Atlantic Oscillation Index (NAOI), nitrite, and epibenthic abundance as most important environmental drivers for taxonomic and trait-based community changes.
Diversity index
Bioturbation
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For marine benthic communities, environmental heterogeneity at small spatial scales are mostly due to biologically produced habitat heterogeneity and biotic interactions, while at larger spatial scales environmental factors may prevails over biotic features. In this study, we investigated how community structure and β-diversity of hard-bottom-associated meio- and macrofauna varied in relation to small-scale (cm–m) changes in biological substrate (an algae “turf” dominated by the macroalgae Gelidium sp., the macroalgae Caulerpa racemosa and the sponge Hymeniacidon heliophile) in a rocky shore and in relation to larger-scale (10’s m) changes in environmental conditions of the same biological substrate (the macroalgae Bostrychia sp) in different habitats (rocky shore vs. mangrove roots). Results showed that both substrate identity and the surrounding environment were important in structuring the smaller-sized meiofauna, particularly the nematode assemblages, whereas the larger and more motile macrofauna was influenced only by larger-scale changes in the surrounding ecosystem. This implies that the macrofauna explores the environment in a larger spatial scale compared to the meiofauna, suggesting that effects of spatial heterogeneity on communities are dependent on organism size and mobility. Changes in taxa composition between environments and substrates highlight the importance of habitat diversity at different scales for maintaining the diversity of the associated fauna.
Meiobenthos
Rocky shore
Spatial heterogeneity
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