Abstract
Assessing how natural environmental drivers affect biodiversity underpins our understanding of the relationships between complex biotic and ecological factors in natural ecosystems. Of all ecosystems, anthropogenically important estuaries represent a ‘melting pot' of environmental stressors, typified by extreme salinity variations and associated biological complexity. Although existing models attempt to predict macroorganismal diversity over estuarine salinity gradients, attempts to model microbial biodiversity are limited for eukaryotes. Although diatoms commonly feature as bioindicator species, additional microbial eukaryotes represent a huge resource for assessing ecosystem health. Of these, meiofaunal communities may represent the optimal compromise between functional diversity that can be assessed using morphology and phenotype–environment interactions as compared with smaller life fractions. Here, using 454 Roche sequencing of the 18S nSSU barcode we investigate which of the local natural drivers are most strongly associated with microbial metazoan and sampled protist diversity across the full salinity gradient of the estuarine ecosystem. In order to investigate potential variation at the ecosystem scale, we compare two geographically proximate estuaries (Thames and Mersey, UK) with contrasting histories of anthropogenic stress. The data show that although community turnover is likely to be predictable, taxa are likely to respond to different environmental drivers and, in particular, hydrodynamics, salinity range and granulometry, according to varied life-history characteristics. At the ecosystem level, communities exhibited patterns of estuary-specific similarity within different salinity range habitats, highlighting the environmental sequencing biomonitoring potential of meiofauna, dispersal effects or both.
Highlights
Biodiversity contributes to ecosystem stability, resilience, function (Loreau et al, 2001; Wardle et al, 2004) and the continued provision of ecosystem services (Schroter et al, 2005), but is subject to a range of natural and anthropogenic forces
In attempts to make predictions about the biodiversity of a typical estuary, many studies refer to the hydrodynamics, salinity range or levels of bioturbasomewhat arbitrary Remane model that models species richness along a numerous phyla at the estuarine ecosystem scale
To complement the we present the results obtained with FlowClus/
Summary
Estuaries are often centres of human habitation (Basset et al, 2012) and are the focus of intensive and costly biomonitoring programmes (Baird and Hajibabaei, 2012) designed for assessing ecosystem health (Rosenberg et al, 2004). D50 and salinity range data were retained and the OTUs across both estuaries, representing 22% of the best fitting model was selected by Akaike informa- OTUs in Thames and 31% in Mersey), followed by tion criterion using a stepwise algorithm. Substantial contributions by Alveolata (173 OTUs), In order to investigate the geographical contribu- stramenopiles (146 OTUs), Arthropoda (138 OTUs), tion to the marine component of estuarine biodiver- Platyhelminthes (89 OTUs) and a range of additional sity, we subsampled UK-only sites from the recent taxa from up to 27 separate phyla (Figure 2 and littoral beach data presented in Fonseca et al (2014) Supplementary Table S3). Samples were taken over a distance of B46 km we used partial least squares (PLS) from Mersey and 106 km from Thames, representing regressions to assess which environmental variables the full spectrum of the salinity gradient in each were the most important drivers of meiofaunal ecosystem. In the outer part of the Mersey estuary (sites The Narrows to Speke), seven families represent the most number of reads: Axonolaimidae, Chromadoridae, Comesomatidae, Desmodoridae, Sphaerolaimidae, Xyalidae and Thames estuary
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