Spatial Relationships between Polychaete Assemblages and Environmental Variables over Broad Geographical Scales

Abstract

This study examined spatial relationships between rocky shore polychaete assemblages and environmental variables over broad geographical scales, using a database compiled within the Census of Marine Life NaGISA (Natural Geography In Shore Areas) research program. The database consisted of abundance measures of polychaetes classified at the genus and family levels for 74 and 93 sites, respectively, from nine geographic regions. We tested the general hypothesis that the set of environmental variables emerging as potentially important drivers of variation in polychaete assemblages depend on the spatial scale considered. Through Moran's eigenvector maps we indentified three submodels reflecting spatial relationships among sampling sites at intercontinental (>10000 km), continental (1000–5000 km) and regional (20–500 km) scales. Using redundancy analysis we found that most environmental variables contributed to explain a large and significant proportion of variation of the intercontinental submodel both for genera and families (54% and 53%, respectively). A subset of these variables, organic pollution, inorganic pollution, primary productivity and nutrient contamination was also significantly related to spatial variation at the continental scale, explaining 25% and 32% of the variance at the genus and family levels, respectively. These variables should therefore be preferably considered when forecasting large-scale spatial patterns of polychaete assemblages in relation to ongoing or predicted changes in environmental conditions. None of the variables considered in this study were significantly related to the regional submodel.

Large-Scale Spatial Distribution Patterns of Gastropod Assemblages in Rocky Shores

“…In general, assemblage patterns over large spatial scales may be explained by (1) the biogeographic context in which taxonomic composition is determined by dispersal and disturbance-colonization dynamics [67], (2) models that predict uniform diversity patterns [68], and (3) environmental models that relate biodiversity fluctuations to environmental drivers, including human induced changes [27]. NaGISA-based results on rocky intertidal assemblages showed differences in taxonomic structure among different LMEs, indicating that these assemblages are not homogenous over large spatial scales and refuting the idea of uniformity in assemblage patterns at such scales [28], therefore, we will focus our discussion in the biogeographic context and the environmental drivers.…”

“…Between one and 11 sites were sampled in each LME. Although this sampling size is clearly an under-representation of each LME [27]–[31], it still allows for comparisons of larger-scale patterns above the local variability (Figure 1). Within each site, five replicate 0.0625 m 2 quadrats (25×25 cm 2 ) were sampled randomly distributed along a 30–50 m transect at the high, mid, and low intertidal strata and at 1, 5, and 10 m (when available) depth in the subtidal.…”

“…Since environmental data could not always be collected or predicted from the exact sampling sites, and there was some inaccuracy of satellite-derived data from optical sea-surface properties (e.g., CHA) at small spatial scales [54], we used the LME scale to allow for the interpretation of large-scale variability. While the nearshore is a notably variable environment at the local scale, large-scale variability has reported to be even higher [27], [28].…”

“…macroalgae, decapods and echinoderms) are very complex and not always follow the expected latitudinal gradient of species diminution towards the poles [27]–[31], or appear to be superseded by regional diversity hotspots [29]. The NaGISA database has also allowed correlation analyses between species diversity or composition and environmental-anthropogenic variables at large spatial scales, showing that potential drivers of diversity at large scale vary depending on the group being analysed [27]–[31]. Given this variability of outcomes for different taxonomic groups, this study will focus on gastropods, one of the most diverse and ecologically important groups in the rocky shore environments.…”

Spatial autocorrelation in the response of soft-bottom marine benthos to gas extraction activities: The case of amphipods in the Ionian Sea

“…Benedetti-Cecchi et al, 2010). Thus, one expects species distribution to be spatially structured with patterns reflecting spatial patterns in environmental variables.…”