Disentangling Diversity Patterns in Sandy Beaches along Environmental Gradients

Abstract

Species richness in sandy beaches is strongly affected by concurrent variations in morphodynamics and salinity. However, as in other ecosystems, different groups of species may exhibit contrasting patterns in response to these environmental variables, which would be obscured if only aggregate richness is considered. Deconstructing biodiversity, i.e. considering richness patterns separately for different groups of species according to their taxonomic affiliation, dispersal mode or mobility, could provide a more complete understanding about factors that drive species richness patterns. This study analyzed macroscale variations in species richness at 16 Uruguayan sandy beaches with different morphodynamics, distributed along the estuarine gradient generated by the Rio de la Plata over a 2 year period. Species richness estimates were deconstructed to discriminate among taxonomic groups, supralittoral and intertidal forms, and groups with different feeding habits and development modes. Species richness was lowest at intermediate salinities, increasing towards oceanic and inner estuarine conditions, mainly following the patterns shown for intertidal forms. Moreover, there was a differential tolerance to salinity changes according to the habitat occupied and development mode, which determines the degree of sensitivity of faunal groups to osmotic stress. Generalized (additive and linear) mixed models showed a clear increase of species richness towards dissipative beaches. All taxonomic categories exhibited the same trend, even though responses to grain size and beach slope were less marked for crustaceans and insects than for molluscs or polychaetes. However, supralittoral crustaceans exhibited the opposite trend. Feeding groups decreased from dissipative to reflective systems, deposit feeders being virtually absent in the latter. This deconstructive approach highlights the relevance of life history strategies in structuring communities, highlighting the relative importance that salinity and morphodynamic gradients have on macroscale diversity patterns in sandy beaches.

Environmental drivers defining linkages among life‐history traits: mechanistic insights from a semiterrestrial amphipod subjected to macroscale gradients

“…Variables were considered as smooth terms using penalized regression splines with degrees of freedom up to 3 (Hastie and Tibshirani ; Barboza et al. ; Gómez and Defeo ). Residuals were checked for all models.…”

Clam community composition and prey shell size impacts moon snail (Gastropod: Naticidae) drilling frequencies in South Carolina, USA

“…Therefore, we do not believe that variation in seafloor composition is the reason for the differences in clam community composition. The differences in clam community diversity could be influenced by biotic (food availability and intraspecific interactions (Schoeman & Richardson, 2002) and abiotic factors (wave energy (Pruss et al, 2011), beach slope, sand moisture, and salinity (Barboza, Gómez, Lercari, & Defeo, 2012). However, food availability is unlikely to be an issue because interspecific competition is low among suspension feeding bivalves (Stanley 2008).…”

Distributional patterns in an insect community inhabiting a sandy beach of Uruguay

“…This is a wide (beach width ca 70 m) dissipative beach with fine to very fine (grain size ¼ 0.20 mm) well-sorted sands, a gentle slope (2.7%), a wide surf zone and high macrofauna richness, total abundance and biomass (Defeo et al, 2001;Barboza et al, 2012). The active dunes are covered by a great abundance of the perennial herb Panicum racemosum (Poaceae) and some halophilous annual species such as Blutaparon portulacoides (Amaranthaceae), Cakile maritima (Brassicaceae) and Calycera crassifolia (Calyceraceae).…”

“…On the other hand, insects are the most abundant terrestrial invertebrate group inhabiting coastal dunes and the supralittoral fringe of sandy shores, playing a key role in trophic webs (McLachlan and Brown, 2006). Recent deconstructive analyses based on taxonomy indicated that species richness of these four taxa increased from reflective (steep slopes, coarse sands) to dissipative (flat slopes, fine sands) beaches (Defeo and McLachlan, 2011;Barboza et al, 2012).…”

“…This beach has the highest macrofauna richness (including insects) and it is the widest ocean one among all Uruguayan beaches (Barboza et al, 2012). Specifically, it is assessed whether within-year environmental changes translate into temporal differences in species richness, abundance, diversity and composition of insect community.…”